THE  GIANT  AFRICAN   SNAIL
 
THE GIANT
AFRICAN
SNAIL:
A PROBLEM
IN ECONOMIC
MALACOLOGY

ALBERT  R. MEAD
THE    UNIVERSITY    OF    CHICAGO    PRESS
LIBRARY OF CONGRESS CATALOG CARD NUMBER: 61-14949
THE UNIVERSITY OF CHICAGO PRESS, CHICAGO & LONDON
THE UNIVERSITY OF TORONTO PRESS, TORONTO 5, CANADA
© 1961 BY THE UNIVERSITY OF CHICAGO. PUBLISHED 1961
COMPOSED AND PRINTED BY THE UNIVERSITY OF CHICAGO PRESS
CHICAGO, ILLINOIS, U.S.A.
TO   MY  WIFE
ELEANOR
WHO   WAS   MY   FIRST  AND   BEST   STUDENT
 
PREFACE
There is no comprehensive work in any language encom-
passing the area of our knowledge that can be defined as Economic
Malacology. In fact the subject is just beginning to be recognized as a
discipline in its own right. The mission of the present work is to
bring together its widely scattered literature, which goes all the way
from typewritten, mimeographed, or dittographed official reports to
publications in obscure foreign journals. It has taken over ten years
of searching, examining, evaluating, digesting, collating, and editing
to bring this work to its present status. During this process many
essentially unimportant or irrelevant papers were encountered, par-
ticularly in the area of snail control. In nearly every case these were
not included in the bibliography because either they made little in the way of an original contribution or they contained information
not relevant to the general problem of the economics of terrestrial
gastropods. To this extent, the bibliography is a selected bibliogra-
phy. And, in a broader sense, the subject of economic malacology em-
braces the problems presented by the freshwater snails. Such prob-
lems and the literature that treats of them, however, are vast indeed—
so vast that it is completely impractical to consider them here, except
for an occasional reference. Also, the problems and their solutions
vary so much between the two groups of snails that there is little in
the way of common applicability or of comparative value. Further,
because many of the problems involving freshwater snails have a dis-
tinct medical flavor, far greater attention has been given to them—
witness, for example, the vast literature concerning the snail hosts of
the schistosomiases.
Because the original sources of information will not be available
to the greater segment of the readers, the essence of the contributions,
in each case, has been incorporated in the text in so far as it has been
practicable to do so. Some authors quoted or referred to in this work
may be judged as not being truly qualified to make sound reports. It
should be borne in mind, therefore, that the inclusion of certain of
vii
viii	PREFACE
these works was for the completeness of the record; inclusion is not
an endorsement. Where it is believed that a given author is in error,
this is pointed out. But under no circumstances was any reference ex-
cluded simply on the basis of its being at variance with the conclu-
sions set forth in this book.
The pertinent information in the literature has been combined
with considerable field data which I collected in Africa, Asia, and
Oceania. Supplemental information has been obtained from many
correspondents who have had firsthand experience with terrestrial
snail problems. Throughout this book, credit is given on the spot
where credit is due; and sincere efforts have been made not to imply
by omission that originality rested with me, even though I may have
independently arrived at the same conclusion. The reader therefore
can trace back to the original source almost any item of information.
No matter how hard one tries, inevitable errors, omissions, and
misinterpretations will creep into any work of this size. These are as
regrettable as they are unavoidable. Certainly every effort has been
made to keep them to a minimum. New contributions in the field of
economic malacology are continuing to appear in the literature just
often enough that it has not been possible to keep pace with them
right up to the last minute. As a compromise, reference to recent,
pertinent works is made only in the bibliography. It has been a
temptation to prolong the editing of the manuscript in the expecta-
tion that all points of difficulty would be removed. But it is much
more realistic and practical to get all of this information as soon as
possible into the hands of those who need it and have been asking for
it for years. Hence, with a good measure of apprehension and with
a full awareness of the shortcomings involved, this work is being re-
leased in the fond hope, not that it will serve the needs perfectly, but
that it will serve them well.
During the years that it has taken to produce this work, there has
accumulated a vast indebtedness in a multitude of ways; and the task
of attempting to indicate here anything approaching the gratitude
that is felt, seems overwhelming and irrevocably foredoomed to in-
adequacy.
Those for whom I feel the greatest gratitude, I would like to men-
tion: Dr. Yoshio Kondo of the B. P. Bishop Museum, whose sound
judgment has tempered many ideas presented in this book, and whose
companionship in the field is without equal; Dr. Joseph C. Bequaert
of Harvard University, whose interest, encouragement, and advice in
Africa sixteen years ago provided a great turning point in my life;
Dr. Harold J. Coolidge, executive director of the Pacific Science
PREFACE	ix
Board, whose faith in my research, when others grew doubtful, gave
me encouragement when I needed it most; Dr. George A. Baitsell of
Yale University, whose advice precipitated two $500 Sigma Xi—RESA
grants-in-aid which made it possible to prepare the greater share of
the original manuscript; Dr. W. Wayne Boyle of Pennsylvania State
University, whose many months of help in Hawaii brought forth
some of the most valuable data in this work concerning the great
need for, and the value of, long-range studies on the giant African
snail; Dr. W. Harry Lange, Jr., of the University of California, who
critically examined the chapter on chemical control and offered many
profitable suggestions and leads in this complex aspect of the subject;
and A. P. Messenger and H. M. Armitage of the California State De-
partment of Agriculture, who have been my constant guides in all
matters involving quarantines.
Grant funds from several sources have permitted me to gather field
data and conduct research without which the present work would
not have been conceived. The Pacific Science Board of the National
Research Council, through the National Academy of Science, pro-
vided ONR funds in 1948 to study the anatomy of a number of
achatinids at Harvard University; and additional funds were allotted
in 1957 to permit me to chair a symposium on the giant African snail
at the Ninth Pacific Science Congress in Bangkok, Thailand. The
Office of Naval Research (NR 161 472) paid for all expenses in an ex-
tensive survey of the problem of the giant African snail in the Trust
Territory of the Pacific Islands during the three summer months of
1949. The National Science Foundation made one of its early grants
(G-519) in 1953 in support of the successful search in Ceylon for a
predicted disease in the giant African snail. Dr. A. D. Ross, Honor-
able Secretary of the Pan Indian Ocean Science Association, made it
possible for me to attend the Second Pan Indian Ocean Science Con-
gress in Perth, Australia, in 1954. The National Institutes of Health
have provided funds (E-1245[C3j) since 1957 which have financed
considerable research at the University of Arizona and the University
of Hawaii on the disease syndrome in the giant African snail. Ada P.
McCormick of Tucson, Arizona, furnished funds and secretarial help
which were indispensable in the early stages of preparing the manu-
script.
Edward A. Steinhaus and Yoshinori Tanada of the University of
California patiently discussed at length with me my proposed re-
search and hypotheses on the disease syndrome in the giant African
snail. Chemical and bio-assays of the snail meal were conducted by
Arthur R. Kemmerer, Mitchell G. Vavich, and Edward L. Breazeale;
x	PREFACE
and the more complex mathematical computations were made by
Donald L. Webb and Samuel R. Browning—all of the University of
Arizona. In Hawaii, the following provided all sorts of help in many
ways over a period of several years: Henry A. Bess, George D. Butler,
Walter Carter, Q. C. Chock, C. H. Edmondson, Jim Kim, C. E.
Pemberton, Alexander Spoehr, Alan D. Thistle, and the late Paul
W. Weber.
Many investigators in foreign countries generously contributed,
among other things, valuable information which helped tremendous-
ly in piecing together the otherwise exasperatingly fragmentary data
in some of the literature. The following were of especial help: A. F.
Caldwell of the University of Malaya in Singapore; Silverio M.
Cendana of the University of the Philippines; R. E. Dean, superin-
tendent of gardens, Hong Kong; G. S. Dun of the Lowlands Experi-
ment Station, New Britain; K. C. Ghose of the City College of Cal-
cutta; John R. Hendrickson of the University of Malaya in Kuala
Lumpur; Mr. and Mrs. Peter J. R. Hill of Koror, Palau Islands;
Alan J. Kohn of Florida State University, who supplied informa-
tion from the Maldive Islands during the 1957 Yale-Seychelles
Expedition; J. C. van der Meer Mohr of the Deli Proefstation, Me-
dan, Sumatra; and George D. Peterson, Jr., the entomologist of the
government of Guam. During the five weeks that Yoshio Kondo, the
late Dan Langford, and I were in the Bonin Islands in 1949, we be-
came greatly indebted to the people of Chichi Jima and, particular-
ly, to the head councilman, Roderick Webb, and the entire Savory
family. For nine months in Ceylon, I received help from many more
than I could possibly list here; but I must acknowledge help particu-
larly from the following members of the Department of Agriculture
in Peradeniya: Henry E. Fernando and Yasatileka Elikawela of the
Division of Entomology, Dr. J. W. L. Peiris of the Division of Plant
Pathology; and A. Bandaranyake and W. Fernando of the Veterinary
Research Laboratory.
Assistance in translating from the Dutch was given by L. J. M.
Butot of the Museum Zoologicum Bogoriense in Java and by H.
Reerink, agronomist of FAO in Ceylon. M. Dale Arvey of Long
Beach State College translated one long, important article from the
Japanese; and William Osuga of the University of California East
Asiatic Library gave considerable help in locating and translating
portions of several other articles in Japanese. Donald M. Powell and
Lutie L. Higley of the University of Arizona Library patiently fer-
reted out a number of elusive references.
I am indebted to several of my colleagues for the use of photo-
PREFACE	xi
graphs. Specific credit has been given in each case where the illustra-
tion is not mine. I am especially indebted to Donald B. Sayner, who
is the instructor in scientific illustration in the Department of
Zoology at the University of Arizona, for the two excellent line draw-
ings and to Robert Broder, the departmental photographer, for the
greater share of the photographic work. For the jacket photograph,
I wish to thank Drs. William J. Clench and Ruth D. Turner of the
Harvard Museum of Comparative Zoology.
My sister Jennie S. Burnett and Virginia A. Miles typed the early
drafts of the manuscript; and Ruth I. Spiller miraculously typed the
entire final draft in just a few days. Charles D. Miles and Robert J.
Drake cheerfully assisted in the long, monotonous task of proofread-
ing the several drafts, copies, and proofs. The constant help of my
wife and the willing hands and sharp eyes of Ruth and Jim in the
field have been my greatest blessings in the long task that now lies
behind me.
 
CONTENTS
List of Illustrations	xvii
I. Introduction	1
II. Dispersal of the Giant African Snail	4
BISMARCK ARCHIPELAGO   /   6
BONIN ISLANDS   /   6
BURMA   /   7
CAROLINE ISLANDS   /  7
CEYLON   /   8
CHINA   /    8
FORMOSA   /    8
HAWAIIAN ISLANDS   /    8
HONG KONG   /    9
INDIA   /   9
INDONESIA   /   9
JAPAN   /    11
MALAYA   /    11
MALDIVE ISLANDS   /    11
MARIANA ISLANDS   /   11
MAURITIUS   /   13
NEW GUINEA   /   13
NORTH BORNEO   /   13
PALAU ISLANDS   /   14
PHILIPPINE ISLANDS   /   14
REUNION   /   14
RYUKYU ISLANDS   /   15
SARAWAK  /   15
SEYCHELLES   /   15
SINGAPORE   /    15
xiii
xiv	CONTENTS
THAILAND   /   15
VIETNAM   /   l6
III.	Factors Favoring Dispersal and Survival	17
MAN—THE PRINCIPAL AGENT OF DISPERSAL   /   17
LONGEVITY  /   21
REPRODUCTIVITY  /   21
VARIABILITY   /   24
ESTIVATION AND HIBERNATION   /   25
HARDINESS  /   28
PAUCITY OF NATURAL ENEMIES   /   32
PERIOD OF ACTIVITY  /   33
AVAILABILITY OF CALCIUM   /    33
ESCAPE REACTION AND MIGRATION CYCLE   /    34
IV.	Economic Status	36
CURRENT OPINION   /   36
DAMAGE TO PLANTS   /   39
EVALUATION OF DAMAGE   /   49
INDIRECT DAMAGE   /   52
NUISANCE FACTOR  /   54
HEALTH FACTOR  /   55
ROLE AS SCAVENGER   /   57
UN JUST CHARGES   /   59
V.	Chemical Control	61
CHEMICALS AND COMPOUNDS   /   62
CHEMICAL CONTROL—AN EVALUATION   /   84
VI. Control through Mechanical Devices	92
BARRIERS   /   92
BURNING-OVER /  94
CLEAN CULTURE  /   95
DROWNING  /   97
HAND COLLECTING AND DESTROYING   /   98
SHIFTING CULTIVATION   /   1OO
TRAPS  /   1OO
VII. Biological Control	102
AMPHIBIANS  /   1O2
ANTS  /   105
CONTENTS	xv
BEETLES   /   1O6
BIRDS   /    113
CRABS   /    1l6
FLIES  /   118
HELMINTHS   /   12O
MAMMALS   /   121
MICRO-ORGANISMS   /   123
MITES   /   125
REPTILES   /   125
SNAILS   /   126
MISCELLANEOUS   /   136
BIOLOGICAL CONTROL—AN EVALUATION   /   136
VIII. Control through Human Use	146
HUMAN CONSUMPTION   /   146
REPUTED POISONOUS PROPERTIES   /   155
EXPERIMENTS IN EATING THE GIANT SNAIL   /   156
FOOD FOR POULTRY   /   159
CHEMICAL ASSAY OF SNAIL MEAL   /   l6o
VITAMIN ASSAY OF SNAIL MEAL   /   164
AMINO ACID ASSAY OF SNAIL MEAL   /   165
FOOD FOR LIVESTOCK   /   167
FISH BAIT  /   167
FERTILIZER  /   167
PRODUCTION OF SNAIL MEAL  /   l68
IX.	Control through Legislative Action	172
X.	Population Decline	180
POPULATION SENILITY   /   182
STERILITY   /   l82
STARVATION   /   183
EXPOSURE  /    183
TRAUMATIC BREAKS   /    183
PREDATORS   /    184
GENETICS  /    184
DISEASE  /    185
MULTIPLE FACTORS  /    193
xvi	CONTENTS
XI. Outlook	195
DISPERSAL   /   195
BIONOMICS   /   199
CONTROL  /   199
DECLINE   /   203
Bibliography	205
Index	247
ILLUSTRATIONS
FIGURE	FACING PAGE
1.	The largest living Achatina fulica Bowdich ever photographed      46
2.	Army Hill population of giant African snail, 1949	47
3.	Achatina fulica and several possible control snails	47
4.	Giant snails sold and used as human food	78
5.	Giant snail on trunk of Artocarpus heterophyllus	78
6.	Shells showing characteristic damage	79
7.	Variability in Achatina fulica Bowdich	79
8.	The "bent-nose" type of giant African snail	79
9.	The common hermit crab preys on giant African snail	110

10.	Evidence of widespread disease found among older snail popu-
lations	110
11.	Thousands of giant snails in Rota tomato patch	111
12.	Dead snails as source of lime	111
13.	Full-grown larva of Lamprophorus tenebrosus feeding on snail     142
14.	Giant snail with two natural enemies	142
15.	Inspectors discover giant snails in Los Angeles	143
map
Dispersion of the giant African snail	5
chart
The giant African snail and its environment	137
xvii
 
CHAPTER   1
INTRODUCTION
The study of economic malacology is largely the story of
the giant African snail, Achatina fulica Bowdich. More than any-
thing else, the relatively rapid development of this species into the
most serious land snail pest plaguing man today has precipitated the
need for creating the separate discipline of economic malacology.
But although the giant African snail dominates the subject, there are
a surprising number of other land snail species, particularly those
that have wandered from their native heath, which have become
serious and even major garden pests. The problems presented by
them will be with us for a long time to come. The giant snail and
most other pestiferous species have defied all efforts to eradicate
them and they seem to have the capacity to resist control measures
indefinitely. Some of these snails are destined to become worse pests in
the future. And new ones will make their appearance. For example,
the announcement of Torres (1950) that the giant South American
snail Strophocheilus oblongus has been attacking the coffee plant
seems patently prognosticative.
The groundwork from which economic malacology has emerged
was laid largely during the multifold campaign to control the giant
African snail in the Indo-Pacific region. Initial research was con-
ducted in Southeast Asia, particularly in Ceylon, Malaya, Singapore,
and Java. In the Pacific, it was the Insect Control Committee for
Micronesia (which later became the Invertebrate Consultants Com-
mittee for the Pacific) of the Pacific Science Board of the National
Research Council that led the way in the program of delving into
some of the deeper problems associated with the economics of land
snails, and of the giant African snail in particular. It was not known
how far the giant snail had spread; how it was spreading; why it was
2	INTRODUCTION
spreading so rapidly; why it was building up in unprecedented num-
bers; to what extent it was really causing horticultural and agricul-
tural damage; whether it ever practicably could be used for human
consumption; or what control measures—chemical, mechanical, bio-
logical, legislative—have been attempted with what measure of suc-
cess. The early investigations led to new and unsuspected findings.
The enigmatic phenomenon of population decline has been shown
to produce dramatic results in some of the older snail populations.
Disease as a factor in natural control has just entered the increasingly
more complex ecological picture. Other phenomena are hanging in
the near shadows.
In an effort to determine the amount of research currently in prog-
ress in the problem of the giant African snail, letters of inquiry were
sent to all major infested areas, either to known investigators or to
directors of agriculture. The response was disheartening in the ex-
treme. With only a few exceptions, the answers presented one or
more of a host of good reasons why no work, except perhaps for a
small amount of routine control, was being done on the problem.
Irrespective of the validity of most of the good reasons, the situation
is indeed deplorable, especially when it is compared with that of
other types of major agricultural pests. Time after time, however,
there could be sensed the tacit confession that, regardless of the ex-
cuses offered, too little was actually known or could be discovered
about snail problems. They would complain: "We are fighting in the
dark." "We do not know what control measures have been tried."
"Our experimental results have been inexplicably inconsistent." It
is little wonder that many investigators have become discouraged and
have actually turned their backs to the problem.
With the emergence of the discipline of economic malacology out
of the grief caused by the giant African snail, we must look both to
the past and to the future. We must survey critically the many and
varied contributions regarding both the giant snail and other snails;
and we must look at what lies ahead so that we will be in better posi-
tion to tackle the predictably worsening problems and still other
problems yet to come. As a matter of fact, we have right now weapons
of control which ironically are not generally known by those who are
charged with trying to effect controls. In some cases, discoveries of a
complementary nature in research have not yet been brought to-
gether. Wholly unpredictable avenues of approach will be discovered
when all pertinent information extant is brought together and syn-
thesized. Even to this day, problems in economic malacology are in-
variably passed on to the economic entomologist, who finds his
INTRODUCTION	3
knowledge of malacology too limited (if indeed it exists at all) and
the insect control methods almost completely useless to him. This
places a premium on putting into the proper hands all available
pertinent information on the economics of terrestrial snails. Attempts
are made in the following pages to do just this.
Now that there has been brought together at last the rather sub-
stantial fund of information tucked away in the far corners of the
literature, and this has been combined with the discoveries in recent
research, it is hoped that investigators in many quarters will be
stimulated with renewed enthusiasm to take vigorous steps in seek-
ing the answers to a host of major and fundamental questions sur-
rounding the giant African snail and other land snail pests. When
this becomes a reality, economic malacology truly will be on its way.
CHAPTER 2
DISPERSAL
OF THE
GIANT
AFRICAN
SNAIL
Much has been written about the travels that Achatina
fulica has made since it left its original home in East Africa. The
most outstanding treatises on the subject are: Bequaert (1950b),
Lange (1950), Pemberton (1954), Rees (1951), and van Weel (1948)
in the English language; Kalshoven (1950) in Dutch; Merle (1949) in
French; Boettger (1951) in German; Sonan (1936) and Esaki and
Takahashi (1942) in Japanese; and Aguayo (1950) in Spanish. An
examination of the rather considerable literature on the subject has
revealed many disturbing discrepancies and conflicts. In so far as it
is possible to do so, these have been resolved, clarified, or explained
in order to arrive at a better understanding of what has taken place
and what will probably take place in the next relatively few years.
Chief among the items of misinformation being perpetuated in the
literature are those which concern the presumed establishment of
this snail pest in the "South Pacific," New Caledonia, Yap, the Mar-
shall Islands, the continental United States, and the West Indies.
There is also the frequent misstatement that A. fulica has been eradi-
cated in Hawaii. It should be emphasized that the only place in the
United States where this snail is established is Hawaii, although it
has been intercepted and destroyed in Arizona (Mead 1959a, b) and
4
6	DISPERSAL OF THE GIANT AFRICAN SNAIL
in a number of ports in the continental United States. It also should
be emphasized that, so far as we know, the giant snail has not be-
come established anywhere in the Marshall Islands.
Because people have been alerted to the dangers and the rapid
spread of this snail, any large snail has been immediately suspected
by the uninitiated as being A. fulica. For example, it was possibly an
Amphidromus which caused van Brero (1933) to miscalculate the
time A. fulica had been in Java (Leefmans 1933b). A large Vivipara
in New York caused an "Achatina invasion" scare which was dra-
matically played up in the local papers. The campaign in Los An-
geles in 1951 to rid itself of a Mediterranean edible snail, Otala lac-
tea, ran headlong into trouble because the announced common name
of the snail, "the African snail," created the impression in many
parts of the country, through newspaper channels, that the giant
African snail had already become established in California (cf. Wib-
berley 1951).
In the following paragraphs there has been set up under each
appropriate geographical title, as far as the available information
permits, a concise statement of the history of the establishment of the
giant African snail, its development, and its present status. Special
efforts have been made to avoid any secondary source of reference.
Bismarck Archipelago The first record of the giant African
snail appearing in New Britain and New Ireland brought the news
that this pest was present in great quantities (Anon. 1947a, c}. It
seems apparent that the original introductions were made by the
Japanese forces prior to 1945 (Anon. 1948e). G. S. Dun of the Low-
land Experiment Station at Keravat in New Britain has conducted
considerable valuable research on the giant snail in this region. Un-
fortunately, much of it has not yet found its way into the literature.
He reports (in litt. April 21, 1950) that the snail has also become
established in the Duke of York Islands.
Bonin Islands (Ogasawara Gunto) Mead and Kondo (1949)
with the late D. B. Langford made the first survey of these islands to
discover the snails well established on Chichi Jima, Haha Jima, and
Ani Jima. The snails were introduced in Chichi Jima from Japan in
1937-38 as an item of primitive medicine (see p. 151). Five to six
years later the snails were seen quite commonly in the lowlands
about the harbor (Futami Ko). Jerry Savory reported that they were
plentiful in June, 1943, when he was evacuated from Chichi Jima to
Japan. On April 2, 1946, a high tidal wave washed over a good por-
tion of these lowlands and for the rest of that year and the succeeding
year there were relatively few snails seen. In 1948, however, the
DISPERSAL OF THE GIANT AFRICAN SNAIL
7
snails appeared in unprecedented numbers and in 1949 they were
still more abundant (Mead 1950b). Ten years later the snails were
reported to be continuing as a serious pest.
Wilson Savory stated that the snails were introduced on Haha
Jima soon after they were introduced on Chichi Jima. The farmers
on that island, however, soon recognized that the snails were a pest
and they did everything they could to prevent their spread. The
island was completely evacuated in 1944. The absence of man as a
disseminating agent and the presence of the hermit crab, Cenobita
perlatus, as a predator probably account for the fact that the eleven-
to twelve-year-old population was found in 1949 to be limited to a
surprisingly small area in the abandoned port village of Okimura.
The Ani Jima population in 1949 appeared to be limited to the
southwest portion of the island. The giant snails introduced on the
tiny island of Higashi Shima were reportedly wiped out by the large
endemic population of hermit crabs. The fishermen of Chichi Jima
reported that in their numerous trips to Muko Jima and Ototo Jima,
no giant snail had ever been seen; and they seriously questioned that
the snails had ever been introduced in these islands.
Burma Essentially nothing is known of the status of the giant
African snail in Burma except that it has been established there for
a number of years. The infestation started either from the nearby
populations in Bengal or, more likely, from Malaya through the
agency of the Japanese occupation forces.
Caroline Islands According to Esaki and Takahashi (1942),
the giant snails were first introduced into Ponape, near the village of
Kolonia, in the fall of 1938; the specimens were reportedly brought
from Okinawa by a Mr. Junki Miyahira. By 1949, the snail was
found well established in a number of localities in the vicinity of
Kolonia (Mead 1950b). At that time, searching parties found no sign
of the giant snail on the nearby islands of Pingelap, Mokil, or Kusaie.
Dublon was apparently the first of the Truk Islands to become in-
fested (Townes 1946). The snails were probably brought in prior to
1940; and because of the concentration of health resorts on this
island, it is possible that the snails were intended to be used for their
presumed medicinal properties (Mead 1950b). As nearly as could be
determined from questioning the Trukees, the giant snails were in-
troduced into Moen and Romalum from Dublon by the Japanese
some time prior to 1945; but they did not show up in Uman, near
Sapota, and Fefan, near Sannuk, until 1948.
Esaki and Takahashi (1942) were responsible for the often quoted,
erroneous report that the giant snails are on Yap Island.
8	DISPERSAL OF THE GIANT AFRICAN SNAIL
Ceylon In 1900 Oliver Collett, an enthusiastic conchologist,
introduced into his estate at Rozelle (near Watawala) specimens of
the giant snail which he obtained either from Mauritius or India
(Green 1910b). On the advice of E. E. Green, as many specimens as
possible were collected and destroyed, but not before some had acci-
dentally been carried on vegetables to the coastal town of Kalutara.
In ten years' time, the "Kalutara snail" (Singhalese: gombela or
golubela) was found so well established in both the original sites and
adjacent areas that eradication was considered impossible. Today it
is found in every province in Ceylon (Mead 1955b).
China Herklots (1948) found full-grown specimens of the
giant snail in the Amoy University compound in June, 1931. Upon
inquiry, he learned that they had been brought on plants imported
from Singapore. Jarrett (1931, 1949) identified the specimens and
made the official announcement. No recent word has been received
about this infestation; but it is more than likely that the snails have
spread from Amoy Island to the mainland. From the initial main-
land infestation, other sites of infestation inevitably will become
established.
Formosa A dozen specimens of the giant African snail were
introduced into this island from Singapore by a Formosan govern-
ment official, Mr. Kumaichi Shimojo, in January, 1932. Because of
the cold weather and improper rearing techniques, all the specimens
died. In April, 1933, twelve additional specimens were brought in
and these survived and propagated to form breeding stock for subse-
quent introductions to Japan and Micronesia (Esaki and Takahashi
1942). By 1940, the giant snail had spread almost throughout the
island (Kaburaki 1940). Vosburgh (1950) made interesting observa-
tions on this snail in the interior of Formosa.
Hawaiian Islands Pemberton (1938) has given us a complete
and detailed report of the introduction of the giant snail on Oahu
and Maui. In 1936, a young lady returning from Formosa brought
two specimens of the giant snail in her baggage and released them in
her Oahu garden for aesthetic reasons. The specimens were neither
declared nor discovered by the port inspectors. In November of that
same year, a man imported specimens through the mails from Japan
to breed them in his home town of Makawao in Maui and to sell
them as materia medica. Esaki and Takahashi (1942) were not cor-
rect in indicating that the imported specimens came from Okinawa.
The infestations were not discovered until June, 1938 (Fullaway
1939), and in spite of intensive and continuous control measures,
eradication proved impossible, notwithstanding the frequent state-
DISPERSAL OF THE GIANT AFRICAN SNAIL
9
ments in the literature to the contrary. On Oahu, the snail quickly
spread from Pauoa Valley to Kaneohe on the windward side; and
on Maui it spread from Pauwela Gulch to other parts of the island.
By 1944, there were eight foci on Oahu and six on Maui (Fullaway
1941, et seq.). These populations were successfully corralled for sev-
eral years; but by 1951, new foci many miles away were making their
appearance (Wong 1951, Thistle 1953b, Weber 1954). Today, the
populations on Oahu are numerous and scattered. The infestation
on Roundtop near Honolulu is clearly among the most dense on
record (Mead 1959b). Although snails were found in the possession
of two men on Lanai, there has been no report of an infestation on
that island (Pemberton et al. 1939). In March, 1958, however, these
snails were found well established near Mana in the northwest tip of
Kauai; and two months later an infestation was first noticed near
Hilo on Hawaii (Mead 1958a, b, 1959b; Thistle 1959a).
Hong Kong On April 3, 1941, Jarrett positively identified as
A. fulica several snail specimens from the Happy Valley—Sookunpoo
area in Hong Kong Island (Herklots 1948). It was his belief that the
pest had been brought from Amoy, China, by Chinese duck farmers
four years previously. This would establish the date of the original
infestation as 1937 (Jarrett 1949). Within a decade, the infestation
had spread to a number of places on the mainland (Dean 1950).
India In February, 1847, W. H. Benson (1858) collected
specimens of A. fulica in Mauritius and released them the following
April in the Chouringhie Gardens near Calcutta. Later he learned
that they had spread a great deal. He also learned that all the speci-
mens released by Captain Hutton in Mussoorie (Masuri) at 6,600
feet altitude at the foot of the Himalayas in the Dehra Dun district
of the United Provinces died because of the severe winter. By 1907
they were common in the gardens of Calcutta (Annandale), and by
1910 the infestation reportedly had spread all over northern Bengal
and new foci had developed in Bombay (Green 1910c, d) and further
north in Rajkot (Comber). Ghose (1960) indicates that this snail is
found in some districts of Eastern Pakistan and in the northern and
eastern parts of West Bengal, but it is rare in the western parts of
West Bengal. The snail is also to be found in parts of Orissa and
Bihar (Behura 1955). H. C. Ray of the Zoological Survey of India
adds to this list the Central Provinces and Berar, although neither he
nor Ghose was able to obtain information regarding the present
status of the Bombay infestation.
Indonesia Probably more has been written about the intro-
duction and spread of the giant snail in Java than about the situation
10	DISPERSAL OF THE GIANT AFRICAN SNAIL
in any other place except possibly Hawaii; unfortunately, however,
the records are not always in agreement. Kalshoven (1950), for exam-
ple, reported that the giant snail was first brought into Buitenzorg
(Bogor) from Singapore in 1922; but it has also been stated (Anon.
1925) that they arrived in 1925 in a shipment of grass plants from
Peradeniya, Ceylon. Leefmans (1933a, b) said that specimens were
introduced clandestinely into Sukabumi, a suburb of Batavia (Dja-
karta), in 1930-31 and were taken into Batavia by plant breeders in
1933. Riel (1933) discovered the snails near Batavia in 1933 and
learned from the local inhabitants that they came from Singapore.
Van Weel (1948) and Jaski (1953) add confirmatory evidence. Ben-
them Jutting (1952b), Djaenoedin (1942), Franssen (1936), van der
Goot (1939), and Waterschoot (1933) contribute further information
on the continued spread of the snail. The most complete early paper
on the subject is that of Leefmans and van der Vecht (1933a, b, c).
L. J. M. Butot, formerly of the Museum Zoologicum Bogoriense,
makes the following statement regarding the giant snail population
in Java (in litt. Aug. 1, 1952), "I venture to say that the whole of
Java is infested except the mountain region upwards of 1000M and
some uncultivated parts below that level."
Van der Meer Mohr (1935, 1940, 1941, 1948) and van Weel (1948)
give the best accounts of the spread of the snail in Sumatra. This pest
apparently first made its appearance in northeastern Sumatra near
Tandjong Poera, northwest of Medan, in 1930 or 1931, although it
has been speculated that the snail may have been on the island since
1921. It showed up in southeastern Sumatra near Palembang in 1931
or 1932. Shortly after that, it appeared almost simultaneously in a
number of localities (Anon. 1941, Heubel 1937, Kalshoven 1950).
Latif (1933a) reported achatina from Poelau Bintan, Riouw Archi-
pelago, and explained that the inhabitants had seen the snail in that
region since about 1903. Van Weel (1948) justifiably questions the
initial date of establishment and sets it conservatively at 1932. The
original specimens apparently came from Singapore (Leefmans and
van der Vecht 1933a, b, c).
Latif (1933c) reported the giant snail for the first time from East
Borneo, indicating that it was found in Balikpapan in 1921 and ten
years later it was found in Samarinda. It was discovered in Koetai in
1938 (Witkamp 1941) and in Tenggarong about two years after that
(van Weel 1948).
G. S. Dun has stated (in litt. Aug. 12, 1949) that the giant snail is
found in Celebes and in Halmahera of the Moluccas Islands; but this
information has not been confirmed.
DISPERSAL OF THE GIANT AFRICAN SNAIL	11
Japan The giant snail (Japanese: katatsumori) was imported
a number of times into Japan proper from Formosa. Esaki and Taka-
hashi (1942) believed that the first shipments started in 1935; but
Tokubei Kuroda stated (in litt. Dec. 20, 1949) that they started
''previous to 1933." This would set the date close to the time when
the snails made their first appearance in Formosa; for this reason,
Boettger's (1951) date of 1925 would seem to be out of line. A num-
ber of magazine and newspaper articles popularizing the raising of
snails for food and medicinal purposes were instrumental in precipi-
tating a rather large-scale importation of snails into Kobe, Osaka,
Nagoya, and Nara. In May, 1936, it was recognized by the Ministry
of Agriculture and Forestry that the giant snail was a menace. Regu-
lations were set up immediately to confiscate and destroy all live
specimens in the country and prohibit the entry of further ship-
ments. The timely, thorough measures, along with the severe winter
climate, were completely effective in preventing the establishment of
this snail pest; and to this day, it is believed not to be present any-
where in Japan.
Malaya Both South (1923b, 1926b) and Jarrett (1923, 1949)
agree that the giant snail first entered Malaya in its northernmost
section, in Kedah, in 1911. From Kedah the snail was apparently
taken in 1922 to Province Wellesley by Chinese duck farmers who
used the snails as duck feed. From these northern infestations, the
snail quickly spread south into many areas of the peninsula (Birkin-
shaw 1928, Corbett 1929, Doscas 1929, South 1922, et seq.). There
has been much speculation as to the origin of the initial infestation.
It may have been imported directly from India or Ceylon, or it may
have come from India via Burma. In a relatively recent colonial pub-
lication (Anon. 1954), it is stated that the snail was probably intro-
duced from Ceylon in 1911.
Maldive Islands During the Yale Seychelles Expedition in
1957, Alan J. Kohn collected specimens of A. fulica on Hitadu Island
and Gan Island in the Addu Atoll; but he encountered no snails on
Ile du Coin, Peros Banhos Atoll, in the Chagos Archipelago. The
comparatively large amount of commerce between these islands and
Ceylon makes it most probable that the giant snail has been intro-
duced from Ceylon not once but several times.
Mariana Islands    All available evidence points to the conclu-
sion that the giant snail first made its appearance in the Marianas al-
most simultaneously in Rota, Saipan, and Tinian some time between
1936 and 1938 (Mead and Kondo 1949).
Esaki and Takahashi (1942) state that Hiroshi Kuwahata of Saipan
12	DISPERSAL OF THE GIANT AFRICAN SNAIL
made an investigation of the snail problem on that island in April,
1941, and concluded that the snails had been introduced the previ-
ous month. But the very widespread nature of the infestation at that
time makes his conclusion untenable. Other estimates place the date
nearer 1940 (Abbott 1949, Bequaert 1950, Lange 1950). Mr. Joaquin
Guerrero, who was acting director of the Naval Government Agri-
cultural Experiment Station in Guam in 1949, gave the author permis-
sion to quote the following from his report of December 26, 1945
which was addressed to the head of the Commerce and Industry De-
partment: "Mr. Jose Roberto volunteered the statement that during
the Japanese administration, he was shown a sample of these snails
preserved in alcohol by the Japanese authorities and was told they
were deliberately introduced into Saipan and Rota by the Okinawans
for use as food from one of the islands of the East Indies."
Guerrero's report announced that the presence of the giant snail
on Guam first came to the attention of the American authorities just
eight days previous to his report and that an investigation brought to
light a single area of infestation at Santa Rita. Guerrero states, "In
order to determine the possible time when this plant pest made its
invasion into Guam, I made an inquiry from Mr. Jose I. Shimizu, a
Japanese half-caste and old resident of the island, and was told that
the subject snails first made their appearance in Guam in 1943 when
the Japanese shipped into Guam sweet potatoes from Rota island."
Inquiries made by the author and Kondo did not bear out the often
quoted alternative suggestion that the giant snails were brought into
Guam in 1946 on pandanus leaves shipped from Saipan for native
handicraft (Abbott 1948, 1949).
By July, 1946, three separate infestations were found on Guam. At
least seven in north and central Guam existed in the fall of 1949
(Kondo 1950a, c). Four years later, infestations appeared in the
southern part of the island and it was predicted that it was only a
matter of time until the rich farming valleys in that section of Guam
would be overrun with snails (Peterson 1957).
The giant snail undoubtedly was taken from Tinian or Saipan to
the small island of Agiguan (Aguijan), just off the southwest coast of
Tinian, shortly before World War II; for it was found to be well
established when it was first discovered on this uninhabited island in
July, 1949 (Mead and Kondo 1949). The experimental introduction
of the predatory snail Gonaxis kibweziensis on this island has caused
more to be writen about its giant snail population than that of al-
most any other island in the West Pacific. Davis, Kondo, Mead,
Owen, and Peterson have been the main contributors.
DISPERSAL OF THE GIANT AFRICAN SNAIL	13
During the period September 21-October 1, 1949, Kondo (1950a,
c) made an intensive survey of Pagan Island and found it to be the
most northern of the infested islands in the Mariana chain. He
states, "The snail was first introduced in 1939 by Sato Gumi whose
wife had an infected lung. He raised the snails for medicinal purpose
but a man named Sonohara raised many of them for food."
Mead and Kondo visited the inhabited islands of Agrihan and
Alamagan in 1949 and found no verbal or environmental evidence
of the giant snail.
Mauritius Bequaert (1950b) offers convincing evidence in
support of his belief that A. fulica did not become established on the
island o£ Mauritius much before 1800. He translates the following
from the earliest published record of the infestation here (Bosc 1803):
"I have heard from an inhabitant of Mauritius that the wife of a gover-
nor of the island, ailing of the chest, had on doctor's orders fetched
from Madagascar many of these snails, since there were none in this
part of the colony. She died shortly after and the snails spread over the
island, increasing to the extent of becoming a calamity. They have
been hunted several times, but they are even now very common."
This at last sets straight an often quoted story which Benson (1858)
erroneously associated with the introduction of this pest on Reunion.
Since the original home of this species is in East Africa (Bequaert
1950b), it has been assumed that the snails were taken from East
Africa to Madagascar in recent times by natives who intended estab-
lishing them as an accustomed source of food (Dollfus 1899). Prob-
ably from there they were taken to the Comoro Islands (Morelet
1860). A short time before 1847, a second species, Achatina panthera,
was introduced into Mauritius by Sir David Barclay (Benson 1858).
Recent reports from Mauritius indicate that this newcomer has taken
over the lowlands from sea level to 1,200 feet, forcing A. fulica to
maintain its populations at the 1,200-2,000-foot level.
New Guinea There is little doubt that the Japanese forces
were responsible for the introduction of the giant snail into this
island prior to 1945, about the same time that it was introduced in
nearby New Britain and New Ireland (Anon. 1948e). Allan (1949),
Morrison (1950b) and De Wilde de Ligny (1953) have reported on
the New Guinea infestation.
North Borneo G. S. Dun of the Lowlands Agricultural Ex-
periment Station in New Britain, reports (in litt. Nov. 25, 1949) that
he had learned that the giant snail first appeared in British North
Borneo about 1939 and that it was "introduced to rubber plantations
outside Beaufort on infested budwood brought from Malaya."
14	DISPERSAL OF THE GIANT AFRICAN SNAIL
Palau Islands In their search for information about the his-
tory of the giant snail populations in the Palau Islands, Esaki and
Takahashi (1942) learned from the Palau Office of the Micronesian
government that the first introduction was made about May, 1938, by
Shoichi Nishimura, a farmer on Babelthaup (Asahi-mura), who
planned to breed them for use as food. Because for two years the
giant snail had been prohibited in Japan and Formosa, it is pre-
sumed that he obtained his specimens from Okinawa. In November
of that year a flood washed the snails into the lowlands of the
Garumisukan River. They survived the flood and began multiply-
ing. But before this some of the breeding stock sent by Nishimura to
several people on Koror made the inevitable escape from inadequate
cages, and natural populations were soon developing in the field.
Although in 1939 Hatai and Kato (1943) could hardly find any speci-
mens on Koror, by 1940 drastic control measures had to be instituted
in a vain attempt to halt the manifestly rapidly expanding popula-
tion.
In addition to Babelthaup and Koror, Kondo (1950a, c) found
Auluptagel (Aurapushekaru) and Peleliu infested with the snails.
Mead (1950a, c) added Anguar and Urukthapel to this list; and
Lange (1950) added Malakal and Arakabesan. Other infested islands
unquestionably exist.
Philippine Islands     There still remains considerable uncer-
tainty regarding when and how the giant snails made their way to
the Philippines. G. H. Halden writes (in litt. Nov. 1, 1949) that he
observed them in Pampanga and Santo Tomas, Luzon, during the
Japanese occupation, and he sent to the author a shell specimen
which he had collected at that time. It has been suggested that they
were brought from Formosa by Japanese soldiers (Anon. 1946a).
Pangga (1949), who gives the best account of the problem in this
area, follows this suggestion and sets the date of entry as 1942, al-
though he states that people claim specimens were collected in Pasay,
Rizal Province, before the war. By 1949 most of the provinces of
Luzon were infested, including the following: Batangas, Bulacan,
Camarines Sur, Cavite, Laguna, Nueva Ecija, Nueva Vizcaya, Pam-
panga, and Rizal.
Reunion        Bequaert (1950b) concluded that the giant snail
reached Reunion early in the nineteenth century, shortly after it be-
came established on Mauritius. Ferussac found it present in 1821. It
was Lesson's (1830) feeling that this species had been brought to
DISPERSAL OF THE GIANT AFRICAN SNAIL	15
Reunion from Madagascar; but Bequaert stated that it came from
Mauritius.
Ryukyu Islands       Nothing in the printed record has come to
light to indicate when the giant snail was first introduced into the
Ryukyus. It is most likely, however, that specimens from Formosa
were brought to Okinawa some time in 1934 or 1935, that is, shortly
after this pest became established in Formosa. It should be recalled
that it reportedly was from Okinawa that specimens were introduced
into some of the Mariana and Palau islands several years before the
war. The latest information is that the snail has become established
in Amami Oshima, which is close to half way between Okinawa and
Kyushu, the south island of Japan (Mead 1958a, b).
Sarawak According to Jarrett (1931, 1932), the giant snail
was introduced into Kuching in 1928 by Chinese farmers who in-
tended using the snails as feed for poultry. Tom Harrisson of the
Sarawak Museum writes (in litt. Aug. 25, 1952), "The snails have
steadily spread in the last 20 years but still have not reached far up
most of the rivers nor into the uplands. Centers of introduction seem
to have been in the southeast and southwest, and the distribution
gets lower and lower as one goes north."
Seychelles It is not known when the giant snails were taken
to this group of islands. Dufo recorded them as being present in
1840. Rees (1951) concluded that the snails were introduced from
Mauritius. Dupont (1935) listed A. fulica as being on Mahe, Praslin,
and Silhouette.
Singapore In February, 1922, Jarrett (1923) received several
snail specimens from the Balestier District of Singapore for identifi-
cation. These he identified as A. fulica. From an examination of the
infestation, he concluded that they could not have been introduced
into the island before 1917 (Jarrett 1949). This places the Singapore
infestation six years later than the first infestation in northern Ma-
laya and sets straight some of the confusion in the earlier literature (cf.
South 1926b). It is of the highest likelihood that Singapore received
its infestation from Malaya, and not once, but many times.
Thailand Living specimens from Thailand were obtained in
1938 by Boettger (1951); from this he concludes that at least by 1937,
the first snails entered from infested areas in Malaya. This agrees
with the estimates of Abbott (1949) and Rees (1951). Ariyant Manji-
kul of the Central Research Station in Bangkhen writes (in litt. Feb.
14, 1952): "In Thailand this snail is confined to the southern prov-
16	DISPERSAL OF THE GIANT AFRICAN SNAIL
inces of the peninsular strip of this country. It is supposed to have
been introduced by the Chinese from Malaya. It makes a very good
feed and the duck raisers collect them for the purpose." In Decem-
ber, 1957, Mead (1958a, b) found thoroughly intrenched infestations
of this snail in central Bangkok.
Vietnam Both Boettger (1951) and Rees (1951) agree that
the giant snail must have reached Vietnam by 1937. Efforts to ob-
tain more recent information on the status of the infestation have
failed.
CHAPTER 3
FACTORS
FAVORING
DISPERSAL
AND  SURVIVAL
Man—the Principal Agent of Dispersal      There are many fac-
tors, both intrinsic and extrinsic, which either directly favor or
otherwise predispose to a greater spread of the giant snail. Chief
among these is the human factor—to the extent that man might justi-
fiably be considered the only effective disseminator. There are many
references in the literature to wilful introductions of achatinas into
uninfested areas. In fact the history of the spread of Achatina fulica
is in its larger portion little more than a series of one intentional
introduction after another. Puteh (1939), for example, relates that
"several peasants from the inland [Singapore] who had never seen
these snails, came to Cherang Ruku and took some specimens for the
purpose of breeding them, saying that they looked very beautiful!"
The stories about one of the Oahu introductions (Pemberton 1938)
and one of the Djakarta introductions (van Brero 1933) read almost
the same way. A check of the literature indicates that to a great ex-
tent the intentional introductions of A. fulica have been cases of
Oriental people introducing the snails for duck feed (e.g., Jarrett
1949). Live specimens of this species were either sent or carried from
Siam to Berlin (Boettger 1951); from East Africa to London (Burton
1949); from Rajmahal, India, to London (Godwin-Austin 1908);
from Singapore to London (Jarrett 1932); from Mombasa, Kenya, to
the Belgian Congo (Anon. 1927a); and from Kenya to London (Rees
17
18	FACTORS FAVORING DISPERSAL AND SURVIVAL
1951).1 In another case, specimens were sent from Singapore to Java
in a tin container labeled "flower seeds" (van Leeuwen 1932). This
same intent to import the giant snails is reflected in a letter from an
Italian correspondent who requested of the author information as to
how he might successfully introduce the giant snail into Italy "where
food is very dear and scarce."
Specimens of an unidentified species of Achatina were sent from
Zanzibar to Germany (Semper 1890); and Longstaff (1921) returned
to England with three specimens of A. zebra from Cape Colony.
Andrews (1948) purchased from a Chicago dealer a specimen of the
huge A. achatina which was kept for some time in his home in Bal-
timore. It escaped once but was found; shortly afterward it laid a
number of eggs which fortunately were improperly cared for and
none hatched. He suggested that these snails might be developed in
Florida as an additional source of food for us. This drew an imme-
diate sharp rebuke from Hanna (1948). Similarly, the taking of this
species into California by Dickinson (1946) was exposed and cen-
sured by Hanna (loc. cit.) and Mead (1949b). At least until a very
few years ago, specimens of A. fulica, A. achatina, and A. ventricosa
were to be found alive in the National Zoological Park in Washing-
ton, D.C. A similar situation exists in the larger zoological parks in
Europe and elsewhere.
As for the unintentional introduction of giant snails, Connolly
(1912) reports specimens of A. fulica arriving in Durban, Natal, in
flower pots sent from Mauritius. Other specimens were found in
Java in the soil of a shipment of grass plants from Ceylon (Anon.
1925, Leefmans and van der Vecht 1933a). Latif (1933a) records an
instance in Riouw Archipelago in which orchid shipments, appar-
ently bound for Java, were found infested. Many other interceptions
of this species are on record. Other species of giant snails have also
been taken under similar circumstances. Archachatina marginata
was found in Berlin on a bunch of bananas originating in the Cam-
eroons (Boettger 1937, 1938). Paravicini (1926) states that Achatina
craveni was being spread in East Africa through shipments of plants.
Still other records of the interception of achatinids have been com-
piled by Boettger (1947). It would be utterly impossible at this point
to give any conception of the multiplicity of reports in the literature
of introductions, intentional and otherwise, of live mollusks into
1 Dartevelle (1952b) reports that a small shell of A. fulica hamillei has been found in
what was then called the Belgian Congo. Since this species is not endemic in this area,
he assumes that the specimen was imported as an amulet from East Africa by one of
the natives.
FACTORS FAVORING DISPERSAL AND SURVIVAL	19
non-endemic areas. This has been going on for years and will con-
tinue indefinitely. It thus remains as one of the big forces with which
to reckon in setting up control programs.
The reason for most of the unintentional introductions of snails,
and of A. fulica in particular, may be found in the sheer mechanics
of the many diverse and varied activities of man. As one extreme,
Campbell (1897) relates in an unintentionally humorous vein how
snails even can be "carried about unconsciously by persons on their
clothing." The single greatest human factor contributing to the
spread of the giant snail is the desire and necessity for members of
the human species to be frequently on the move. Coupled with this
is the propensity of the snail for crawling back into recesses—recesses
which all too often are in the possessions of man. These are carried
from place to place and, thus, so are the snails. For this reason, com-
mercial traffic in produce can be particularly threatening and it is
therefore the main avenue checked in carrying out quarantines. The
author has witnessed in Micronesia the transportation of A. fulica
in bunches of bananas, a favorite among native peoples for gifts and
trading, and this evidence is offered as the most likely explanation
for the spread of this species to several islands in the Truk group
(Mead 1950b, c). Shipments of inedible plants or plant products (e.g.,
grass thatching) provide ideal retreats for the snails (cf. Jarrett 1923).
Even soil, especially that containing nursery stock, is not to be over-
looked as it may harbor both eggs and snails. It is thus not surprising
that Corbett (1933) found the giant snails in the exhibition ground
of the Malayan Agri-Horticultural Association. Estivating snails
often attach themselves to stored or abandoned war equipment. This
helps to explain why war salvage equipment has consistently yielded
the greatest share of the giant snails intercepted by quarantine au-
thorities in the United States. Messenger (1952:253-54) has shown
illustrations of this type of contamination. This also explains why
railroad yards (Corbett 1933), shipyards, and the like have often
been found to be the primary site of establishment of new popula-
tions. Pereira (1926) has stated that the giant snail was carried into
new areas in Ceylon through the agency of motor vehicles. Abortive
attempts to effect a control have in some cases succeeded only in
spreading the snails still further, for example, attempting to drown
the snails in streams (Green 1910c). It is significant that the giant
snail population on uninhabited Haha Jima in the Bonin Islands
was found to be restricted to a relatively small area, whereas the
equally old snail population on inhabited Chichi Jima was found
20	FACTORS FAVORING DISPERSAL AND SURVIVAL
scattered all over the northern part of the island from valleys to
mountain tops (Mead and Kondo 1949).
The pronounced appetite for rotting and decaying materials is
the main reason that the snails have frequently been reported con-
gregating in garbage dumps and refuse heaps. And for the same
reason, the normal accumulation of material of this sort around the
habitations of people living in the tropics has fostered the main-
tenance, spread, and sometimes restriction of these snails to inhab-
ited areas. Abandoned native crops provided a similar situation,
particularly when the exigencies of the war caused many to abandon
their land just at the crest of the invasion of the giant snail. In other
cases, the crops were abandoned because of the depredations of the
snails, thus contributing directly to the expanding snail population.
One thing is certain: whenever man enters the picture, he introduces
undetermined, altering, ecological factors which make the environ-
ment more suitable for snail invasion and maintenance. The effect
of these factors seems to carry on for some time after man leaves the
area; but as the abandoned land gradually returns to native bush, it
strangely becomes less and less acceptable to the snails.
Among the more subtle factors operative in man's contributing
to the dispersal of the snail is the almost universal strong objection
in the non-endemic areas to the very thought of eating snails. But,
even more than a matter of innate repulsion, in some areas eating
the flesh of such a lowly earth-dwelling animal as a snail is a distinct
taboo. The dominance of the Buddhist and Hindu religions in many
of the Far Eastern snail-infested areas is directly responsible for the
actual "protection" of these pestiferous snails. One good Buddhist
acquaintance of the author complained that even in the city where
she lived, the snails were so abundant that every night she collected
two baskets full, and by the next night, there were as many more in
her small garden. Knowing that she certainly had not killed the
snails, I asked what she does with the baskets of snails after they
are collected. To this, she answered, "Oh, I just take them across
the street and dump them on the other side." If her Buddhist neigh-
bor across the street is as fastidious as she, it can be imagined that
these two ladies have been trading snails for a long, long time! As
one might guess, attempting to set up any sort of control program
in these Far Eastern countries is frustrating in the extreme; for even
though one may have the co-operation of the well-educated local
official, the most orthodox laborers steadfastly refuse to be parties
to the crime. Hence, if control measures are set up at all, they more
often are half-hearted and ineffectual. It can be seen, then, that al-
FACTORS FAVORING DISPERSAL AND SURVIVAL	21
though man is basically the single greatest factor known in the
"natural" control of the giant African snail, there are whole areas
of the world where this factor has virtually been eliminated. Man,
therefore, once again has unwittingly fostered the spread of the giant
snails.
Longevity The specimen of A. fulica which van Leeuwen
(1932) kept in captivity for nine years is clearly the record for this
species. It is very possible, however, that his specimen spent a large
portion of its life in estivation. Because the body processes are at
their lowest ebb during estivation, it is altogether logical to reason
that the resultant economy in the physiological mechanisms delays
the normal gerontologic changes that bring on senescence and death.
Longevity could thereby conceivably be extended by an amount
comparable to the capacity to withstand estivation, although ex-
cesses in frequency or duration in estivation could produce just the
opposite effect. As is shown below, this species will readily retreat
into quiescence for protracted periods. It is felt, therefore, that van
Weel (1948) was probably correct in assuming that van Leeuwen's
specimen represents "an exceptional case." But as a case it does seem
to emphasize the fact that estimates of the longevity of this species
have probably been on the low side.
According to Pelseneer (1935:620), Gibbons reported that A. fulica
lives for at least two and a half years. The closely related A. zebra,
however, lived for six and a half years in captivity in London (Long-
staff 1921). The only other record for an achatinid is that of Flower
(1922), who states that a small Limicolaria from Sudan lived in
captivity for one year and twenty-one days. In strong contrast are
the records of longevity of much smaller pulmonates (e.g., twelve
years for Rumina decollata [Vignal 1919], thirteen years for Helix
spiriplana [Vignal 1923] and twenty-three years for Oxystyla capax
[Baker 1934]). Considering the length of life in other pulmonate
gastropod species (cf. Woodward 1880, Pelseneer 1935), it is felt that
an average life span of five to six years is a conservative estimate for
A. fulica. Where specimens are in areas perennially offering opti-
mum conditions for protracted activity, the normal life span possibly
may be shortened by a year or more.
Reproductivity  In determining the reproductive potential of
A. fulica, one must know how long it lives, how soon it begins to lay
eggs, how often it lays eggs, and how many eggs are laid at a time.
One additional factor has been well known from the first: This
animal is hermaphroditic and therefore each individual is a pro-
22	FACTORS FAVORING DISPERSAL AND SURVIVAL
ducer of eggs; further, any two sexually mature individuals have the
capacity for being mutually receptive in cross fertilization.
Van der Meer Mohr (1949b) reported that he had repeatedly ob-
served "self-fertilization" in A. fulica in Sumatra. Rees (1951) inter-
preted the report as a warning with the words, "This means that
the introduction of a single snail to a new country is enough to start
a colony." In correspondence with the author, van der Meer Mohr
later stated that his conclusions had been based on the fact that
snails of seven and a half whorls kept in isolation for as long as 382
days still laid viable eggs. To check his conclusions, van der Meer
Mohr (in litt. Nov. 5, 1951) kept "virgin" specimens in isolation for
two years. None laid eggs. He therefore retracted his original con-
clusion and reinterpreted his data to mean that a single copulation
was sufficient for the fertilization of a number of batches of eggs laid
intermittently over a period of many months. It would now appear
that van Leeuwen's specimen kept in captivity for nine years with-
out laying eggs had apparently never copulated. In the absence of
autofertilization, Rees's warning still is to be taken almost as seri-
ously as it was given; for a single, fertilized, young specimen is
capable of laying a great many viable eggs, even after months of
estivation.
Information regarding the period necessary for attaining sexual
maturity was given by G. S. Dun (in litt. Nov. 25, 1949), who re-
ported that snails raised by him from the egg laid their first batch
of eggs at the tender age of five to eight months. This concurs almost
exactly with the unpublished findings of Daniel B. Langford in
Guam. Garnadi (1951) independently reports it as eight months.
Earlier, Leefmans (1933c) stated that with an abundant supply of
CaCO3 the first eggs were laid in six months; and without it, nine
months were required.
According to observations in Micronesia, the number of eggs laid
at a time by the average, normal appearing adult snail was found to
be close to 300. In Ceylon, the number was found to be nearer 200.
Mature pygmy individuals in the Isley Field population in Saipan,
however, produced only 30-60 eggs at each laying. Kondo has indi-
cated that the maximum number may go over 500 eggs. Atoda's
maximum of 733, as reported by Hatai and Kato (1943), quite prob-
ably represents total productivity during the period of observation
as his largest snail specimen was only 66 mm. long from base to apex.
The whole question of total productivity of A. fulica still rests very
much in the realm of speculation as the existent figures are based
on specimens held in captivity for only a portion of their life or
FACTORS FAVORING DISPERSAL AND SURVIVAL	23
until they happened to die. Field observations, however, indicate
strongly that under optimum conditions, this species will lay a batch
of eggs every few weeks for apparently an indefinite period of time
or until the advent of unfavorable conditions. There probably is a
natural tapering-off in productivity with advanced age; but this also
has not been determined for certain.
Green (1911b) assumed that A. fulica lived two years and that it
laid 100 eggs the first year and 200 the second. From these pure
assumptions, he estimated that one gravid individual would give rise
to 10,930,442,400, or approximately 11 billion snails, in a period of
five years. This figure has been quoted many times in the literature.
Van Weel (1949), however, points out that the annual output of eggs
would actually be nearer 900-1200; but he makes no estimate as to
how these higher figures would alter Green's total. Morrison's esti-
mate (1950b) was ten times that of Green, but it is still too conserv-
ative. In the light of our present knowledge of the life history of
this snail, and figuring very definitely on the conservative side, let
it be assumed that the snails mature in nine months after hatching,
produce four batches of eggs a year of 150 eggs each, and live for at
least five years. At the end of a three year period, the progeny from
one gravid individual, if all lived, would total 7,783,764,301 or nearly
8 billion. With numbers building up exponentially in multiple
geometric series, another two years would show an increase to 16,-
121,432,399,695,050 or somewhat over 16 quadrillion!
In order to grasp fully the significance of the latter figure, it is
almost necessary to interpret it in terms of time and distance. Thus,
if we conservatively assume that each individual is 4 inches long and
that all the progeny is arranged in a straight line, there would be
15,840 snails per mile for 1,017,767,196,950 miles. This distance
would be equivalent to over 2,130,494 round trips to the moon or
over 5,477 round trips to the sun. And with light traveling 186,300
miles per second, it would take well over two months for it to travel
the distance from the first to the last individual. On the other hand,
if one were to count these 16 quadrillion snails, day and night, at
the rate of one a second, it would take over half a billion years. This
in reverse would take the counter back to the mid-Cambrian, during
which period most of our oldest fossils were formed. And as a final
comparison: This number of snails would permit each man, woman,
and child in the world today to have over 80 million all to himself
—or somewhat over 125 acres of snails packed just as closely as pos-
sible in a single layer.
This prodigious reproductive potential of A. fulica significantly is
24	FACTORS FAVORING DISPERSAL AND SURVIVAL
in strong contrast to that of predatory snails. According to Kondo
(1951b), the predatory snail Gonaxis kibweziensis gives rise ovip-
arously to only three or four encapsulated, advanced embryos at a
time. These are brought forth at an apparent maximum average rate
of every ten days during the breeding season for a "reproductive
potential of 11 maximum per year (in laboratory)" (Kondo 1956).
         Variability  Among the most striking impressions one gets as
one examines the various populations of A. fulica is the pronounced
difference in appearance of the snails. This point has been empha-
sized and elaborated upon by both Kondo (1950a, c, 1952) and Mead
(1950b, c). Jaski (1953) has been so impressed with the variability in
the specimens in Java that he has suggested an explanation might
be found either in "recent spontaneous mutation" or "cross-breed-
ing" of the Japanese introduced stock with the stock issuing from
the original infestation.
In the Santa Rita and Laguna populations on Guam, the shells are
commonly close to six inches in length and are exceedingly thick.
Not far away, giant specimens have been found that have exceeded
seven inches in length. Probably the record specimen was found by
G. D. Peterson; it measured just one-eighth of an inch under eight
inches! In contrast, the Isley Field population in Saipan, in the
midst of an abundant supply of calcium carbonate, was made up
largely of ''pygmy" but mature specimens in a size range of two to
three inches in length. Shells from Anguar Island in the Palaus were
found to have a deep, rich, contrasting color pattern, a thick perios-
tracum, and a high nacreous gloss. Farther north, on Koror Island,
a large share of the snails had shells that were dull, chalky, devoid
of a periostracum, and so pale that they appeared almost white. One
out of every three or four shells in the Army Hill population in Saipan
were also pale and devoid of a periostracum; in addition, however,
they not only had an arcuate axis, which gave them a "bent-nose"
appearance, but had so many lamellate layers of calcareous material
deposited around the aperture that the snail could withdraw only part-
way into its shell. The average specimen encountered in Micronesia
was found to be of moderate size (3 1/2-4 1/2 inches), to be so thin that
they could be broken with ease, and to have a body whorl that was
unicolorous olivaceous-tan. Specimens from Manila and India have
the proportionately larger body whorl as does A. fulica hamillei from
East Africa. On the other hand, specimens from some populations in
Ceylon and Hawaii, besides being considerably darker in color, have
such a long axis and reduced body whorl that they always roll with the
aperture upward when they are placed on a flat surface. Nearly all
FACTORS FAVORING DISPERSAL AND SURVIVAL	25
populations have a small percentage of anomalous forms; Germain
(1921) has made an interesting study of these.
An explanation for these and other apparent differences is not
difficult to discover. Environmental influence, of course, is being
expressed; but the extent has not been determined. In particular,
the works of Moore (1936), Ino (1949), and Wagge (1952) bring forth
convincing evidence to demonstrate that diet has a pronounced effect
upon the appearance, and especially the color, of the snail shell.
Because some variable physical characters persist in the same ex-
pression in individuals of populations under wholly different envi-
ronmental conditions, it is assumed that these characters are of
genetic origin. The genetic makeup of a given population is pre-
determined to the largest extent by the genetic complement possessed
by the invariably few specimens which started the population. As
these first few specimens give rise to subsequent generations, the
various genetic combinations make their appearance. The environ-
ment, in turn, has its own complement of variable ecological factors.
This complement will literally "select'' from the genetically variable
snails the combination of genetic characters which is best suited to it.
Had the original first few snails been of a different genetic makeup,
other genetic combinations would have been available, and the en-
vironment might therefore have selected differently. Another envi-
ronment would have selected still differently. The many different
appearing snail population types, then, would seem to be explained
by the simple combination of small initial population, isolation,
inbreeding, considerable genetic variablity, phenomenal reproduc-
tivity, and environmental diversity. Variability thus is of survival
value and it helps to explain the success this species has had in be-
coming established in the many different environments in which it
now is found. We do not know the limits of genetic potentiality in
producing still different and still more hardy individuals.
Estivation and Hibernation       In 1930 Duval made a significant
finding when he determined that the freezing point was lower in
hibernating Helix pomatia than in active individuals of the same
species. This work was followed quickly by that of von Brand (1931,
1932) confirming the predictable fact that the H2O content of H.
pomatia is actually lower during hibernation than during periods
of normal activity. Kamada (1933) corroborated with the report that
the blood of hibernating H. pomatia was isotonic with 0.69 per cent
NaCl whereas that of active individuals was isotonic with 0.50 per
cent NaCl. These findings meant to Howes and Wells (1934a, b) that
hibernation as a physiological phenomenon requires "elaborate met-
26	FACTORS FAVORING DISPERSAL AND SURVIVAL
abolic preparations," whereas estivation, which is also a resting
phase, is a comparatively simple physiological phenomenon. The
two phenomena are elaborated upon by Pelseneer (1935).
Estivation in A. fulica is of the commonest occurrence. In fact, of
the great many populations of this species that have been examined
by the author in almost every conceivable type of environment there
never has been one in which an estivating individual could not read-
ily be found. A direct correlation between estivation and reduced
moisture in the environment has been independently arrived at by
a number of investigators. But it was not until the observations of
Howes and Wells (1934a, b) that an interpretation was advanced to
explain the presence of estivating individuals even under optimum
conditions for snail activity. It was their conclusion that "there was
a tendency for phases of estivation to alternate with phases of ac-
tivity during the life of any one individual, even under approxi-
mately constant external conditions, so that at any time some of the
animals would be in either phase." They concluded further "that
estivation is the result of a low water content, and that the latter may
be brought about either by dryness of the environment or else by
the natural hydration cycle of the animals." The significance of these
conclusions is tremendous; for in them is found the explanation for
the fact that no combination of even the most rigorous control meas-
ures, under apparently ideal conditions, have ever been effective in
eradicating A. fulica. In other words, it is the well-secreted, estivating
individuals that are responsible for restocking an infested area after
the effects of normal or man-made adverse conditions have dissipated.
Although estivating snails are most often found under protective
conditions that are very superficial, some individuals work their way
into remarkably inaccessible niches. They have been found far under
sizable rocks, deep in hollow trees, in the center of rotten logs, high
in the crotches of trees, far into plant debris, and under many pro-
tective layers of man-made litter. The inhabitants of Chichi Jima
stated that during the winter months A. fulica specimens are found
four to five inches below the ground. In the former Belgian Congo
A. rugosa has been found four inches below the surface of the ground
in a dry, open, sunny spot (Bequaert 1919). Others have been found
"several inches" in the ground (Lang 1919). In Ceylon it was ob-
served that during mildly adverse conditions, such as a brief dry spell
during the rainy season, specimens of A. fulica to a great extent
tended to remain in a quiescent state on the tree trunks. Usually
they were in a range of 3-9 feet from the ground, although specimens
were observed to be as high up as 30-35 feet in the dadap trees. At
FACTORS FAVORING DISPERSAL AND SURVIVAL	27
these times the ground-dwelling predators remained active and it
was therefore a temptation to ascribe a protective function to this
behavior of the snails. When environmental conditions were favor-
able, a large percentage of the snails would make nocturnal visits
to the ground but would retreat to the tree trunks with the approach
of day. Under prolonged adverse conditions, however, the snails
would leave the tree trunks to seek normal estivation sites on or in
the ground. At such times many of their predators, significantly, also
were inactive.
During estivation a thin, fragile, muco-calcareous epiphragm is
formed over the aperture of the shell. This epiphragm is normally
complete except for a thin grooved slit over the pneumostome per-
mitting the reduced respiration to take place. The slightest disturb-
ance may cause the estivating snail to withdraw farther into its shell.
This invariably ruptures the epiphragm. The snail may then repair
it, replace it with a new one, or go into a period of activity. The
general subject of epiphragm formation has been treated by Hora
(1928) and Hora and Rao (1927). The epiphragm of A. immaculata
has been described by Smith (1899); and Williams (1951) has de-
scribed the epipragm of A. albopicta. Of particular interest is his
description and illustration of the tubular epiphragm formed by
specimens estivating on tree trunks. This apparently has never been
observed in A. fulica, although specimens adhering to vertical sur-
faces have very often been observed to attach themselves at the
aperture by a more parchment-like secretion before forming the
normal, flat, complete epiphragm.
It is definitely not known whether A. fulica can actually undergo
hibernation with all its attendant complex physiological adjustments.
In Hong Kong, Herklots (1948) stated, "In the cold, dry winter
months they hibernate. . . ." It is possible, though, that the quiescent
individuals to which he referred were really in a continuing state
of estivation which had been initiated by the dryness of the late fall
months. Specimens in that area examined by the author in January,
1955, behaved no differently from those known to be in estivation
in other areas. The most northerly, well-established populations of
this species are in Ani Jima and Chichi Jima of the Bonin Islands.
The "shivering cold" weather in those islands, however, is quite
comparable to that of Hong Kong inasmuch as weather records for
Chichi Jima indicate a low of 45° F. during a recent thirty-year
period (Kondo in litt. Jan. 6, 1950; cf. Clayton 1927). But irrespec-
tive of whether it is hibernation or estivation, the fact remains that
A. fulica in these cooler areas not only survives, but thrives.
28	FACTORS FAVORING DISPERSAL AND SURVIVAL
Hardiness Coupled with the phenomena of estivation and
hibernation is the physiological faculty of being able to survive pro-
longed periods without food or water. There is strong evidence that
the duration of a period of quiescence is closely correlated with
temperature. Under tropical conditions, A. fulica has been reported
to have survived periods of estivation, without food or water, for
5 1/2 months (Lange 1950), 7 months (Mead 1950b,c}, 10 months
(Corbett and Pagden 1941), and 12 months (G. S. Dun in litt. Nov.
25, 1949). G. S. Butler in Hawaii placed 27 specimens in a jar with-
out food or water in November, 1958; 10 months later, 10 specimens
remained alive. Archachatina degneri was still living after having
been kept under similar conditions for nearly 6 months (Mead 1950a).
In the literature, the record for duration of estivation is 15 years for
an unnamed snail species (Bingley 1829); the scientific accuracy of
this record, however, is open to question. The classical example,
often referred to, is that of Xerarionta veatchii which estivated for
6 years (Stearns 1868). Other records worth noting are Paludestrina
ulvae (a freshwater snail), 5 years (Quick 1924); Helix desertorum,
4+ years (Baird 1850); Otala lac tea, 4+ years (Gaskoin 1850); "many
Helices," 3+ years (Calkins 1877); Bulimulus pallidior, 2+ years
(Stearns 1877); and several common European helicine species, ap-
proximately 1 year (Hartley 1898, Lockwood 1880, Sivers 1872,
Ward 1879). Kew (1893) gives a general treatment of the subject.
Even though the record so far for A. fulica lines it up with the lesser
lights in the literature, the faculty for estivating for a whole year
without food or water equips this species well for surviving even the
slowest, most devious trip to an uninfested land.
Dun (loc cit.) stated that after twelve months in estivation his
specimens of A. fulica had lost approximately 60 per cent of their
original weight. Specimens emerging from estivation were observed
both in the Pacific islands and in Ceylon to "drink'' water by rasping
at drops. In this manner, other species have been reported to take up
80-100 per cent of their weight in water in a short period of time
(Zimmerman 1931). Anatomical examinations of estivating A. fulica
have shown that several of the organ systems are drawn upon for
sustenance. One of the first to be affected is the reproductive system;
this becomes atrophied and proportionately attenuated, resembling
superficially the condition in the juvenile specimen (Mead 1950a,
b, c). This same phenomenon has been reported in other species
(Laviolette 1950). The general subject of resistance to desiccation
has been ably elucidated by Gebhardt-Dunkel (1953). Important as
a consideration in the present study is the classical work of Shelford
FACTORS FAVORING DISPERSAL AND SURVIVAL	29
(1913) which establishes the fact that the rate of evaporation in an
environment is the result of the combined action of wind, tempera-
ture, isolation, and dryness of the air. It is this rate of evaporation
which closely determines, inversely, the rate of activity of terrestrial
gastropods in general; and A. fulica is manifestly no exception. In
fact, it was observed innumerable times in Ceylon and in the Pacific
islands that this species is extremely sensitive to even a slightly ele-
vated evaporative rate.
Food, as a vital factor in the environment, is quantitatively and
qualitatively infinitely more flexible in the life of A. fulica than in
almost any other animal that could be mentioned. As pointed out
below, this snail has a tremendous range of acceptable foods; now
it is apparent that it can go without all food, including water, for
months on end.
The environmental factor of temperature operates apparently in
a much more limited range than the factors of food and water. A.
fulica dies quickly when exposed to the direct sunlight; however, a
humid, tropical climate in general seems to offer the nearest to op-
timum conditions for this species. Such a climate is also conducive
to typically luxuriant plant growth which affords ample protection
for the giant snail during the daylight hours. As this snail has rapidly
extended into many new areas in the past few years, it has "taken
hold" in some environments which seem far indeed from what might
have been predicted as acceptable. For instance, beach populations
were encountered in the Bonin and Mariana Islands, which had
such formidable barriers as open stretches of barren, hot sand, and
adjacent vegetation covered with fine salt crystals from the constant
ocean spray (Kondo 1950c). The fact that this snail was able to crawl
over salt-covered vegetation with apparent impunity attests to its
remarkable adaptability and hardiness. But as far as the excessively
high temperature of the beach areas is concerned, it was the normal
nocturnal habits of the snail which permitted it to forage under the
suitable conditions of reduced temperatures and concomitantly
higher relative humidity. This, incidentally, is a point completely
overlooked by those who are prone to preconception in deciding
whether or not a given environment will be acceptable to the giant
snail. As a parallel, Jarrett (1922) announced on the basis of a small
amount of empirical evidence that the European Helix aspersa could
not take hold in Malaya. Others had similarly predicted that this
species could not survive in the Sonoran southwestern part of the
United States; yet it was recently found to be well established in
southern Arizona (Mead 1952a, 1953a).
30	FACTORS FAVORING DISPERSAL AND SURVIVAL
The capacity of A. fulica to withstand reduced temperatures is an
almost completely unknown quantity. The experiments of Chock
and Nakao (1951) provide the only information extant on this sub-
ject; but even these were very limited in their scope and, therefore,
misleading. Their experiments consisted of placing snail and egg
specimens in "standard refrigerators of various models" set at 20° F.
at r.h. 52-56, 30° F. at r.h. 55-65, 40° F. at r.h. 35-40, and 45° F.
at r.h. 40-50. Specimens were set up in the following groups: eggs
on the surface of soil, eggs buried in one inch of soil, active adults
on the surface of soil, active adults buried with three inches of soil
around them in every direction, and dormant adults on the surface
of soil. The groups were exposed to a given reduced temperature for
a varying number of hours or days. The lethal minimum exposure
for 45° F. was reported as 4 days for active snails on soil, 4 days for
active snails in soil, and 7 days for dormant snails. The eggs proved
to be very susceptible to all reduced temperatures. Some investigators
unfortunately have accepted the reported results of these exploratory
experiments as definitive and have speculated as to just where in the
world A. fulica could become successfully established. Both as a note
of caution and as a guide in future experiments in the problem of
reduced temperature tolerance, certain points should be emphasized.
In the experiments of Chock and Nakao, there are some inconsist-
encies in results which seem significant. Nineteen out of 20 dormant
snails, exposed to a temperature of 40° F. for 24 hours, remained
alive after 5 days; 7 out of 10 active snails, exposed to a temperature
of 30° F. for 8 hours, remained alive after 5 days; and 1 out of 10
dormant snails, exposed to a temperature of 20° F. for 8 hours, re-
mained alive after 5 days. The inference is that larger samples might
have told a somewhat different story, especially regarding survival at
the population level. In strong contrast to these survival rates in the
preliminary series of experiments, the supplementary series conspic-
uously showed consistently complete killing throughout the experi-
mental results. No explanation was given for this. Although humid-
ity was controlled to an extent, it was not treated as a constant; and
this fact doubtless has influenced the results as another variable.
An important consideration which was apparently overlooked in
the experiments is the distinction between estivation and hiberna-
tion. The "dormant" specimens were obviously in estivation; yet
they were subjected suddenly to conditions demanding a hibernation
response. Although it should have been the dormant specimens
rather than the active specimens that were buried in soil during
these experiments, burying them in the manner that they did, with
FACTORS FAVORING DISPERSAL AND SURVIVAL	31
three inches of soil all the way around, did not duplicate conditions
in the field where heat loss takes place essentially from a single plane.
Naturally, there would be in the field an additional insulating effect
produced by superincumbent logs, rocks, plant debris, rubble, and
the like.
The most important factor which has not been taken into con-
sideration in these experiments is that which concerns the acclima-
tization or conditioning of the animal as it gradually is exposed to
lower and lower temperatures. Actually, after a snail has been feed-
ing actively for several days, it extends so far beyond the lip of its
shell in the fully contracted condition that it cannot possibly form
the protective epiphragm even though sudden adverse conditions
may demand it. Normally, a period of less favorable conditions will
effect a gradual water loss which, among other things, will permit
of epiphragm formation. The entomologists have demonstrated
many times that certain insects will adjust to remarkably low tem-
peratures if they are arrived at slowly enough. Cockroaches put
suddenly in a cold chamber will die in a short time; and yet if sev-
eral days are taken to reach gradually the temperature in the cold
chamber, these insects will undergo physiological changes, including
the alteration of the water content of the cells, and withstand suc-
cessfully the lower temperatures for prolonged periods of time
(Wigglesworth 1953). It therefore brings no surprise that many in-
sect pests are infinitely more abundant after a mild winter than they
are after an unseasonably sudden cold snap. It doubtless is this phe-
nomenon of a physiological adjustment that permits the giant snail
to maintain vigorous populations in the Bonin Islands despite the
relatively cold winters. Apropos of this, it has been suggested that
a possible sensitivity to the greater diurnal-nocturnal fluctuations
in temperature at altitudes above 5,000 feet have kept A. fulica
conspicuously only at the lower altitudes (see p. 197).
As an interesting and possibly significant sidelight, Longstaff
(1921) kept specimens of Achatina zebra in London for six and a
half years, during which time the temperature in the conservatory
where they were kept "did not fall below 45° F." He observed that
during the colder months, they remained buried for many weeks
at a time.
The faculty of A. fulica to withstand trauma and even an extensive
loss of its shell attests still further to its general physical hardiness.
Particularly in the islands of the Pacific, specimens are frequently
encountered that have shells almost unbelievably damaged. On in-
spection, it can be seen that the shells have suffered many breaks. Some-
32	FACTORS FAVORING DISPERSAL AND SURVIVAL
times the broken shell pieces are not dissociated and are repaired in
place. But, more often, the pieces break off completely or become bad-
ly dissociated; under such conditions, repair produces an unsightly
shell that gets progressively worse with each subsequent break. Occa-
sionally the mantle becomes damaged and this adds to the distortion
through malformation of the new shell. Kondo (1950c) has reported
instances where specimens have survived the loss of the lower 2-2 1/2
whorls of their shell; and that is considerably over half the bulk of the
shell. As might be expected, there is a direct correlation between the
instances of damaged shells and the barren, hard, or rocky nature of
the terrain. If there is a cover of humus or a thick undergrowth to break
the fall of the foraging snail, there will be little or no damage to the
shell even though it is relatively thin.
In the regions in Ceylon where the jungle crow was commonly
encountered, it was not unusual to find giant African snail speci-
mens which had sustained a considerable loss of flesh as a result of
pecks by these malacophagous birds. Most often, it was the posterior
portion of the foot, that is, the last part to be withdrawn into the
shell, that was amputated and regenerating. Occasionally, however,
specimens were found with one or both ommatophores removed, in-
cluding a portion of the head. Specimens were also found that were
regenerating tissue lost in unsuccessful or incomplete attacks by the
predatory glowworms.
The large, heavy shell and the generous supply of mucus of a
mature giant African snail affords considerable protection both from
the adverse physical factors in the environment and from natural
enemies. Even such avid snail feeders as ducks and geese are unable
to handle the snails if the specimens are more than a few months old.
As will be seen in the discussions below, this species has dem-
onstrated a remarkable capacity to withstand submersion in both
fresh and salt water. The typhoon and flood in Manila (Pangga 1949),
the flood in Babelthaup (Esaki and Takahashi 1942), and the tidal
wave in Chichi Jima (Mead and Kondo 1949), if anything, seemed to
speed up the increase and spread of the giant snail population after
the initial, temporary setback.
Paucity of Natural Enemies As one reviews the entire topic
of the biological control of A. fulica, one is left with the profound
conviction that this animal has remarkably few natural enemies
indeed. Even the natural enemies it does have are of questionable
value in effecting any real control. And this is one of the reasons that
some investigators are now in the process of attempting to discover
and import foreign predators which promise to become new "nat-
FACTORS FAVORING DISPERSAL AND SURVIVAL	33
ural" enemies of the giant snail. A. fulica even seems insensitive to
competition from the endemic species of snails in the areas it has
invaded (e.g., the large Rhysota in the Truk Islands). On the con-
trary, it is felt that some of the endemic species, such as Partula
gibba, are actually losing in the competition for the gastropod niche
in the environment (Kondo 1950c).
Period of Activity      The facts that A. fulica is normally noc-
turnal and crepuscular in its habits, and that it will become active
in the daytime when it is raining or overcast, indicate that light, as
well as temperature, moisture, and food, is a vital factor in its ac-
tivity. To a great extent, activity during these periods permits the
giant snail to escape a number of basically unfavorable environmen-
tal factors operative under normal diurnal conditions. A definite
homing instinct appears to be present in this species. The experi-
ments of Hatai and Kato (1943) indicated that this may be dem-
onstrated by as much as 70 per cent of the active members of a giant
snail population. Such an instinct is of survival value in that it per-
mits the snail to locate readily a protective retreat.
Availability of Calcium In a study of the relationships of
snails to soil, Van Cleave (1953) concluded that "the presence of the
snails is an indicator of available lime supply...." Usually, the
malacologist looks at the correlation from the other direction, name-
ly, that if a good lime supply is present, snails will be found. With
respect to the achatinas in particular, Pilsbry and Bequaert (1927)
found in the former Belgian Congo a direct correlation between
limy soil and abundance of snails. Similarly, Oughton (1948) con-
cluded that the sole nutritional factor limiting the distribution of
snails is the availability of calcium. It is not understood why the
findings of Hagen (1952) were in direct contrast. Adding calcium
to the diet of snails was demonstrated by Oldham (1929a, 1934) to
produce in several European snails a shell somewhat larger and
heavier by three to four times.
With information of this type coupled with the knowledge of the
diversified eating habits of A. fulica, it is understandable why the
coralline islands of the Pacific have managed to support inordinately
large populations of this snail pest. The mineral soils of these islands
is reported to have a pH range that is on the alkaline side (e.g., pH
7.2-8.7 in the Arno Atoll [Stone 1951]). CaCO3 in such soils would
be stable. This is precisely the explanation for the findings of Atkins
and Lebour (1923a, b) wherein snails showed a preference for slight-
ly alkaline soils, being most abundant in the pH range of 7.0-8.0.
These facts, however, made it all the more difficult to understand
34	FACTORS FAVORING DISPERSAL AND SURVIVAL
how the strongly acid soils of Ceylon could support equally large popu-
lations of A. fulica. The soil in the tea-growing areas, for example,
is characteristically near a pH of 4.5. CaCO3 could not possibly last
long in such acidity, especially in the presence of the usual abundant
moisture. The calcium which is present is locked up in silicates and
combinations of iron and aluminum. Plants are able to ''unlock" this
calcium as manifested by the fact that plant leaf analyses in the acid
soil areas of Ceylon revealed as much as 40 per cent calcium in the
ash. When the nocturnally feeding A. fulica were seen to feed ex-
tensively on fallen leaves in these areas, it was then understood where
they were obtaining the lime for their shells. But of even greater
importance was the fact that here were snails independent of an
"available" supply of lime in the soil.
The calcium cycle continues as shells of dead snails are rasped
completely away by those that survive. Even the living snails will rasp
their own shells, especially along the lip of the shell, and particularly
right after a period of estivation. In the Pacific islands, specimens were
encountered with the surface of the shell, which had been exposed
during estivation, rasped by other snails until it was paper-thin. Snails
deprived completely of an external source of calcium are able to draw
upon their own shell for their calcium needs for a long period of time
(Wagge 1952).
Acid soils and a concomitant lack of available CaCO3 in the soil,
then, are no real deterrents to A. fulica. Ironically, man in Ceylon
unwittingly converts a situation which is tolerable for the giant snail
into one that is distinctly favorable. Cacao is being grown more and
more in that country because on the world market it is more depend-
able than rubber. Cacao, however, requires a less acid soil (i.e., in a
pH range of 6.0-7.0). Alkalizing the soil is accomplished by adding
dolomitic lime. This increases the productivity of the cacao; but it
also makes the environment more favorable for the giant snails. Lit-
tle wonder that the largest populations of this snail in Ceylon were
encountered in cacao plantations!
Escape Reaction and Migration Cycle        Specimens of A. fulica
from the Mahinui population in Oahu were marked with white
paint and after a period of confinement were released in their home
area under essentially the same weather conditions in which they
were collected. Observations over the following hours and days re-
vealed an unmistakable "escape reaction" of sustained crawling to
the periphery of the experimental area in surprisingly near-equal
numbers in all directions of the compass. Further experiments are
being conducted. On the basis of what has been observed, however,
FACTORS FAVORING DISPERSAL AND SURVIVAL	35
it has been suggested (Mead 1959b) that there exists a "migration
cycle" comparable to the "hydration cycle" of Howes and Wells
(1934). It is proposed that even under essentially ideal conditions,
specimens from time to time will undergo sustained movement out of
the home area. Stimuli adequate to invoke this reaction may be less
intense in an inverse proportion to the time element since the last
"migration." The most subtle stimulus may be sufficient to initiate
the reaction in some individuals that have been sedentary for a pro-
tracted period of time. On the other hand, a sufficiently strong stimu-
lus might surpass the threshold of a large segment of a snail popula-
tion in an erstwhile reasonably stable environment and precipitate a
"mass migration." Such migrations have been observed many times
in the field by a number of investigators, but they have continued to
remain essentially unexplained. It is more than likely that intercur-
rent stimuli (e.g., prevailing wind [Chamberlin 1952a, b]), would
have a directive influence on the movement.
Proof of the existence of a "migration cycle" would throw much
light on the factors of dispersal and population density.
CHAPTER 4
ECONOMIC
STATUS
Current Opinion As attested by the following quotations,
the majority of earlier investigators in the field have generalized from
their observations that Achatina fulica presents a problem of very
real if not actually serious proportions: "They eat nearly everything
in the garden" (Jarrett 1923); "this snail is a very destructive visitor
[which will devour] anything that is not too hard or distasteful"
(Jarrett 1931); "vast amount of damage to agricultural crops result-
ing from their attack" (Bias and Thamotheram 1939); "a major pest
on a number of larger islands'' (Townes 1946). Many other quota-
tions of a similar nature could be given. Most unfortunately, various
writers who have had no practical experience in the field aspects of
the problem have seized upon these and similar statements, blown
them up, embellished them with the products of overactive imagina-
tions in true Sunday supplement style, confused them with informa-
tion about other agricultural pests, and highlighted them with the
sheerest of fantasy until almost terrorizing proportions have been
reached. Undoubtedly in many instances these confusions and dis-
tortions have been unwitting, but the end results nonetheless have
been very damaging to progress in creating a better general under-
standing of the true proportions of the problem.
Green gave probably the first account of this impending trouble
with his note (1910a) about an article which appeared in the August
28, 1910, issue of the New York Herald (continental edition). He
states that the illustration showing many snails on a coconut stem
was superscribed as representing "Snails Destroying Trunk of Coco-
nut Tree." But the situation was to become worse. Statements which
36
ECONOMIC STATUS	37
accused A. fulica of "chewing to shreds much of the wild vegetation
of the islands'' and of having ''denuded much of the vegetation in the
Hawaiian Islands" were to give way to even greater exaggerations,
such as, "countless millions . . . are gobbling down crops on the
Hawaiian Islands" and "billions upon billions have already eaten
every blade of grass and all the jungle growth on scores of Pacific
islands" (Symontowne 1949). An unchallenged climax was finally
reached in the magazine section of a newspaper in the western United
States (Rhodes 1950). Starting almost immediately in a reinfortsando
of "astronomical numbers have devastated parts of Hawaii, India
and China." the tempo of exaggeration quickened with an account
of a supposed infestation of Ceylon where "the pests appeared in vast
numbers one summer morning and by nightfall several thousand
acres of farmland were literally crawling with the creatures which ate
everything in sight, including the thatched roofs of farmhouses."
Soon all credibility was abandoned and a tremendous crescendo built
up to the explanation that the "next day not a live snail could be
found on the island" and that "it is guessed the snails, impelled by
some strange urge, committed mass suicide in the sea[!]"
In the light of all this excessive exaggeration, it is not only of little
wonder but definitely predictable that just the reverse reaction has
been engendered in many quarters. Skepticism has grown first into
disbelief and finally into complete repudiation of the very idea that
A. fulica has provided anything more than a field day for reporters
and free-lance writers. Such an attitude on the part of some people
has provided the single greatest impediment in setting up protective
legislation and otherwise meeting adequately the threat presented by
this confused problem. To make matters worse, this skepticism has
apparently found its justification in the existence of a fair amount of
indisputable evidence that the damage caused by this snail is actually
considerably more limited than originally believed. Statements in
the literature minimizing the problem have seemed to support fur-
ther the stand of the skeptics. As early as 1910, Green (1910c:56)
pointed out and later reiterated (1911b) that in spite of millions of
snails in a heavily infested area ''evidence of injury could be found
only upon careful search" and that "the casual visitor might pass
through the affected area without noticing anything unusual." Hut-
son (1920), van Weel (1948), and others have supported this stand.
Abbott (1951c) has indicated that the achatinas in their homeland of
Kenya and Zanzibar cause apparently slight destruction to agricul-
tural produce despite their large populations. Townes (1945) re-
ported that there was "little damage to vegetation in general" in his
38	ECONOMIC STATUS
survey of the problem in Micronesia. More recently, J. W. Hes (in
litt. Feb. 5, 1952) stated that in Java the economic importance of this
snail has been overestimated; Chamberlin's investigation in Tinian
(1952a) indicated only "slight damage" to crops on that island and
that the rats and insects provided a far worse threat. Olaf Ruhen of
New South Wales (vide Morrison 1950a) concluded that there was
not even enough evidence against these snails to provide the basis for
an article and that "people are just naturally destructive, and want
things killed for no other reason than that there are a lot of them."
More recently, there has been a tendency even to glamorize the whole
subject, thus minimizing still further the problem at hand (e.g., Pol-
ing 1954).
This swing of opinion from one extreme to the other is kept in a
constant state of vacillation through the appearance in the literature
of a great number of conflicting reports, inconsistencies, and ap-
parent discrepancies. These would seem to reflect inaccuracy or in-
completeness of observations of those making the reports, and in
some instances such is probably the case. In this respect, it is worth
while to point out that Hutson in 1920 reported that there was no
damage to rubber trees through the action of A. fulica. A reversal of
opinion started with the report of Weir in 1929 which indicated that
the damage had not been sufficient to attract attention. But Beeley,
who took over Weir's position, reported six years later positive dam-
age to seedlings and buddings and, shortly thereafter (1938), branded
A. fulica a pest of "serious economic importance in Malaya." Exam-
ples of this sort have quite naturally caused a questioning of other
negative reports.
Bias is also undoubtedly an important factor which has insidiously
flavored certain other reports. The other factors which have helped
create confusion are even more subtle. For instance, in some areas, a
certain food plant is not touched at all by the giant snail and is so
reported; in other areas, that same species of food plant may be the
only one which is at all acceptable and may therefore suffer severe
damage. And even in this latter area the damage may be negligible
during certain seasons of the year when other food items become
temporarily available. During the dry season, damage may be re-
duced considerably through the fact that a great majority of the
snails go into a state of estivation. In some areas advantage is taken
of this "snail-free period," especially in the growing of vegetables in
small irrigated plots. In contrast, South (1926b) reports greater dam-
age during the dry season because of concentration of snails in the
perennially green gardens. The size of the snail population, of
ECONOMIC STATUS	39
course, will greatly influence the amount of damage. And the size of
the population in turn will be determined by many other factors
such as the availability of food, moisture, CaCO3, and temperature
extremes. In the early stages of the invasion of a new area, the popu-
lation quickly reaches its peak and damage is at a maximum; in the
later stages the phenomenon of ''decline'' (discussed below) may re-
duce the population in a very dramatic fashion with a proportionate
reduction in damage.
In much of the recent literature, there is very apparent a growing
indifference to the problem of the giant African snail. Undoubtedly
a number of reasons are contributing to this trend: the people have
lived with the problem long enough to begin to accept it among their
other curses; very limited funds in many cases have permitted the
problem to continue without recent rechecking and the lack of offi-
cial reports has been interpreted elsewhere as evidence of cessation of
importance in the area in question (India is a case in point in this
respect); entomological and mycological problems are so much more
acute in many areas that they demand all or nearly all the attention
of a seriously limited number of specialists; and lastly, the phenom-
enon of "decline" has convinced the authorities in some of the older
areas of infestation that the "worst is over" and that the problem will
continue to diminish.
Damage to Plants At this point, it is more than obvious that
there is a genuine need for determining as accurately as possible the
true economic status of the giant African snail. The first step in mak-
ing such a determination is to check the literature exhaustively for
reports of investigators who have made field observations of damage
in areas invaded by this giant snail. But at the outset one is frustrated
by the frequency of extreme contrast in the nature of the reports
made by observers of varying authoritative stature. In an attempt to
resolve these differences, certain writers in the past have rejected
some, minimized other, and championed still other data which gave
emphasis to their own interpretations. In the present account, how-
ever, an attempt is made to embrace all data and then reconcile the
differences through an explanation of their apparent underlying
causes. In this way, it is hoped that the existing knowledge will be
brought into better perspective than has been the case heretofore.
In the following list an honest attempt has been made to prepare
an unbiased resume, giving as concisely as possible the essence of the
findings reported in the literature or in correspondence. In every
category where this author has made field observations, a note con-
cerning them has been placed first in the series of data and followed
40	ECONOMIC STATUS
by an asterisk (*) when the observations were made in the infested
central and western Pacific islands (Hawaiian, Micronesian, and
Bonin Is.) and by a dagger (f) when the observations were made in
Ceylon. The data of other investigators are identified by appropriate
letters; these in turn are interpreted in the footnote legend.1 In pre-
paring this list there was no attempt to make it completely exhaus-
tive; instead, there was omitted in every case all information which
clearly was quoted from earlier original works already covered or
which concerned plants of little or no significance or economic im-
portance. Where there was doubt, the information was included in
this list.
Air plant (Bryophyllum pinnatum): The common, dense stands of
this plant in the uncultivated areas of the Hawaiian Islands are pro-
viding an almost unlimited source of preferred food.*
Albizzia: Where unprotected from snails, only 30 per cent survival
of Albizzia falcata in E. Java (AV); bark of A. falcata attacked in
Sumatra (He); A. lebbek a preferred food plant in Saipan (L).
Amaranthus spp.: A preferred food in Saipan (L); young plants com-
pletely destroyed, older ones seriously attacked (W).
Amaryllidaceae: Crinum favored in Malaya (Ja); serious damage to
many species (W).
Ampalaya (Momordica charantia): Seriously attacked in Philippines
Arrowroot (Canna edulis}: Seriously attacked in Philippines (Pg).
Bananas and plantain (Musa paradisiaca): The snails are frequently
found on the leaves and trunks; small specimens may work their
way deep into the bunches of fruit. Occasionally young bananas
are rasped; when they mature the skin appears very badly scarred
and is therefore commercially less valuable, though the fruit itself
1 (A)— Anonymous, 1947a; (AV)— van Alphen de Veer, 1954; (Be)— Beeley, 1935; (Be1)—
19386; (Be2)-193&z; (BJ)-Benthem Jutting, 1934, 1952; (Br)-Bertrand, 1928; (Br^-1941;
(C)— Chamberlin, I952a; (C and G)— Charmoy and Gebert, 1922; (Ca)— A. Campbell in
litt. Nov. 19, 1951; (Co)-Corbett, 1933; (Co^-1937; (Co2)— 1941; (Ct)— Cotton, 1940;
(D)— G. S. Dun in litt. Aug. 12, 1949 to Dec. 17, 1953; (Da)— Dammerman, 1929; (E and T)—
Esaki and Takahashi, 1942; (F)— Fairweather, 1937; (Fe)— Feij, 1940; (G)— Green, 1910c;
(G1)-1910&; (G2)-19116; (H)-Hutson, 1920; (H and K)-Hatai and Kato, 1943; (Ha)—
Tom Harrisson in litt. Aug. 25, 1952; (He)-Heubel, 1937, 1938; (Ho)-Holmes, 1954; (Hs)
-Hes, 1949, 1950; (Ja)— Jarre tt, 1923; (Jk)-Jaski, 1953; (K1)-Kondo, 1950c; (K2)-1950a;
(K3)— 1952; (L)— Lange, 1950; (Le)— Leefmans, 1933a,b; (L and V)— Leefmans and van der
Vecht, 19330, 6; (M)-van der Meer Mohr, 1949a; (M-)— 1924; (Ma)-Macmillan, 1943;
(Mi)— Milsum, 1950; (N)-R. C. L. Notley in litt. Dec. 7, 1950; (O)-Otanes, 1948; (Pb)—
Philbrick, 1949; (Pe)-Pemberton, 1938; (Pg)-Pangga, 1949; (Ph)-E. Phillis in litt. Jan.
31, 1950; (Pv)-Paravicini, 1922; (R)-Rappard, 1949; (Ri)-Riel, 1933; (Ry)-H. C. Ray
in litt. July 22, 1952; (S)-South, 1926&; (S J-1923&; (T)-Townes, 1946; (W)-van Weel,
1948-49; (We)-Weber, 1954.
ECONOMIC STATUS	41
is unaltered. If the bananas split open on the tree, they will almost
invariably be consumed by the achatinas frequenting the treetops.
Several native reports indicated that young plantings may be
killed by the attacks of the snails. Total damage is small.* Inhabit-
ants of Tinian report no damage (C); young leaves eaten in Sai-
pan (E and T); leaves and steins of "pisang" attacked only slightly
in Sumatra (He); unverifiable reports in Ceylon that leaves and
apparently blossoms of plantain eaten, therefore fruitless (G); pre-
ferred by larger snails in Palau Islands (H and K); a chief food
plant in Koror, ripening fruit liable to damage (K2); fruit, leaves,
and new shoots are damaged in Saipan (L); young leaves eaten
(Le); attacked in Philippines, peelings eaten (Pg); attacked in Java
(Ri); could not verify damage (W).
Beach morning-glory (Ipomoea pes-caprae]: This very common vine
serves not only as one of the main shelter plants for achatina but
as a good source of food;* a preferred food plant in Saipan (L).
Beans: Fed upon in Saipan (L); eaten voraciously in Philippine
Islands (Pg); Phaseolus radiatus seedlings totally destroyed, foliage
of older plants skeletonized, but the yam bean (Pachyrhizus tubero-
sus) suffered no damage (W).
Betel pepper (Piper betle): Untouched (G); no damage (W).
Bird's-nest-fern (Asplenium nidus): A preferred food plant in Saipan
(L).
Blimbing (Averrhoa bilimbi): Fruit completely stripped in Ceylon
(G).
Bougainvillea: Both large and small snails attacked in Riouw Archi-
pelago (L and V).
Breadfruit (Artocarpus spp.): The fruit of this tree, whether it be
green, overripe, rotting, or dried, is a real favorite of the giant
snails. Although the snails have been seen up to about twelve feet
in these trees, the fruit which had not fallen was never observed
being attacked or showing any signs of attack. Since the native
people of many Pacific islands have abandoned the breadfruit for
the more easily prepared imported staples, the breadfruit crop in
some areas is being allowed to contribute 100 per cent to the main-
tenance of a larger and still larger snail population which other-
wise could not exist. Robert E. Burton of the Agricultural Devel-
opment Station on Ponape reported that all of a number of
sprouted breadfruit clippings brought from the Truk Islands in
1948 were killed by having their bark removed by achatinas.* In-
habitants of Tinian report no damage (C); a chief food plant in
Koror (K2); a preferred food plant in Saipan (L).
42	ECONOMIC STATUS
Cabbage (Brassica spp.): This and other Cruciferae are the most pre-
ferred food plants in the Philippines (Pg); severe damage in Saipan
(L).
Cacao (Theobroma cacao): In Ceylon the giant snails were frequent-
ly seen congregating in great numbers in the areas where the cacao
pods were being harvested; they were observed feeding on the
flowers, broken pods, seeds, and seedling plants in nurseries; dam-
age varied from slight to severe;H fed on young shoots and flowers
in Indonesia (BJ); young seedlings up to two months of age readily
attacked and killed in New Britain (D); no damage (H); direct
damage by consuming freshly planted seeds, indirect damage by
destruction of cuttings of dadap cover crop in Ceylon (N); killed
young plants and injured blossoms of bearing trees, impossible to
plant new clearings in Ceylon (S); seriously attacked and damaged
(W).
Cactus: Opuntia sp. eaten (BJ); Opuntia and Cereus suffered damage
in Java (L and V); damaged (Pg); attacked in Java (Ri).
Calophyllum inophyllum: A definite preference for the leaves of
this plant. *
Canna sp.: Eaten voraciously in the Philippines (Pg).
Carambola (Averrhoa carambola): Fruit reported damaged in Po-
nape.*
Carrots (Daucus carota): Severe damage to both the tops and the
tuberous roots was reported by the inhabitants of Chichi Jima;*
fed upon in Saipan (L).
Cassava (Manihot esculenta): Damage is largely restricted to the
young plants, reported to be a serious problem in Romalum, Truk
Islands;* Tinian inhabitants report no damage (C); badly dam-
aged, young stems heavily peeled off and killed in Java (Fe); leaves
and bark damaged in Sumatra (He); a chief food plant in Koror
(K2); attacked in Philippines (Pg); no damage (W).
Chili peppers (Capsicum spp.): Untouched (G); the fruit, leaves,
and bark of C. annuum are attacked in Sumatra (He); stem and
leaves of C. grossum eaten in Rota but damage not serious (K3);
fed upon in Saipan (L); no damage (W).
Citrus sp.: Near-ripe fallen fruit and foliage of sweet orange (C. si-
nensis) were observed to be eaten on Agiguan;* seedlings seriously
attacked in Philippines (Pg).
Coconut (Cocos nucifera): No damage observed;*H swarming on
fronds but no evidence of injury (G); no damage (H, S).
Coffee (Coffea spp.): Slight damage to berries in Malaya (Co); in Su-
ECONOMIC STATUS	43
matra, young leaves attacked only when other food is not present
(He); observed to attack in Philippines (Pg).
Corn (Zea mays): Only slightest damage to leaves and kernels in Chi-
chi Jima, decaying leaves eaten readily;* inhabitants of Tinian re-
port near destruction of field of very young seedlings, but no
appreciable damage to larger plants (C); only slight damage to
leaves in Sumatra (He); young seedlings readily eaten in Guam
(K2); fed upon in Saipan (L); seedlings sometimes attacked but no
severe damage (W).
Cosmos sp.: Damaged in Philippines (Pg).
Cotton (Gossypium sp.): In Mauritius "it was responsible for a good
deal of damage to cotton seedlings, when the attempt was made to
plant cotton, on a large scale, in 1911" (C and G).
Cowpea (Vigna sinensis): Cover crop in Ceylon almost completely
destroyed (Br); the fruit, leaves, and stems are damaged in Sumatra
(He); young plants completely destroyed, older plants skeletonized
(w)
Cucumber (Cucumis sativus): Very little damage in Koror;* inhabit-
ants of Tinian report serious damage often to entire plant (C);
one of favorite foods in Sarawak (Ha); fed upon in Saipan (L);
seriously attacked in Philippines (Pg).
Cucurbitaceae: Especially liable to damage (D).
Eggplant (Solanum melongena): Plants stripped of bark in Ceylon
(G); fed upon in Saipan (L); attacked in Philippines (Pg).
Elephant ear (Alocasia sp.): Foliage only sparingly eaten in Ceylon
(G); "ape" loaded with snails and eaten (Ki).
Euphorbiaceae: Eaten (BJ); Euphorbia trigona eaten in Java (L and
V); inflorescences eaten, but no serious damage (W) (vide Rubber).
Ferns: Fronds of tree ferns (Alsophila lunulatd) eaten in Palaus;*
young snails especially destructive to garden ferns (Gi).
Flower gardens (general): A wide variety of garden flowers are read-
ily eaten, some of them being quite seriously damaged;*! suffering
extensively in New Britain if they are not carefully protected (D);
the damage killed young Salvia plants in Sumatra (Fe); "whole
gardens devastated" (Jk); do not seem to attack Salvia, Torenia, or
Coleus in Ceylon (Ma); serious pest in Seychelles (Mi); decided
preference for ornamentals in Philippines (Pg); all agree that
greatest damage is to gardens (S); much damage in Malaya (Si); a
real pest in horticulture (W).
Gourd (Lagenaria leucantha): "Upo" seriously attacked in Philip-
pines (Pg).
Grasses: All seem to be nearly completely immune to attack.*H
44	ECONOMIC STATUS
Gynandropsis speciosa: Complete planting failed in Malaya in spite
of controls (S).
Hibiscus spp.: A favorite plant, damage to both flowers and leaves
noted; * hedges of this plant were invariably loaded with giant
snails; all parts of the plant were subject to attack;H fallen flowers
preferred in Palaus (E and T, H and K); damaged in Java (Fe);
attacked in Philippines (Pg) (vide Okra).
Jak (Artocarpus heterophyllus): The fallen fruit is a great favorite;
whole areas of bark, even on mature trees (Fig. 5), may be con-
sumed; young seedlings very susceptible to damage;*H "chew up
whole seedlings up to three to four feet in height overnight" (Ho).
Leguminosae (general): A number of unidentified species consumed
in the field attest to the wide preference for this group; * damage to
the cover crop plant Pueraria thunbergiana was essentially com-
plete on some estates in Ceylon causing indirect damage to Cacao;
the more hardy Desmodium triflorum was only slightly attacked;
bark of Gliricidia maculata and dadap (Erythrina lithosperma)
subject to extensive attack, even in trees in excess of three inches
in diameter; flowers of the dadap are a favorite;f large areas in
Pueraria cover crop in New Britain barren and not reseeding (D);
Centrosema pubescens damaged in Java (Fe); young dadap trees
killed by bark removal in Ceylon (H); in Sumatra, the young
leaves of C. pubescens and the leaves and bark of Deguelia sp. are
damaged, and although under experimental conditions Cassia mul-
tijuga was not touched, the following were readily eaten: Cassia
mimosoides, Crotalaria anagyroides, C. striata, Indigofera suffruti-
cosa, Mimosa invisa, Parkia sp., Tephrosia Candida and T. vogelii
(He); indirect damage to tobacco as young plants of cover and
green manure crop (Mimosa invisa) were stripped of their bark in
Sumatra (M); particularly destructive to dadap cuttings in cover
crop of cacao (N); could not grow leguminous ground cover crops
in Ceylon when achatina was at its height (Ph); young dadaps
girdled and killed (S).
Lettuce (Lactuca sativa): Native people of Tinian indicate no dam-
age (C); severe damage in Saipan (L); plants of all ages completely
defoliated, but only seedlings of L. indica destroyed (W); food of
greatest choice in the laboratory (We).
Leucaena glauca: This exceedingly common introduced species in its
characteristic dense stands is clearly a preferred food plant from
the Hawaiian Islands (where it is known as "Haole koa") to Chi-
chi Jima; all parts are avidly consumed, including the water-soaked
seeds and the exposed roots; the slender stems are frequently seen
ECONOMIC STATUS	45
bent far over under the weight of snails feeding on the leaflets and
tender bark;* occasionally fed upon in Tinian (C); not touched in
Sumatra (He); defoliation of young "lamtoro" trees placed in a
teakwood stand in Java (R).
Liliaceae: Nearly all lilies seem susceptible to attack; *H Crinum and
other lilies preferred (Da); favored plants (Ja); Caladium not at-
tacked (Ma).
Malungay (Moringa oleifera): Observed being attacked in Philip-
pines (Pg).
Melons (Cucumis melo; Citrullus vulgaris): The fruit and vines of
all types are on the preferred list; on Rota, they cause such de-
struction of watermelon vines that the native people walk several
miles to plant their seeds in an achatina-free area; attacks on the
young fruit will badly disfigure it, interfere with proper develop-
ment, and make it worthless for consumption;* inhabitants of
Tinian report serious damage often to entire plant (C); severe
damage in Saipan (L); rinds consumed (Pg).
Montanoa hibiscifolia: The bark and pithy stems deeply and exten-
sively grooved in Hawaii.*
Morinda (Morinda citrifolia): Both the leaves and the mushy, white
fruit were among the most preferred items in Koror;* preferred in
Saipan (L).
Oil palm (Elaeis guineensis): Prefer overripe or underripe fruit in
Malaya (Coi, Co2); attack mainly fallen fruit but also ripening
fruit on branches (F); will attack leaves only if very hungry (He).
Okra (Hibiscus esculentus): Plant practically defoliated and fruit in-
jured to such an extent as to make it valueless in Ceylon (G);
severe damage in Saipan (L).
Onion (Allium spp.): No damage (W).
Orchids: Phalaenopsis and Vanda damaged in Riouw Archipelago
and Java (L and V); Phalaenopsis spp. damaged in Philippines
(O); attacked in Java (Ri).
Pandanus spp.: No damage observed;* occasionally fed upon (L).
Papaya (Carica papaya): A great many times the snails were seen high
up in the trees; both fruit and bark are damaged; in Ponape mis-
sionaries complained bitterly of attacks on the fruit; *H a fallen
tree was completely consumed in a week, a near-prostrate tree
suffered damage to buds and flowers, snails seldom seen in top
of erect trees in Tinian (C); older trees in New Britain are de-
prived of their bark until they wilt and die, seedlings are eaten
away completely (D); ripe fruit damaged in Saipan (E and T);
leaves eaten, young stems ringed and killed (Fe); flowers consumed
46	ECONOMIC STATUS
in Ceylon (G); fruit, leaves, and bark of young trees damaged in
Sumatra (He); preferred by larger snails in Palaus (H and K);
chief food plant in Koror, fruit liable to damage (K2); preferred
food plant in Saipan (L); eaten in Java (L and V); fruit eaten in
Philippines (Pg); climb trees and eat ripe fruit (T).
Passion flower (Passiflora spp.): One of the commonest plants of
choice in the Pacific; fruit, flowers, and leaves eaten; in many areas
it is the main if not the sole food item;* greatest preference in
Tinian (C); the leaves and ripe fruit are preferred items in Saipan
(L); most of the snails' food is the old yellowing leaves and ripe
fruit (T).
Peanut (Arachis hypogaea): A planter in New Guinea abandoned
peanut cultivation largely because the snails made continual ap-
preciable inroads in his fields (D); attacked the leaves, stems, and
nuts in Sumatra (He); young plants completely destroyed, older
ones seriously defoliated (W).
Pepper vine (Piper nigrum): Young pepper vines planted at the base
of Gliricidia trees in an unthrifty cacao plantation in Ceylon suf-
fered 100 per cent kill because the palm frond shields, set up to
protect the vines from the sun, provided shelter for great quanti-
ties of hungry achatinas;f plant killed by eating outer layers of
stem; Tinian inhabitants report vines often killed by snails (C);
leaves attacked in Sumatra (He).
Pineapple (Ananas comosus): No damage observed or reported in
the East Caroline Islands, Hawaiian Islands, or Ceylon; *f no rec-
ord of feeding on pineapple (Pe).
Pipturus albidus: The fallen leaves of the common "mamaki" of the
Bonin Islands were observed to be a definite favorite.*
Pumpkin (Cucurbita pepo): In Chichi Jima, the pumpkins had to be
raised in protected boxes and then transplanted to prevent them
from being chewed off as fast as they came up;* inhabitants of
Tinian reported serious damage often to entire plant (C); species
introduced by Japanese in New Britain entirely eliminated by the
snails in some areas (D); leaves skeletonized and stems barked in
Ceylon (G); fed upon in Saipan (L).
Radish (Raphanus sativus): All parts of the plant attacked in Suma-
tra (He); fed upon in Saipan (L).
Ramie (Boehmeria nivea): Attacked in Philippines (Pg).
Rice (Oryza sativa): No damage (G, H, He, W); no harm except
breaking down plants with their weight (S).
Roses (Rosa spp.): Do not seem to attack in Ceylon;f attacked in
Philippines (Pg).

ECONOMIC STATUS	47
Rubber (Hevea brasiliensis): Occasional specimen seen feeding on
latex at tapping site; disfiguring or killing damage to young plants
in nurseries considerable in some areas ;H feed on young seedlings
and buddings, continued destruction of buds produces distinctive
type of fasciation (Be); drink latex and eat sweet cambium layer
of bark exposed by tapping thus causing wounds (Be2); serious eco-
nomic importance in Malaya (Be1); feed on young shoots and
flowers (BJ); damage to young rubber rather serious in Ceylon
(Br1, Ct); G. A. C. Herklots indicates no very considerable losses
in rubber industry (Ca); young trees severely damaged in Sumatra;
bark removed, stems ringed, leaves consumed, growing tips and
replacement growth damaged to such an extent that death resulted
in some cases; older trees not seriously affected although the snails'
consumption of latex (proved by crushing snails and observing the
latex in the gut) contaminated the latex, sidetracked its flow, and
caused the collecting cups to fall to the ground (Fe); no damage
(H); young leaves and bark damaged only when more acceptable
food is not present (He); bark stripped off, killing young plants;
achatinas seen by the hundreds in Ceylon sucking sap in latex cups
(N); "learned to drink rubber latex" (Pb); strip succulent bark
from young plants, drink latex (Ph); drink a considerable amount
of latex (Pv); impossible to plant new clearings in Ceylon in 1916
(S); seriously attacked (W).
Scaevola frutescens: Both leaves and flowers are preferred items.*
Soursop (Annona muricata): No apparent damage in Dublon, Truk
Islands;* a preferred food plant in Saipan (L).
Squash (Cucurbita spp.): Attacked in Philippines (Pg).
Staple crops (general): Left unharmed in Malaya (Be2); no appre-
ciable damage in Malaya (Si); damage only a fraction if at all (W).
Sugar cane (Saccharum officinarum): Often found congregating in
great numbers on the leaves but damage was practically nil;* dam-
age to leaves on Saipan (E and T); damage in Java, especially to the
leaf axils where there is much less concentration of silica cells, but
of no real economic importance (Hs); a chief food plant in Koror
(K2); no record of damage (Pe).
Sweet potato (Ipomoea batatas): The vines provide cover often for
phenomenal numbers of snails but damage to leaves and exposed
tubers was invariably inappreciable;* not eaten in Tinian accord-
ing to inhabitants (C); many snails but no damage was noticeable
in Ceylon (G); a chief food plant in Koror (K2); attacked in Philip-
pines (Pg); foliage sometimes attacked but no serious damage (W);
foliage a food of choice in the laboratory (We).
48	ECONOMIC STATUS
Taro (Colocasia esculenta): Foliage is not infrequently attacked,
though seldom skeletonized; rarely, damage is caused to exposed
roots; total damage is surprisingly almost inconsequential even
in areas overrun with snails;* a lot of damage in Kabunga, New
Guinea (A); feed only on fallen leaves, but according to the in-
habitants of Tinian, the rarely exposed tubers are eaten (C); only
slightly affected in New Britain as it is particularly hardy and
fast growing (D); foliage eaten very sparingly in Ceylon (G); fallen
leaves eaten in Palaus (H and K); not affected in Guam (Ki); a
chief food plant in Koror (K2); only occasionally fed upon in Sai-
pan (L).
Tea (Camellia sinensis): Every report in Ceylon was negative;H young
shoots and flowers are eaten (BJ); no damage in Ceylon (H); young
leaves attacked only when there is little else to eat (He).
Teakwood (Tectona grandis): Year-old plants damaged in S. Suma-
tra (AV); up to 90 per cent lethal damage to young plants in Java
(R).
Thespesia populnea: A preferred food plant in Saipan (L).
Tobacco (Nicotiana sp.): Bark removed from base of plant, stalk
weakened so that it blows over easily; leaves of young plants eaten;
total damage negligible; will never become a serious pest (M).
Tomato (Lycopersicon esculentum): Foliage seriously damaged in
Guam immediately following the first big rain of the season;* not
attacked in Ceylon (Ma); decaying fruit consumed (Pg); indiffer-
ent to plants (W).
Tree nettle (Laportea crenulata): Stems and branches completely de-
nuded, killing the trees; practically exterminated in some locali-
ties (G).
Vegetables (general): Most varieties were found to be attacked at
least to some extent; in some cases serious damage was caused,
especially in small plots adjacent to abandoned or uncultivated
areas; *t suffering extensively in New Britain if they are not care-
fully protected (D); certain plants defoliated and others denuded
in small vegetable patches (G2); damage to fresh vegetables caused
mainly by the smaller specimens (H and K); a pest (H); farmer in
Sinajana-Ordot area of Guam reported that it was not possible to
raise vegetables as they were too vulnerable to attack by snails
(Ki); serious pest in Seychelles (Mi); decided preference for succu-
lent vegetables in Philippines (Pg); a serious pest in Ceylon (Pv);
"great depredations" in Calcutta (Ry); in some localities in Malaya
the growing of certain vegetables has become almost impracticable
(S); particularly destructive (T); seriously attacked (W).
ECONOMIC STATUS	49
Vegetable sponge (Luffa spp.): "Patola" seriously attacked in Philip-
pines (Pg).
Weeds and uncultivated plants: Many species are attacked; some are
definitely preferred and others are only occasionally eaten; *f
Lange (1950) has prepared an impressive list for Saipan and as far
as known, it is the only such list extant.
Xanthosoma braziliense: Leaves and stems of "Tahitian spinach"
eaten in Hawaii (Ki).
Yam (Dioscorea alata): The leaves are an obvious favorite; eaten ex-
tensively in Ceylon;f no appreciable damage in Tinian (C); young
plants eaten down to the ground in Ceylon (G); impossible to
plant yams in Rota when snails were abundant (K3); severe damage
in Saipan (L); "ubi" seriously attacked in Philippines (Pg).
Zinnia linearis: Attacked in Philippines (Pg).
Evaluation of Damage In examining critically the above list,
one is left with the very definite conviction that considerably more
in the way of careful observation is required before there can be
made an accurate evaluation otA. fulica as an agricultural and horti-
cultural pest. A review of the reports of damage caused by this snail
discloses the fact that the greater share of them are qualitative only.
That is, we know what the snail will attack, but we do not know to
what extent the snail will attack it. Studies of quantitative damage
therefore must be made. Then, when it is known, for example, that
the maximum damage to a certain type of plant is negligible, the
presence of A. fulica in stands of that plant will not cause the need-
less initiation of elaborate and costly control measures. In spite of
these difficulties, certain generalizations and a number of rather spe-
cific conclusions can be made at this time. These at least will assist in
arriving at a reasonably satisfactory tentative evaluation.
Garden flowers and ornamentals of a great many varieties are
among the most susceptible to the attacks of A. fulica; often all parts
of the plant in all stages of development are eaten. Most vegetables,
but especially those belonging to the Cruciferae, Cucurbitaceae, and
the Leguminosae, often suffer severe damage. Cuttings and seedlings,
even of plants not attacked in the mature state (e.g., breadfruit, cassa-
va, teakwood, etc.), are also preferred food items of this snail; damage
to these is caused by their complete consumption or by the removal
of bark. According to Jaski (1953), the young snails, up to about four
months, feed almost exclusively on young shoots and succulent leaves.
Cover crops, and especially those that are leguminous, represent the
fourth and last major category of plants which may be severely dam-
50	ECONOMIC STATUS
aged. In most cases the effects of the damage rest not so much in the
physical destruction of the cover crop plants as in the secondary
damage to the main crop for which the cover crop is used for green
manure, shade, soil retention, moisture retention, and/or nitrogen
restoration. A case in point is the almost complete destruction of the
leguminous cover crop Pueraria thunbergiana in the Dodangoda
Post of the Godahene estate in Ceylon. The cacao plants suffered
from the reduction of available nitrogen in the soil; and the soil, in
turn, suffered marked erosion particularly in the steeper denuded
areas. The more woody, hearty legume, Desmodium triflorum was
substituted because it was more resistant to the attacks of the giant
snail; but this cover plant grows more slowly, produces a less dense
cover, adds proportionately less nitrogen, and succumbs more readily
to one of the plant diseases.
A. fulica, however, comes rightfully by this type of destruction as
Spence (1938) has reported related achatinids (Limicolaria zebra and
L. numidica) in their native home of British Cameroons destroying
leguminous cover crops of Calopogonium, Centrosema, and Puer-
aria, which were interplanted with oil palms. Not only did the cover
crops suffer from the attacks, but the palm fruit itself was eaten.
Similarly, there has been reported damage to sesame and coffee by
Achatina craveni Smith (Salaam 1938); damage to sisal and cotton by
A. zanzibarica (Tomaszewski 1949); damage to papaya and other
plants by A. albopicta (Williams 1951); and damage in nurseries by
Limicolaria distincta and L. lucalana (Dartevelle 1954).
Although many plants of little or no economic importance are
attacked by A. fulica, it is significant that the majority of plants
which suffer the greatest damage are conspicuously of the cultivated
type. Taylor (1894) quotes from Gain data which similarly show that
cultivated plants form nearly two-thirds of those "acceptable" to the
snail Cepaea hortensis.
Several reports of damage listed above are considerably more sig-
nificant than they might appear to the casual reader. The observed
damage to citrus fruit and seedlings sounds an ominous warning of
what might happen should these giant snails become settled in the
great citrus growing areas of the world. It has already been estab-
lished that the climatic conditions particularly suitable for citrus are
very nearly equally suitable for A. fulica. And, for the skeptics,
stranger things than this have happened in the field of malacology.
For example, although it was well known that Theba pisana had a
strong propensity for citrus fruit (both leaves and bark) in its native
home (de Stefani 1913) and in California (Basinger 1923a, c, 1927;
ECONOMIC STATUS	51
Gorton 1919; Smith 1919a, b, 1922), most malacologists would have
been somewhat hesitant to announce that its near-relative, Helix
aspersa, if given the opportunity, could become an almost equally
serious pest. But within recent years, just that has happened in
Southern California (Anon. 1929; Basinger 1931, 1940; Gammon
1943; Lewis and LaFollette 1941, 1942a, b; Persing 1943-45; Wog-
lum 1943).
The over-all damage that results from the feeding of A. fulica on
rubber trees, fortunately, is not critical in any real sense of the word.
Under certain conditions, however, there can be significant and even
serious local damage to the young saplings, especially in nurseries.
R. C. L. Notley, chairman of the Planters' Association of Ceylon, and
E. Phillis, director of the Rubber Research Scheme of Ceylon, have
reported in correspondence numerous incidents of serious damage of
this sort. In the literature, the works of Beeley and Feij are particu-
larly convincing. The snails' strange but not unique appetite for the
fresh rubber latex makes them a nuisance and sometimes a pest on
the larger trees when they are being tapped. Green (1909, 1910a),
Keuchenius (1914), and Meer Mohr (1924) have shown that the en-
demic sluglike snails Mariaella dussumieri and Parmarion reticulatus
can be, in the same respects, equally serious pests on rubber. Paravi-
cini (1922) adds the well-known plant pest Bradybaena similaris to
this list.
All parts of the papaya tree seem inordinately susceptible to the
attacks of the giant African snail; and as its fruit is a universal favor-
ite wherever it is available for human consumption, losses would be
particularly felt in the areas where the snail is abundant.
Reports of damage to peanut and pepper vines seem to be more
than a little significant as these plants figure very prominently in
world commerce. In both cases the extent of damage needs to be de-
termined accurately. In the meantime, it will be hoped that the lack
of more reports of this sort is indicative of only slight general
damage.
Consistent reports of very little or no damage to certain other
crops are, in many respects, even more significant than reports of
appreciable damage. For example, all members of the grasses, such
as sugar cane, corn, rice, and the "grains," are very conspicuously im-
mune to all but occasional, relatively insignificant damage. And this
sems to hold pretty well in all regions of the world, although Herr-
strom (1953) reports slug damage to stored winter wheat. Consider-
ing the tremendous importance of these products in the economy of
the world, it is a blessing indeed that there is such universal immu-
52	ECONOMIC STATUS
nity. Other staple starchy crops such as the taros and sweet potatoes
are almost as free from serious damage, although the cassava suffers
some damage, especially in the young stage; and in some areas the
yam is seriously attacked. Newspaper accounts and other reports
(e.g., Zuk 1949) to the contrary notwithstanding, the giant African
snail cannot be considered in any possible way a threat to the coco-
nut industry. The same can be said for other economically important
"woody" plants like the pineapple and the pandanus. The betel pep-
per, onions, most varieties of chili peppers, and many other highly
aromatic or irritating plants are understandably not among the pre-
ferred items of A. fulica; but one cannot completely generalize from
this, as the tree nettle, cactus, and tobacco are appreciably damaged
in some instances. The literature is conspicuously almost completely
devoid of anything but the most incidental report of damage to cof-
fee and tea plants. From this we can infer that the giant snail can be
written off as a possible pest of these plants since otherwise its abun-
dance in the tea- and coffee-growing areas of the East would surely
have caused many reports of damage to have been made by this time.
Other species of snails, however, have been listed as principal pests
of coffee in Brazil (Fonseca and Autuori 1932). The other great
beverage plant, the cacao, unfortunately suffers a fair amount of di-
rect and indirect damage.
Of fruits themselves, only the papaya seems to be damaged to a
serious extent; the others either have not been reported as damaged
or have been reported as damaged only slightly. Perhaps an explana-
tion for this can be found in the fact that there is a definite prefer-
ence for rotting and therefore fallen fruit. At any rate, it seems safe
at this point to assume that another whole category of plant products
can be considered very nearly free from significant damage. It should
be borne in mind, however, that many of these apparently "immune"
plants can and do sometimes suffer complete destruction in the un-
protected young stages.
Indirect Damage So far, the only example that has been given
of indirect damage to plants concerns the destruction of cover crops.
There are others which must be taken into consideration if a fair
evaluation of the problem is to be made. Quite probably, many of
these have not found their way into the literature because they have
not been recognized as damage resulting from A. fulica. For exam-
ple, rice and other plants which are not eaten by the giant snail
nevertheless may be badly damaged under conditions where the
sheer weight of the snails causes the plants to break. Another exam-
ple, with an ironic twist, is reported by Dr. E. Phillis who states (in
ECONOMIC STATUS	53
litt. Jan. 31, 1950) that in Ceylon some land on tea estates has been
rendered unfit for growing tea because the snails were collected and
buried in such quantities that the acid soil, demanded by the tea
plant, became too strongly alkalized. An equally provocative situa-
tion is found in Sarawak where Tom Harrisson states (in litt. Aug.
25, 1952) that the Chinese market gardeners and others are required,
in order to minimize damage by A. fulica, to keep their plots so clean
all the year around that excessive soil erosion has occurred.
Because the giant snail competes with other animals for food, and
because it, in turn, provides an increasing source of food for certain
carnivorous animals, including paradoxically some with which it is
competing, the entering of A. fulica into an environment invariably
produces a series of ecological chain reactions which in some cases
result, via the most devious channels, in damage of a completely un-
predictable nature. The snail's potentiality in this respect should
never be underestimated. This whole topic of environmental inter-
relationships is discussed under several headings below and sum-
marized in the figure on page 137.
Under the heading of indirect damage must also be considered the
possibility that A. fulica might carry plant diseases. This possibility
finds support in our knowledge of some predisposing aspects of the
biology of this snail, viz., the formation of plant wounds through
rasping, the proclivity for decaying and rotting vegetation, and the
contact with many plants over a relatively short period of time. But
although there is no positive evidence in the literature of this snail
being implicated in this manner, the lack of experimental evidence
one way or the other clearly indicates both the need for such experi-
mentation and the danger of attempting to draw any conclusions at
this time. It is apropos, however, to mention at this point references
which establish a vector role for gastropod mollusks. Wagner (1896)
demonstrated that snails could act as vectors of fungous spores. Later,
Gravatt and Marshall (1917) reported that snails were capable of
spreading white pine blister rust in greenhouses; on the other hand,
slugs apparently were not able to transmit tobacco mosaic to healthy
plants (Purdy 1928). Rands (1924) reported that he had repeatedly
confirmed the fact that Zonitoides arbor ens is a vector of "root rot"
of sugar cane in Louisiana; and Robbs (1946) listed Deroceras reticu-
latum as one of the disseminators of black rot of cabbages and other
Cruciferae. Plate and Fromming (1951) offer additional information
on the vector role of slugs in the transmission of fungous diseases of
plants. More recently, Fromming (1955) has implicated various spe-
cies of slugs and snails in the dissemination of potato diseases. Cer-
54	ECONOMIC STATUS
tainly the disease vector aspect of the achatina problem needs badly
the attention of a qualified investigator, especially since a danger of
this sort could exist without raising the suspicions of the average
observer.
Nuisance Factor As a nuisance factor, the giant African snail
at the height of its invasion can be listed among the worst which
plague man. Corbett (1933) was one of the very first to recognize the
importance of this factor. The snails multiply in such unbelievable
numbers that they crawl all over and into everything, they crush or
slip out from under foot almost wherever one steps, they cover things
with their excreta and sticky slime trails, and they die in great quan-
tity for various reasons and create rank odors. In this manner they
very seriously interfere with normal living and thus assume an im-
portance which may far outweigh any damage they may do to the
vegetation. Therefore, in judging the undesirability of A. fulica, the
nuisance factor must not be lost sight of as it alone more than justi-
fies efforts to keep this snail out of uninfested areas. Unfortunately,
those who are prone to minimize completely the threat that this snail
presents seem invariably to overlook this very important point.
The highways and other thoroughfares may be lined for miles with
living and dead snails. Individuals attempting to cross to the other
side may be crushed into a slimy mess, and as such they provide one
of the choicest food items for those that survive. But, ironically, those
that feed upon the crushed carcasses all too often become crushed
themselves and in turn attract other snails which may suffer the same
fate. In this manner a genuine road hazard may be formed, especially
on the curves and grades. This has been observed in Saipan by Ab-
bott (1949), the present writer, and others. Apropos of this, the fol-
lowing words of Kalshoven (1950) do not need translating, "Toen
de Amerikaanse troepen er in 1945 landden, waren de slakken er zo
overvloedig, dat de jeeps er slipten." R. C. L. Notley (in litt. Dec. 7,
1950) reports them similarly forming "stinking nightmares" on the
highways of Ceylon.
Their appetite for whitewash (which contributes lime to their
shell) permits them almost to exceed their capacity as a nuisance; for
although damage to painted surfaces is rarely extensive, it is disfigur-
ing and adds substantially to maintenance costs. A number of inves-
tigators have reported damage of this sort, but Witkamp (1941) has
illustrated and made more recent special mention of it.
In Guam, the giant snail so incessantly interfered with the derati-
zation program, by consuming with apparent impunity the warfarin
rat bait, that it was necessary either to prebait with a molluscicide or
ECONOMIC STATUS	55
to use concurrently both a snail bait and a rat bait (Peterson 1957b).
R. K. Enders observed in his survey of the rat problem in Micronesia
in 1949 that rat traps set with ordinary baits, such as peanut butter,
cheese, bacon, etc., often caught more giant snails than rats. It will
be left to the reader's imagination the slimy mess that is created when
a rat trap snaps on a snail!
Health Factor By their sheer multiplicity the snails will often
find their way into open wells, creeks, and other bodies of water.
Their rotting carcasses not only render the water unfit for drinking
but present a hazard to health. But the hazard does not rest there
alone. The thousands upon thousands of dead and dying snails in a
heavily infested area form potent breeding sources for filth flies
which are carriers of enteric diseases. Annandale (1919) reported the
breeding of "blue bottle flies (Pycnosoma or Lucilia dux)" in this
way and associated their appearance in Silpur, India, with epidemics
of "enteric." Smedley (1928) similarly reported in Malaya the breed-
ing of Megaselia xanthina (i.e., Aphiochaeta) which he indicated can
produce a myiasis in the human intestine. Lange (1947), Williams
(1951), and others have made comparable observations. In Chichi
Jima and Haha Jima of the Bonin Islands, Musca domestica and
other filth flies were found breeding in such great quantities that
keeping them from one's food even while eating was almost an im-
possible task. In this particular situation, however, their breeding
was made much worse because the inhabitants gathered the snails in
large barrels and allowed them to die in the sun and become maggot
infested before crushing and using them as fertilizer. Cockroaches
presented an equally serious problem in these islands. Since they
were often seen at night feeding on dead achatinas, it is assumed that
at the very least the snails have aggravated this problem if not actual-
ly precipitated it. The health hazard under such conditions is a very
great one but its full epidemiological potentiality will not apparently
be realized unless and until an enteric disease agent, for which the
native people have little or no resistance, is accidentally introduced
by outsiders.
The propensity of these snails for feeding on the excrement of hu-
mans, household pets, and livestock presents a somewhat different
type of problem (Lange 1950; Mead 1950b, c; Garnadi 1951; Wil-
liams 1951). Green (1910c) apparently was the first to make this ob-
servation; but he believed at the time that by consuming such mate-
rial, the snails were providing a real source of service. Van Weel
(1948), however, interpreted this information in a different way, viz.,
that the snails would, in addition to their other sins, cause the spread
56	ECONOMIC STATUS
of "contagious diseases." Actually, this would only be the case if (1)
the snails were used for human consumption in the raw or insuffi-
ciently cooked state, or (2) flies fed upon the dead, infected snails and
in turn contaminated human food, or (3) the disease producing
entities were able to pass through the snail and be deposited in an
infective state some distance from the original source of infection. It
can be seen that none of these alternatives contributes anything of a
significant nature to the epidemiological factors involved. In the case
of the latter two alternatives, the filth flies themselves are so effective
in carrying enteric disease agents that any possible part the snails
might have would be inappreciable indeed. Although the first alter-
native is an extremely unlikely one, Schnell (1919) has indicated that
it is not an impossibility as he reports on a case of mass infection of
the dwarf tapeworm (Hymenolepis nana) in prisoners of war who
had eaten raw Weinbergschnecken (Helix pomatia).
It is of interest to note in passing that Lebour (1915) demon-
strated that the slugs Deroceras reticulatum and Arion circumscrip-
tus would naturally consume proglottids of the tapeworms Moniezia
cxpansa of sheep and Cittotaenia pectinata of rabbits. Since the ova
were found to pass through the digestive tract in a viable state, it is
believed that these slugs act as incidental disseminators of disease
agents. In the following year, Railliet similarly found fair evidence
that carrier pigeons were becoming infected with the tapeworm Ber-
tiella delafondi by consuming D. reticulatum which had earlier fed
on infectious material. This same species of slug as well as three
different species of land snails were shown by Taylor (1935) to be
capable of acting as the intermediate host of the gapeworm of poultry
(Syngamus trachea). Both D. reticulatum and Arion ater were found
to be carrying on the surface of their bodies viable ova of two
nematode parasites of humans, Ascaris lumbricoides and Trichuris
trichiura (Galli-Valerio 1918). Hanson (1930) and Blaisdell (1950)
report, respectively, that the slugs D. reticulatum and Prophysaon
andersoni are the intermediate hosts of the microscopic tapeworm
of chickens (Davainea proglottina) and the slug Arion circumscriptus
is an intermediate host of the cat lungworm (Aelurostrongylus ab-
strasus). Similarly the common land snail pests Bradybaena similaris
and Subulina octona are intermediate hosts of the cecum fluke of
poultry (Postharmostomum gallinum) (Alicata 1938, Thistle 1959a).
The rat lungworm, Angiostrongylus cantonensis (Chem), was found
to be carried normally by unidentified species of garden slugs
(Mackerras and Sandars 1954). Recently, Fromming (1952b) empha-
ECONOMIC STATUS	57
sized that the coprophagous habits of slugs strongly implicates them
in spreading the diseases of humans and plants.
But these items are only suggestive in the case of A. fulica. Under
no circumstances can there be found any grounds for the fears of
Morgenstern (1949) who believes that these snails could spread the
several dread fluke diseases of humans.
In East Africa, Williams (1951) observed mosquitoes breeding in
empty achatinid shells and thus brought attention to a factor which
conceivably could be of the utmost importance in areas where dis-
ease-carrying mosquitoes prefer this type of breeding site.
Role as Scavenger It has been mentioned that A. fulica pro-
vides at least an incidental benefit by consuming human and livestock
excrement. A closer examination, however, shows that this is only
one example of many which attest to the fact that this snail contrib-
utes much to the plus side of the ledger by acting as a general scav-
enger par excellence. For example, even a dead black rat near Agafia,
Guam, was observed by the author to have been eaten by these snails
(cf. Dalgliesh 1907). The fact that they avidly consume the shell and
flesh of dead and even putrifying individuals of their own and other
species is of but the commonest knowledge. Pangga (1947) has stated,
"Growing plants furnish the major portion of its food." The major-
ity of investigators do not concur in this. Instead, they feel that rot-
ting, soggy, and decaying vegetables, fallen fruits, leaves, and even
entire plants are definitely the most frequently selected food items,
even in a great many cases where the plants are never touched in the
fresh or growing state (Chamberlin I952a; Esaki and Takahashi
1942; Green 1910^ 19116; Hatai and Kato 1943; Townes 1946; etc.).
Jaski (1953) states that after a snail reaches the age of four months,
it shows a definite preference for decaying matter. Garbage and trash
of almost any sort, especially if they are wet (e.g., water-soaked card-
board boxes), are also preferred food items (Esaki and Takahashi
1942, Pangga 1949)—so much so, in fact, that Rees (1951) has been
moved to conclude that this explains the abundance of snails about
native villages. It would seem, however, that their abundance in such
places more clearly reflects the fact that the natives themselves have
provided the best means for spreading these otherwise very slow snails
from one village to another and that their garbage, trash, and waste
material are only contributory factors. It is assumed that the frequent
consumption of moist soil by these snails is still another expression
of scavenging which not only brings in an additional amount of de-
composing organic material but assures under normal conditions an
adequate intake of certain essential inorganic compounds.
58	ECONOMIC STATUS
Barnes (1949b) minimizes the importance of the scavenger role of
terrestrial gastropods with the suggestion that all the material they
eat would normally be broken down by other biological agents. But
even in the tropics, agents to which he doubtless refers, viz. bacteria
and fungi, reduce the material at a much slower rate. Further, they
do not build it back up into an available source of highly nutritious
proteins as do the snails, the economic significance of which is em-
phasized below. Although Green (1910c), Corbett (1933), and a very
few others have emphasized the importance of this scavenger role,
it is a topic which in general has been ignored by the majority of
investigators, probably because the disappearance of dead and decay-
ing material, by its very nature, is neither noticed nor contemplated.
On the other hand, even with full cognizance of this scavenger role,
it is difficult to evaluate. And, further, because of the unwanted
nature of the material consumed, it apparently has seemed pointless
to attempt such an evaluation. It will be shown later, however, that
a careful evaluation is of worth in that it automatically suggests a
very constructive method of control. But, beyond this, it must be
concluded that it is the dominance of this scavenger role which un-
equivocally explains the apparent paradox of great concentrations of
these snails existing in uncultivated areas with little or no patent
signs of damage to the vegetation. It is quite another story, however,
when such concentrations exist in or adjacent to cultivated areas
planted with flowers, vegetables, cover crops, or young seedlings or
cuttings. In such areas, it is both the normally reduced amount of
plant debris and a high preference for succulent plant tissues which
decrease scavenging and invite damage. From these statements it can
be inferred that in the uncultivated areas A. fulica, through its
scavenging, may actually contribute more good than harm and that
just the reverse obtains in cultivated areas where the plantings are
especially preferred. The nuisance and health factors, of course, will
detract in either case to a degree depending upon the nature of the
human element. Because this snail spreads largely through the hu-
man agency and because it spreads relatively very slowly on its own,
there is a strong tendency for snail populations to build up and stay
close to inhabited areas. This explains why in the majority of in-
stances the giant African snail must be looked upon as detrimental
rather than beneficial. And even in inhabited areas where it causes
only a minimum amount of harm, its potentiality for becoming worse
argues against maintaining an attitude of indifference.
At any rate, there is at this point clearly neither evidence nor ex-
cuse for the tall tales which liken A. fulica to a plague of migratory
ECONOMIC STATUS	59
locusts. It is only in the most localized areas, under unusually favor-
able conditions, that damage by these snails will approach anything
near the absolute. A not uncommon example of this is found in the
small, unprotected, native garden plot surrounded by snail infested
bush. The first rains after the dry season may cause the snails to come
out of estivation, move into the garden plot en masse and virtually
clean it out overnight. But, even under these conditions, the alert
native can anticipate this damage and take effective steps to reduce
it very considerably. Such measures, however, demand unrelenting
effort, and the snail menace therefore still is reduced only to a most
undesirable, persistent harassing agent. And in fact it is in this very
capacity that the snail assumes its usual role with respect to the
susceptible crops of man.
Unjust Charges A final aspect in attempting to determine the
actual economic status of the giant African snail is found in the
subject of ''unjust charges." First of all, the nocturnal feeding and
secretive habits have given an insidious flavor to the damage caused
by this snail. This in turn has caused the snail to fall victim to a
great deal of circumstantial evidence. As in many other systems where
trouble is afoot, there is need for a scapegoat, and A. fulica has been
a "natural" for this role wherever it has gone. Its large size, recent-
ness of arrival, and ubiquitousness have all contributed to the "case"
against it. In areas where this snail has invaded, it is not difficult to
find one or more individuals adjacent to plant damage of any sort.
The frequency of such observations has persuaded the native people
in many quarters to blame the giant snail for almost everything.
A closer inspection may show that some smaller, less conspicuous
animal is either largely or entirely to blame for the damage. As an
example, the purported damage by A. fulica to sweet potato vines in
several of the Micronesian islands proved quite clearly to be simple
cases of circumstantial evidence. The snails were found in abundance
among the obviously chewed vines; however, a more critical exam-
ination by the author revealed that it was actually a cutworm and a
small flea-beetle which were producing the observed damage. Green
(1910c) made comparable observations. The mere presence of many
snails seeking the shade of banyan trees, sugar cane, coconut palms,
and other essentially immune plants has persuaded native people and
certain incautious observers to conclude that even though no dis-
cernible damage could be found, damage somehow must be there—
and it has been so reported.
In Guam some of the native peoples bitterly accused the snails of
4'poisoning'' their cats and dogs when in reality death was caused
60	ECONOMIC STATUS
from biting the commonly introduced giant toad, Bufo marinus,
which is protected by very toxic skin glands. Other, less conspicuous
pulmonate gastropods in certain areas join A. fulica in creating dam-
age, but actually may escape accusation. Cases of joint damage of
this sort have been reported on tobacco (van der Meer Mohr 1949a),
oil palm (Corbett 1941), corn (Mead 1950b), gardens (Corbett 1933),
and rubber (Beeley 1938a, b; Robson 1914). In certain areas at least,
damage to fruits, such as the papaya, may be caused more frequently
by birds and rats than by the giant snail (Chamberlin 1952).
The many exaggerated claims and cases of misinformation alluded
to earlier are also included under the heading of "unjust charges."
In contrast to the statement that they will "eat anything that will
hold still," there is an impressively long list of economically impor-
tant plants which are seldom or never attacked. Actually, their only
lack of dietary specificity rests in the eating of dead and decaying
material.
CHAPTER 5
CHEMICAL
CONTROL
There is embraced under this heading a vast and widely
scattered literature consisting of every possible intergradation be-
tween authority and quackery, detail and superficiality, circumstan-
tial evidence and proof. It has taken the utmost effort and an inor-
dinate amount of time to examine, edit, condense, and work into
some semblance of suitability the multitude of facts, which together
give us a fair conception of which chemicals, formulations, and
methods hold the greatest promise for bringing under control our
pestiferous terrestrial gastropods. Probably a fair share of responsi-
bility for the many discrepancies in the literature in the field of
economic malacology rests in the fact that too little is known about
the bionomics of terrestrial mollusks; hence there is little in the way
of "standards" upon which to base results of toxicological experi-
mentation. Most often, it is the economic entomologist who is given
the task of probing into the essentially unexplored field of mala-
cological toxicology; it is therefore not strange that some of the
results have a strong entomological flavor. Because there are so few
who have worked in the field, and because of the general reluctance
to do work in a strange field, there has been a tendency to "pass on"
as authoritative the results, conclusions, and recommendations of
earlier workers, and not always with proper credit, until only by
virtue of frequency of appearance in the literature have certain
methods become accepted as basic and standard. To make matters
worse, some authors will incorporate into the recommendations,
without adequate experimental testing, certain modifications which
occur to them as being likely improvements. From another angle,
61
62	CHEMICAL CONTROL
nurserymen and even garden enthusiasts will make their own "dis-
coveries," for which they do not have adequate testing facilities, and
report upon them all too often in obscure publications. Discoveries
of this sort not infrequently have real merit and warrant further
investigation.
A very large portion of the literature in malacological toxicology
concerns the problem of controlling medically important freshwater
snails (Mozley 1952). Because of the aquatic medium and the special
nature of the fluviatile and lacustrine environments, the require-
ments for a suitable molluscicide1 are vastly different than for those
of terrestrial snails and slugs. Hence, with only a rare exception, the
present coverage of the literature has been limited to that which
concerns the terrestrial forms. But even this has been difficult to
classify. Under the circumstances it has seemed best to make sum-
marizing comments under an alphabetically arranged series of sub-
headings based on the more important toxicants, with a small meas-
ure of cross reference. In the majority of cases, the less important
toxicants have been grouped under such collective subheadings as
"Attractants," "Contact Poisons," "Repellents." And, finally, an
evaluation is made on the basis of the survey of the literature. This
has been made with a twofold purpose: First, as far as possible, to
put at the disposal of the reader the very best of, and all the help
that, the literature has to offer so that he may determine what com-
bination of known measures will best meet his needs under the
circumstances in which he is working—especially where the giant
snail is involved; and, second, to emphasize the disturbing paucity
of truly dependable information, the serious chasms in our knowl-
edge, and the genuine need for funds and qualified investigators to
bring mollusk toxicology at least somewhere near equality with
insect toxicology. For over twenty years, no molluscicide of a spec-
tacular nature has been discovered. Progress has largely been limited
to modifications in formulation and application. This is indeed a
sad state of affairs in a field destined to play a proportionately greater
role in our agricultural economy!
Chemicals and Compounds
Alum (potassium aluminum sulphate): Anderson and Taylor (1926)
dusted this chemical on the slugs Deroceras reticulatum with
completely negative results, but sprinkling with an aqueous solu-
1 In the American literature especially, there is a tendency to spell this word "mol-
luscacide"; but, both orthographically and etymologically, such spelling is not acceptable.
The recent introduction of the hybridized word "snailicide" is unfortunate.
CHEMICAL CONTROL	63
tion was reported to be lethal to both snails and slugs (Anon.
1930). According to Merrill (1929, 1930), in regions where calcium
arsenate-bran baits are in competition with green vegetation,
Storer found that a spray, consisting of 1/2-l lb. of either potassium
alum or ammonium alum in a gallon of water, was superior as a
killer of slugs. Smeaton and Smeaton (1906) compounded and
patented a vicious but apparently unsuccessful formulation of
powdered alum, coconut fiber, silver sand, and—ground glass!
Aluminum Sulphate: The use of this chemical as a molluscicide was
first recommended by Durham (1920). Hodson (1924) suggested
that by combining 1 lb. with 5 gal. of saturated solution of quick-
lime in water, the scorching effect on the vegetation could be over-
come. Later (1925), he recommended a 1:2 by weight powder
mixture with lime, broadcast at the rate of ca. 56 lb. per acre, as
giving "very efficient control" of D. reticulatum; but he empha-
sized that it was not practical on a large scale both because of the
high cost and the damage to young foliage. Similarly, MacDougall
(1931) found aluminum sulphate impractical as a molluscicide;
and in the same year, Miles et al. failed to find it lethal to the slug
Milax sowerbii.
ARSENICALS2
Calcium arsenate: Lovett and Black (1920) tried a great many dif-
ferent chemicals in the control of D. reticulatum and found
Ca3(AsO4)2, both as a dust and a spray on chopped lettuce leaves,
to be the best. Basinger (1923a, b, 1927) modified the recommen-
dations of Lovett and Black and developed, in the control of Theba
pisana, a highly effective calcium arsenate-bran bait (1:16 by
weight, made moist, but not wet, by water and scattered 1 lb. of
bait to approximately 1,458 sq. ft.). He warned that this is a slow
acting poison and that its effectiveness should not be judged until
two to three days after it has been scattered. This period should
apparently be extended to four days in the case of A. fulica (van
Weel 1949). Basinger found, however, that calcium arsenate used
as a dust was of no value in controlling T. pisana. He later showed
(1931) that the calcium arsenate-bran bait could be used with
equal success on Helix aspersa (cf. Anon. 1949h). Lewis and
LaFollette (1941) labeled it the best bait for this species, although
Hely (1946) warns that it will cause considerable fruit and leaf fall
if, as recommended by Lewis and LaFollette (1942a, b), it is scat-
tered in the trees during periods of high humidity. A combination
2 See also Paris green.
64	CHEMICAL CONTROL
of 25 lb. of bran, 2 lb. of calcium arsenate, 3/4 gal. of molasses, and
1 gal. of water (or 2 lb. of sugar and 1 1/2 gal. of water), produced
a reported 99 per cent kill of T. pisana in South Africa (Joubert
and Walters 1951). If slugs were also involved, it was suggested
that there be added to the above formulation 1/2-1 lb. of meta fuel
or 6 pints of methylated spirits. Lange and MacLeod (1941) found
that the mixture of calcium arsenate and metaldehyde was more
effective than either chemical alone. The failure of Persing (1944b)
to concur in this conclusion was later explained by Lange and
Sciaroni (1952) when they warned that increasing the metaldehyde
from 1 per cent to 5 per cent by weight in arsenical baits produces
a repellent effect. More and more, however, it is being recom-
mended that metaldehyde baits be fortified either with calcium
arsenate or sodium fluosilicate (e.g., usbepq 1953).
A number of investigators have explored the possibilities of
using calcium arsenate in the control of A. fulica. Beeley (1938a)
recommended Basinger's formula for the control of this species in
Malaya and gave comparative cost figures. FitzGerald (1947) sup-
ported this recommendation. Pangga (1949), however, found it
not very attractive to the giant snail. He tried the powdered cal-
cium arsenate on banana peel, but it had no effect; in contrast,
van Weel (1949) found the powder very effective. Since the snails
are attracted to and will consume lime, Corbett (1937) suggested
the use of balls of lime poisoned with calcium arsenate and,
similarly, Rees (1951) recommended a 1 per cent solution of this
poison sprayed on lime covered walls. The creation of a longer
lasting bait by the addition of cement to the calcium arsenate—lime
mixture was first suggested and favorably reported upon by Leef-
mans (1933^). Its use was strongly recommended by Garnadi
(1951); but Fairweather (1937) had "little success" with this new
type of bait. Beeley (1938a) recommended a fairly strong bait con-
sisting of one part of calcium arsenate, six parts of slaked lime,
and two parts of cement by volume (or 1:4:2 by weight) and suffi-
cient water to form a consistency of ordinary concrete mix. This
was dried in thin slabs, broken into small pieces and scattered in
the areas frequented by A. fulica. A considerably stronger formu-
lation (8:11:1 by weight plus water to make a thin paste) has been
effectively used for the past several years as one of the chief means
of combating this snail in Hawaii (Fullaway 1949). This mixture
is painted on rocks, posts, tree trunks, and the like. Where there
are no such objects, stones or cinders are coated with the mixture
and broadcast; or wooden lath is painted with the mixture and
CHEMICAL CONTROL	65
placed on the ground as a barrier (Thistle 1954b). According to
Thistle (1953b) and Weber (1954), better results have been ob-
tained when small coated stones (1/2-l inch in diameter) were
placed two feet apart than when the same weight of large stones
(about 2 by 4 inches) were placed ten feet apart. Similar methods
are currently being used in a number of other areas including
Ceylon (Mead 19556) and New Guinea (where they use crushed
coral instead of lime). Because of the high coralline content of the
soil in Guam, however, the snails were not sufficiently attracted
to the poisoned whitewash to make it effective as a method of con-
trol (Peterson 1957). Chipman and Seibert (1939) have patented
a molluscicide which combines calcium arsenate and Paris green.
Lead arsenate: Lovett and Black (1920) found that slugs would read-
ily eat this poison, but few were killed by it. Torres (1950) recom-
mends its use with sugar and wheat bran (1:1:10 ratio by weight)
as a bait to kill the giant South American snail (Strophocheilus
oblongus) in coffee plantations. Cameron (1951) and Araujo
(1952) recommend similar formulations. A weaker formulation
(1:2:17) is claimed by Pereira and Gon^alves (1949) to give an
88 per cent kill of slugs and snails; the addition of 2.5 per cent
metaldehyde and the substitution of honey for sugar made no
significant improvement in the bait.
Sodium arsenate: It is not readily eaten by slugs and tends to blacken
lettuce bait (Lovett and Black 1920).
Sodium arsenite: This chemical ("penite" is a 40 per cent commer-
cial solution) was used in the form of a spray in early, futile at-
tempts in 1946 to eradicate A. fulica in Guam. More recently it
has been used quite successfully as a 1 per cent spray (i.e., a 2 1/2
per cent "penite" solution) against this same pest in Hawaii, es-
pecially where infestations are heavy (Lennox 1953, Weber 1954).
Later, the spray was used as a 0.5 per cent solution with no reduced
effectiveness (Thistle 1953b). Experiments conducted by Q. C.
Chock (in litt. Jan. 7, 1946) gave strong indications that poisoning
was effected through absorption by the foot, although Weber as-
sumes that some have been killed by ingesting the poison-covered
leaves. Since much of the vegetation dies within a few days after
being sprayed, this chemical is generally considered a "weed killer"
(cf. Basinger 1927). Its highly toxic nature makes it dangerous to
use under most conditions where the snail is found. Furthermore,
it is expensive to use, even under limited conditions, and a rain
quickly dispels its effectiveness.
66	CHEMICAL CONTROL
White arensic: This was found not to be eaten readily by slugs; when
it was eaten, the kills were low (Lovett and Black 1920). Pangga
(1949) found it ineffective in the control of A. fulica.
Ashes: In the control of A. fulica, ashes or a suitable substitute (e.g.,
sawdust, charcoal, cinders, etc.) as a repellent barrier have been
recommended by many, including Green (1911c), Hutson (1920),
South (1926b) and Corbett (1933). Most often, it is suggested that
they be used in combination with copper sulphate (q.v.). The con-
tinued use of ashes introduces the danger of moving the soil pH
too strongly in the alkaline direction.
ATTRACTANTS3
Bran of wheat, rice, or other grains is almost the universal attractant
(vide Diluents) in snail and slug baits in spite of the fact that its
availability and cost vary considerably from area to area. Lewis
and LaFollette (1941, 1942a, b) and Persing (1944a) found in
southern California that fresh orange pulp (in a 20—25:1 by weight
ratio with calcium arsenate) was about equally effective in control-
ling H. aspersa in citrus groves but only one quarter as expensive
as when bran was used. A combination of equal parts of bran and
pulp was shown to be more effective than either one alone. The
dried pulp however proved to be inferior to bran. On the other
hand, dried citrus peels have been demonstrated to be effective
both as an attractant and a diluent. Lime and calcium carbonate
in various forms have been used as attractants in a number of
poison baits, but particularly in those containing calcium arsenate
and/or metaldehyde (q.v.)• Metaldehyde itself has been considered
by many to be a specific attractant for snails and slugs under
proper conditions. A great many different substances were re-
cently tested in Hawaii in an effort to find an effective, practical
attractant for A. fulica. Metaldehyde emerged as the only one with
any real possibility (Thistle 1953b, 1954b); and even this in the
dry form or in solution proved to be "entirely negative" in these
experiments, as was wheat bran in either the dry or fermented
state. Many commercial bait preparations contain amyl acetate as
an attractant.
Barium Fluosilicate: A spray of this chemical was used in attempt
to control H. aspersa in citrus groves in Australia but was not
3 The less commonly used term "attrahent" is not used here because of its medical
connotation suggesting, antithetically, an irritant.
CHEMICAL CONTROL	67
found to be effective enough to be of value (Hely 1946). Levy
(1938) patented a snail poison containing this chemical and metal-
dehyde.
Benzene Hexachloride (BHC}: Pereira and Goncalves (1949) men-
tioned without elaboration that for killing snails and slugs, this
chemical was inferior to metaldehyde. On the other hand, Rao
et al. (1953) reported that a 5 per cent dust broadcast about 25 lb.
per acre of drained paddy was superior to a 2 per cent metaldehyde
bait in that it "killed most of the snails in the fields." Pappas and
Carman (1955) found it slightly less than moderately effective in
killing H. aspersa.
Bordeaux: This mixture of lime and copper sulphate was shown to
be an ''excellent repellent for slugs and non-injurious to foliage"
(Lovett and Black 1920). Miles et al. (1931) similarly recommended
its use. It was found to be only of limited use however in repelling
H. aspersa (Lewis and LaFollette 1941). Similarly, Basinger (1927)
discontinued its use against T. pisana because it did not give de-
sired results. On the other hand, a spray consisting of a Bordeaux
mixture (2:2:80), white oil emulsion (1 gal.), and nicotine sulphate
(34 pint) was found to be more effective than any other control
measure of H. aspersa in citrus groves in New South Wales (Hely
1946). Later reports (Anon. 1949h) suggested the omission of the
nicotine sulphate and pointed out that the spray not only had a
considerable knockdown effect on the small snails, but this effect
was retained in a residual fashion for a period of several months.
Pangga (1949) reported that a spray of this mixture was toxic to
only the young specimens of A. fulica.
Carbon Disulfide: This gas was used in Sidney, Australia, to re-
fumigate (after hydrocyanic acid gas treatment) a shipment of
copra infested with A. fulica (Harrison 1951).
Chlordane: Pappas and Carman (1955) demonstrated in field tests
that this insecticide is of essentially no value in the control of
H. aspersa. Pangga (1949) reported without elaboration that the
"Octaklor spray" had toxic effect upon only young A. fulica.
Coal tar: The use of tarred coconut fibers around the trunks of fruit
trees to protect them from the attacks of A. fulica was apparently
first reported by Green (1910c) and reiterated by Hutson (1920)
and van Weel (1949). G. S. Dun (in litt. April 21, 1952) put a ring
of coal tar around plantings in his own yard in New Guinea; this
very successfully and inexpensively repelled the giant African
snails. The rapid growth of weeds, however, demanded replace-
ment about every two weeks. In Ceylon, R. C. L. Notley (in litt.
68	CHEMICAL CONTROL
Dec. 7, 1950) succeeded in keeping the tar moist by mixing it with
old engine oil. Boards painted with this mixture and laid about
the garden formed an effective barrier against this snail.
contact poisons
Carbolic acid (vide Phenol), cedar oil emulsion, clove oil emulsion,
gasoline, nicotine sulphate, nicotine resinate, oil of lemon, oil of
tar emulsion, sodium hydroxide, sulphur and tobacco dust were
used by Lovett and Black (1920) in various combinations and
concentrations on the slug D. reticulatum with varying results.
Even with this small naked gastropod, these substances were con-
sidered to be of "decidedly minor value in practical field work."
Another series of chemicals was tried by Hodson (1924) in an
attempt to find a good contact poison for slugs. The following
were without effect: dichlorbenzene (10 per cent sol.), potassium
bichromate (10 per cent sol.), derris powder, derris solution, mus-
tard (brown) solution, and sodium silicofluoride (10 per cent sol.).
Potassium xanthogenate solution, sodium hyposulphite (10 per
cent sol.) and, very strangely, copper sulphate (10 per cent sol.)
were reported as having only transient effects. Chloral hydrate (10
per cent sol.) proved to be irritant, but its cost made it econom-
ically impractical; on the other hand, borax was "extremely le-
thal" but it was destructive to vegetation.
Miles et al. (1931) tried still other substances on the slug Milax
sowerbii. Dusting specimens of this species with the following did
not prove lethal: aluminum sulphate, ammonium chloride, cop-
per carbonate, copper sulphocyanide, flake naphathlene, flowers of
sulphur, green sulphur, lead sulphocyanide, potassium perman-
ganate, precipitated chalk with chlorcresylic acid, precipitated
chalk with creosote, sodium nitrate, thiourea, and "used'' calcium
carbide. On the other hand, they found that the following sub-
stances would kill the slugs within a few minutes after being
dusted on them: ammonium sulphate, ammonium sulphocyanide,
barium sulphocyanide, calcium carbide, calcium cyanide, corro-
sive sublimate, drained creosote salts, potassium sulphocyanide,
sodium carbonate and sodium sulphocyanide. Of these, only cal-
cium cyanide was sufficiently lethal at practicable concentrations
to be considered for use in field conditions; its very deadly nature,
however, makes serious consideration completely out of the ques-
tion. Mixing ammonium sulphate with steamed bone flour gave
negative results as a contact poison for slugs (Anderson and Taylor
1926). More recently, Lange and Sciaroni (1952) reported that
CHEMICAL CONTROL	69
dusts of hydrated lime, cupric oxide, and nicotine were effective
as contact molluscicides for only a short period of time. The in-
secticide hexaethyl tetraphosphate (HETP) was ineffective as an
aerosol in fumigating greenhouses infested with snails (Smith et al.
1948). A Russian patent suggests that a spray consisting of at least
a 0.1 per cent aqueous solution of ethylene chlorohydrin (2-chloro-
ethanol) will kill slugs (Paikin et al. 1949).
Copper sulphate, Bordeaux mixture, and metaldehyde may be
classified as contact poisons, but they have been treated in detail
under separate headings.
copper  compounds
The following compounds of copper were used in aqueous solution
of 1 per cent or less by Lovett and Black (1920) in an attempt to
find a control for the slug D. reticulatum: acetoarsenate, benzoate,
carbonate, chloride, chromate, cyanide, ferrocyanide, and sulphate.
Only the chloride and sulphate compounds produced a burning
of foliage. The results of their experiments caused them to dis-
miss summarily all of these compounds as having no promise in
slug control. Basinger (1927) found the use of CuSO4 impractical
in the control of T. pisana because it caused damage to plants.
Using lower concentrations of this chemical, MacDougall (1931)
reported effective control of slugs with no damage to plant foliage.
Anderson and Taylor (1926) similarly recommended as a "deadly"
control for slugs a 4-6:100 by weight mixture of CuSO4 in the less
toxic kainite fertilizer (hydrous potassium-magnesium chlorosul-
phate), distributed 2-3 hundredweight per acre. Miles et al. (1931),
after considerable experimentation with this chemical, cautiously
suggested that a precropping treatment with crystalline CuSO4 at
the rate of one hundredweight per acre might bring protection
from the slug pest M. sowerbii; but they warned against damage
to foliage if this chemical is broadcast after the crops have come up.
To prevent slug migration, they recommended sprinkling periph-
eral ditches with CuSO4 or a mixture of this chemical and ground
limestone. For slug control Lange and Sciaroni (1953) suggested
a dust containing monohydrated copper sulphate and hydrated
lime in a 20:80 ratio.
These and other experiments with CuSO4 focused attention
upon this chemical in early attempts to control A. fulica. Green
(1910c), Hutson (1920), South (19266), Corbett (1933), and Fer-
nando (1952) have recommended its use in almost every conceiv-
4 See also Bordeaux, Paris green.
70	CHEMICAL CONTROL
able manner; shallow ditches around gardens were filled with
wood ashes, coconut fiber dust, or sawdust treated with a 4-10
per cent solution of CuSO4; some of this same mixture was spread
around small beds and individual special plants; coir ropes were
treated with 10 per cent solution and placed around vegetable
gardens and around the bases of trees; small crystals of CuSO4
were placed at the surface of the ground near plants needing spe-
cial protection; a solution consisting of one lb. of CuSO4 to ten
gal. of water was sprinkled on the ground where the giant snails
were numerous; stone walls specially constructed around vegetable
gardens were watered two to three times a week with a solution
of one lb. CuSO4 in a gal. of hot water; and snails collected by
hand were first drowned in a 4 per cent solution before being
discarded. To insure against attacks by A. fulica in Ceylon, the
sticky seeds of the cacao are rolled in a mixture of CuSO4 and
ashes before being planted (R. C. L. Notley in litt. Dec. 7, 1950).
Pangga (1949) tried 1-10 per cent solutions of CuSO4 on giant
snails and found that, although the young individuals were readily
killed, only a few adults were affected.
The copper-based commercial fungicides, Greenol, Omazene,
Crag 658, Cunimene 2243 and Corona 53 all failed to control slugs
without phytotoxic effects (Karlin and Naegele 1958).
Corrosive Sublimate: A 1:1000 aqueous solution proved "highly
efficient as a repellent" in combating M. sowerbii (Miles et al.
1931). This recommendation has subsequently been indorsed by
a number of investigators. Even in low concentrations, however,
this is a dangerous chemical to use.
Creosote: One per cent mixture of creosote in precipitated chalk gave
"outstanding" results as a slug repellent (Miles et al. 1931).
Cryolite (sodium fluoaluminate): This spray was shown by Lewis and
LaFollette (1941, 1942a, b) to be of little value in controlling
H. aspersa in California citrus groves. The same conclusions were
announced by Hely (1946) in Australia.
DDT: The few experiments which have been performed to deter-
mine the possible molluscicidal properties of this insecticide in-
dicate definitely that further experimentation is needed. Buck-
hurst (1947) had at first only slightly encouraging results with the
0.1 per cent aqueous emulsion, the 5 per cent dust, and the "DDT
bait." Slugs did not touch the bait and only very slight kills were
produced by the dust and the emulsion; there was however a very
clear deterrent effect. But when he increased the strength of the
CHEMICAL CONTROL	71
emulsion to 0.2 per cent and applied it at the rate of 2 gal. per
100 sq. yd., he found it produced "an excellent control of slugs
without damage to growing cabbage plants." It was determined
that the killing power of the application was retained for at least
two weeks. Thomas (1948) tried a DDT-bran bait and found that
although the slugs were attracted to it (undoubtedly because of
the bran, vide Attractants), they were not killed by it. This insecti-
cide in a kerosene emulsion was tried in an undisclosed percentage
on A. fulica by Pangga (1949); young specimens were killed but
the adults remained unaffected. Fromming (1949, 1950) and later
Fromming and Riemschneider (1952) and Fromming and Plate
(1952) failed to demonstrate any molluscicidal action in prepara-
tions of DDT and other insecticides. Hely (1946) found DDT of
essentially no value in controlling H. aspersa in citrus orchards
in Australia; Pappas and Carman (1955) concurred in this. Pereira
and Gon^alves (1949) and Karlin and Naegele (1958) tried it on
slugs and snails but did not recommend it. When it was used as
an aerosol to fumigate snail infested greenhouses, it proved to be
ineffective (Smith et al. 1948).
Dieldrin: W. H. Lange, of the University of California at Davis, has
indicated in a preliminary report (in litt. Jan. 29, 1952) that, even
when combined with metaldehyde (q.v.), the action of dieldrin on
H. aspersa suggests that it has relatively little value as a mollusci-
cide. Pappas and Carman (1955) concur in this. Karlin and Naegele
(1958) found it "ineffective" in controlling slugs in greenhouses.
diluents
The most desirable diluent in snail baits is one that acts as an attract-
ant (q.v.) and is relatively inexpensive. Wheat bran has long been
the diluent of choice, especially in metaldehyde and calcium arse-
nate baits. More recently, apple pomace has been successfully used,
particularly in a 1:1 combination with wheat bran. In the Orient,
in particular, rice bran is more commonly used; and although it
has been reported to be less good than wheat bran, its much lower
price makes it more economical to use (Callan 1941). Coconut
meal, corn meal, rice husk, sawdust, and other diluents have been
used with lesser varying degrees of success. Sawdust in particular
is of uncertain value because of the aromatic nature of some wood,
even when thoroughly seasoned. In cases where only a mediocre
diluent is available, some compensation may be made through the
addition of an attractant, for example, amyl acetate.
72	CHEMICAL CONTROL
Ethylene Dibromide: This was shown by Balock (1951) to be seven-
teen times as effective as methyl bromide in killing immature
stages of the oriental fruit fly in papaya. It is immediately apparent
that serious consideration should be given to the replacing of
methyl bromide, carbon disulphide, and hydrocyanic acid gas
(q.v.) by this more toxic chemical in the fumigation of snail in-
fested cargoes.
Ferrous Sulphate: When specimens of T. pisana were placed on a
surface dusted with an approximately 80 per cent proprietary
mixture of this chemical, they displayed great irritation, withdrew
into their shells for four weeks, but remained alive (Basinger
1927). Pierce (1931) enthusiastically recommends dusting this
chemical about the garden to kill slugs and snails indicating that
not only are good kills obtained but the chemical itself is a plant
food and stimulant.
Gammexane (gamma isomer of hexachlorocyclohexane): Two inves-
tigators report on the use of this chemical in the control of A.
fulica. Pangga (1949) states without elaboration that gammexane
was "ineffective." In direct contrast, J. A. Tubb states (in Hit.
Jan. 8, 1952) that it is "effective" in North Borneo. Since this
insecticide imparts an off-flavor to fruits and vegetables, it at best
would be of limited use. Fromming and Riemschneider (1952)
report that HCH was ineffective on limacine slugs both as a con-
tact poison and a stomach poison.
Hydrocyanic Acid Gas: The Bureau of Plant Quarantine in Cali-
fornia has used this gas to fumigate the holds of ships infested with
A. fulica. It was used for the same purpose in Vancouver, British
Columbia (in litt. W. Reed Mar. 9, 1951; cf. Zuk 1949), and in
Sydney, Australia (Harrison 1951).
Isolan: This toxicant was found to be considerably more effective
as a molluscicide than any of 31 other promising chemicals tested
by Pappas and Carman (1955). Both as a spray and a bait it ap-
proached metaldehyde in effectiveness.
Kerosene Emulsion: This was tried, in a manner not indicated, by
Pangga (1949) on A. fulica and was found unsatisfactory inasmuch
as it was toxic only to the young snails.
Lime: Dusting hydrated lime, Ca(OH)2, about slug infested plants
(Massee 1928) or even on the slugs as a contact poison (Anderson
and Taylor 1926) gave unsatisfactory results, especially since some
plants may be damaged in the process (Anon. 1930). Blauvelt
(1952) suggested that CuSO4 be added to the lime; and similarly,
Lange and Sciaroni (1953) report that lime has only transient
CHEMICAL CONTROL	73
value unless it is combined with 20 per cent monohydrated copper
sulphate (vide Bordeaux). Pangga (1949) combined it with sulphur
and tested it on A. fulica, but it proved toxic only to immature
specimens. Where lime is lacking or low in the soil, it can be used
successfully as an attractant (q.v.) in snail baits; but its prolonged
use in acid soils, or the practice of "liming" soils, in general cre-
ates a more favorable environment for snails (Atkins and Lebour
19230, b).
Metaldehyde: According to Gimingham (1940), this chemical was
first used as a molluscicide in 1934 in South Africa, although it
apparently was not used in this manner in England until 1936
(Jary 1939). In an earlier work by Gimingham and Newton (1937)
and in a fairly complete summary by Barnes and Weil (1942), there
is indicated much uncertainty, approaching the legendary, as to
just how the molluscicidal properties of metaldehyde were dis-
covered. It is an inflammable polymerized form of acetaldehyde
with a chemical formula of (CH3CHO)4, and is the chief constituent
of the solid, commercial "meta fuel," a form in which it is often
sold. Its solubility in water is low in the extreme—being 0.018
per cent at 0.5° C., 0.020 per cent at 17° C. and 0.026 per cent at
30° C.—with no detectable tendency to depolymerize in neutral
or alkaline aqueous solutions even after standing for over six
months (Cragg and Vincent 1952).
There is no unanimity among investigators as to just what is
the action of metalhyde on various mollusks. Many agree that it
is a specific attractant. This was early questioned by Jary (1939).
It was further questioned by Corbett and Pagden (1941), who
announced that individuals of A. fulica will crawl toward bait
containing metaldehyde and then change their course just before
they get to it. Weber (1954) reported that in carefully controlled
experiments dry metaldehyde and metaldehyde "in solution''
failed to attract A. fulica. Lewis and LaFollette (1942a, b") went a
step further by concluding that under certain conditions it is
actually repellent to H. aspersa. Lange and Sciaroni (1952) ex-
plained this and warned that in higher concentrations, metalde-
hyde becomes a repellent. Lewis and LaFollette further concluded
that slugs are more susceptible to metaldehyde than are the snails.
Gammon (1943) drew the same conclusion; but Thomas (1948)
suggested that just the reverse is the case.
Jary and Austin (1937) were apparently the first to conclude
that metaldehyde is both a contact and a stomach poison. This
conclusion was supported by Cameron (1939) and Lange and
74	CHEMICAL CONTROL
MacLeod (1941). In contrast, Thomas (1948) believed that the
action of metaldehyde, as far as snails are concerned, is entirely
that of a stomach poison. And inversely, he explained that the
action on slugs is threefold, viz., an irritant effect, causing exces-
sive production of mucus, from which the slug will recover if it is
washed off and kept from desiccating air; an anaesthetic effect
causing complete immobility except under the most severe stimu-
lation; and last, an irreversible, lethal, toxic effect which pro-
duces a characteristic transparency in the gut wall. The classical
work of Cragg and Vincent (1952) confirms some of Thomas' con-
clusions and disproves others. They demonstrate indisputably that
metaldehyde is not only a contact and a stomach poison, but that
it has a progressively greater toxic action in the haemocoele, in the
crop, and on the surface of the body; hence they recommend its
greater use as a contact agent. They could not confirm a "charac-
teristic" transparency of the gut wall emphasized by Thomas. Nor
could they detect any fumigant action. However, they did indicate
that as a physiological reaction to metaldehyde, there is a loss of
water which continues even under conditions of 100 per cent rela-
tive humidity.
Lange and MacLeod (1941) stated that metaldehyde will pro-
duce greater kills of slugs and snails in unshaded areas because of
the killing action of the sun on the "stunned" individuals. Essen-
tially the same explanation was made by Woglum (1943) and later
by Persing (1945b), who reported that a substantial percentage of
H. aspersa will recover from metaldethyde poisoning during
cloudy weather or in the shade (cf. Lewis and LaFollette 1942a, b).
Although the same reason is not given by Corbett and Pagden
(1941), they imply reaching the same conclusions through their
recommendation that less meta is needed for A. fulica when the
bait is placed in exposed places. Later Lange and Sciaroni (1952)
stated that "in protected situations metaldehyde does not seem to
be an active enough poison to give high mortalities when used
alone in baits." Lange subsequently determined that an excessively
high concentration of metaldehyde stuns the snail before it can
consume a lethal dose.
Under conditions of high relative humidity, Lange and Mac-
Leod obtained greater kills, but Stringer (1946) reported less favor-
able results because of the greater recovery of the slugs. Thomas
(1948) explained that when metaldehyde is used during warm, wet
weather, there will be a greater number of slugs caught but only a
small percentage of them will be killed; and inversely, during cold,
CHEMICAL CONTROL	75
dry nights, the number caught will be smaller but the percentage
of kill will be larger. From this he concluded that the maximum
kill can be obtained when metaldehyde is used during wet, warm
nights which are followed by dry, warm days. Again, Cragg and
Vincent (1952) beautifully elucidated the several points of appar-
ent confusion. First, they indicated that metaldehyde intoxication
causes immobilization, inhibition of feeding, and a loss of water
through secretion of mucus. Under optimum conditions of high
humidity and low temperature, the snails and slugs may recover.
But with low humidity, there is a greater loss of water and death
ensues. High temperatures similarly produce a greater incidence
of death through the greater uptake of poison, the increased toxic
action, and the greater activity of the snail. It should be pointed
out, however, that increased activity of the snails, and therefore
increased opportunities for contacting the metaldehyde, depends
not only upon a higher temperature but a concomitant high hu-
midity—which high humidity, ironically, reduces the killing effect
of metaldehyde! Moreton (1953) takes advantage of this informa-
tion by suggesting that during dry weather, lower concentrations
of metaldehyde may be used effectively.  And conversely,  it is
recommended that during cool, wet weather metaldehyde baits be
fortified   either   with   calcium   arsenate   or   sodium   fluosilicate
(usbepq 1953). The more recent works on this subject unfortunate-
ly seem to neglect the important factor of the killing action of the
sun; hence the ideal conditions, as set forth by Thomas, should be
amended to read, "clear, dry warm days." Apparently because of
the confused picture presented by the interplay of several of the
irregularly variable ecological factors, some German investigators
have come to question seriously the reliability and practicability
of metaldehyde baits (Fromming 1951, 1952b; Fromming and Plate
1952; Plate and Fromming 1952), although Trappmann (1952) in
rebuttal stoutly defends their use. Lange (in litt. Feb. 14, 1956) adds a
welcome clarifying note with the following words: "In my experi-
ments I can get from practically no control with metaldehyde to
100 per cent kill within a few feet difference in location, depend-
ing upon whether the affected mollusks are exposed to desiccatory
conditions or to high humidities. The variations in results with
metaldehyde I am convinced are due to the multiple and variable
climatic conditions prevailing at any particular time."
A variety of "carriers" were tried with metaldehyde by Barnes
and Weil (1942) in an attempt to formulate a more effective bait.
Considering practicability and percentage of kill, none proved
76	CHEMICAL CONTROL
more promising than the old standby, wheat bran. At first, an ex-
cessively strong formulation of 1:2-1:2 1/2 was used (Newton 1937).
Shortly after that, however, it was decided that a bait of approxi-
mately the following proportions was adequate: 1/3 oz. "meta," 1 lb.
bran, and 1 pt. water (Cameron 1939, Esslement 1938, Thomas
1944, et al.). Without the water, the bait is considerably less effec-
tive (Pereira and Goncalves 1949). It has been suggested (Anon.
1949h) that to the above formulation 1 oz. of calcium arsenate or
y2 oz. of Paris green be added for a greater kill. Reflecting a very
definite, recent trend, a stronger bait has been recommended by
the usda through the usbepq Farmers Bulletin No. 1895 (1953) in
that to a mixture of 1 oz. of metaldehyde and 2 lb. of wheat bran,
corn meal, or similar material, there be added either 2 oz. of cal-
cium arsenate or 1 oz. of sodium fluosilicate. This mixture is mois-
tened with water just before use and applied to small gardens at
the rate of 1 lb. per 1,000 sq. ft. or 40-50 lb. per acre in larger areas.
On large scale operations, it is recommended that the bait be ma-
chined into pellets and broadcast at the rate of 5-10 lb. per acre.
The addition of lead arsenate and honey to the metaldehyde-bran
mixture apparently makes no improvement in the bait (Pereira
and Goncalves 1949). Putting sugar or molasses in the basic formu-
la did not increase significantly its attractiveness as a bait but it did
increase the percentage of kill (Thomas 1948). But baits of this
sort understandably spoiled more quickly.
In an attempt to overcome some of the difficulties of a mealy
bait, Thomas made bait "biscuits" by combining plaster of Paris
(dry), metaldehyde, and bran in a 1:1:10 proportion by volume,
mixing, adding water to permit molding into 3 by % inch discs, and
sun-drying until completely hard. These proved to be more attrac-
tive to slugs but they produced less of a lethal effect than the stand-
ard mix. Substituting casein glue for plaster of Paris made the
"biscuits" more attractive and more lethal only to slugs with car-
nivorous proclivities. A formula for a more conventional biscuit is
under British patent (Boot's et al. 1939). In addition to metalde-
hyde, the biscuits contain bran, flour mucilage, lard, and a leaven-
ing agent, and are baked at about 130° F. to avoid volitalization of
the metaldehyde. Another novel, but dubiously effective, approach
to the problem of making a ''lasting'' bait was made by Beekler
(1944) who suggested that finely divided metaldehyde be sus-
pended in paraffin!
Ever since shortly after its discovery as a molluscicide, consider-
able use of metaldehyde has been made in combating A. fulica. In
CHEMICAL CONTROL	77
fact, there undoubtedly is no infested area of any appreciable size
in which metaldehyde has not been tried in some form or combi-
nation. Beeley (1938a) in Malaya was probably the first to suggest
its use for this pest. He recommended a 1:64-1:32 (1.6-3.1 per
cent) mixture, by weight, with rice bran, moistened and distrib-
uted three pounds to the acre. Dias and Thamotheram (1939) and
Fernando (1952) in Ceylon made similar recommendations but
indicated more specifically the addition of approximately 26 oz.
of water (about 1 1/4 pt.) per lb. of the bait mix. Similar formulations
were used in Mauritius (Anon. 1942), Sumatra (Feij 1940), and
elsewhere. The relatively unimportant catches made by this bait
(van Weel 1949) suggested the need for a stronger formulation.
The percentage of metaldehyde was increased to 5-10 per cent by
Pangga in the Philippines (1949) with 'Very satisfactory" results.
In the same area, Cendafia (in litt. Feb. 12, 1952) used a 10 per cent
mixture on slices of ripe papaya and managed to produce a kill of
33,863 giant snails with two kilos of bait. He complains, however,
that the bait lasted only about three days; but that is not a new
problem. Dr. J. J. H. Szent-Ivany reported at the Ninth Pacific
Science Congress that Dr. Bridgeland of New Britain successfully
protracted the effectiveness of metaldehyde by mixing it with par-
affin oil.
Corbett (1938) attempted to protect metaldehyde from rain and
to keep it from poisoning poultry by putting it in impractical
cigarette-can cages. Dias and Thamotheram (1939) suggested the
use of a hood of corrugated iron. A shield of bamboo has been sug-
gested by others (Beeley 1938a, Anon. 1942). Inverted wooden
blasting powder boxes were used successfully in Guam (Peterson
1957). R. C. L. Notley (in litt. Nov. 17, 1951) met the problem in
Ceylon by putting the metaldehyde-bran bait on the underside of
curved tiles. Elsewhere in Ceylon the author observed the use of
metaldehyde bait shields made by interlacing two large leaves,
petiole-to-midrib. When the potency of the bait had been spent,
however, these shields afforded excellent sanctuary from the killing
sun. In some cases, the vast accumulation of snail excreta vouched
for the fact that the leaves had provided effective shelter for a con-
siderable period of time.
To get a more durable bait, Altson (1950b) mixed metaldehyde
with cement and lime to form a so-called "brick bait." This he
found durable but insufficiently attractive. The addition of rice
bran as a fourth ingredient, however, produced a bait which was
attractive both to snails and slugs and was clearly superior to the
78	CHEMICAL CONTROL
cement-lime-calcium arsenate "brick bait" in areas where lime was
naturally abundant. Numerous experiments showed that increas-
ing the bran increased the attractiveness of the bait; and increas-
ing the cement increased its durability. It was suggested that
metaldehyde, lime, rice bran, and cement be compounded by
weight in the ratio of 1:2:6:6. Since rice husk is cheaper, three
parts of it can be substituted for two parts of the rice bran and the
cement can then be reduced by one part.
A number of modifications of the basic metaldehyde-bran bait
have been made by various investigators. Powdered CaCO3 has
been used in place of, or in addition to, the bran with greater suc-
cess in areas where the soil is low in lime (Notley loc. cit.). Banana
peelings (Pangga 1949) and papaya fruits (Cendafia in litt. Feb. 12,
1952) similarly have been used as attractants with metaldehyde.
Cutting the cost of the bait by substituting sawdust for the bran
produced a less attractive bait, but one that was effective for 8-10
weeks (G. S. Dun in litt. April 17, 1950).
The use of the straight metaldehyde in either the pellet or pow-
dered form has been advocated by many (FitzGerald 1947, Townes
1946, etc.); this is not only more expensive than the mixed baits,
but it is actually less effective. Speyer's conclusions (1954) bear out
this assumption. If it is effective at all, the only thing that can be
said in its favor is that it does not require costly preparation.
To increase the spreading effect as a contact poison, Jary (1939)
mixed the powdered metaldehyde with sand and obtained impres-
sive results. In an effort to meet a similar need in protecting or-
chids with a thin cover of metaldehyde, Alicata (1950) used a 1 per
cent aqueous suspension spray with a far better killing effect than
was found with the metaldehyde baits. Blauvelt (1952) emphasized
that a 10 per cent metaldehyde dust on orchids killed more slugs
by contact than would be attracted to baits. These reports per-
suaded Jefferson (1952) to make comparative studies of sprays and
dusts. He prepared his wettable powder by grinding the metalde-
hyde with a silicate clay in a hammer mill. The 66.6 per cent
metaldehyde-clay concentrate powder, in turn, was mixed with
pyrophyllite to produce metaldehyde ''dusts" of varying concen-
trations. After considerable experimentation, he found that a 15
per cent dust with a coverage of 1-2 lb. per 1,000 sq. ft. was most
economical and more effective than heavier coverages of lower per
cent dusts. The dust should be applied at night and in at least
three applications at 7-10 day intervals. A 10 per cent dust is re-
ported to be effective in contact killing not only the adult slug,
CHEMICAL CONTROL	79
D. reticulatum, but the eggs as well (Lange and Sciaroni 1952). Ac-
cording to Jefferson, 10—15 per cent metaldehyde dusts were not
satisfactory for H. aspersa and Oxychilus cellarius. Dusts composed
entirely of 42-50 per cent wettable powder, however, were lethal
to the snails, but obviously were economically unfeasible. A spray
consisting of 6 lb. of 50 per cent wettable powder to 100 gal. of
water and distributed at the rate of 1 gal. per 30-35 sq. ft. proved
lethal to snails. It was recommended, however, that in addition to
this spray metaldehyde baits be used as a supplementary measure.
Jefferson pointed out that the sprays have a disadvantage in that
they are more costly to prepare and more difficult to apply than the
dusts. Doucette (1954) determined that a 15 per cent dust, in the
absence of rain, was effective for a maximum of only 6-7 days, in
contrast to a 2 per cent pellet bait which was effective for 12 days.
He therefore concluded that the baits should be used on fallow
ground; but in gardens, where the bait would be in competition
with green foliage, metaldehyde dusts should be applied in bands
in such a way that they would have to be crossed to get to the
plants. In contrast to Jefferson's spray application equivalent to
ca. 40 lb. of metaldehyde per acre, and more in keeping with the
findings of Cragg and Vincent, Moreton (1953) recommended a
spray application equivalent to 2.5 lb. of metaldehyde per acre,
with the comment that increasing it to 5 lb. per acre brought in
only slightly higher catches. But even at the lower amount, he
contrasted it with the 0.5-0.75 lb. of metaldehyde per acre required
in the distribution of "standard bran baits" and pointed out the
greater cost must be weighed against the potentially greater effec-
tiveness of a contact poison as compared with a stomach poison. In
quite the other direction, Leoni (1953a, b) recommended an im-
practical and admittedly expensive spray containing linseed oil and
whole milk in addition to an excessively high percentage of metal-
dehyde.
Jefferson determined that wettable powders and dusts of metal-
dehyde deteriorated rapidly and therefore must be prepared only a
short time before use. Cragg and Vincent and Moreton demon-
strated experimentally that metaldehyde sprays and dusts after
application lose their effectiveness within a very few days; hence,
treatment must be repeated periodically. These findings are in
sharp contrast to the report of Blowers (1954) wherein he states,
without presentation of experimental evidence, that a recently re-
leased commercial suspension of metaldehyde will leave a semi-
persistent coating of metaldehyde "sufficient . . . for many weeks."
80	CHEMICAL CONTROL
Similarly, Karlin and Naegele (1958) found a 15 per cent metalde-
hyde dust superior to a 20 per cent spray in that it remained effec-
tive for a period of three weeks in killing slugs.
The relatively evanescent property of metaldehyde in sprays and
dusts, and the consequent need for repeated frequent application,
sharpen just that much more the contrast to the proportionately
small amount of metaldehyde required when standard baits are
used. The experimental work with metaldehyde teaches us that,
in the final analysis, the most economical type of application can
be determined only when the density of the snail population, rela-
tive humidity, temperature, sunlight, available shade, extremes in
the diurnal-nocturnal temperature cycle, and other environmental
conditions are known or can be discovered.
At the present time, only in the Hawaiian Islands have metalde-
hyde dusts and sprays been used against A. fulica. Although it has
been used in strength equal to that of the dust, the spray has given
much better results (Weber 1954). Regarding the spray, Thistle
(1953b, 1954b) reports that "while transitory in effect, it is useful
. . . where arsenical or other highly toxic sprays cannot be used."
Lange and MacLeod (1941) reported that the following alde-
hydes mixed with bran in 3 per cent strength were not observably
attractive to slugs and snails: acetaldehyde, paraldehyde, hexalde-
hyde, butyraldehyde, propionaldehyde, valeraldehyde, and heptal-
dehyde. In carefully controlled experiments with D. reticulatum,
Cragg and Vincent (1952) found no contact, haemal, or stomach
poison effect in acetaldehyde and paraldehyde. Leoni (1953a, b)
submitted corroborative evidence.
Methyl Bromide: Higher and higher concentrations of this deadly
gas have had to be used by the California Bureau of Plant Quaran-
tine in order to insure a 100 per cent kill of the giant snails in the
cargoes of ships coming in from infested areas (A. P. Messenger
in Hit. Jan. 4, 1950). There still is much uncertainty as to the
amount actually needed under a given set of conditions.
Naphthalene: Uncertain and variable results were obtained by
Massee (1928) when this chemical was used in an attempt to con-
trol slugs. Miles et al. (1931) found it neither lethal nor appre-
ciably repellent to the slug M. sowerbii. In contrast, out of a num-
ber of chemicals tested Dustan (1927) recommended naphthalene
flakes as the best general repellent. To a large extent, his recom-
mendation was based on the fact that naphthalene flakes are re-
sistant to the leaching action of rain.
CHEMICAL CONTROL	81
Parathion: A 2 per cent parathion and 5 per cent metaldehyde contact
dust was found to be very effective in controlling slugs (Lange and
Sciaroni 1952). There are suggestions of a synergistic action in this
combination. Karlin and Naegele (1958) branded parathion as
"unreliable" and warned of its extreme toxicity. Unimpressive
results were obtained in field tests on H. aspersa (Pappas and Car-
man 1955).
Paris Green: Lovett and Black (1920), in their experiments with D.
reticulatum, showed that Paris green had a definite repellent effect
upon this slug and that it was eaten only under stress; but even
though it was eaten sparingly, it was usually fatal. Apparently the
recommendations of Hodson (1925) were incorporated in the slug
bait formula of Douence (1929), viz. 1 lb. of Paris green, 20 lb. of
bran, and sufficient water to make a "damp" bait. This was re-
ported to be sufficient for an acre. The 1:30 formulation of Miles
et al. (1931) gave uncertain results against M. sowerbii. Thomas
(1944) tried a 1:28 formulation as a slug bait and produced "SO-
SO per cent kills." Cameron (1939) added to a 1:25 formulation
1/2 pt. of molasses, instead of "a little sugar" as recommended by
Hodson; but he obtained less good results than he did with metal-
dehyde baits. Plaster of Paris, bran, and Paris green "biscuits"
were made by Thomas (1948) but they did not prove effective in
controlling slugs. Pangga (1949) found Paris green ''ineffective"
against A. fulica though he did not indicate the nature of his ex-
periments.
Phenol: Along with a number of other suggestions for slug control in
Australia, French (1906) recommended the use of "carbolized saw-
dust." Ewart (1910) claimed an improvement in this repellent by
moistening a bucket of sawdust with a solution made up of 1-2
cups of "phenyle" in 10-20 large cups of water. Severe burning of
foliage by "crude carbolic acid" was demonstrated in the experi-
ments of Lovett and Black (1920) and it was therefore considered
to be of little practical use in the control of slugs. A 1:500 aqueous
solution was reported by Miles et al. (1931) to be effective in con-
trolling M. sowerbii. The formulation of Ewart was suggested by
Green (191 la) as a possible control measure for A. fulica.
Potassium Permanganate: The experimental use of this chemical as
a contact poison for slugs was claimed by Hall (1932) to be "excel-
lent." Miles et al. (1931) found it not lethal to the slug M. sowerbii.
Potassium Cyanide: This exceedingly poisonous chemical was found
by Lovett and Black (1920) to darken various baits and render
them unattractive to slugs and snails.
82	CHEMICAL CONTROL
Pyrethrum: A mixture of this insecticide and bran (Thomas 1948)
was shown to be attractive to slugs (probably largely if not entire-
ly because of the bran), but no kills were produced. Pangga (1949)
found pyrethrum toxic to young A. fulica but not to the adults.
repellents
Although a great many chemicals and compounds, including several
listed here under separate headings, are repellent in nature, by
far the majority produce only transitory irritant effect, or effects
which last only while the snail or slug remains in contact with
them. In cases where the irritant effect is so severe that death is
produced, the substance is more correctly referred to as a contact
poison (q.v.). From this, it is obvious that the difference between
a repellent and a contact poison may be simply a matter of dif-
ferent concentration of one and the same chemical. And, further,
repellents may be considered most effective when they are also con-
tact poisons.
Lovett and Black (190) conducted the first extensive experiments
to find an efficacious slug repellent. Certain combinations of car-
bolic acid, sulphur, gasoline, lime, and sodium hydroxide were
found to be temporarily repellent but the damage to foliage made
them impractical. Combinations of hellebore (Veratrum), nicotine
sulphate, sulphur, lime, and tobacco dust similarly had a tempo-
rary repellent effect, but it was lost or greatly reduced with rain.
In their early experiments, nicotine sulphate solution (1:800
aqueous) and air slaked lime and tobacco dust (5:1 by weight)
were recommended as "excellent" repellents. Later, Paris green,
copper sulphate, and especially Bordeaux mixture (q.v.) were
shown to be the best repellents. Unidentified slugs were exposed to
eleven different substances by Dustan (1927) in an effort to find a
good chemical repellent. He found that naphthalene flakes, be-
cause of their resistance to heavy rains, proved to be the best of the
lot. In order of decreasing importance, he recommended four
others, viz., sodium fluoride, magnesium fluosilicate, sodium chlo-
ride, and creolin (5 per cent aqueous). Tanglefoot, hydrated lime,
fish oil emulsion, flowers of sulphur, tobacco dust, and calcium
fluosilicate were insufficiently repellent to warrant further con-
sideration. Miles et al. (1931) ran other extensive tests and found
that aluminum sulphate, ammonium chloride with phenol,
ammonium sulphate, copper sulphate, drained creosote salts, po-
tassium permanganate, and sodium carbonate were definitely re-
pellent to the slug M. sowerbii. Phenol in a 1:500 aqueous solu-
CHEMICAL CONTROL	83
tion was particularly good. The best repellents were stated to be
creosote in powdered chalk and 1:500-1:1000 aqueous solutions of
mercuric chloride. Chlorcresylic acid in chalk, naphthalene, and
nitrate of soda were shown to have little or no effect as repellents.
Tryon (1899) recommended the use of tobacco waste as a repellent
and contact poison in the control of vaginulid slugs. Ferrous sul-
phate is reported by Basinger (1927) to be repellent to T. pisana.
A solution of rubber in crude oil effectively repels A. fulica in
Malaya (Altson 1950a). Trenches sprayed with crude oil were com-
pletely effective in repelling the giant snail in Guam (Peterson
1957). In Ceylon this snail is reportedly repelled when the aromatic
Khas Khas (Vetiveria zizanoides) is used. Several authors (e.g., Hall
1932) have recommended the use of sheets of zinc as repellent bar-
riers. Others suggested using plain sawdust (e.g., "R.B." 1952). An
early investigator (Miege 1906) recommended hog bristles!
Soap solution: Soap solution has proved to be only moderately prom-
ising in controlling slugs (Lovett and Black 1920). Similar results
with A. fulica have been reported by Pangga (1949).
Sodium Chloride: Common table salt has long been a household
method of killing slugs and snails. Although Anderson and Taylor
(1926) used it against slugs in field tests without satisfactory results,
Dustan (1927) and Vandenberg (1929) found it effective. Latif
1933a) used it as a repellent to protect potted orchid plants from
the giant African snail. Hall (1932) recommended the use of an
aqueous solution rather than the dry salt; but Pangga (1949) was
able to produce kills with the solution in only the young specimens
of A. fulica. In Guam, salt water sprays proved practical only in
areas where there would be incurred no damage to the soil, for
example, in beach zones and along roadways (Peterson 1957).
Sodium Dinitro-orthocresylate: G. S. Dun (in lift. Nov. 25, 1949)
quite accidentally discovered that this weed killer produced a con-
tact killing effect on A. fulica in New Britain. This observation
warrants investigation.
Sodium Fluoride: The slug D. reticulatum was shown to do very
little feeding on bait poisoned with this chemical (Lovett and
Black 1920). Dustan (1927) and MacDougall (1931) were able to
obtain good slug kills with it; but MacDougall did not recommend
its use because of the burning effect it had upon plant foliage.
Hodson (1924) had earlier come to the same conclusion.
Sodium Fluosilicate: In the revised edition of the USDA Farmers
84	CHEMICAL CONTROL
Bulletin No. 1895, it is recommended that metaldehyde baits be
fortified with either this chemical or calcium arsenate.
Soot: This has been recommended for controlling slugs and snails,
but with the warning that unless carefully applied to plants, there
may be damage (Anon. 1930). Earlier, Durham (1920) found that
even when it was combined with lime, it was of little use in killing
slugs.
stomach poisons, miscellaneous
Baits containing diethylparanitrophenyl thiophosphate (i.e., Rhodia-
tox) and dinitro-o-cyclohexylphenol were found by Pereira and
Gon^alves (1949) to be less effective than metaldehyde and there-
fore were not recommended. Levy (1938) patented a bait containing
rotenone; but there is no evidence in support of its questionable
effectiveness.
Strychnine Sulphate: In spite of the fact that this was readily eaten
by slugs, it did not have a killing effect (Lovett and Black 1920).
Sulphocyanides: Although some of these were very lethal to the slug
M. sowerbii, they were so deliquescent that they were considered
useless in any large scale operation (Miles et al. 1931).
Tartar Emetic (potassium antimonyl tartrate): Lewis and LaFollette
(1942a) report high kills of H. aspersa with a spray of tartar emetic.
Persing (1944a) states that such sprays "show exceptional promise"
especially as an emergency measure to stop immediately damage to
citrus trees and fruits. He recommends adding 2 lb. of tartar emetic
and 4 lb. of white or brown sugar to 100 gal. of water and applying
it with a boom gun or boom sprayer at the rate of 3-4 gal. per
orange tree. A 6:12:100 ratio is used if the solution is applied with
a spray-duster.
Warfarin: In Guam, achatinas consumed with apparent complete
impunity rat bait containing warfarin (Peterson 1957).
Whitewash, Poisoned: The lack of natural limestone in Ceylon en-
courages the giant snails to remove the whitewash from the houses.
This has suggested the use of bags of poisoned whitewash as a con-
trol measure (Connolly 1931). Because some parts of Java are
equally poor in limestone deposits, Benthem Jutting (1934) has
recommended the same type of control.
Chemical Control—an Evaluation Any attempt to evaluate on
a comparative basis the various chemicals and compounds listed
above is frustrated from the outset because there has been reported
in the literature too little of an exact nature upon which to base
CHEMICAL CONTROL	85
scientifically a comparison of any great extent. Although a number
of the experiments with molluscicides have been adequately con-
trolled, the conditions under which they have been conducted have
been so variable that their results are not reducible to any sort of
common denominator. For example, the animals used in the various
experiments have been different species of slugs and snails, with vary-
ing tolerances to the different molluscicides. This is complicated by
the general belief that there is a fundamental marked difference be-
tween slugs and snails in their capacities to withstand toxic effects.
Therefore merely because a certain formulation is shown to be effec-
tive in controlling slugs, it does not necessarily follow that it will be
equally effective in controlling the giant African snail. On the other
hand, many of the reports in the literature are inadequately sup-
ported by factual detail. A case in point is the work of Pangga (1949)
on A. fulica. Without giving a single detail as to the nature of many
of his experiments, he simply states that certain chemicals have little
or no effect upon this giant snail. In other cases in the literature,
there is very strong evidence of insufficient or no controls in the ex-
perimentation. Such, of course, are fruitful grounds for biased or
specious conclusions. So little is known about the normal physiology
of terrestrial gastropods that to a great extent, the toxicological
effects of the various molluscicides are simply not understood. But in
spite of these drawbacks, much of a positive natare can quite safely
be concluded from the collected and collated data.
First of all, it is more than apparent that a poison, even approach-
ing the ideal for the giant African snail, has not yet been found.
"Repellents" as such, by their very nature, are of the most limited
value and they therefore can almost completely be dismissed at this
point. They are of use only on a small scale; for example, to protect
individual plants or small garden plots. They therefore are to be
considered more in terms of a protective measure rather than of a
control per se. In contrast, "poison baits'' have been put to consider-
able use in control programs and they still continue to provide much
promise of help as new combinations are being formulated. The re-
quirements of a good poison bait, however, are very great and un-
fortunately in practice they are sometimes basically antagonistic to
each other. Ideally, a poison bait should contain a powerful attract-
ant and toxicant; it should consist largely of a readily available, in-
expensive diluent; it should have a high degree of stability; and its
application should provide the very minimum of difficulty.
With the appearance of the comprehensive work of Kieckebusch
(1953), there no longer can be justifiable doubt about the existence
86	CHEMICAL CONTROL
of a very keen olfactory sense in snails. But finding a suitable attract-
ant, which will not be neutralized or made impracticable by some
local or environmental factor, is anything but a simple problem. For
example, lime is generally considered a good snail attractant, but in
areas where there is a natural great abundance of calcareous mate-
rial, it is very much less effective. Lewis and LaFollette (1941, 1942a,
b) showed that substituting fresh orange pulp for bran as the attract-
ant-diluent in arsenical baits used to control H. aspersa in California
citrus groves not only appreciably increased the effectiveness, but re-
duced the cost 75 per cent. An attractant of this sort however has the
disadvantages of being obtainable in only a very restricted area and
of spoiling quite rapidly under usual field conditions (Persing 1944a).
Sugar similarly increases the attractiveness of baits but it hastens
their spoilage (Thomas 1948). Bran itself quickly loses its attractive-
ness under conditions of high humidity. Metaldehyde is an attract-
ant, but if it is used in excess, it may actually serve to "protect" the
snail from the poison bait by interfering with the amount it can
consume. The discovery of a positive anemotaxis in A. fulica (Cham-
berlin 1952a, b) suggests that the attractant qualities of a bait can
be taken fullest advantage of if the bait is placed upwind to the
greatest concentration of the snails.
Obtaining a suitable toxicant presents equally difficult problems.
Some of them chemically alter the other constituents of the bait.
Others have been demonstrated to be highly toxic to snails, but they
are of such a nature that they are seldom consumed and hence they
act more like repellents than toxicants. To find a toxicant which will
be effective under all conditions of weather is even more difficult.
Quite naturally, optimum concentration of the chemical is of prime
importance and it is therefore necessary to take into consideration
the dilution factor of environmental moisture. Some toxicants pro-
duce the greatest total kills under warm, moist conditions; but such
conditions favor rapid spoilage of the bait—especially through the
development of mold. Other quite effective toxicants when exces-
sively diluted, become mere irritants from which the snails may sur-
vive by throwing off a great deal of slime. This is especially the case
during rains, which may actually wash the toxicant completely away
in a few minutes' time. On the other hand, the supplemental killing
effect of the sun, through desiccation, upon individuals stunned by
the toxicant may be rather badly offset by the fact that in the mean-
time the bait has dried out and become ineffective. Even though
some baits, such as those containing metaldehyde, can be rejuvenated
after dehydration simply by remoistening, the mechanics of the proc-
CHEMICAL CONTROL	87
ess on a large scale would become a considerable item both in time
and cost. It is an obvious fact that tropical conditions in general are
basically antagonistic to any measure of stability in snail baits. Pro-
viding some sort of shelter for the bait, no mater how simple, inevita-
bly is impractical except on the smallest scale. Moreover, shelter for
the bait often means shelter for the snail; thus damage to plants may
actually be increased through the unwitting provision of an attrac-
tive shelter from the killing action of the sun, persisting long after
the poison has lost its effectiveness. The use of cement in baits has
provided a very welcome element of stability; but this has its short-
comings in making the bait less attractive and in some cases less toxic.
In general, oil base baits hold up better under moist conditions.
In the final analysis, the practicability of application of a specific
bait or toxicant is the decisive factor. No matter how effective a snail
poison is, if it requires anything more than a minimal amount of
labor in its application, if it is expensive in the least, if it provides
dangers to the lives of other animals, if it produces appreciable
scorching of plant foliage, or if it is difficult to prepare, its use most
definitely will be very limited. Even if each of these problems is ade-
quately met, the actual effectiveness of a molluscicide is influenced to
a considerable extent by such environmental factors as humidity, sun-
light, contrast in the temperatures of night and day, rainfall, soil
type, terrain, and plant cover. It becomes necessary then to determine
optimum conditions under which snail poisons can be used. For
example, it would be a senseless waste of time and materials to dis-
seminate a poison, no matter how effective it is, at a period when
environmental conditions have forced a majority of the snails into
estivation. If under the same conditions, however, local irrigation
brought the snails out of estivation, disseminating the poison would
be clearly indicated. But the interplay of the various environmental
factors can produce strange results. In certain regions in Ceylon,
and in the Pallekelle District in particular, there was the strongest
evidence that an intensive poisoning campaign (metaldehyde bait
put out weekly for eight months) actually brought about an increase
of the population of giant snails!
Metaldehyde and calcium arsenate unquestionably are to date the
chemicals of choice in attempts to control A. fulica. However, there
is among investigators no general agreement as to which is the more
useful or even whether there is any synergistic factor in their combi-
nation. Some (e.g., Lange and MacLeod 1941, Anon. 1949h, usbepq
1953) indicate that in controlling slugs and snails, metaldehyde-bran
baits are more effective, especially under dry conditions, than cal-
88	CHEMICAL CONTROL
cium arsenate-bran baits, and that the addition of calcium arsenate,
sodium fluosilicate, or Paris green to a metaldehyde bait increases its
effectiveness. Others (e.g., Lewis and LaFollette 1942a, b; Persing
1944a) insist that, at least as far as the control of H. aspersa is con-
cerned, calcium arensate baits are better than the metaldehyde baits
and that, except during hot weather, the greater cost of combining
the two chemicals in a bait cannot be justified. Apropos of this gen-
eral subject, it is unfortunate that Altson (1950b) did not extend his
experimentations to include the addition of calcium arsenate to his
"brick baits" of cement, lime, metaldehyde, and rice bran. Thomas
(1944) convincingly reports on the superiority of meta-bran baits
over Paris green-bran baits. In screening thirty-two possible mollusci-
cides, including the promising Isolan, Pappas and Carman (1955)
found none superior to the commercial pelleted bran bait containing
6.75 per cent calcium arsenate and 1.5 per cent metaldehyde. Peter-
son (1957) used this formulation in Guam and makes the following
report regarding its action on the giant African snail: "Following in-
gestion of the bait, snails usually became paralyzed within 10 to 15
minutes and died within 30 minutes to 1 hour. It was found that mi-
grating snails killed by the bait and left on the ground would be par-
tially eaten by other snails the following night and additional snails
would be killed."
Recent extensive correspondence with investigators in the field has
revealed the fact that a rice bran-metaldehyde bait is still considered
in most areas infested with A. fulica to be the only practicable chem-
ical control method. According to Pangga (1949), calcium arsenate-
rice bran bait was much less effective on this species than was the
meta-bran bait. In the Hawaiian infestations, however, the metalde-
hyde baits were found less practical and in the long run more expen-
sive than the calcium arsenate-slaked lime-cement mixture. Broad-
casting straight metaldehyde in the form of pellets is a simple, ex-
pensive, and relatively much less effective method of controlling
snails, and its use in this form has quite understandably been dis-
continued in many areas. Disseminating metaldehyde in sprays and
dusts similarly is costly, but very much more effective; the unfortu-
nately transient nature of the effectiveness of such applications, how-
ever, increases the labor and cost factors far beyond practicability in
most cases.
No matter what chemicals or baits are used, invariably there are
disadvantages and even dangers involved which must be taken into
consideration and which must condition their use. Of prime concern,
of course, is the possibility of endangering the lives of humans, live-
CHEMICAL CONTROL	89
stock, and poultry (cf. Douence 1929). This is particularly the case
when the relatively effective sprays of sodium arsenite or corrosive
sublimate are used. The indiscriminate use especially of arsenicals
and metaldehyde introduces very real problems in this direction.
And although the element of danger in the use of arsenicals is fairly
well understood and appreciated, the same probably cannot be said
for metaldehyde. Within months after the initiation of its use as a
molluscicide, J. P. Hudson (1937) announced with obvious concern
that birds were seen to be removing dead slugs and snails from
metaldehyde baits. A few weeks later, the fears he expressed were
confirmed in the report of R. H. Hudson (1937) who stated that a
blackbird and a starling, after feeding on metaldehyde bait, soon
"fluttered about screaming in obvious agony, and . . . died about
half-an-hour later. . . ." To obviate this danger, Carbett (1938) sug-
gested the construction of special bait cages that would permit the
entry of snails but would exclude fowl. In an attempt to determine
the poisonous nature of metaldehyde to pets, Shewell-Cooper (1938)
checked with the Royal Society for the Prevention of Cruelty to Ani-
mals and obtained a significant report, a part of which follows:
". . . in several instances dogs have died from eating meta, which was
apparently put down to destroy slugs. ... In one case we had an
analysis made of a dog . . . and the result of the analysis clearly
showed that the dog died from consuming meta." The following
year, Jary indorsed the stand of exercising great caution in using
metaldehyde and introduced the suggestion that it might be harmful
to earthworms—a point which seems to have been ignored since then.
That same year, Lewis et al., echoing the earlier warnings of Giming-
ham and Newton (1937), presented the medical history of a thorough-
ly convincing case of death in a child from metaldehyde poisoning.
According to their report, accidental death of other children and
attempted suicides of adults are on record. They warn, without pres-
entation of evidence, that ". . . the method of mixing it with bran
has been responsible for the innocent slaughter of many of our wild
birds." In direct contrast to these reports, Cameron (1939) fed two
chickens for four weeks on a total of two pounds of a 1:50 meta-bran
mixture along with their regular feed. Even though it is believed
that this amount is in excess of what they would be picking up under
normal field conditions, the chickens remained unaffected. Fernan-
do (1952) similarly minimized the dangers of metaldehyde by stat-
ing: ". . . dogs, cats and poultry will sometimes taste the bait and
reject it without ill effects." Among many other toxicants used
against invertebrates, Tilemans and Dormal (1952) list metaldehyde
90	CHEMICAL CONTROL
as a nerve poison with an LD50 of 170-200 mg/kg for man and 250
mg/kg for dogs. For intoxication, the symptoms of which they de-
scribe, they recommend vomitives and an antispasmodic of chloral
chlorhydrate. When either metaldehyde sprays or dusts are used,
there apparently is no phyticidal effect even on such delicate plants
as orchids (Jefferson 1952, Moreton 1953).
If bait containing toxic agents is broadcast instead of being placed
in heaps, any possible hazard is considerably reduced—but unfortu-
nately so is the efficacy of the bait. This leaves still unaltered the
problem of soil contamination; for example, the prolonged use of
arsenicals eventually interferes with normal agricultural practices in
that the accumulation in the soil builds up beyond the tolerance
point of some arsenic-sensitive crop plants (Pierce 1931). In areas
subjected to periods of drought, there is danger of a surface concen-
tration of molluscicides through the siphon action of deeper soil
moisture being drawn up by capillarity to replace evaporated surface
moisture. If copper exists as a contaminant in the arsenical, subse-
quent insecticidal fumigation of the plants with cyanide may pro-
duce severe injury to the foliage (Gammon 1943). In Hawaii, it was
not the poisonous nature of the calcium arsenate-cement—lime mix-
ture to which some of the complaints were directed; it was the fact
that stones, painted with this mixture, were broadcast in grassy areas
where they caused damage to lawnmowers!
Unfortunately, the promising tartar emetic sprays henceforth will
be used in the United States only on a very limited basis because of
the discontinuance of the large scale commercial production of potas-
sium antimonyl tartrate.
Copper sulphate has seemed to be inordinately popular in the
recommendations of many who have been faced with the control of
the giant African snail. To a fair extent, this is unfortunate. The fre-
quent rains in the tropics quickly wash away this chemical and re-
quire the addition of more. Its continued use not only builds up an
abnormally high concentration of the copper ion, but it very appre-
ciably increases the acidity of the soil. In the strongly basic soils of
the coralline islands, this change in pH might be an advantage; on
the other hand, it might be quite deleterious to crops which are sensi-
tive to acid soils. Miles et al. (1931) have suggested the concurrent
addition of an equal quantity of lime to offset this acidifying effect.
This brings up the point that the molluscicidal use of lime will con-
versely alkalinize the soil. This directly favors the survival of the
snails but not certain crops, such as tea, which demand an acid soil.
Plants which have been injured by the feeding of snails absorb CuSO4
CHEMICAL CONTROL	91
rapidly at the wound site and die. But even healthy plants may be
burned severely by this chemical if it is applied in too high a concen-
tration. Pangga's experiments (1949) suggest that there has been an
overemphasis of the use of CuSO4 against A. fulica.
The value of ashes has similarly been overrated. For one thing, ex-
cept under the most unusual conditions, ashes in any quantity will
not be found in the tropics. When it becomes soaked with rain, it is
useless and will need replacing. Besides, the washing of ashes into the
soil will alkalinize it with the resultant disadvantages indicated
above.
Of the poison gases used in fumigation of cargoes infested with the
giant snail, ethylene dibromide seems to hold much greater promise
than methyl bromide, hydrocyanic acid, or carbon disulphide. Accu-
rate determination of adequate concentration of any of these gases to
insure a 100 per cent kill has yet to be made.
Some of the newer insecticides may be found, after much more ex-
tensive experimentation, to possess sufficiently great molluscicidal
properties to be of use in giant snail control programs; but the re-
sults so far have been neither spectacular nor promising. For exam-
ple, the work of Pappas and Carman (1955) appears to have quite
convincingly eliminated from further serious consideration, except
for some possible synergistic effect, such common insecticides as
aldrin, chlordane, DDT, dieldrin, endrin, isodrin, malathion, and
parathion. W. H. Lange, of the University of California at Davis,
however, believes that at elevated temperatures, some of these insec-
ticides become effective. He is currently conducting tests which
promise to bring to light new organic toxicants of unprecedented
molluscicidal properties.
CHAPTER 6
CONTROL
THROUGH
MECHANICAL
DEVICES
Various mechanical methods have been devised to control
Achatina fulica, and other pestiferous snails, especially in the absence
of suitable chemicals. Some of these provide under a great variety of
conditions the only, and sometimes the best, means whereby snail
pests can be held in check. At the very least, however, they serve as
valuable adjuncts to other types of control.
Barriers Fences made of closely placed bamboo sticks are
used in many places to create a mechanical barrier against the giant
snails. But even where the fence is six to eight feet high, the barrier
effect is only temporary; for the larger snails scale the fence and the
smaller ones manage to work their way through the gaps. Nonethe-
less, erecting a fence in conjunction with hand picking and destroy-
ing, is probably the most common method of control that is used,
other than just hand picking alone. G. S. Dun (in litt. Dec. 17, 1953)
found that painting a board fence with crude creosote increased con-
siderably its effectiveness as a barrier.
Effective barrier fences have been constructed of other materials.
Large experimental vegetable plots at the Agricultural Development
Station in Ponape are surrounded by a very high fence of closely
placed strips of wood. Torres (1950) similarly suggests erecting a
wooden fence to protect coffee plants from the attacks of the giant
South American snail, Strophocheilus oblongus. The people in Chi-
92
CONTROL THROUGH MECHANICAL DEVICES	93
chi Jima strapped together large sheets of corrugated iron around
their garden plots to keep out the giant snail. The fact that these be-
come excessively hot in the bright sunlight should not suggest added
protection, as the heat quickly dissipates before the crepuscular and
nocturnal snails come in contact with them. Actually, the corrugated
iron sheets can be more easily and more quickly scaled than wooden
or bamboo fences. Because of vast surplus stores of these sheets in
Guam, it was recommended by high government officials in 1949
that they be used for snail barriers. Sheet zinc is recommended by
Hall (1932) as being an absolute deterrent to snails and slugs; but of
course their use as a mechanical barrier is quite out of the question
from the standpoint of cost in anything but the most small-scale con-
trol measures.
As early as 1933, Corbett suggested without elaboration that flower
beds could be protected from the giant African snail by surrounding
them with an 18 inch high, 1/4 inch mesh wire netting. Bryan (1949)
repeats the suggestion. Independently of these recommendations,
Peter J. R. Hill of the War Memorial Laboratory in Koror (Palau
Islands) erected around his 65 by 45 foot vegetable garden a 6-8 inch
high, 18-mesh copper wire screen barrier. The screen was buried in
the ground at a 45° angle so that the top of the screen leaned away
from the garden. The horizontal wires were removed from the upper
inch of the screen, the last one of which was removed at an oblique
angle so that the vertical wires were alternatingly vertical and almost
horizontal. This produced a double row of inch-long sharp projec-
tions along the top of the wire fence. This type of barrier is very
effective because of the following advantages: the screen helps to
break the suction of the foot and the snail's own weight tends to pull
it off; the angle of the fence increases the effectiveness of the pull on
the foot and causes the snail to fall away from the fence; the sharp
vertical wires force the snail to loop way out in an attempt to circum-
vent it, leaving such a small portion of the foot in contact with the
screen that purchase is invariably lost; and in the areas where a
double barrier of this sort was set up, the snails which did manage to
get over the first fence were imprisoned between two fences and died
because of exposure to the hot sun the following day. But these ad-
vantages were found to be offset by disadvantages. With the fence
only 6—8 inches high, the snails were found to pile up along the fence
in certain areas to such an extent that others could crawl upon them
and drop over the other side. Even though the fence is relatively in-
expensive, it still is considerably beyond the means of most native
people. And since the necessity of removing the snails, as they accu-
94	CONTROL THROUGH MECHANICAL DEVICES
mulate along the fence, is still not obviated, the native people find
it more economical not to erect the fence and simply resort to fre-
quent hand collecting. A possible improvement of this fence might
be effected if it were constructed along this same design but built to
stand one foot high. The upper four inches of this could then be
bent away from the garden plot at a 90° angle. This would force the
snail to crawl upside down for a way even before it got to the barrier
of the double row of vertical wires. The drop-off should be 100 per
cent. But, again, this would significantly increase the cost.
Kondo (1952) announced that his description and figures of the
"Peter Hill snail fence" were mimeographed in 1949 by naval per-
sonnel and distributed in the Trust Territory. As an apparent out-
come of this, Manuel Mendiola of Rota used the fence to protect his
extensive bell pepper plantings. Kondo gives a vivid and detailed ac-
count of the effectiveness of this approximately 1,400 foot fence, re-
emphasizing the advantages and the inherent difficulties in the use of
this type of barrier (see Fig. 11).
It has been suggested by Lange (1947) that brush taken from clear-
ings be piled up around the periphery as a mechanical barrier to the
giant snail. Such accumulations of decaying plant material are par-
ticularly attractive to these snails because of the almost ideal condi-
tions of food, moisture, and protection from the sun. It would seem
then that such a practice might invite the build-up of dangerously
high peripheral populations. On the other hand, this method coupled
with other control measures, such as the use of molluscicides, might
be very effective.
Rattan or coir fiber tied to the trunks of trees susceptible to the at-
tacks of the giant snails has proved effective (Feij 1940, Bertrand
1941). Even coir fiber rope was considered by South (1926b) to be of
value in setting up a mechanical barrier around gardens. But experi-
mental plantings of thorny mimosa plants did not produce any bar-
rier effect at all (Feij 1940). Trenches filled with sawdust have also
been recommended (South 1924b). In the Pallekelle estate in central
Ceylon, freshly planted cacao seeds and young seedlings were pro-
tected from the ravages of the giant snail by specially constructed
wire cages; but this practice soon became economically prohibitive.
Technically, repellents are chemical barriers and should be con-
sidered here; however, they have already been treated above in the
discussion of chemical control.
Burning-Over This practice has been resorted to by native
peoples in many parts of the world primarily because it is the easiest
and quickest means of clearing land before planting. It is very effec-
CONTROL THROUGH MECHANICAL DEVICES	95
tive in killing a high percentage of snails present in spite of the fact
that this benefit is only incidental. Burning-over is most often done
during the dry season and at this time a great share of A. fulica are in
estivation. Estivation often takes place right on the surface of the
ground under vegetation or other superficial types of protection. To
a great degree, snails under such conditions will be killed in the
burning-over process. Other specimens, however, will go down into
the ground as much as four or five inches before estivating. These
will survive and re-establish the population with the return of nor-
mal conditions. Other species of the giant snail were shown by Lang
(1919) to survive in the same manner the annual grass fires in the
former Belgian Congo. No matter how thoroughly it is done, burn-
ing-over is not eradicative by any means. But besides this, snails from
contiguous high-pressure population areas will quickly invade the
burned-over area and speed up repopulation just that much more.
Tsetkov (1940) emphasizes this point. Early unsuccessful attempts to
"burn out" A. fulica in Agafia, Guam, gave further convincing proof.
The systematic use of the flame thrower, after clearing the land of
vegetation, proved much more effective than simple burning-over in
controlling T. pisana in California (Basinger 1923a, Gammon 1943).
But even this method, in efforts to control H. aperta in southern
California, was disappointing because this species has a greater pro-
pensity for estivating at comfortable distances below the ground. In
contrast, but with similar results, Henderson (1936) found Polygyra
uvulifera survived grass fires where other species did not, simply be-
cause it habitually retreated to large, thick protective leaves. Joubert
and Walters (1951) found that burning-over fields heavily infested
with T. pisana was very effective in South Africa.
Clean Culture As early as 1926, it was suggested by Pereira
that the responsibility for a renewed outbreak of A. fulica in Ceylon
rested in the fact that the people had failed to destroy weeds and to
clean up accumulated refuse. Leefmans (1933c), Corbett (1933), Feij
(1940), Lange (1947), Anon. (1947a), van Weel (1949), Rees (1951),
and Peterson (1957) have further emphasized the importance of re-
ducing the numbers of the giant African snail through clearing and
weeding. There is no question about it; rubbish, debris, wild plant
growth, and the like do afford a sanctuary for these snails. A premium
therefore is put on their removal. Lovett and Black (1920) produced
"remarkable results" in reducing slug and snail damage through the
simple expedient of cleaning away all possible refuge in areas adja-
cent to crops. Although keeping the ground free from plant debris
may be conducive to good snail control, it is contrary to the long
96	CONTROL THROUGH MECHANICAL DEVICES
established agricultural practice of allowing the trimmings especially
of green manure plants (e.g., Gliricidia and Erythrina) and the leaves
of crop plants (e.g., cacao) to accumulate as a natural mulch.
Through this practice, weed growth is kept down, moisture is re-
tained, nutrients are added to the soil, and, unfortunately, insect and
snail pests are increased.
The nocturnal and crepuscular habits of A. fulica normally permit
it to escape the killing effect of the sun. It has been observed over
and over again in the field that snails which were unable to find pro-
tection from the sun, after a night's foraging, were quickly immobi-
lized and soon killed. In fact, in many places, by far the majority of
deaths in the snails can be attributed to overexposure to the sun. The
drying effect and the excessive heating of both the snail and the
ground are probably the causes of death; but the work of Carmichael
(1928, 1931) suggests that it may be the ultraviolet rays which pro-
duce the lethal effect. At any rate, advantage can be taken of this
knowledge by removing as much as practicable of anything which
affords protection from the sun. This was tried on a large scale on an
experimental farm in Tinian by Nelson Young. A large field was
plowed over, leaving exposed to the sun both snails and their eggs.
This essentially neutralized area was then planted and by harvest
time, the snails in the adjacent uncultivated areas had been able to
move only a short way into the big field. Damage was limited to the
peripheral areas. Of course, similar peripheral damage in a smaller
plot would exact a much higher percentage of loss. In fact, the usual,
very small native garden plot is so small that the snails can often
reach its center in a few hours' time during a single night. This does
emphasize, however, the importance of clearing around the plot as
large a buffer area as practicable. The daily removal of snails from
this buffer area, especially in the early morning, would greatly in-
crease its effectiveness. Clearing through the use of weed killers has
been tried in only a few instances (e.g., in Guam in 1949), and it is
possible that with the introduction of more effective weed killers we
will see them more frequently used for this purpose. But as far as
large-scale farming is concerned, little help of a practical nature can
be expected. The necessity for mechanized farm equipment, for one
thing, would put it completely out of the question for the majority
of native peoples. Whether the clearing is done on a large or a small
scale, it introduces still another difficulty, viz., soil divested of its
normal plant cover not only quickly loses its nutrients through
leaching, but it is subject to rapid erosion. In the coralline islands
especially, where the soil is often exceedingly thin, this would be a
CONTROL THROUGH MECHANICAL DEVICES	97
real tragedy. Where the cover of vegetation is thick, as in the case
of grass, not removing it entirely, but cutting it down to a stubble
is a compromise measure put to effective use at the Agricultural
Experiment Station in Peradeniya, Ceylon.
Drowning Anyone who has attempted to drown a snail or
slug in order to preserve it in an extended condition, knows full well
how difficult it is to produce a kill by this method (cf. Fromming
1929, Courtois and Duval 1927). Even when the dissolved oxygen
had been driven off by boiling the water, Rees (1951) was able to
demonstrate that it took 48 hours for young A. fulica hamillei to die
after complete submersion. Earlier, van Weel (1948) stated that it
took 20-24 hours for the giant snail to drown (cf. Meer Mohr
1949b:5); but the water was probably maintained at a higher tem-
perature. He introduced evidence to show how this capacity has per-
mitted the giant snail to survive apparent drownings and spread
more rapidly to adjacent uninfested areas (c.f. van der Goot 1939).
He stated that snails dumped into the Mahakam River at Teng-
garong, East Borneo, were apparently able to withstand a long trip
in the water; for just a year later a healthy infestation was found in
Djambajan, over eleven miles downstream. Scarcely one-tenth this
distance was covered upstream via other means of transportation.
Meer Mohr (1950) observed this snail apparently "deliberately" en-
tering pools of water during the rain and drowning; on the other
hand, Davis (1958a) observed a small specimen successfully negotiate
a trip across standing water.
Submerging snails in sea water has not seemed to produce appre-
ciably better results. One of the classical experiments was that of M.
Aucapitaine of Corsica in which he plunged specimens of several
species of land pulmonates in the ocean for fourteen hours (Caziot
1928). He obtained 87 per cent survival! Dartevelle's observations
(1952b) were less dramatic but just as significant. A. fulica has simi-
larly demonstrated its capacity to withstand such treatment, Soma-
nader's remarks (1951) to the contrary notwithstanding. In 1923,
Jarrett reported that specimens of this species were being destroyed
in Malaya by dumping them in the ocean. Later (1931), however, he
indicated that such specimens were found to wash ashore in a viable
condition. Of course, a number of factors, such as temperature of
the water, salinity, oxygen tension, and onshore wind, would un-
doubtedly seriously affect survival rates; but even when such factors
are far from favorable, there is great enough survival to warrant the
use of caution when resorting to this method. Crushing the snails
before dumping them in the water would seem to eliminate all
98	CONTROL THROUGH MECHANICAL DEVICES
danger of this sort. Under any circumstances, the possibility of foul-
ing the water must be taken into consideration.
Floods provide only a temporary setback in the snail population
as witnessed by South (1925, 1927) in northern Malaya. A tidal wave
in 1946 in Chichi Jima similarly caused a delay of less than two years
in the expanding snail population on that island (Mead 1950b).
Hand Collecting and Destroying Without question, no single
control method has gained a broader general acceptance than the
simple expedient of collecting the snails and eggs by hand and de-
stroying them. An examination of the literature shows over and
over again that this, almost without exception, is the method re-
sorted to in the very earliest phases of an invasion by A. fulica.
Frequently, in fact, participation is stimulated by offering bounties
for both the snails and eggs. Invariably, the bounties are discon-
tinued after a relatively short time because the rapid increase in the
snail population, in spite of the collections, soon exhausts even the
most generous funds that have been set up for this purpose. Such
has been the experience of many, many areas, including quite re-
cently Hawaii (Wong 1951). For the same reason, people despair of
the seemingly endless and ineffective collecting, discontinue their
efforts, and let the snails ''take over" (vide, e.g., Bertrand 1928). One
thing is certain, no matter how assiduously this collecting is done,
it is never eradicative; that is, if countless unsuccessful attempts in
the past are any criterion. Nor can it ever be eradicative except on
the very smallest scale, despite some of the optimistic statements in
the literature to the contrary (e.g., Peterson 1957). But this does not
justify dismissing summarily this method as an impractical one.
Actually, when the giant snail population is vigorously building up,
as in the early stages of invasion, this method is least effective. On
the other hand, after the snail population has reached stability or
a "climax," collecting and destroying the snails, especially on an ex-
tensive and intensive scale, has been shown in a number of recent
instances to reduce the population to a point where it never again
completely recovers. Factors of population senility and "decline"
doubtless enter into the picture at this phase. These points are dis-
cussed below.
But quite aside from whether or not the population is increasing
or decreasing, hand collecting and destroying on the largest practi-
cable scale is still the only inexpensive, effective method to which the
poor native peoples can turn. For this very reason, it is currently
being used on a far greater scale than any other method, especially
in and around flower and vegetable gardens—where the greatest
CONTROL THROUGH MECHANICAL DEVICES	99
damage is done. Because the eggs and young are easily overlooked
and because of the tremendous reproductive potential of these snails,
the task of collecting resolves itself into an indefinite, daily harvest-
ing. This is usually done in the early morning when the snails are
still quite active, although occasionally it is done at night with the
aid of a light. Rough terrain or dense vegetation makes this method
impossible or impracticable (Corbett 1937). Unfortunately such con-
ditions are common in areas where A. fulica abounds.
It is of interest and perhaps significance at this point to note the
effect of hand collecting in the control of other terrestrial gastropods.
Both Basinger (1923a, 1927) and Gammon (1943) strongly indorse
this method; in fact, Gammon goes so far as to say that it "in many
instances has constituted the difference between success and failure"
in the control of T. pisana in California. Lewis and LaFollette (1941),
on the other hand, report that it is of some value in controlling H.
aspersa in California citrus groves but, in general, is "not satisfac-
tory." Barnes (1949b) removed between 10,000 and 17,000 slugs per
year for four successive years in a garden in Harpenden and "in
spite of removing these numbers no reduction in population was
observable."
The real problem in this method, however, is not the mechanics
of collecting the snails but what to do with them after they are col-
lected. At first thought, this problem would not seem to be a big
one; but one reconsiders when one learns that large-scale collections
will bring in tons of snails almost indefinitely. What then? South
(1926b) was the first to make a number of suggestions in an attempt
to answer this question. These and other suggestions should be con-
sidered here for what they are worth.
Usually, the snails are dumped into pits, crushed, and covered with
soil. In Java during the early phases of the invasion by the giant
African snail, 2,105,743 snails and 491,350 eggs were collected in a
few weeks' time and disposed of in this manner (Leefmans 1933c).
In some cases, they had not even been crushed; but a two-foot layer
of superincumbent, well-packed soil insured a complete kill. Plung-
ing the snails into boiling water; dusting them with CaO; letting
them soak in solutions of CuSO4 (4 per cent) or NaCl before burying
them—all have proved successful. Such methods, however, add need-
less expense and man-hours of labor. Further, the addition of these
chemicals to the soil in any great quantity can produce unfortunate
changes in the soil and therefore the plant cover it can support. And,
as pointed out above, even the addition of CaCO3 in the form of
snail shells will change the soil pH in a basic direction. In strongly
100	CONTROL THROUGH MECHANICAL DEVICES
acid soils, this might have an advantage; but in cases where the crops,
such as tea, demand an acid soil, a change of this sort could reduce
crop yields. Such actually has been the case, for example, in some
parts of Ceylon.
Dumping the live snails into the ocean or rivers has already been
shown to be inadvisable. Crushing them before dumping them in
the ocean would seem in many respects to be the best way to dispose
of them. Unfortunately, collections of snails made even a reasonably
short way inland manifestly could not practicably be disposed of by
this means, to say nothing about the danger of starting new foci of
the infestation along the route. Burning the snails in incinerators or
on piled brush has been frequently resorted to and, although this
method has merits, the offensive smell and its effect upon health
have to be taken into consideration.
Obviously, the best method of "disposing" of the collected snails
involves making use of them for the benefit of man. This whole
subject is discussed in detail in chapter eight.
Shifting Cultivation In many areas, for example in the colony
of North Borneo, the natives practice shifting cultivation to insure
continued high yields in their crops. They clear off an area and put
in their crops. The giant snails gradually invade the preferred cul-
tivated plots from adjacent second growth areas. Hand collecting by
the natives simply and effectively impedes this invasion. By the time
the snail population has built up sufficiently to cause concern, the
few harvests and the tropical rains will have removed the greater
share of the soil nutrients, and it will be time to move on anyway
to another area which has not recently been cultivated and which
naturally supports only a small snail population—or perhaps none
at all.
In contrast, some native people will travel long distances to plant
crops in achatina-free areas. A case in point was found in Rota in
1949. According to Frank L. Brown of that island, the inhabitants
travel almost ten miles on foot to the opposite side of the island to
plant their watermelons, of which the giant snails are inordinately
fond. In that achatina-free area, examined by Kondo and the author,
the watermelons grow to full maturity with practically no care. Such
was almost impossible in the snail-infested areas.
Traps So far as can be determined, no elaborate trap has
been devised to control A. fulica. In fact, trapping as such has been
quite incidental to other control measures even in intensive pro-
grams. Typical of trapping methods in general, the little trapping
that has been done has been designed to take advantage of a partic-
CONTROL THROUGH MECHANICAL DEVICES	101
ular proclivity or appetite. The snail's manifest fondness for decay-
ing vegetation has encouraged some people to pile plant debris pe-
ripherally around an area to be protected and then periodically
either collect and destroy the snails that this debris has attracted or
burn the debris to kill the snails. Fortifying the debris with a mol-
luscicide is an obvious alternative and although this would increase
the cost, it would reduce the labor of maintenance. In fact, to neglect
unfortified peripheral piles of plant debris "traps" would seem only
to invite greater snail damage.
Appealing to the snail's propensity for crushed individuals of its
own kind has also been used in setting up traps. A group of snails
is piled in a protected place and crushed, and when these have at-
tracted other snails, they in turn are crushed only to increase the
amount of "bait." A system of periodic visits to a series of such traps
to kill any live snails in the vicinity has been reported as being very
effective. An ever increasing accumulation of rapidly putrifying
flesh and the flies it would attract are only two of several obvious
drawbacks to a control measure of this sort.
Any device which would cause the snails in quantity to become
stranded in the hot sun would be effective, as, for example, setting
up temporary shelters in clearings and then removing them in mid-
morning. Again, however, the problem of the rapid accumulation
of dead snails introduces great difficulties. An interesting though
unintentional modification of this method was observed on Agiguan
Island. Giant snails had sought refuge under large pieces of corru-
gated iron, only to be cooked to a turn the following day as the
sun's rays heated the iron like a stove.
Chamberlin's work in Tinian (1952a, b) strongly suggests that the
positive anemotaxis in A. fulica should be taken advantage of in
setting out baits and traps by placing them upwind of the snail
concentrations.
CHAPTER 7
BIOLOGICAL
CONTROL
Since before the turn of the century, the study of the pred-
ators and parasites of mollusks has been a matter of at least academic
interest. As a consequence, some excellent, detailed, and compre-
hensive papers have appeared in the literature, including those of
Bequaert (1926), Fromming (1954b:311-14), Gain (1896), Keilin
(1919, 1921), Pelseneer (1928, 1935), Pilsbry and Bequaert (1927:
470-79), Plate (1951), Simroth and Hoffmann (1928), Taylor (1894-
1900), and Wild and Lawson (1937). Now that there has arisen a
genuine need for a suitable predator or parasite of the giant African
snail, however, this study has taken on a very practical aspect. Even
more than that, it actually demands an inventory and reassessment
of the information on record. With this thought in mind, there has
been prepared below a series of discussions, under the subheadings
of the main predator or parasitic types, which will bring the subject
of biological control more sharply into focus. An examination of
this, in turn, will permit of a more accurate evaluation of the bio-
logical means of control—especially as it compares with other types
of control.
Amphibians Noel (1891) effectively demonstrated the fact
that toads and frogs introduced into gardens would have a telling
effect upon the slug and snail population. It was knowledge of this
sort that persuaded the American authorities in 1937 to introduce
the giant Central American toad, Bufo marinus, into Guam from
Hawaii in an attempt to control the destructive, large, black slug,
Veronicella leydigi. This biological control measure was very effec-
tive and, as a consequence, the Japanese were persuaded subsequent-
102
BIOLOGICAL CONTROL	103
ly to introduce the toad into Rota, Tinian, Saipan, and Yap (Townes
1946). In 1938, it was introduced into Mauritius from Puerto Rico
in the hopes that it would control the sugar cane pest, Phytalus
smithi Arrow (Anon. 1939). More recently, this toad has been pur-
posely and in some cases perhaps accidentally introduced in a num-
ber of the Micronesian islands. In Ceylon, Bertrand (1928) reported
that the only control of Achatina fulica in Madagascar was a "big
bull-frog." In spite of his recommendation, the Director of Agri-
culture in Ceylon decided against introducing this giant amphibian
predator. Pemberton (1938) announced that Bertrand was apparently
in error, that it was Mauritius and not Madagascar, and that the
amphibian in question was not a "bull-frog" but probably a ''large
toad common in Mauritius." Pemberton stated further, "It is prob-
able that Bufo marinus would feed on the young snails, should the
pest ever become established in regions where the toad occurs." This
prediction was shown by the author in 1949 to be correct—at least
on the island of Ponape where the stomach contents of this giant
toad were examined. Not only were small specimens of A. fulica and
Opeas sp. found, but pieces of the flesh and shell of large specimens
of the giant snail were even more commonly encountered (cf. Lever
1939). The presence of dead fly maggots with the latter quickly told
the story. The toads were apparently attracted to the crushed larger
snail specimens on the roads because of the activity of the maggots.
The abundance of the giant snails in all sizes, especially in the Jokaj
region of Ponape, and the markedly emaciated condition of the
numerous giant toads strongly suggested that B. marinus was pro-
viding little in the way of biological control. Such were also the
conclusions of Lange (1950) on Saipan. More recently, however,
Gressitt (1954:90, ICCP 1953) reports that it is believed by some that
B. marinus is responsible for the decreasing snail population in
Ponape. This is questionable, notwithstanding the fact that Jaski
(1953) found "with an astonishing frequency" achatinas in the stom-
achs of a species of toad in Java. Dartevelle (1954) has reported that
certain amphibia in the former Belgian Congo seek out the eggs of
the endemic achatinas.
Frogs would be even less effective than the toads, as they are less
independent of the aquatic environment. Garnadi (1951), however,
in Indonesia found the frog Rana tigrina Daud. in several instances
in the vicinity of egg masses of A. fulica; one dissected specimen
revealed pieces of achatina egg shell in the stomach. Earlier infor-
mation from Pilsbry and Bequaert (1927:473) and from Kirkland
(1904:8), wherein only 1 per cent of the stomach contents of the
104	BIOLOGICAL CONTROL
American toad was shown to consist of snails, suggests that amphib-
ians figure in only a minor way in the consumption of snails.
To sum up the effects of introducing B. marinus, however, simply
by stating that it does effectively control V. leydigi but not A. fulica,
is to ignore the indirect effects, some of which are of considerable
importance but infinitely subtle in their connection with the original
introduction. As an example on the plus side of the ledger: The
great quantity of dead achatinas in a heavily infested area causes the
cockroach population to build up often to serious proportions. B.
marinus will thrive on cockroaches (Pemberton 1949); both are noc-
turnal. It should be recalled at this point that the toad will also
feed on fly maggots. In the absence of experimental evidence, it is
quite safe to reason a priori that, even though the introduction of
B. marinus will not produce an appreciable effect upon the giant
snail population, it may reduce substantially some of its side effects
of public health importance.
On the other side of the ledger, however, we find an indirect effect
which is felt through a wondrously devious chain reaction. The early
traders accidentally introduced the pestiferous, disease-carrying rats.
In the zoos in Japan, the giant monitor lizard (Varanus) fed avidly
on rats. The monitor lizard was therefore introduced, as a biological
control measure, into the Micronesian islands where it had not
earlier become established. Then came an astounding discovery.
The monitor lizard is diurnal and the rat is nocturnal. To make
matters worse, the biological faux pas proved irreversible. The mon-
itor lizard quickly became a pest by consuming eggs and young
chickens—precious items indeed in Micronesia, especially since chick-
ens, too, will do their bit in consuming young achatinas. The intro-
duction of B. marinus, strangely enough, brought some relief to this
problem. The giant toads do not hide as effectively as rats during the
day and the monitor lizard would easily find them in its search for
food. The toads, however, have potent poison glands in their skin
and the meal would prove fatal (cf. Gressitt 1954:142). The prey,
paradoxically, was controlling the predator! This was an unexpected
benefit which seemed to give further support to the advisability of
introducing the toad; in fact, after this was discovered, the toad was
purposely introduced into other islands to control the lizard bio-
logically. The benefit, however, was not without serious side effects;
for the monitor lizards in the meantime had developed a healthy
appetite for the number one agricultural enemy of the Pacific, the
grubs of the rhinoceros beetle, which kill the coconut palm—a far
more important agricultural item than chickens (Gressitt 1952).
BIOLOGICAL CONTROL	105
Also, the lizards have been demonstrated to feed on another enemy
of the coconut palm—the coconut crab (Birgus latro) which inciden-
tally, in turn, feeds on the giant snail, as does the lizard itself (vide
infra). But the complications did not stop even there. When the
barnyard pigs caught the toads and ate them, they became sick or died
(Townes 1946). The dogs and especially the cats, as they are largely
nocturnal, also discovered the giant toads and similarly were killed
when they bit them or attempted to eat them. This was a tragedy,
for the dogs and cats were the best rat catchers in the islands! Who
could have guessed that introducing B. marinus would, in addition
to reducing the black slugs, aggravate the rat problem, kill the mon-
itor lizard, reduce natural control of coconut pests and the giant
snail, bring some relief to the poultry industry, kill pigs and house
pets, and ameliorate a public health problem of cockroaches and
flies brought on by the introduction of giant African snails? As a
final ironic twist, the native peoples are convinced that their dogs
and cats have died from eating the "poisonous" giant African snails!
Ants    Green (1910c, 1911b) was the first to suggest that ants
might be a factor in the control of A. fulica by reporting that he had
observed a predaceous ant "Phidelogeton affinis [sic: Pheidologeton]
swarming in a batch of eggs that was just hatching." As it is stated,
there is only circumstantial evidence of any attack per se on the
snails. This evidence nonetheless has been accepted as fact and even
embellished by subsequent investigators (Hutson 1920, South 1926b,
van Weel 1949). This assumption, however, has proved to be a safe
one, for in Indonesia this same species of ant has very recently been
shown by Butot (1952b) to carry to its nest other species of snail
(Opeas gracile, Gulella bicolor^ and Geostilbia moellendorffi). Other
species of Pheidologeton have also been shown to indulge in snail
robbing. Meer Mohr (1931b,c) reported P. diversus was similarly
observed carrying away specimens of Bulimulus sp. (cf. Rothney 1889).
In a letter to the author (Dec.  16,  1949), Professor Silvario M.
Cendana of the University of the Philippines wrote that a species
of ground ant common in Los Bafios helped check the rapid increase
of the giant African snail in that area. Apparently the same species
of ant is referred to by Pangga (1949) as Solenopsis geminata Fabr.;
he reports that they sometimes attack newly hatched A. fulica. It is
of interest to note that Martinson (1929) reports that in Ghana the
worst of the natural enemies of the local achatinids are the "red and
black driving ants."
A number of times during the survey of Micronesia conducted
by the author and Kondo ants were seen to be swarming over dead
106	BIOLOGICAL CONTROL
or dying achatinas. In every case, it seemed quite clear that the snail
was either dead before it was attacked by the ants or was dying from
overexposure to the hot sun. The same species of ant would com-
pletely ignore healthy snails in protected areas. At no time were any
ants seen to show the slightest interest in the young snails or the
thick-shelled eggs. Occasionally, eggs would be laid in an empty shell
and ants were seen to crawl over these to get into the upper whorls
of the shell where there still was some decaying flesh. An incautious
observer might have been led to believe that the ants were attacking
the eggs. It is probable that Lawson (1920b) was similarly misled in
his observations and that Bequaert's skepticism was justified (1926).
From the evidence accumulated so far, it is questionable that ant
raids on young A. fulica are producing an appreciable control except
under the most limited conditions.
Beetles Several beetle families are notorious for having spe-
cies that live largely or entirely upon pulmonate gastropods. Be-
quaert (1925, 1926) has summed up admirably the widely scattered
literature on this subject. Significant contributions that have ap-
peared since Bequaert's works, other than those directly pertaining
to predation on A. fulica, are the following: Cros (1926), Drilus
mauritanicus consuming Rumina decollata; Moore (1934), Carabus
violaceus killing Arion hortensis; Tomlin (1935), C. violaceus car-
rying off Agriolimax agrestis (Deroceras agreste), Milax gagates, and
small H. aspersa; Ingram (1950), Calosoma sp. feeding on Triodopsis
albolabris and Ventridens intertextus; Metteo (1946), Ablattaria
laevigata consuming Eobania vermiculata and Helicella variabilis;
Fincher (1947), Lampyris noctiluca attacking Arion ater; Schwetz
(1950), Luciola sp. attacking Planorbis tanganyicensis. Clausen (1940)
reports that Lampyris noctiluca has been imported into New Zealand
from England for the control of H. aspersa.
Until recently, at least, the beetle most famous for its predation
on A. fulica is the so-called India glowworm, Lamprophorus tene-
brosus (Walker) (Lampyridae), endemic in Malaya, Ceylon, and
India. Paiva (1919) was the first to draw attention to this nocturnal
predator by giving considerable significant information about its life
history. Additional studies of this type were reported upon by
Hutson and Austin (1924), Austin (1924), Jacobson (1936), Fernando
(1952), and Bess (1956). A study of the egg laying of the closely re-
lated L. dorsalis was made by de Hass (1937). The work of Hutson
and Austin, wherein they report that a male larva will consume
20-40 achatinas and a female larva will consume 40-60 achatinas
during their development, has in particular been responsible for a
BIOLOGICAL CONTROL	107
growing optimism as regards the controlling effect the larva of this
beetle can and does have. Hutson himself (1920) anticipated this by
announcing that it was his belief that L. tenebrosus was an impor-
tant factor in the control of the giant African snail in India. South
(1926b), Jarrett (1931), Philbrick (1949), Rees (1950), Somanader
(1951), and others, including several of the author's correspondents
in southeastern Asia, in the absence of further supporting evidence
have continued to add to this optimism until this beetle has been
given, in the minds of many, at least the greater share of the respon-
sibility for the increasing sharp decline in the A. fulica populations
in Ceylon.
Understandably, this whole matter headed the agenda in the au-
thor's investigations in Ceylon. Five species of lampyrids were found
to be predatory upon both A. fulica and the endemic snails. The two
most abundant were L. tenebrosus and an unidentified species of
the genus Diaphanes. The other three species were considerably
smaller, they were only rarely encountered, and they were not suc-
cessfully reared to the adult stage and hence could not be identified.
Of the two larger species, L. tenebrosus (Singhalese: adult is "kala-
madiriya"; glowworm larva is "rabadulla") was by far the more
common. In contrast to local reports, it was not restricted to the
higher altitudes of the interior but was found at a few hundred feet
of altitude in Mankulam in the north and Ratnapura in the south.
The glowworm of Diaphanes sp. was found in drier environments
and its ruptive coloration plus its habit of feigning death made it
difficult to find. Unlike L. tenebrosus, the glowworms of Diaphanes
not infrequently co-operated in their attack on the snails, as many
as five being found feeding at the same time on a single snail.
In both L. tenebrosus and Diaphanes sp., the attack on the snail
was initiated by stabbing and pinching with the long, ice-tongs-like
mandibles. The area of attack was invariably the flesh on the left
side of the foot near the base of the columella of the retracted snail.
When the snail specimen was large or the glowworm was well fed,
the attack was limited to the removal of a small amount of flesh in
this region. In such cases, the snails would survive the attack and
subsequently regenerate the lost flesh. In contrast to the report of
Somanader (1951), this suggested very strongly that there was no
toxic, proteolytic substance injected into the bite site, as reportedly
is the case in Luciola (Alicata and Bess 1952). Pieces of flesh lacerated
from the snail were seen to be squeezed by the bowed mandibles as
one might hug a pillow. The mandibles were seen to be kept in a
constant state of alternating with each other, first anterior and then
108	BIOLOGICAL CONTROL
posterior, after the manner of sharpening two knives together. As
this motion continued, the pieces of flesh became smaller and smaller.
When no more tissue juices could be extracted, the small wad of
flesh was gradually worked onto the dorsal surface of the head and
then pushed aside. Once again, then, the glowworm would plunge at
the equally rapidly retracting snail, remove another piece of flesh,
and work it over as before. This would normally continue until all
or nearly all of the snail flesh had been removed. The chances that
a snail specimen would be attacked were found to be in inverse
proportion to its size.
After feeding, the glowworm apparently crawls only a short dis-
tance away before curling up in some shallow refuge to digest its
meal. Glowworms in this state were often found in the immediate
vicinity of achatina egg masses; but there was no positive evidence
that they consumed the eggs. Similarly, there was only circumstantial
evidence of cannibalism among the glowworms. Moist snail "re-
treats" were often found to be harboring several glowworms in addi-
tion to a great many snails. During prolonged dry spells, the glow-
worms sought refuge under rocks and in other deeper retreats. With
the advent of the rains, the snails made a noticeably quicker return
to activity than the glowworms, hence giving the snails a predator-
free period in which to forage. There is strong evidence that L.
tenebrosus is not limited to the single seasonal cycle suggested by
Hutson and Austin (1924). Somanader (1951) reports that the glow-
worm dies after a straight diet of A. fulica. Even when starved, full
grown glowworms would not attack specimens of achatina that were
larger than 40 mm. in length (Peterson 1957a).
Since 1953, the Board of Agriculture and Forestry in Hawaii has
made several attempts to introduce L. tenebrosus in Oahu as a bio-
logical control agent (Pemberton 1957, Thistle 1957, 1959a, b).
Probably the earlier introduction into Hawaii of other lampyrids
(Luciola cruciata, L. lateralis, and Colophotia praesta) to control the
aquatic snail hosts of disease-producing flukes has done much to
encourage further work of this type (Alicata and Bess 1952, Fullaway
1952, Bess and Alicata 1953, cf. Lutz 1927). The first shipment of the
live glowworms from Ceylon was kept under subquarantine con-
ditions as attempts were made to rear the specimens to maturity.
Eventually, all specimens died (Thistle 1953a, Weber 1954). Subse-
quent shipments of L. tenebrosus from Ceylon were made by Bess
(1956). Altogether, he sent over 1,000 glowworms of this species to
Oahu for immediate release. Similar shipments directed in 1955 to
FOA entomologist Edgar Dresner in Djakarta, Java, were kept un-
BIOLOGICAL CONTROL	109
der observation and all specimens died before they could be released.
Still other shipments were sent to George Peterson, government en-
tomologist of Guam, and during the first few months of 1955, 933
specimens were released on that island (Peterson 1957a, b). In Oc-
tober, 1958, additional releases were made on Oahu and Maui (Davis
1959). Considering the nature of the ecological conditions and the
extent of the releases, it might be assumed that L. tenebrosus has
become successfully established both on Oahu and Guam. Subse-
quent recoveries of specimens in the release areas in Guam lend
substance to this assumption; however, to date, no recoveries have
been made on Oahu or Maui.
In attempting to evaluate the possible effectiveness of this pred-
ator in the control of the giant snail, it might be kept in mind that
in Area Seven of the Pallekelle division of the Pallekelle estate in
Central Ceylon, both L. tenebrosus and A. fulica have been together
for a minimum of twenty-five years, and yet the giant snail still re-
mains common to abundant (Mead 1955b, 1956a).
All specimens of the lampyrid Diaphanes from Ceylon, intended
for release on Oahu, died while under observation in the laboratory;
and renewed efforts were not made to determine the value of this
species as a biological control agent (Thistle 1957).
Beetles of the family Drilidae also have come into serious consid-
eration in proposed biological control measures. The work of Des-
marest (1824), Mielzinsky (1824), and Lucas (1842, 1870, 1871)
brought early attention to the pronounced malacophagous1 proclivi-
ties of the drilid beetles. According to Bequaert (1926), further ob-
servations of their biology were made by: Bellevoye (1870), Crawshay
(1903), Bayford (1906), Rosenberg (1909), Schmitz (1909), and
Deubel (1913). The work of Cros (1926, 1930) should be added to
this list. It was not until the work of de Peyerimhoff (1914), however,
that beetles of this family were known specifically to attack achatin-
ids, at least in East Africa. The observations of Williams (1951),
set forth in considerable detail, leave no doubt as to the readiness
with which the drilid beetle larvae of East Africa will attack and
consume the endemic achatinids, including A. fulica hamillei.
Achatinas up to 115 mm. in length were observed to be attacked by
nearly mature drilid larvae. Living specimens that were sent to
Hawaii by Williams failed to multiply and consideration of their
use in the biological control of the giant snail was thus abandoned
(Pemberton 1954). Entering into this consideration was also the fact
that the drilid life cycle is a long one.
1 Not "malacovorous" of some authors.
110	BIOLOGICAL CONTROL
In his investigations in East Africa, Williams also found that large,
black, voracious beetles of the genus Tefflus (Carabidae), in both the
larval and adult stages, would consume the giant African snail.
Several live adult specimens of this beetle, along with larval speci-
mens of drilid beetles, collected by Williams in and near Mombasa,
Kenya, were sent in May, 1948, to the Hawaiian Board of Agricul-
ture and Forestry. The announced purpose for this shipment was
to enable the Hawaiian authorities to observe under subquarantine
conditions the biology of these beetles so that their worth in the
biological control of A. fulica might be ascertained (Williams 1953).
N. L. H. Krauss, the entomologist of the Board of Agriculture and
Forestry, made a second trip in 1951-52 to East Africa and sent back
to Hawaii 107 additional live specimens of two species of Tefflus.
At first, the larger species, ca. 45 mm. long, was reported to be T.
hacquardi; and the smaller species, ca. 25 mm. long, was reported
to be T. carinatus (ICCP 1952). Krauss informed the author, how-
ever, that P. Basilewsky of the Museum van Belgish Congo, Tervuren,
Belgium, has identified the larger species as Tefflus zanzibaricus
alluaudi Steinberg and the smaller species as Tefflus purpureipennis
wituensis Kolbe (cf. Krauss 1955). Q. C. Chock of the Hawaiian Board
of Agriculture and Forestry successfully raised in cages several hun-
dred specimens of the smaller species (Lennox 1953). The highlights
of their biology have been reported upon by Weber (1954). Of partic-
ular interest is their ability to emit an irritant, when disturbed, which
will burn the skin if it is not soon removed.
Unfortunately, novel research of this sort, that is, enlisting large
beetles to attack, kill, and consume giant snails, has been too much
for some overenthusiastic newswriters. The ridiculously humorous
article of Milhon (1948, 1949) only inferred that Tefflus would be
used against the giant snail. But other articles, for example that of
Ferguson (1948), treated the matter of their release as a fait accompli
with such statements as: ". . . and soon Guam resounded with the
crunching sound of beetles dining on giant snails." Efforts were
made to correct this misinformation (Mead 1949d). At least partially
in response to unrelenting pressure from the people of Hawaii and
in spite of earlier decisions to the contrary, it was decided by the
Board of Agriculture and Forestry in June of 1952 to release in the
giant snail infestation in the Kaneohe area (three-quarters of a mile
south of Mahinui) ten marked adult Tefflus zanzibaricus (Weber
1953). A few days later, ten more were released (Lennox 1953). The
next year, twenty more were released (Thistle 1953a). During 1953
the beetles being raised in cages became less and less thrifty until
BIOLOGICAL CONTROL	111
in 1954, it was decided to release all that remained—eleven specimens
(Thistle 1954a). During the following several years, only one un-
marked adult Tefflus was recovered (Chong 1954, Weber 1954); and
it was therefore believed by many that the beetle had not become
successfully established (Dwight 1955). However, in September, 1959,
a second live, unmarked specimen was found (Thistle 1959b). This
discovery, nearly five years after the first unmarked specimen was
found, has raised new hopes in certain quarters that this beetle has
been able to maintain at least a beachhead population. Arrangements
have been made with Richard LePelley, senior entomologist of the
Department of Agriculture in Nairobi, Kenya, to make additional
large shipments of Tefflus to Hawaii for immediate liberation in the
expectation that they will eventually become firmly established. An
earlier tentative decision to introduce Tefflus concomitantly with
the predatory snail Gonaxis in the experimental island of Agiguan
was fortunately postponed, in spite of the fact that it was done in
Oahu.
More recently, the giant carabid beetle Damaster b. blaptoides
Kollar from Fukuoka, Kyushu, Japan, has been considered a possibly
more suitable predator for achatina because of its spectacularly large
size. Specimens under observation in 1958 in Hawaii avidly con-
sumed larger snail specimens than Tefflus could manage. On July 3,
1958, fifty specimens were released on the Old Pali Road in Oahu
and on July 9, 1958, twenty-five specimens were released in Haiku,
Maui. Forty-six specimens of the closely related D. b. rugipennis
Motchulsky from Sapporo, Hokkaido, Japan, were released on Tan-
talus, Oahu, on July 28, 1958. Although it is still too soon to deter-
mine whether or not establishment has taken place, it should be kept
in mind that these beetles come from a temperate zone and the
Hawaiian climate may prove inadequate for breaking the diapause.
The same may be offered as an explanation for the fact that Scaphi-
notus striatopunctatus (Chaudoir) and Scaphinotus sp. from Cali-
fornia have not been recovered since their release on Oahu in No-
vember, 1956. It is probably too early to determine whether or not
specimens of an unidentified species of Tefflus from the Congo and
Thermophilum hexasticum Gerstaecker from Kenya have become
established since their release in October, 1956, and May, 1957, re-
spectively (Thistle 1959a).
But, even at this early date, both Tefflus and Damaster already
have become involved in other aspects of the over-all biological
program. Tefflus is a night feeder, as is its snail prey. This is good.
But the introduced toad, Bufo marinus is also a night feeder and it
112	BIOLOGICAL CONTROL
is particularly fond of beetles. Is this the reason why Tefflus has
been recovered only twice in five years in the release areas? Damaster
should escape this threat, as it is a day feeder; but at that time, the
giant snails characteristically retreat to the tree trunks out of harm's
way. It has been suggested that an excessive immediate scattering of a
released biological control agent may preclude its establishment. In
an effort to offset this, Damaster was released in Oahu in a sizable
inclosure. The introduced mongoose is also a day feeder and in addi-
tion is fond of beetles. One got into the inclosure and put a finish
to the experiment. Perhaps the mongoose did a better job on Tefflus
and L. tenebrosus than it did on the rats, for which it was intro-
duced to control. But, as will be shown below, both the mongoose
and the rat will consume the giant snail and probably other species,
including the introduced predatory snails, for which they may have a
preference!
The advisability of releasing any predatory beetle, as will be seen
below in the discussion of the predatory snails, is still problematical
and therefore pretty much of a controversy. The experiments in
rearing Tefflus in Hawaii have been carried on for only a relatively
short time and have revealed little more than the fact that these
beetles can be reared in captivity with difficulty. The extent to which
they are possibly effecting a control of achatinas in East Africa has
not been determined in the slightest. Even though it can be reasoned
that the cause for the achatinas being less abundant in East Africa
might rest in the fact that there are also at hand predatory beetles
and predatory snails, it is as risky as it is unscientific to reason a priori
that the introduction of these predators elsewhere will produce simi-
lar results and that therefore introductions are justified in the ab-
sence of experimental confirmation. There is already evidence that
although the predators do not manifest a high prey-specificity, they
do show a preferential selection in what they will attack and con-
sume. The fact that the drilid larvae will apparently more readily
attack the East African predatory snails (Gonaxis and Edentulina,
vide infra] than they will the achatinas (Williams 1951, Krauss 1951)
warns that in a similar fashion, introduced predatory beetles might
consume the endemic snails, or even some other invertebrate, in
preference to A. fulica. Thus a new problem may be created in addi-
tion to the unimproved original one. In a partial answer to this
problem, the information has been offered that both adult and larval
Tefflus purpureipennis not only seem to show a preference for A.
fulica, but they have little proclivity for climbing trees, thus giving
a certain degree of immunity to such important endemic, arboreal
BIOLOGICAL CONTROL	113
genera as Partula and Achatinella. It should be recalled at this point,
however, that it was T. zanzibaricus, not T. purpureipennis, which
was released in Hawaii. In reference to this specific matter, Kondo
(1951 b) has pointed out that what is of infinitely greater significance
is the danger to such terrestrial gastropod families as Amastridae,
Endodontidae and Zonitidae.
Small, unidentified lampyrid beetle larvae were seen by Williams
to feed on quite small and newly hatching achatinas; but their quick
dismissal from all but a brief mention suggests that they cannot or
are not to be considered in a biological control program. Krauss
(1951) similarly gives them only a slight mention in the reports of
his East African investigations. A very detailed account of the feed-
ing habits and life history of this type of beetle is given by Newport
(1857). A quite common coprine beetle (Scarabaeidae) in East Africa
was observed by Williams to frequent the sites of dead achatinas;
but since it was only the disintegrating snail flesh which attracted
the beetles, they were obviously not a factor in biological control.
           Birds   The work of Kleiner (1931, 1936) has demonstrated
the fact that examination of bird stomachs on an extensive program
may show snail remains not only in a majority of cases, but in a
great many different avian species. Further, he interestingly dem-
onstrated that in spite of the high frequency of appearance, snails
bulk small in the total content of the stomachs (2.69 per cent).
Similarly, McAtee (1918) found that mollusks formed only 5.73 per
cent of the total food intake of the mallard, and Collinge (1921)
found that they formed 6.5 per cent of the animal food ingested by
the starling. From these one cannot safely conclude that birds in
general find snails uninteresting; for not just the relative degree of
appetite for snails but the general availability of snails would deter-
mine the percentage consumed. Actually, Kleiner's most important
finding is that a wide variety of birds will consume snails, notwith-
standing the fact that in some cases the snails may have been taken
into the digestive tract accidentally. But this conclusion is independ-
ently reached when one surveys the vast literature that has accumu-
lated especially in the past century on the subject of birds consuming
snails. In discussing the natural biological control factors of the
pestiferous Theba pisana in Italy, de Stefani (1913) lists crows, mag-
pies, and owls. To this list, Basinger (1927) in California added the
Hudsonian curlew, pigeon, English sparrow, chickens, and ducks.
The domesticated duck has the reputation of being the most avid
consumer of snails (e.g., cf. Panos Marti 1952). In fact, there is in
correspondence and in the literature the persistent report (e.g.,
114	BIOLOGICAL CONTROL
South 1923b, Jarrett 1931) that the giant African snail was trans-
ported into uninfested areas, especially in Malaysia, with the intent
that they would provide suitable food for ducks. Just the reverse
process is concurrently being undertaken; that is, the ducks are be-
ing enlisted in local control measures to keep down the population
of the snail. G. A. S. Barnacle (in litt. Jan. 15, 1950) states that ducks
were "introduced" in this manner in various areas in Ceylon. Essen-
tially the same report was given by R. C. L. Notley (in litt. Dec. 5,
1950) with the addition that some ducks got pieces of snail shell
stuck in their throats. In Thailand, Ariyant Manjikul (in litt. Feb. 14,
1952) states that the giant African snail makes 'Very good feed and
the duck raisers collect them" for this purpose. A similar report
comes from Guam (Peterson 1957b). In Singapore, R. E. Dean writes
(in litt. Jan. 17, 1952) that he has been informed that the common
practice there is to allow the local strain of domestic ducks free
range over the compounds and that they will attack the giant snails
with gusto. In that same region, A. F. Caldwell gives supporting
evidence (in litt. April 23, 1953) in the following statement: "I used
to keep a few ducks and fed them a number of these [giant African]
snails daily as part of their diet. If the shells are broken ducks eat
the snails with obvious relish." A similar report is made by Jaski
(1953). The practice of using ducks in an attempt to control H.
aspersa in California citrus groves, according to Lewis and LaFollette
(1941), proved to be of "some value," but it was not recommended.
On the other hand, Hely (1946) recommended it as "excellent." In
flower and vegetable gardens, however, the ducks may cause more
damage than the snails, especially if succulents and seedlings are
present.
Not only ducks, but chickens will feed on achatinas (Hutson 1920,
South 1926b). Lang (1919) also observed this in the Congo. The
larger, thick-shelled specimens, however, are not effectively attacked
by either ducks or chickens unless they are crushed (van Weel 1949).
In South Africa, Joubert and Walters (1951) report that turkeys as
well as ducks will eat large numbers of the serious snail pest T. pisana.
The utilization of the giant snails as a food supplement in poultry
has been treated in detail below, under the discussion of control
through human use.
As early as 1911, Green proposed the idea that insectivorous birds
might be important in controlling A. fulica. South (1926fo) and later
Philbrick (1949) announced that Centropus chlororhynchus, the
"jungle crow" (also called "pheasant crow" or "cockoo") attacks and
consumes the giant snail in Ceylon. This was recently verified by the
-BIOLOGICAL CONTROL	115
author during field observations in Ceylon. In areas frequented by
jungle crows, shells with characteristic damage were commonly en-
countered. Of 98 live achatina specimens examined on the Warriapolla
estate near Matale, 9 (9.2 per cent) were found with diamond- or
triangle-shaped wounds. These indubitably were caused by bird
pecks. Even in the cases of extensive trauma, tissue regeneration
was sufficiently advanced so that it seemed apparent that the snails
would survive. Keeping them under observation in the laboratory
confirmed this assumption. An explanation for their escaping fatal
injury seems to be found in the words of E. Phyllis (in litt. Dec.
11, 1950), who states that he has seen the jungle crow in Ceylon
hunting for the giant snail for hours on end and that it does not con-
sume more than a part of the snail after it finds one. Introducing the
jungle crow into a non-endemic area as a biological control agent to
control the giant African snail is completely counterindicated; for
this bird is a foraging rogue with the strongest raiding and robbing
proclivities, eating in particular the eggs and young of ground-dwell-
ing birds.
Krauss (1952) reports that in the northwestern part of Madagascar,
a large native bird, the famakankora ("snail-breaker"), Anastomus
madagascariensis (Ciconiidae), is said to feed on achatina and other
animal food. It may have been the anvils of this type of bird which
Jaski (1953) saw in South Africa. He reports that scores of A. achatina
were found hammered to smithereens.
Observing the snail-eating habits of some of the larger birds has
persuaded a few people to recommend introducing them into areas
infested with the giant African snail. R. S. Gardiner states (in litt.
Nov. 22, 1949) that in Chile the thick-kneed plovers or so-called
"queltehue" birds (Burhinus superciliaris), kept in inclosed gardens
by clipping their wings, are exceedingly effective in removing all
sorts of terrestrial mollusks. Her suggestion that they be used in con-
trolling A. fulica, however, is no more practical, for several obvious
reasons, than Eyerdam's recommendation (1952a, b) that the New
Guinea bush hen or bush turkey (Megapodius spp.), the rhea (Rhea
spp.), and the cassowary (Casuarius spp.) be used. With Eyerdam's
suggestion in mind. It was of more than passing interest to read in a
recent list of offerings of a dealer in live animals that a cassowary
could be purchased for a mere $3,000! Gressitt (1952) and others
have reported megapode birds on some of the western Pacific islands
(e.g., the northern Mariana Islands) which are not infested with the
giant snail. It is possible, though, that both snails and megapodes
116	BIOLOGICAL CONTROL
have come together in some of the Palau Islands. This is a matter
distinctly worth investigating.
Crabs In Micronesia, the ubiquitous hermit crab, Cenobita
perlatus Edwards (called "humpa" by the Bonin Islanders) has been
observed (Mead and Kondo 1949, Mead 1950b, c) not only occupy-
ing as high as 21 per cent of the empty A. fulica shells encountered in
beach populations but actually consuming the live snail by pinching
off small pieces of the flesh with the chelae. This species spends long
periods of time on land; specimens were found in Chichi Jima at an
altitude of approximately six hundred feet and over one and a half
miles from the nearest seashore. There is, however, an apparently
geometrically progressive reduction in their numbers in an inland
direction. Even in achatina shells abandoned by the hermit crab,
there are unmistakable evidences of their work. The shell becomes
highly polished, not just on the underside but all over, due to the
rough treatment it gets; and invariably the columellar surface of the
ultimate whorl is characteristically abraded away, making more room
for the hermit crab. Wilson Savory of Chichi Jima stated to the
author that he released half of a flour sack of small achatinas on the
tiny island of Higashi Shima, just off the northeast coast of Chichi
Jima in 1942. He said that when the island was visited again the
following year the hermit crabs were found to have taken over the
achatina shells entirely.
A mysterious "achatina-free" area, approximately three-quarters of
a mile long and at least five hundred feet wide, bordered by dense
populations of A. fulica along the east coast of Rota, proved upon
examination to be nothing more than a region where the hermit
crabs were completely dominant (Mead 1950b, c}. Conditions along
the adjacent coast seemed to be particularly favorable for hermit
crab reproduction and existence, and the recent immigrant A. fulica
had not yet successfully invaded and infiltrated that region. Burning-
over the land to plant watermelons, had apparently neutralized the
area; but the hermit crabs had relatively rapidly reinvaded the area
and kept it free of live achatinas. Paradoxically, the hermit crabs
caused greater damage to the melons than did the achatinas; and yet
it was the snails which were indirectly responsible for this damage as
it was their abundant empty shells that provided vital protection for
the soft bodies of a greater population of hermit crabs than otherwise
could have built up. A brief reinspection by Kondo (1952) of this
achatina-free area and two other similar areas on Rota, emphasized
the need for a thorough ecological study to determine what decisive
factors are actually operative.
BIOLOGICAL CONTROL	117
So far as can be determined, no other endemic predator in Micro-
nesia, with the possible exception of the coconut crab, produces a
greater kill of the giant snail. Even so, the effect upon the snail popu-
lation is undoubtedly a minor one, except in localized beach areas or
on relatively small islands, where the hermit crabs may have a deci-
mating or even exterminating effect. Davis (1954) concluded that
"Cenobita was not a predator of Achatina." This conclusion, how-
ever, was based to the largest extent upon the undependable be-
havior of caged specimens. Somanader (1951) describes and pictures
unidentified hermit crabs which take over the shells of A. fulica in
the Kalkudah beach area of eastern Ceylon; but he does not suggest
that there is predation.
On the island of Auluptagel (Aurapushekaru) in the Palau group,
there was found a large, conspicuous cave of a robber crab or coconut
crab (Birgus latro L.) on the slope of a hill. Well over fifty broken
shells of A. fulica were found strewn three to four feet below the
opening of this cave. Sharp, angular breaks in the very thick, large
shells clearly indicated that these had been broken open by the coco-
nut crab. The characteristic droppings gave further convincing evi-
dence. The coconut trees have become virtually extinct on this island
because of the work of the introduced coconut beetles (Oryctes rhi-
noceros and Brontispa mariana), and it seems obvious that the coconut
crab has had to turn to some other source for its food. It is a curious
thing that the introduction of beetle pests has predisposed to the de-
struction of a snail pest! Kondo (1952) reports that on Agiguan, this
crab and the rats together kill more than twice as many giant snails
as does the predatory snail Gonaxis. Direct and indirect evidence of
the consumption of achatinas by this crab were reported upon by
Davis (1954). Because the coconut crab is so highly prized as an
article of food and therefore diligently hunted for by the Micro-
nesians, and because the eating of snails by the coconut crab is only
incidental in its catholic diet, Birgus latro unquestionably has but
the smallest part in the biological control of A. fulica.
An unidentified land crab in the Diani Beach area of Kenya was
observed by Williams (1951) to consume live achatinas; and, in at
least one case, the snail was considerably larger than the crab. Its
predation, however, is apparently limited to the peripheral beach
zone. Dartevelle (1954) tentatively identifies this crab as belonging to
the genus Ocypode.
The so-called "paddy crab" was reported in several instances to
feed on the giant snail in Ceylon. Although this was not verified in
118	BIOLOGICAL CONTROL
the field, it is altogether possible that this crab is of some local, minor
value as a biological control agent.
Flies Sarcophagids, sciomyzids, phorids, and other diptera
have been reported by a number of observers to come from the dead
bodies of various land snails. In by far the majority of the cases, it
has been established, or very strongly suggested, that the fly larvae
are saprophagous rather than parasitic. And in only a very few in-
stances (e.g., Rostand 1920, Mercier 1921, Mokrzecki 1923, Berg
1953, 1955, Muma 1954, 1955) has there been more than circumstan-
tial evidence of a possible normal parasitic role. Keilin (1919, 1921),
Seguy (1921, 1935), Bequaert (1925, 1926), and Pelseneer (1928) have
made the major contributions and have surveyed the literature for
reports on the general subject of diptera-mollusk associations. With
the exception of those that concern the giant snails, more recent
works which should be mentioned are those of Bhatia and Keilin
(1937), Lopes (1940), Metteo (1946), Berg (1953, 1955), and Muma
(1954, 1955). A. R. Main of the University of Western Australia is
conducting significant investigations of dipterous parasites which he
has reared from the endemic land snails Bothriembryon spp.
Muma in particular has done a significant piece of work on the
biological control factors apparently operative in keeping down the
numbers of a presumed "beneficial" tree snail in Florida citrus
groves. He reports that dipteran parasites are the most important
agents in reducing the snail population. His rearing experiments
convinced him that he had found true parasites and not just sapro-
zoites. From the "parasitized" snails, he raised four sarcophagids, one
phorid, and one chloropid, viz., Sarcophaga lambens Wd., S. morio-
nella Aid., Johnsonia elegans Aid., /. cf. frontalis Aid., Megaselia sp.,
and Hippelates dissidens (Tuck.). As a complication he found that
some of the sarcophagids were being attacked, but apparently not
seriously, by the epiparasites Aphaereta auripes (Prov.) and Melit-
tobia sp.
The wingless phorid flies of the genus Wandolleckia were appar-
ently first observed on achatinas by Cook (1897) in Liberia, where he
saw them running about on the surface of living Achatina variegata
(i.e., A. achatina). The following year, Wandolleck offered the sug-
gestion that the flies feed on the slime of the snails. Bequaert (1919)
not only supported this suggestion but advanced the idea that they
are perfectly harmless to the snails. He gave further information on
the history and biology of this species (W. achatinae] and in subse-
quent papers (1925, 1926), he discussed two other species of this
genus, viz. W. indomita and W. biformis (cf. also Pilsbry and Be-
BIOLOGICAL CONTROL	119
quaert 1927:472; Brues 1907). The latter species has been shown to
live on A. rugosa chapini (Bequaert and Clench 1934). Baer (1952)
considers the "commensal" W. biformis synonymous with W. acha-
tinae and reports finding it on A. achatina L. and Archachatina ven-
tricosa Gould in the Ivory Coast, Liberia, Cameroons, and the former
B. Congo. Rodhain and Bequaert (1916) reported a number of lar-
vae of Mydaea bivittata Macq. devouring the achatinid Burtoa nilo-
tica Pfeiffer.
As far as can be determined, Senior-White (1924) was the first one
to report phorid flies from A. fulica. These, which were bred from a
dead snail, he described as new—Megaselia achatinae. Brues (1942)
has suggested that it is possible Senior-White actually had the ubiq-
uitous Megaselia xanthina Speiser. It was this latter species which
Smedley (1928) in Malaya bred from the eggs of A. fulica. Because he
reports the flies as being capable of producing human intestinal
myiasis, Smedley emphasizes the public health implications rather
than those of biological control. The phorids bred from a dead speci-
men of A. fulica in Hawaii by Yoshio Kondo were described by Brues
(1942) as new—Megaselia biformis. At that time, Brues advanced the
suggestion that in spite of the lack of experimental evidence, some
of the phorids "may be true internal parasites of living snails."
In 1949, Van Emden reported Ochromusca trifaria Bigot to attack
A. craveni E. A. Smith at Fort Johnston, Nyasaland. Captain W. A.
Lamborn, the collector of the specimens at Fort Johnston, later re-
ported to Krauss (1951) that the flies were bred from dead snails and
had not been observed to come from live individuals. This report re-
moved earlier optimism about the fly being of use as a biological con-
trol weapon.
An unidentified fly is described by van Weel (1949) as being a
possible parasite of the eggs or young of A. fulica in Java. The weak
spot in his evidence is that, despite the fact that the "narrow cleft" in
the breeding container was not wide enough to permit the adult fly
to enter and lay eggs, it was certainly sufficiently wide to allow ovipo-
sition within the container at the site of the cleft. Hence it is not pos-
sible to determine whether or not the fly larvae had access to the
snails or eggs before death from some other possible cause. Hardy
(1952) later announced that it was a new species of the phorid genus
Pericyclocera.
A slightly larger phorid was commonly encountered by the author
in the giant snails in Ceylon. Specimens were sent for identification
to the British Museum, through the Commonwealth Institute of
Entomology. According to D. E. Hardy (in litt. April 18, 1956), these
120	BIOLOGICAL CONTROL
are being described by C. N. Colyer as a new species of Spinophora.
Under the many circumstances in which these flies were observed,
there was never evidence of anything but a saprozoic role with respect
to both the endemic and the giant snails. Snails killed in the labora-
tory would attract in a few hours numerous phorid flies from the
nearby bush. Snails killed and being fed upon by the glowworm were
observed to contain at the same time female flies busily laying eggs in
characteristic patterns on the lip of the shell. Typical larvae were
found in insects which had been killed and allowed to decompose. It
has been suggested that these phorid flies may be implicated in the
transmission of a disease in A. fulica (Mead 1956a).
In Saipan, Lange (1950) reared Sarcophaga gressitti Hall and
Bohart and S. dux Thomsen from dying and dead A. fulica. Near
Diani Beach, Kenya, East Africa, Krauss (1951) found fly larvae and
pupae in the shells of Achatina "in which the snails were dead and
decomposing, and often reduced to a black foul liquid." These were
later identified by Van Emden as: Aethiopomyia steini Curr., Allu-
audinella bivittata Macq. (Muscidae); Sargus sp. (Stratiomyidae); and
Discomyza similis Lamb (Ephydridae). In the same area, Williams
(1951) was able to find species of the muscoid genera Sarcophaga^
Panaga^ and Aethiopomyia in only the dead or dying achatinas.
Other saprophagous but unidentified flies were observed on dead
achatinas by Pangga (1949) in the Philippines. The large maggots of
filth flies were not uncommonly seen by Kondo and the author in
several of the islands in Micronesia and especially in the Bonin
Islands; unfortunately, a tightly packed itinerary did not permit rear-
ing them for identification. There was, however, absolutely no dis-
cernible evidence of parasitism in any of the thousands of snails
specimens examined. Krauss similarly found no evidence of dipteran
parasitism in his investigations in Kenya, Zanzibar, Tanganyika, and
Madagascar.
Recent initial efforts to use Johnsonia elegans, which attacks Dry-
maeus in Florida, and a Tetanocerid fly from New York in the bio-
logical control of A. fulica in Hawaii have failed completely (Thistle
1959a).
Helminths  There has been found in the literature no report
of helminths of any type being found in the achatinid snails. Pilsbry
and Bequaert (1927:472), Pelseneer (1928, 1935), and Adam and
Leloup (1943) refer to records of helminths being found in other
gastropods. The work of Chitwood and Chitwood (1934) is valuable
in that it lists the nematodes encountered in gastropods. An uniden-
tified rhabditoid nematode was encountered by the author during
BIOLOGICAL CONTROL	121
the examination of the lower one-quarter of the intestinal tract of
several specimens of A. fulica in Ceylon. However, all evidence sug-
gests that this worm is only an incidental symbiont of low incidence
and little consequence. Dying specimens of A. fulica found in 1957
in Maui, Hawaiian Islands, by Lew Akaka, were discovered to con-
tain many nematodes; but, in the highest probability, these were
saprophagous and not parasitic. Actually the whole subject of gastro-
pod helminthiasis has been seriously neglected and it is hoped that
in the near future attention will be given to it by qualified specialists.
           Mammals  As in the case of bird stomach examinations, the
contents of the stomachs of a great many species of mammals have
been found to contain the remains of terrestrial or aquatic snails.
Without much question, by far the larger share of such cases clearly
represent incidental, accidental, or subsistence consumption of the
snails. It therefore would be as pointless as it would be misleading
to attempt to compile an exhaustive list of mammals known to have
consumed snails at one time or another and offer it as a list of the
mammalian enemies of snails. There are however certain mammals
which have a manifest appetite for snails. Chief among these prob-
ably is the shrew (Hamilton 1930, Ingram 1942b, 1944), which Clench
(1925) brands as one of the worst enemies of land mollusks. Signifi-
cantly important among the others are: rabbits (Lawson 1929, 1930,
Oldham 1929b, Wright 1909), mice (Coghill 1909), and rats (Adams
1938, Hoffman 1936, Lawson 1920a).
Of the mammals mentioned so far, only the rat has been linked def-
initely with A. fulica. Meer Mohr (1935) illustrated damage to giant
African snail shells which was suspected to be caused by rats or birds.
Abbott (1951c) and Williams (1951), similarly cautious, implicate
the rat. The survey in Micronesia conducted by Kondo and the au-
thor, however, removed all doubt. Rat nests containing the chewed
remains of A. fulica shells were found in one or more instances in
Guam, Chichi Jima, Haha Jima, and Tinian. In each case, the shells
were numerous, fairly small in size, and showed unmistakable evi-
dence of rat work. Numerous arcuate shell flecks in the nest debris
indicated that the shells were brought to the nest before being eaten.
As the entire columella was destroyed in many specimens, it is prob-
able that all of the soft parts were removed. In northern Saipan (Mag-
pi) two instances were witnessed where rats were feeding on crushed
achatinas on the road; but the rats were emaciated and apparently
using the snails for subsistence. After considerable field study, Kondo
(1952) concluded that on Agiguan the rats are more effective preda-
tors of the giant snail than the experimentally introduced carnivo-
122	BIOLOGICAL CONTROL
rous snails. The report of Davis (1954) was in sharp contrast. How-
ever, it is felt in general that, with certain fairly clear-cut, localized
exceptions, the over-all controlling effect the rats have on the giant
snails is relatively minor. On the contrary, the giant snails are often
to be considered contributory to the rat problem by providing them-
selves as an additional source of food. As an ironic twist, the giant
snails on Guam contributed still further to the rat problem by con-
suming with apparent impunity the warfarin bait intended for the
rats (Peterson 1957b).
The omnivorousness of domestic pigs suggests correctly that they
will consume the giant snails and that their foraging near habitations
provides some small measure of control. South (1926b) lists the wild
pig among the enemies of: A. fulica.
The mongoose, Herpestes mungo, is said to eat the giant snail in
Ceylon (Philbrick 1949, Rees 1950). While the author was in Ceylon,
a great deal of circumstantial evidence was collected implicating this
predator in the destruction of achatinas. For example, on several
occasions freshly broken snail shells and partly consumed snail car-
casses were found in the immediate vicinity of burrows which the
local inhabitants declared were those of the mongoose. Equally often,
piles of broken shells were found scattered around a prominent rock
indicating that the mongoose had used the rock as a "hammer stone."
Some of the shells were remarkably broken almost exactly longitudi-
nally. The hepatopancreas or "liver" of the snail not infrequently
was left untouched, suggesting that it was distasteful or at least less
appetizing than the rest of the snail carcass.
In numerous instances in the field in Ceylon, there were found
shells which had been flecked open, hence indicating that they had
been attacked by a small mammal of some sort. Informants stated
that rats, both the "wild" type and the introduced type, were known
to eat the giant snails. In other cases they stated that it was the giant
squirrel, "Dondolena" (Sciurus macrurus Pennant). In still other
cases, for example on the Godahene estate near Kalutara, there was
the strongest evidence that it was the Bandicoot, "Uru-miya" (Bandi-
cota malabarica) which was breaking the shells and eating the snails.
The "mongoose" of East Africa to which Abbott (1951c) refers is
quite probably the civet cat, Bdeogale tennis and B. crassicauda,
whose snail-eating habits are interestingly described by Williams
(1951). The jackal in Ceylon (Philbrick 1949, Rees 1950) and the
baboon in East Africa (Abbott 1951c) are also reported to eat the
giant snail. In Ghana, an endemic wild cat, referred to by the natives
as "odompo," is believed to feed on giant snails. Since the snails are
BIOLOGICAL CONTROL	123
an important food item to the natives, the "odompo" is hunted and
killed at every opportunity. And as an interesting elaboration, a
snake—the deadly horned Cerastes—is known to attack the "odompo"
and has been seen in the company of the giant snails; it is therefore
believed by the natives to be the protector of the snails (Martinson
1929).
The large musk shrew, Suncus murinus (L.) became established on
Guam in 1953 and in two years' time it had spread considerably
(Peterson 1959). For a time, it was hoped that this predator would
prove to be a potent new biological control agent in the battle
against the giant snail; but field and laboratory observations indi-
cated that there was little hope for anything of this sort (Peterson
1957b).
As a strange effect of mammals on snails, Peterson (1954) and
Davis (1954) report that the great many feral goats on Agiguan Island
are apparently responsible for killing and injuring the giant snails by
trampling and crushing them as they get under foot.
Micro-organisms The most neglected aspect in the problem
of the giant African snail, and in fact in the entire field of malaco-
logical biology, is the study of the role of micro-organisms in molhis-
can symbiosis and pathology. A search of the literature reveals few
references indeed on this important subject, and none of these con-
cerns a virological investigation. The work of Drz (1913), which has
not gone unchallenged, reports the presence of bacteria in special
cells between the kidney and stomach in Cyclostoma. Wurtz and
Gray (1939) found in the intestine of Triodopsis albolabris what ap-
peared to be eight new species or varieties of bacteria belonging to
the genera Escherichia, Alkaligenes, and Bacillus. Edward Steinhaus
recently reported to the author that in France an Aerobacter infec-
tion in colonies of commercially raised Helix. Pan (1956) found in
tissue sections of the freshwater snail Australorbis glabratus an
obligate, intracellular, acid-fast bacillus in various organs of the
body, and a "fungus spore or yeast-like agent" in the nervous tissue.
Spirochetes were found by Fantham (1921) in the hepatopancreas of
South African pond snails; their role however was not determined.
Dartevelle (1954) similarly reports the spirochete Borrelia in the
hepatopancreas of 10 per cent of the achatinas examined in a study
in the Congo.
For an early basic work on the protozoa of snails, one should turn
to that of Kuhn (1911). Pelseneer's survey of this portion of the
literature (1935) brings the subject more nearly up to date although
he does not mention the work of Hegner and Chu (1930), wherein
124	BIOLOGICAL CONTROL
the ciliate Balantidium haughwouti was reported to be found in
Philippine fresh water snails. More recently, the species of the sporo-
zoan genus Klossia, found in the kidneys of several genera of snails
and slugs, have been discussed by Nabih (1938). The contributions
of Kozloff (e.g., 1946) on the mastigophoran symbionts of gastropods
stand out among the best in this whole field. The mastigophoran
Trypanoplasma isidorae and an amoeba have been reported from the
seminal receptacle of the pond snail Bulinus (Isidora) tropica; unde-
scribed amoebae were also found in the slug Arion fuscus (Fantham
1923, 1925). As far as can be determined, the only protozoan (and,
for that matter, the only micro-organism) that has been described
from the giant snails is Trichodina achatinae found in the seminal
receptacle of Achatina zebra (Fantham 1924, Fantham and Robert-
son 1927); and, although it has been referred to as a "parasite," there
is not at present sufficient experimental evidence to warrant such a
classification. At two different times, diflagellate protozoans were
found in smears of the intestinal tract of A. fulica in Ceylon; but
contamination could not be ruled out as a possible explanation for
their presence. There was absolutely no evidence of pathogenesis.
Gain (1896) refers to Laurent's work wherein the eggs of Dero-
ceras reticulatum are claimed to have been found infected with a
fungus even before they were deposited. The more careful work of
Tervet and Esslemont (1938) revealed the fact that the eggs of this
slug were infected with the fungus Verticillium chlamydosporium
Goddard. Even though they felt that this fungus exerted "a strong
natural control" of the slug, they considered "impracticable" its use
in biological control. The significantly high percentage of infection
in the eggs which they collected in the field might find an explana-
tion in the possibility of a sequela of fungous infection subsequent to
mechanical injury to the eggs during field collecting and transport-
ing to the laboratory. It is at this instant apropos to point out that
Lovett and Black (1920) found fungous diseases "particularly active
and virulent" in their breeding cages of slugs; but their field observa-
tions indicated that such diseases were "of minor importance under
natural conditions."
In looking back over the reports extant in the field of malacologi-
cal microbiology, it is immediately apparent that the surface of the
multifold problems has hardly been scratched. In most cases, the
reports have been made by investigators unqualified to do definitive
work in microbiology. Hence, if the organism is identified at all, the
identification is still very much open to question, as is the particular
type of symbiosis (sensu lato), that is, whether it is commensalism,
BIOLOGICAL CONTROL	125
mutualism, or parasitism. Or, for that matter, even the possibility of
the association being incidental, accidental, or contaminatory in
nature seems hardly or not at all to have been considered. For the
problem at hand, however, there is needed not only the information
that parasitism exists but that a pathogenesis per se is detectable.
Then an investigation of such problems as mode of transmission,
epizootiology, methods of culture, possible epiparasitic contamina-
tion, and introduction into the field can be undertaken. It is obvious
that there is still a long way to go in this phase of the investigations;
this notwithstanding, in the long run it will probably prove to be the
most practical, productive, and revolutionary method of control. In
fact, the possibility of a spontaneous biological control of the giant
snail rests almost completely in the field of microbiology.
The possible role of micro-organisms in the so-called "diseased
snails" and in the phenomenon of "decline" is discussed under the
proper headings below.
Mites Anyone attempting to raise snails or slugs may all too
soon find the specimens infested with small, swarming mites. As was
the author's experience in raising the giant slug Ariolimax, the mites
can become so abundant that they even interfere with normal loco-
motion and feeding. Banks (1915) made early, inconclusive observa-
tions on malacophilus mites.
Andre and Lamy (1930, 1931) have given us our only comprehen-
sive work on the mites of mollusks. There are no known records of
mites being found on A. fulica. But Bequaert (1925, 1926; Pilsbry
and Bequaert 1927:472) reports an unidentified, "ecto-parasitic"
mite on a live achatina in the former B. Congo; he also cites from that
same area, Stuhlmann's records of mites on A. schweinfurthi and
A. stuhlmanni. Nothing is offered as to the possible parasitic effects
upon the snails; however, Turk and Phillips (1946) in their mono-
graph of the slug mite Riccardoella limacum (Schrank) (i.e., Erey-
netes limacum) give convincing evidence that mite and mollusk live
together in commensalism of a fairly high order. Baker and Wharton
(1952) support this interpretation. On the other hand, a closely re-
lated species is believed to be at least contributory to an unthrifty,
malformed condition in Arianta arbustorum (Oldham 1934). Sim-
roth and Hoffmann (1928) list from the literature a questionable
record of the tick Amblyomma variegatum being found on the
achatinid Limicolaria adansoni.
Reptiles In the former B. Congo, the large monitor lizard
Varanus niloticus (Linne) has been observed by Lang (1919:55) to
feed principally upon half-grown achatinas. This observation was
126	BIOLOGICAL CONTROL
supported by Pilsbry and Bequaert (1927:473) and elaborated upon
with the information that the stomach of one specimen was found to
contain four large snails. They quote from Schmidt, who earlier
pointed out that the teeth of Varanus niloticus are adapted for crush-
ing snails. Species of this reptilian genus occur endemically or have
been introduced on a number of the snail-infested islands of the
Pacific (Loveridge 1945). There has been no adequate examination
of the stomach contents of these lizards to determine the extent to
which they are feeding upon A. fulica. As far as is known, the only
studies of the feeding habits of this lizard in the Pacific area are those
of Kondo (1952) and Davis (1954); but, unfortunately, negative
stomach contents in two specimens and the reluctance of two other
captive specimens to feed on achatinas cannot be considered any-
thing but inconclusive. It has already been pointed out however that
the lizard, because of its appetite for young chicks and eggs, presents
a fair threat to poultry, especially where other food is not available
(Mead 1949d). This has caused Eyerdam (1952a, b) to conclude that
Varanus in the Pacific is at best pretty much of a neutral value. Nor
does the fact that the lizard will readily consume the coconut crab
(Birgus latro) materially change the picture; for, although the crab is
a pest of the coconut palm, it will attack and consume the giant
snails—undoubtedly far more than will the lizard. But with the
recent announcement that the lizard will consume the grubs of
Oryctes rhinoceros (L.), which is in many respects the most serious
agricultural pest in the Pacific, the scales seem to be tipped very
much in the favor of Varanus (Gressitt 1952). Although V. monitor
and V. salvator were commonly encountered in some snail-infested
areas of Ceylon, there was no evidence that they were anything more
than of incidental value in controlling the giant snail.
The only chelonian known to attack A. fulica is the pond turtle
Nicoria trijuga thermalis of Ceylon (Green 1911b). During the au-
thor's investigations in Ceylon, it was determined that because of the
strongly aquatic affinities of this turtle, it was essentially of no value
as a biological control agent.
Recently, Vianney (1953) reports that a small Javanese snake
Pareas c. carinatus, in captivity, fed frequently on very young acha-
tinas, swallowing them shell and all, although somewhat older speci-
mens were ' 'seized in a peculiar way and . . . extracted from their
shells by the freely moving mandibles."
Snails In spite of the fact that A. fulica will readily and even
avidly consume the flesh of injured, dying, dead, and even putrifying
individuals of its own species, there is absolutely no evidence of
BIOLOGICAL CONTROL	127
predation per se. Even the eggs and delicate young are apparently
completely safe in the presence of larger individuals. Green (1911b)
was the first to emphasize this point; and it should be re-emphasized
here so that it will be understood that except for competition for
food, the giant snails do not provide any direct limiting factor among
themselves. It is of real interest to note, however, that an injured or
dying snail has a very positive attraction which brings out the latent
cannibalistic tendencies of foraging snails. This suggests that there is
released in the injured or dying snail some substance which is not
apparent in the normal, healthy individual. Many pulmonate gastro-
pod species have been reported in the literature to display occasion-
ally a propensity for cannibalism (e.g., Elliot 1918).
In 1927, Pilsbry and Bequaert (p. 469) indicated that perhaps the
most important predacious enemies of the African land mollusks
were the rapacious streptaxid snails. Bequaert later reiterated this
point (1950a). To determine more specifically what the natural ene-
mies of A. fulica were in East Africa, where this species is autochtho-
nous, the Pacific Science Board of the National Research Council
and the Office of Naval Research in the fall of 1947 sent F. X. Wil-
liams to Kenya and Zanzibar for several months. Interesting accounts
of the information gathered in the field are on record (L. C. Williams
1949, F. X. Williams 1951, 1953). The following May, live specimens
of the two endemic predacious snails in the Diani Beach area of
Kenya, Edentulina affinis C. R. Boettger and Gonaxis kibweziensis
(E. A. Smith) (Streptaxis), were sent by Williams to the Board of
Agriculture and Forestry in Honolulu, Hawaii (iccm 1948, Bryan
1949). The near maximum length of these species is 50 mm. and 22
mm., respectively. The purpose behind sending these alive was to
observe under subquarantine conditions their biology so that the
possibility and practicability of using them in the biological control
of the giant African snail could be determined.
While these observations were still in progress in the summer of
1949, Kondo and the author made a survey of Micronesia, under the
same auspices, to determine among other things what island, infested
with A. fulica,, would be most suitable on which to conduct an ex-
perimental introduction of the predatory snails. Reports from these
two investigators (Mead and Kondo 1949, Kondo 1949, Mead 1949a,
1950b, c) emphasized the complexity of the problem and recom-
mended that in the selection of an island for the proposed experi-
ments the following factors be kept in mind: size, topography, prox-
imity, available transportation facilities, accessibility, inhabitance,
isolation, quarantinability, horticultural and sylvicultural crops at
128	BIOLOGICAL CONTROL
stake, relative abundance of A. fulica, types and abundance of indig-
enous snails, and practicability of possible subsequent eradication
of the introduced predatory snails. After reviewing the recommenda-
tions in March, 1950, it was determined at the Fourth Annual Meet-
ing of the Insect Control Committee for Micronesia, of the Pacific
Science Board, that the small (3 by 1 mi.) uninhabited island of
Agiguan (Aguijan), about five miles off the southwest coast of Tinian
in the Mariana Islands, would be most suitable (cf. Gressitt 1954:53).
Kondo, R. E. Enders of Swarthmore College, and Mead had deter-
mined for the first time that A. fulica was actually on this island
and that for other reasons the island had possibilities. At the same
ICCM meeting, it was decided that R. T. Abbott should go to
East Africa, collect Gonaxis and Edentulina, and return to Guam
with them for release on the selected experimental island which was
to be maintained in quarantine (ICCM 1950). This mission was ac-
complished during the following May and June (Abbott 1951 b, c).
On May 31, 1950, and within approximately ten days after 545
living specimens of Gonaxis kibweziensis had been sent via air ex-
press to Guam by Abbott, about 400 surviving individuals2 were re-
leased on the first terrace of the southwestern end of Agiguan by
Robert P. Owen, entomologist and staff quarantine officer of the
Trust Territory of the Pacific Islands (Owen 1950, 1951). On August
30, 1951, Owen returned on the third expedition to Agiguan to de-
termine what progress had been made in the trial field experiment.
He was accompanied by George Peterson, Jr., the entomologist of the
government of Guam, and J. Lockwood Chamberlin, who was con-
ducting an ecological study of A. fulica in Tinian. Due to an unfor-
tunate set of circumstances, they were able to spend only three hours
examining the area where Gonaxis had been introduced the previous
year; but they were able to obtain evidence indicating that this preda-
tory snail had survived, that it was reproducing, and that it had
spread at least 300 feet beyond the point of release (Owen 1951).
There remained undetermined such important points as: whether or
not Gonaxis was actually feeding on the giant snail; whether there
was being effected any appreciable control of the giant snail; whether
any inroads were being made on the endemic snails; and whether any
deleterious side effects were being demonstrated as a result of the
introduction of Gonaxis. The ICCM, which had now become the
Invertebrate Consultants Committee for the Pacific, decided at its
Sixth Annual Meeting in February, 1952, that these and other points
should be investigated over a period of a number of days by Kondo
2 This number was later reported to be "229" (Owen 1953) and "407" (Davis 1954).
BIOLOGICAL CONTROL	129
during the following summer. In accord with the suggestions of the
ICCP, Kondo took with him 100 live specimens of Gonaxis, raised in
Hawaii, for release in a high, forested area near the old village on the
third terrace of the east end of Agiguan. At least 95 per cent of these
were alive at the time of release. During his seventeen days on Agi-
guan, in the company of four other assistants and investigators, in-
cluding Owen and Peterson, Kondo (1952, Anon. 1953a) made a
number of discoveries; among the most significant are the facts that
Gonaxis had actually been feeding on A. fulica, that it had effected
only about a 19 per cent kill, and that in two years time, the original
lot of approximately 400 Gonaxis had increased to an estimated
21,750. This great population build-up notwithstanding, Kondo an-
nounced that Gonaxis could not be considered a strong factor in the
biological control of A. fulica.
But before this time, Kondo had eminently qualified himself for
this field work by spending a number of months in Hawaii making
careful observations of the biology of several predatory snails, includ-
ing Gonaxis. The predatory snails sent by Williams to the Hawaiian
Board of Agriculture and Forestry were transferred to the laboratory
of the Hawaiian Sugar Planters' Association in January, 1950, where
Kondo was asked to take charge of them. Their numbers had dwin-
dled considerably and it was thought wise to put them under the
care of a trained malacologist. By the spring of 1952, the number of
Gonaxis had increased from the low of 22 late in 1949 to 439 living
specimens.
Under a joint agreement between the ICCP and the Hawaiian
Board of Agriculture and Forestry, N. L. H. Krauss, entomologist of
the board, was sent to East Africa, Australia, New Caledonia, and
adjacent areas for a period of several months in 1950-52 to seek fur-
ther into the problem of finding a suitable predator or parasite of
A. fulica (Coolidge 1950, 1951, 1952). Additional live specimens of
G. kibweziensis and Edentulina affinis were sent to the Board of Agri-
culture and Forestry (Krauss 1951-52, ICCP 1953, Lennox 1953).
Besides these and specimens of the beetle Tefflus, Krauss sent speci-
mens of several other predatory mollusks so that their potential as
biological control wapons might be determined by Kondo. All of
approximately two hundred specimens of the omnivorous Oxychilus
cellaria from Sydney, Australia, died within four months; the cause
is attributed by Kondo to the inability of this temperate zone snail to
adapt to the summer heat of tropical Hawaii. A similar fate was suf-
fered by eight specimens of Strangesta capillacea (Rhytida) and 45
specimens of Paryphanta compacta (Victaphanta), both from Sydney,
130	BIOLOGICAL CONTROL
as well as eleven specimens of Rhytida spp. from the dense rain for-
ests of New Caledonia. Kondo (1950a) reports that, of the latter,
Rhytida inaequalis (Ouagapia) quite unlike the smaller predatory
species attacked some of the large specimens of A. fulica. When Wil-
liams was in East Africa, he found that carnivorous snails belonging
to the genus Gulella were "probably effective enemies of quite young
Achatina" (1951, 1953). Their small size, however, eliminated them
from consideration. Williams also examined the paryphantids in
New Caledonia and found them frequenting moist, dense ravines.
G. S. Dun (in litt. April 17, 1950) concluded from this that predator
and prey might not overlap sufficiently to effect any appreciable con-
trol, especially since A. fulica tends to be more abundant in the less
dense areas frequented by man. As the giant snail is fortunately not
in New Caledonia, there is no way of determining what the predator-
prey relationships might be. Recently, de Wilde de Ligney (1953)
made the following interesting report on the spread of A. fulica in
New Guinea: "It is believed that this snail is unable to cross the
patches of jungle isolating the small farms from the town and from
each other. This assumption is supported by the fact that a concen-
tration of empty shells was often found in the outer regions of the
forest surrounding the town. In a few cases naked snails, probably
parasitic [sic!], were observed on the shells of the giant snail. Experi-
ments will be made to ascertain the carnivorous habits of the naked
snail."
The Edentulina sent to Hawaii by Williams, including an addi-
tional 48 specimens sent by Abbott, maintained a steady decline in
spite of plenty of food (young A. fulica) and moisture until in June,
1951, the colony numbered but eleven individuals (Kondo 1951b).
At least in the laboratory, this species proved itself less hardy than
Gonaxis. Perhaps the same explanation is behind the fact that Wil-
liams, Abbott, and Krauss encountered it in the field far less com-
monly than Gonaxis. At any rate, it is not difficult to understand why
earlier tentative plans to introduce Edentulina in Agiguan, after the
establishment of Gonaxis, were given up. In June, 1957, a fresh ship-
ment of Edentulina was received from Mombasa, Kenya, and was
released on Oahu; but to date there have been no recoveries (Thistle
1959a).
At this point, it is appropriate to review the very interesting ex-
periments of McLauchlan (1949), which concerned a biological study
of the carnivorous snails Strangesta capillacea (Ferussac) and Heli-
cella cellaria (i.e., Oxychilus) in Mosman, New South Wales. The
fact that these snails will attack and consume the introduced Helix
BIOLOGICAL CONTROL	131
aspersa is of particular interest in the present discussion. However, it
is McLauchlan's belief that a diet made up largely or exclusively of
H. aspersa causes a high mortality in these predators either because
of excessive gorging or because of some toxic factor in the prey.
He presents the following additional factors which tend to mitigate
against the effectiveness of especially S. capillacea as a biological con-
trol agent: cannibalism among the predators, a primary preference
for the native snails (species of Paralaoma and Egilomen), a second-
ary preference for only the young H. aspersa, the absence of a tend-
ency for young Strangesta to attack young H. aspersa, the relatively
very slow growth and development of the predator as compared with
the prey, the general retiring nature of the predator, and the tend-
ency for H. aspersa to move out of the range of Strangesta. Benthem
Jutting (1952b) reports on, but does not elaborate upon, a communi-
cation from J. Hope Macpherson to the effect that a similar study
was conducted in New Britain to determine the predation of H. eel-
laria and an Australian Rhytida on the eggs and young of A. fulica.
Kondo (1952) found in field observations of feeding Gonaxis that
the largest specimens of A. fulica which would be attacked were al-
most never greater than 35 mm. in length. This immediately brings
up the question as to whether or not the size of the predator is of
any importance. G. S. Dun (in litt. Dec. 29, 1950) feels that a small
predator is about as effective as a large one since the older specimens
in his breeding cages were shown to be sterile. This is not a safe con-
clusion, however, as it has been found that dietary imbalance in
caged specimens of the giant slug Ariolimax will invariably produce
sterility and genital anomalies (Mead MS). The combination in
A. fulica of a tremendous reproductive potential and immunity from
attack after the first relatively few weeks of growth suggests at least
that Gonaxis is not an ideal predator and, further, implies that the
role of Gonaxis might ultimately be reduced merely to that of con-
suming the multitudinous young which would have been eliminated
anyway by other causes. It was reasoning of this sort which en-
couraged Mead and Kondo (1949) to recommend that if predatory
snails are to be used in the biological control of A. fulica the larger
snail predators should be considered, for example, the giant pary-
phantids of Australia. Subsequently it was pointed out (Mead
I950b, c) that, since in predation the degree of prey-specificity is not
as high as is host-specificity in parasitism, the search for a suitable
predator of A. fulica need not and should not be limited to the area
where this snail pest is indigenous, viz., East Africa. That is, merely
because the predator has the same endemicity as its prey, it does not
132	BIOLOGICAL CONTROL
necessarily follow that no better predator can be found. The field
work of Krauss and Williams, the observations of Dun, and the re-
ports of Kondo all indicate that the giant predatory paryphantids of
the temperate regions are not as promising as hoped. Their inability
to adjust to tropical climate suggests automatically that a large tropi-
cal molluscan predator might be tried. None is found in the area
now occupied by A. fulica.
The large species of the voracious, tropical American Euglandina
would seem to be worth serious consideration if biological control is
to be investigated further. The eggs of Euglandina are proportionate-
ly gigantic and the hatching individuals are therefore so large that by
far the majority of the endemic molluscan fauna of the Pacific
islands, consisting of small or minute species, would escape their
ravages. In addition, the juveniles and adults could attack larger
specimens of A. fulica, eat more, and live longer than the small en-
demic predators of East Africa. It is of interest to note that Euglandi-
na was imported into France nearly fifty years ago in an attempt to
control snail pests of truck crops and was said to confer "immense
benefits on market gardeners" (Anon. 1913). Euglandina rosea (Fe-
russac) of our own Gulf States area is well known for its vicious at-
tacks upon other snails (Pilsbry 1946:2:1:188). As will be seen below,
this relatively small species has already been introduced into Hawaii.
Muma (1954, 1955) has observed it feeding upon a reputedly bene-
ficial tree snail Drymaeus dormani (Binney) in the citrus groves of
Florida (cf. Norris 1952, Nunn 1953). He reports unenthusiastically
about it, though, with these words, "Experiments with Euglandina
. . . have demonstrated that it is not a heavy feeder and probably not
of great importance."
The only other frontier in the search for a molluscan predator is
in Mauritius. Both A. fulica and A. panthera have been introduced
on that island (Dupont 1878) and there is recent strong evidence that
in the ensuing competition the latter species is quite successfully
taking over in the areas below 1000-1200 feet in altitude whereas
A. fulica remains dominant in the area 1200-2000 feet (J. Vinson in
litt. Dec. 24, 1949). Deep in the interior, where significantly the
achatinas have not yet successfully penetrated, there are found about
thirty native species of predatory streptaxids. Efforts by G. S. Dun
and the author to stimulate by correspondence a scientific investiga-
tion of the relationships between the achatinas and the streptaxids
have failed. Coolidge (1951) reported that a conchologist, Dorothy
Getz, planned to visit Mauritius and would be given assistance to
permit her to obtain information there about the problem of the
BIOLOGICAL CONTROL	133
giant African snail. Her findings, however, have thrown no new light
on the possibility of natural biological control being in operation in
Mauritius (Coolidge 1952).
On June 3, 1952, while Kondo was still in Agiguan in the process
of attempting to determine among other things the nature of precau-
tions which might properly be taken in introducing Gonaxis else-
where, the Hawaiian Board of Agriculture and Forestry made a deci-
sion and took action which has stimulated a considerable amount of
controversy. The preliminary results of the trial field experiment in
Agiguan and the laboratory studies in Hawaii, coupled with extreme
pressure from the people of Hawaii to "do something" about the new
outbreaks of A. fulica in Oahu and Maui, persuaded the Board to
introduce Gonaxis kibweziensis into the Hawaiian Islands without
waiting for additional results from the projected program. Twenty
specimens, along with ten specimens of the predatory beetle Tefflus,
were released near Mahinui in the Kaneohe district of Oahu, where
the giant snail has extended its range considerably (Lennox 1953,
Weber 1953). Through a singularly unfortunate oversight, however,
stones covered with a cement-lime-calcium arsenate bait, scattered
there to control the giant snail, proved equally tempting and fatal
to all of the introduced Gonaxis specimens. A second introduction
of 200 specimens of Gonaxis was made in this same area in Septem-
ber, 1954. At the time 300 specimens were introduced only a rela-
tively short distance away, near the insane asylum. In January, 1955,
this latter site was inspected by the author and there was found to be
every evidence of successful establishment of this predatory snail. It
was the plan then to move 100 of the specimens from that site to a
third location on the east side of Oahu as an initial step in a pro-
jected plan to spread Gonaxis as rapidly as possible. A few weeks
later, specimens were released on Maui (Weber 1956).
In 1953, efforts were made to introduce Gonaxis from Kenya into
the achatina-infested Seychelles Islands; but because of a prevailing
precaution on the part of the administration, the plans were tabled
indefinitely.
During the period January 12-16, 1954, G. D. Peterson (1954)
accompanied by three assistants, conducted the fifth expedition to
Agiguan. He concluded that considerable changes were taking place
in the various animal populations on that island, that Gonaxis was
apparently exacting a greater toll on Achatina than estimated by
Kondo, and that if the later point could be proved during a subse-
quent expedition, immediate steps should be taken to establish
Gonaxis on other infested islands. From July 21 to August 11 of that
134	BIOLOGICAL CONTROL
same year, Davis (1954), accompanied by Peterson and two assistants,
conducted a follow-up survey with the results essentially re-empha-
sizing and elaborating upon Peterson's earlier conclusions. The
elaborations underscored the complexity of the ecological conditions
which were obviously in a significant state of flux. The most impor-
tant announcements were: That the 100 Gonaxis released two years
earlier by Kondo had increased to an estimated population of 80,800;
and that the ca. four hundred Gonaxis released four years earlier,
and which had built up to an estimated 21,750 in two years' time,
had died out almost completely. In September, 1954, 88 specimens of
Gonaxis from Agiguan were marked with plastic paint and intro-
duced by Peterson into Guam (Peterson 1957, b). A few months
later, young specimens of the third generation were found, indicating
that successful establishment had taken place.
By this time, the authorities in charge of the biological control
program in the Pacific area were convinced that a full scale "Gonaxis
Program" should be undertaken. Accordingly, a seventh expedition
to Agiguan was planned for November, 1955, with the specific mis-
sion of obtaining as many Gonaxis specimens as possible for intro-
duction into other islands of the Trust Territory, into other areas on
Oahu and Maui, and into California as a biological control agent for
two introduced helicine pests (Mead 1955c, Anon. 1956b, c). Re-
portedly, over 5,000 live Gonaxis were collected (Coolidge 1955,
Kondo 1956, Anon. 1956a). Of these, 2,000 were sent to Hawaii and
200 were sent to California. The remaining specimens were divided
into lots and released in one or more sites on Saipan, Tinian, Rota,
Ponape, Truk, and the Palaus. Subsequently, specimens were intro-
duced in New Britain. Introductions into still other areas soon fol-
lowed, as implied in the words of Pemberton (1956), ". . . our Com-
mittee has been besieged from many sources requesting colonies of
Gonaxis."
G. kibweziensis, however, still has as its main drawback the fact
that its small size restricts it to attacking only the smaller achatina
specimens. In an effort to improve the situation, the Hawaiian Board
of Agriculture and Forestry introduced on Oahu in June, 1957, and
subsequently on Maui, the east African Gonaxis quadrilateralis
(Preston), which is almost exactly twice the size (Thistle 1959a). Two
years after its release, it was still holding a weak second place; and, in
general, the slow, uncertain developments were disappointing.
But even before this, more and more attention had been turned to
Euglandina rosea as a third possible molluscan predator. A number
of live specimens from Florida, collected by Krauss, were sent to
BIOLOGICAL CONTROL	135
Hawaii in 1955 as the initial step in introducing this species as a bio-
logical control agent. Their introduction was speedily approved and
616 specmens were released later that same year in Oahu (Weber
1956, Kondo 1956). In contrast to both species of Gonaxis, this ag-
gressive, vigorous, rapacious snail took hold immediately and spread
rapidly. By 1957, it was considered clearly the most promising of all
biological control agents being used in the giant snail control pro-
gram. In addition to feeding on Achatina, it was found to feed on the
snail pest Bradybaena similaris and the liver fluke snail, Lymnaea
(Fossaria) ollula Gould (Thistle 1959a). In both Makiki and Hauula
release sites, the snail had moved far afield, even into Gonaxis release
sites. Ironically, Gonaxis have been found in the egg clutches of
Euglandina. By July, 1958, the Hauula population had built up to
the point where it was possible to remove 12,000 specimens for re-
lease in many other sites in Oahu, Kaui, Maui, Hawaii, New Guinea,
Okinawa, and the Palau, Philippine, and Bonin Islands.
In January, 1956, 25 specimens of a fifth molluscan predator,
Oleacina oleacea straminea (Deshayes) from Cuba, were released on
Oahu (Kondo 1956, Thistle 1957). About four hundred specimens of
the predatory snail Gulella wahlbergi (Krauss) from South Africa
were released in January, 1957, on Oahu and subsequently others
were released on Maui. A number of specimens of Gonaxis vulcani
Thiele and an unidentified species of Gulella, both from the former B.
Congo, were released on Oahu in November, 1956 (Thistle 1959a).
There is no evidence to date that any of these four predators has be-
come successfully established. Similarly, little hope is held that the
giant predatory snail Natalina sp. (i.e., Rhytida), under examination
in Hawaii, will prove to be effective enough to warrant its release, in
spite of the fact that its body attains a length of 7-8 inches. Another
possible candidate, Varicella similis from Jamaica, died in the labo-
ratory before it could be decided that it might be released on Oahu.
Gulella bicolor Hutton from the Philippine Islands proved to be of
negative value so far as preying upon Achatina is concerned; but it
proved to be such an effective predator of the snail pest Subulina
octona, which is also the host of the cecum fluke of poultry (Post-
harmostomum gallinum), that it was released in large numbers on
Oahu and Hawaii in 1957 and 1958 (Thistle 1959a, Davis 1959).
Those absorbed in the economic aspects of the problem have
judged this expanded program of predatory snail releases as a strate-
gic, timely, and reasonably safe one, although some naturalists have
condemned it as unwise, premature, and irrevocably threatening to
the unique native mollusk fauna of the Pacific Islands. For example,
136	BIOLOGICAL CONTROL
Fosberg (1957) deplores the "almost hysterical program of importa-
tions of predators in an attempt to control the giant African snail"
in Hawaii and concludes that "these will almost surely bring about
destruction of many members of the extraordinary Hawaiian land
snail fauna." It undoubtedly will take years to determine positively
the actual value of these irreversible introductions. One thing is cer-
tain. There is to date absolutely no scientific justification for such
a statement as, "The snail [Gonaxis kibweziensis] ultimately proved
very effective in the control of the giant African snail" (Peterson
1957b).
Miscellaneous In New South Wales, McLauchlan (1949) re-
ports that unidentified "tiny insects in the soil also destroy the eggs"
of the predatory snail Strangesta capillacea (Ferussac).
Biological Control—an Evaluation South (1926b) was probably
the first to consider seriously the possibility of attempting to control
A. fulica by enlisting the help of some of its "natural enemies" from
East Africa. He accordingly made contact with authorities in Kenya,
Uganda, and Tanganyika; but for some unexplained reason, the
program died in its tracks. Since then, the subject has been alluded
to from time to time; but it was not until Townes (1946) made his
survey of the problem in the Pacific that the matter clearly came out
into the open once again with the statement that "the most feasible
control for it is to find and introduce a natural enemy." This recom-
mendation was picked up as a keynote by the Pacific Science Board
of the National Research Council and subsequently by its Insect
Control Committee for Micronesia (Ryerson 1947, ICCM 1947). In
this manner, it has influenced to a very great extent the character of
the research on the giant snail in the Pacific.
The first major undertaking in the investigation of the biological
control of A. fulica was the exploration of the native heath of this
snail in Kenya by Williams (1951, 1953). The early reports that no
parasites but several predators were found brought definitely mixed
reactions (ICCM 1948), the record of which might be considered a
crystallization of the basic philosophy underlying the current bio-
logical control program. Had specific parasites of the giant snail been
found, the method of undertaking the project would have been
clearly indicated. But with only non-specific predators, some felt that
at least a fair amount of precaution was needed. It was this feeling
that caused Rees (1950) to announce that "the American authorities
are reluctant to release these predators in new countries lest they
should become greater pests than Achatina." Since that time, how-
ever, the program of biological control of the giant African snail has
138	BIOLOGICAL CONTROL
become well established. Not one, but nineteen predatory inverte-
brates have been introduced in the various infested areas. And more
apparently are to follow, as there are currently several others under
consideration.
As this program continues to develop, there still prevails a mixed
feeling as to the element of risk involved. All agree, however, that
this so-called "natural control'' is exceedingly attractive from the
standpoint of its being self-perpetuating. Any other method of con-
trol that has been devised requires maintenance; and, at best, main-
tenance on an indefinite basis is a serious consideration because of
the cost, either in money or man-hours of labor, or both.
The literature is replete with reports on the general subject of the
dangers of introducing alien species (e.g., Kew 1893; Thompson
1922; Schlesch 1928; Anderson 1934; Storer 1931, 1934, 1949; Hanna
1948; Wodzicki 1950; Rees 1955; and Heim 1956). On the specific
subject of the introduction of alien animals to control the giant
snail, Aguayo (1950), Clench (1949), Jaski (1953), Mead (1949b, c, d,
1950b, c, 1955a, b, c, 1956b, c), Morrison (1950b), and others have
sounded a warning. Lennox (1949) and Pemberton (1956), in turn,
have minimized the dangers and emphasized the importance of con-
tinuing with the biological control program. In many ways, Morri-
son (1950b) comes close to the heart of the dilemma with the follow-
ing words: "The man who introduces a new predator into a country
undertakes a grave responsibility. Before it is regarded as safe, it
must have been proved conclusively that the candidate for intro-
duction will rather die than touch native fauna or flora or local
economic products. Such proofs take a long time to establish, and
meanwhile the giant snail is eating its way through the Pacific."
As pointed out earlier, the predatory snails Gonaxis kibweziensis
and Euglandina rosea have taken the limelight almost entirely in
the program of the biological control of A. fulica. Contrary to var-
ious current reports (Anon. 1956b,c)y there is no evidence that
Gonaxis effects any real control of the achatinas in East Africa
(Abbott 1951c). Similarly, the several endemic predators of A. fulica
in Ceylon have been reported to be of relatively little value as "nat-
ural controls" (Fernando 1952, Mead 1955b, I956d). But this seems
to be the usual story. For example, Ingram (1942a) was able to deter-
mine that the native carnivorous snail Haplotrema minimum in
California had an inappreciable effect upon the introduced H.
aspersa even though it preyed freely upon its young. An explanation
for this phenomenon seems fairly simple. It is probable that the
foreign species has a biological advantage in that it is in an environ-
BIOLOGICAL CONTROL	139
ment lacking its own specific natural controlling factors, while the
endemic predators continue to be held in check by their own nat-
ural controlling factors, despite the increase in acceptable prey.
This explanation becomes more tangible if it is assumed that the
more effective ''natural controlling factors" are specific disease agents
that become proportionately more limiting in their effect as the host
population increases. Although the idea has not been presented in
support of the predatory snail program, it would appear, by extend-
ing this same reasoning, that if in a given environment both predator
and prey are recently introduced foreign species the predator would
be at an advantage. If under these conditions, however, disease of
either the predator or prey should enter the ecological picture, it
could be completely decisive in its effects, one way or the other. On
the other hand, if disease of both prey and predator should enter the
picture, the outcome obviously would depend upon the differential
of such factors as the severity of the disease, immunity, tolerance,
physical hardiness, and a whole host of other factors.
But disease, as a complicating factor, has scarcely entered consid-
eration in the "Gonaxis Program," in spite of its importance. Even
without it, the picture is far from simple despite the glib accounts,
especially in the more popular articles and newspaper accounts,
which suggest that after consuming all the achatinas Gonaxis will
turn cannibalistically upon its own members and finally exterminate
itself (e.g., Mahoney 1955). As an aside, Bodenheimer and Schiffer
(1952) have convincingly demonstrated mathematically why there
almost never is extermination under natural conditions, even in
parasitism. Durham (1920), however, puts over the point more hu-
morously with the following: "I may point the tale with reference
to the flea and the louse. With great and enduring pertinacity their
'natural enemies/ the monkey, the dog and cat, nay even on to mice
and men, are hunting them day by day and into the night season,
but they still abide in their haunts."
Some have pointed out that the predicted predation-to-extinction
and self-predation-to-extinction already have taken place on Agiguan
Island since all Achatina and all Gonaxis have been found dead in
the area of the first release of the predator. If that is so, how then
can one explain the similar disappearance of Achatina in other areas
on that island where Gonaxis has not penetrated? (cf. Davis 1954:15,
23) First or all, it should not be forgotten that animal populations
under adverse conditions may apparently disappear, only to reappear
months or even years later. Hence, merely because specimens could
not be found, it cannot safely be assumed that extinction has taken
140	BIOLOGICAL CONTROL
place in either population. The question, however, does emphasize
the fact that in the present case control factors other than Gonaxis
are effectively operative. If we assume that both Gonaxis and Acha-
tina have not become extinct, but have been reduced in numbers
beyond the point where they can be encountered in the field, we
should naturally turn our attention to the factors influential in
bringing about a recovery of the populations of both prey and pred-
ator. Some of the more obvious of these factors are: general hardiness,
versatility in appetite, intraspecific cannibalism (Kondo [1951b] has
shown this often to be severe in Gonaxis), longevity, duration of
estivation, reproductive potential, and adaptability to varying types
of environment. In every case, Achatina has a distinct advantage.
From this it can be assumed that at least Achatina would make a
faster "comeback."
As still another facet in the complex ecological setting in which
we find the Gonaxis-Achatina problem is the role of the endemic
snails. Kondo found that Gonaxis shows a definite preference for
several species of terrestrial and arboreal endemic snails in Oahu
(1950b, 1951b) and for Omphalotropis erosa on Agiguan (1952). As
long as the arboreal snails remain in the vegetation they will be safe,
as Gonaxis manifests little tendency to leave the ground. The terres-
trial snails, however, would surely suffer (Anon. 1956d). This is re-
grettable; for the terrestrial snails "because of their secretive habits
form precious 'keys' indeed for unlocking the vast zoogeographic
storehouse of the Pacific" (Mead 1955c).
The question has been raised regarding the possibility of Gonaxis
turning to some other prey, such as earthworms, after the achatinas
and the endemic snails have become scarce. Although other carniv-
orous pulmonate gastropods are known to consume earthworms,
Kondo (1950b) failed to demonstrate in the laboratory any tendency
of this sort in Gonaxis. Nothing is known about the extent to which
other invertebrates might be attacked. There is strong evidence,
however, that certain other terrestrial invertebrate populations may
undergo substantial change because of the indirect effects of intro-
ducing Gonaxis. The reports of Peterson (1954) and Davis (1954)
show that four years after Gonaxis was introduced on Agiguan, the
hermit crabs (Cenobita perlatus] decreased in numbers markedly,
whereas the coconut crabs (Birgus latro] definitely increased. Concur-
rently, the vertebrate populations went through corresponding
changes. The monitor lizard (Varanus indicus] went into a definite
decline; the rats virtually disappeared; and the ferral goats increased
in a very pronounced fashion. The plant communities also under-
BIOLOGICAL CONTROL	141
went changes, a more significant one of which is the serious increase
of the poisonous plants Jatropha gossypifolia and /. curcas (Peterson
1954). In attempting to explain this whole series of changes, one
finds one's self face to face with the exceedingly ramified and little
understood subject of ecological chain reactions. Some notable ex-
amples of ecological chain reactions have been presented above. A
general treatment of the subject as it concerns the biota of the islands
of the Pacific is to be published soon (Mead in MS). Because of the
high state of flux of the fauna and flora of Agiguan, some have felt
that ecological chain reactions are actually in progress and that
greater changes are in store before an equilibrium once again is
attained. Unfortunately, however, what has happened so far has not
met with unanimity of interpretation by the several investigators.
For example, when Enders, Kondo, and Mead made the initial sur-
vey of Agiguan, there was a manifest abundance of rats; Kondo
announced later that the rats in combination with the coconut crabs
were killing more giant snails than the predatory snails were; but
when Davis and Peterson arrived on the scene, they found such an
"extreme scarcity of rats" that they concluded Kondo had "weighed
the evidence too strongly in favor of the rats" (Peterson 1957b).
So far, Gonaxis has demonstrated twice on Agiguan that in two
years it can go from a few dozen individuals to populations esti-
mated to be in the thousands. It is not clear, though, just what
takes place following the population buildup. The first population
went to an estimated 21,750 in two years; but in an additional two
years, practically no living individuals could be found during two
different intensive searches. The second population, in another area
on that island, went to an estimated 80,800 in two years. At its
apparent population peak, over 5,000 individuals were recently re-
moved for introduction into other areas. If this second population is
due to continue its increase, the removal of 5,000 individuals should
not have any appreciable effect; if however the population has gone
into a decline, as the first one had at this stage of its development,
then there could conceivably be a very material effect. (It is apropos
to recall that hand collecting as a control method for A. fulica is most
effective after the population has gone into the apparently inevitable
"decline.") But we dare not extrapolate from one population to the
other; for the populations are not only in different areas, but the
populations of the other animals on the island have continued to
undergo such pronounced changes that they are bound to cause dif-
ferent repercussions in this second population of Gonaxis, and even
in the first population, if it is still recoverable.
142	BIOLOGICAL CONTROL
The "Euglandina Program" similarly is producing in some cases
truly remarkable and even enigmatic results. For example, Euglan-
dina has been in the Makiki area on Oahu for two years, yet in some
of the sections where the giant snail is most abundant, this predator,
along with G. kibweziensis, is surprisingly only seldom encountered.
Specimens that have been collected more often than not are emaciated
in spite of the abundance of food. Adult Gonaxis have been found
consuming the egg clutches of Euglandina; but on the other hand,
Euglandina in the laboratory will often select Gonaxis and the small,
introduced snail pest Bradybaena similaris in preference to the giant
snail. In some cases, Euglandina steadfastly refused to attack an
acceptably small Achatina even after fasting two to three weeks. In
other cases, specimens which did consume giant snails in the lab-
oratory mysteriously died within a day or two in contrast to others
in the same lot that refused to feed. This brings to mind McLauch-
lan's suggestion of a "toxic factor." The emaciation has suggested
the possibility of disease. Individuals have been found with leuco-
dermic lesions apparently identical with those of "diseased" giant
snails. It is possible that Euglandina is more susceptible to the disease
than Achatina.
Another differential between these two species is the giant snail's
infinitely greater capacity to withstand prolonged estivation with a
consequent lack of food and water (Mead 1959b). A protracted dry
period could therefore enforce estivation and cause death through
starvation in spite of living food being nearby in abundance. Essen-
tially nothing is known of the population dynamics of Euglandina
and it is altogether possible that this cannibalistic species, as is char-
acteristic of predators in general, will not maintain high populations
in limited areas. This may explain why the highest concentrations
of this predator have consistently been found at the periphery as an
advancing crest in a relatively rapidly expanding population.
Threading through this entire problem as an element of still fur-
ther uncertainty is the genetic factor. The study of genetics teaches
us that each species has its own spectrum of hereditary traits and
rate of genetic mutability. From the study of population genetics we
learn that different populations of the same species may have dif-
ferent complements of the total possible hereditary traits. In some
cases, the differences are great enough so that two populations of the
same species may be considered distinguishable as two subspecies.
The selecting factors operative in the different environments quite
understandably vary in their relative value. It is the sum total of the
effects of the selecting factors in a given environment that determines

BIOLOGICAL CONTROL	143
which available hereditary traits will be selected and perpetuated as
most suitable in the population in that environment. In the ten
to fifteen years that A. fulica has been in the western Pacific Islands,
it has displayed such a remarkable variability from one population
to another, with respect to size, color, thickness of shell, and even
as to what plants it will preferably attack, that a taxonomist, un-
acquainted with the history of this species would be tempted to des-
ignate the populations at the very least as those of different "races"
(Mead 1951a, 1955b). When these same thoughts are applied to the
"Gonaxis Program," we cannot but wonder what this predatory
species will do in a like period of time. It has been suggested that
even a greater versatility in appetite in Gonaxis is not outside the
realm of possibility (Mead 1955, 1956b), notwithstanding the re-
marks in the literature to the contrary (Pemberton 1956). This car-
ries the disquieting implication that the environment might well
select unsuspected and undetectable undesirable traits. There is no
way in which this risk can be eliminated; for even though the animals
may be "screened" in the laboratory for their feeding proclivities,
there cannot be duplicated in the laboratory the population dynam-
ics or the multiplicity of environmental factors operative in a natural
population. Therefore, one may not really safely conclude that,
merely because all of, say, 2,000 experimental animals refused to eat
"Alpha" and died when it was their only source of food, "Alpha"
will not be jeopardized in any way with the release of the experi-
mental animals. The 2,000 experimental animals may have been too
small a sample to express the full spectrum of genetic variability in
character determiners influencing feeding habits. But grant that this
was an adequate sample. How can one anticipate ecological chain
reactions which might threaten "Alpha" indirectly?
Actually, there have been developed in insect biological control,
methods which substantially reduce the greater share of the elements
of risk. But these methods demand such an inordinate amount of
precious time that, where the life cycle is long or the economic pres-
sure is great, compromise or short-cut measures may be adopted.
Such measures have been strongly opposed.
Some have questioned the advisability of introducing multiple
predators of the giant African snail in Hawaii. To date, there have
been introduced nine predatory beetles, two presumably parasitic
flies, and eight predatory snails. In insect biological control, the con-
current introduction of two or more parasites of an insect pest is
a common practice (e.g., in the fruitfly control program in Hawaii).
The rationale behind this practice is that if one parasite does not
144	BIOLOGICAL CONTROL
effect a control perhaps another one will; or, together, the multiple
parasites will do the required job; or, one parasite may take over in
one type of environment and another will take over in a second type
of environment. Although these thoughts make good sense, putting
the idea into practice introduces new difficulties. In the case where
predators instead of parasites are introduced, predators may consume
predators, even in preference to the intended prey. Although Peter-
son (1957 a, b) reported that in the laboratory Lamprophorus would
not attack Gonaxis it has been pointed out that Tefflus can consume
Lamprophorus, Lamphrophorus can consume Euglandina, Euglan-
dina can consume Gonaxis,, and Gonaxis can consume its own kind
(Mead 1955b). In addition, a number of the factors, discussed above
in terms of the "Gonaxis Program" and the "Euglandina Program,"
would also pertain to these other predators. The complexity be-
comes geometric in its proportions.
Still other difficulties are introduced when different methods of
control are concurrently used. Molluscicides and other agents of
snail destruction will kill predatory snails quite as quickly as they
will A. fulica. This was convincingly demonstrated at the time
Gonaxis was first released in the Hawaiian Islands; and it surely
must have been demonstrated again when both Euglandina and
metaldehyde were used in concentric, contiguous zones of defense in
the Mana district of Kauai when the giant snail was first discovered
on that island. In the same manner, insecticides used in the field are
a threat to the beetle predators of the giant snail. As an apparent
"double threat," some snail baits are fortified with insecticides; in
other cases, the molluscicides are known to be insecticidal in their
effects. And, as a provocative additional thought, there was evidence
in Ceylon that a snail dying of metaldehyde poisoning provided a
temptingly lethal morsal for the marauding Lamprophorus.
It is perfectly obvious at this point that, despite the attractive
features of molluscan biological control, the method has more than
its share of difficulties. If true specific parasites of A. fulica can ever
be found, a great share of the intercurrent problems will be removed
automatically. The recent works of Muma (1954) and Berg (1953,
1955) on malacophagous fly larvae are also encouraging; but Berg's
reference to the fly larvae as "relatively unselective snail predators"
seems to sound a familiar note of warning.
The work on diseases of snails (vide infra) has only just begun
(Mead 1956a); and, although it is exciting to contemplate, it is ob-
viously too early to do more than speculate as to how much promise
micro-organisms offer as potential biological control weapons. A
BIOLOGICAL CONTROL	145
factor distinctly in favor of micro-organisms is their characteristically
high host specificity. But at least in one outstanding respect, micro-
organisms are potentially more dangerous than the metazoan pred-
ators and parasites. It is agreed that their phenomenal biotic potential
insures the capacity under favorable conditions to build up rapidly
a population capable of causing an epizootic. Ironically, however, it
is this same biotic potential which increases the chances of there
appearing a mutant type whose metabolism is just different enough
to produce undesirable results. The story behind the use of the
myxomatosis virus in the biological control of rabbits in Australia is
a case in point, particularly with the subsequent appearance of non-
virulent, but immunizing, strains in the field (Ratcliffe et al. 1952,
Fenner and Day 1953, Mykytowycz 1953). It is felt, however, that in
the final analysis it is truly the disease-producing agents in an envi-
ronment which determine both qualitatively and quantitatively the
biota the environment will maintain (Mead 1955b). In other words,
when organisms are in the presence of, and in harmony with, the
agents that produce disease, their numbers will not be excessive
ecologically and there will be at least a semblance of endemicity. The
mission of this phase of biological control, then, is either to bring
the foreign species into reasonable balance with the other organisms
in the environment through the introduction of a natural disease-
producing agent, or to attempt to eradicate the foreign species by
introducing an unnaturally virulent disease-producing agent. This
mission is a big one and it will not be fulfilled until the biological
control man, the malacologist, the microbiologist, and the ecologist
all work together on a closely integrated program. Together, they
should be able to speed up and intensify the natural process of popu-
lation decline which sooner or later overtakes an invading species.
This decline, it is felt, is nothing more than an indication that the
disease factor has finally caught up with the invading species. Dis-
ease is the ultimate controlling factor; and it is one that must be
recognized and properly evaluated in the problem of the giant Afri-
can snail.
CHAPTER 8
CONTROL
THROUGH
HUMAN USE
Human Consumption The human consumption of land
snails has been practiced since the very earliest times, and even dur-
ing the height of the Roman Empire it was of such common practice
that special utensils were devised so that the soft parts of the snail
might be more easily extracted and eaten (Taylor 1900). The demand
for the edible helicine snails has been so great that "heliculture" or
snail farming, especially in parts of Europe, is today a very sizable
industry. Not only have snails been raised in almost unbelievable
quantities for shipment alive to domestic and foreign urban areas,
but with the modern facilities for refrigeration and quick shipment,
snails are prepared with butter and spices ahead of time at the snail
farms so that all the consumer has to do is to warm the "instant
snails'' for a few minutes in the oven before eating them. Their very
high nutritive value has been expounded upon by Leger (1925) and
Moretti (1934). Simon (1940) has pointed out that they are neither
fish nor flesh and their consumption is permitted on meatless days.
As might be expected, there has been much written, in several lan-
guages, on every conceivable phase of raising, preparing, and market-
ing edible snails. Among the most notable contributions are those of
Locard (1890), Rust (1915), Boisseau and Lanorville (1931), Arnould
(1933), Kaibo (1935), Ri (1935), Maubert (1943), Pardo (1943),
Metteo (1946), Ben them Jutting (1952a), and especially Cadart
(1955). Rust urged the American people during the trying periods of
World War I to become more adventurous in their eating and,
146
CONTROL THROUGH HUMAN USE	147
as a substitute for meat, partake of the edible helicine snails already
introduced into parts of this country. Even the canning of pickled
snails was encouraged (Anon. 1914).
In France, Remlinger (1916) made a more practical suggestion by
recommending that snails be used instead of precious beef in pre-
paring bacteriological culture plates. The Second World War
brought a return of the suggestion that they be used for human
consumption (Aguayo 1944b). The fact that native gastropods were
already being eaten by people in this country was pointed out by
Allen (1916) in this reference to the consumption of the giant slug
Ariolimax in parts of Oregon and Washington and Triodopsis albo-
labris in Massachusetts. Earlier, de Stefani (1913) reported that great
quantities of Helix pisana (Theba) were being sent from Sicily to
the United States. (It is significant that this species later became a
serious pest in California.) Some idea of the amount of helicine snails
consumed in this country is indicated in figures released by the U.S.
Bureau of Entomology and Plant Quarantine wherein 721 cases and
24,969 baskets of living snails were imported into New York City
alone between May, 1947, and April, 1948 (Mead 1951b). It has been
stated that for a number of years almost exactly 1,000,000 pounds
of snails has been imported annually into this country just from
Morocco (Heifer 1949). With approximately fifty snails to the pound,
the total number of snails would figure close to 50,000,000; or, in
linear measurement, close to a thousand miles of snails. Who would
have guessed that such an appetite for snails existed in this country!
In France, however, the amount of snails consumed is understand-
ably about fifteen times as great (Cadart 1955).
In British West Africa, various species of Achatina and Archacha-
tina are eaten to a very great extent. In Ghana, these snails actually
form the largest single item of animal protein in the diet of the
common people. It was in that country that the author saw the na-
tives eating giant snails which had been put in boiling water or on
hot coals, removed from the shell, freed of the soft visceral mass,
chopped, and combined with some starchy dish, such as cassava or
cocoyam, and palm oil or peanut oil to form their standard meal of
"fufu." Lang (1919) similarly describes the methods used by the
natives in the former Belgian Congo and adds further that the snails
are occasionally served at the tables of Europeans. He did not indi-
cate, however, how well they were received in the latter case. During
the dry season, the snails tend to go into estivation and they become
very difficult to find. They are therefore collected in great quantities
during the rainy season. To assure a supply throughout much of
148	CONTROL THROUGH HUMAN USE
the year, a large portion of the catch is dehydrated. The shells are
broken to remove the animals, which are eviscerated, washed in water
but a single time, drained, impaled on split bamboo sticks, smoked
and partially dried for six hours over a slow fire of wood embers,
and, finally, completely dried in the sun before they are stored
(Martinson 1929, cf. Dartevelle 1953). For many years now, such
inroads have been made on the native achatinas of West Africa that
their collections have had to be regulated by the colonial forest con-
servation laws, through the co-operation of the local native chiefs.
To maintain jurisdiction over the collecting areas is a sovereign right
of the chiefs; they set the collecting dates and determine what per-
centage of the catch is to be given to them as tribute. The increasing
scarcity of achatinas has forced a greater and greater limitation of
the collecting period. This in turn has put a high premium upon
making use of every available moment during the short collecting
period. The seriousness with which the natives regard this matter is
reflected in the words of G. Saunders of Kintampo, Ghana, who
writes (in litt. Feb. 6, 1952) that "the date of a baby-show had to be
postponed because it coincided with the opening of the snail-collect-
ing season, and all the mothers go snail hunting!" Conolly (1939)
stated that A. fulica in its native heath of East Africa is regarded as
a ''culinary delicacy." In the region of Kenya and Zanzibar, however,
Williams (1951) was unable to confirm this in the inquiries he made.
This may help explain why Williams, Abbott, and Krauss found the
native species of Achatina considerably more abundant than Bequaert
and the author found in certain comparable regions of central West
Africa.
Torres (1950) has indicated that the native South American giant
land snail, Strophocheilus oblongus, known as "Arua," is consumed
by the aborigines in that region. Ernest G. Holt, of the U.S. Soil
Conservation Service, stated to the author that years ago he actually
saw indisputable evidence of the fact that the natives eat this snail.
As far as its use for human food is concerned, it quite likely is com-
parable in many ways to the giant African snail. Monte (1944) and
Anon. (1945) report on other snails used in South America as food
and medicine.
It was known before World War II that the Malays and Chinese
would eat A. fulica (Jarrett 1923, 1931). This knowledge, coupled
with the very rapid spread of the snail during the Japanese occupa-
tion and the persistent rumor that the Japanese ate the snails, appar-
ently was responsible for the appearance in the literature of the
assumption that the Japanese people considered the giant African
CONTROL THROUGH HUMAN USE	149
snail a "great delicacy," for example, Abbott (1948), Anon. (1948b,
1949f, g), Herklots (1948), Rees (1951), Somanader (1951), and Zuk
(1949). As doubt about this increased, efforts were made to soften it
with the suggestion that the Japanese ate them, but with wry faces
(Anon. 1949j). Rumors from other quarters carried the story that the
Japanese people actually disliked the snails and would not touch
them at all. This was elaborated with the suggestion that the Japanese
soldiers introduced the snails into the islands for sheer spite. It was
perfectly obvious at the time that the problem of the giant African
snail was surveyed in Micronesia that this whole question had to be
elucidated with as much supporting evidence as possible. The infor-
mation which was gathered was almost entirely hearsay; but the story
from the most reliable and probably least biased sources was always
the same, viz., that the Japanese very definitely did consume the giant
snail.
It was in Chichi Jima that the bulk of the information was ob-
tained. Moses Savory of that island stated that he had not only seen
the Japanese soldiers eat the snails, but he himself had eaten them.
He described how the achatinas were roasted in their shells, removed,
washed in two changes of water to clear them of most of the slime,
eviscerated, and eaten with soya sauce; that is, essentially only the
muscular foot was eaten. He said that they were something like
limpets and were "not bad," though his lack of enthusiasm in re-
lating the details and the expression on his face seemed to tell a
somewhat different story. His brother Hendrick added that it was
his belief that the Japanese soldiers "liked" the achatinas, that they
were especially fond of soup for breakfast and that they would often
prepare "snail soup" for that first meal of the day. Wilson Savory
and Mrs. Oste Webb, also of that island, concurred with details of
their own observations.
The native skipper of a boat that took the author from Moen to
Dublon, in the Truk Islands, stated through an interpreter that the
Japanese people had eaten the giant snails on Dublon. According to
him, they were heated in the shell, removed, cooked again, evis-
cerated, and eaten with soya sauce. The people of Moen gave a simi-
lar story. In Guam, Mr. Joaquin Guerrero of the Naval Government
Agricultural Experiment Station turned over to the author a copy
of a letter which he had addressed to the head of the Commerce
and Industry Department in Guam on December 26, 1945. The fol-
lowing quotation from the letter, made with Mr. Guerrero's kind
permission, presents earlier convincing evidence: "Mr. Jose L. Shimi-
zu further stated that while he was imprisoned at the stockade, Island
150	CONTROL THROUGH HUMAN USE
Command, he overheard statements made by the Japanese prisoners
to the effect that while they were hiding in the woods, they sometimes
ate these snails."
While in Koror, Palau Islands, Kondo (1950c) obtained the fol-
lowing information on this subject: "The African snail . . . was intro-
duced by an enterprising Japanese just prior to the war to be raised
for canning. A small factory or 'koba' was constructed and Okina-
wans were employed to gather and to process the snails. The inform-
ant stated that the canned product was excellent eating but he him-
self would not take the trouble of gathering the living snails to pre-
pare them for the table. With the advent of the war the . . . factory
closed down. It is not known whether the canned snails were ex-
ported to Japan but presumably they were since the objective of
most of these enterprises was to send the finished product back to the
mother country. It is also not known how the snails were prepared
for canning but because most of the shellfish were cooked in soy-
sugar sauce the same method was probably applied in this instance."
Additional information from Saipan is reported by Jones (1949).
He states, "Japanese soldiers consumed them in quantity when nor-
mal meat supplies were short. It is reported by reliable native sources
that these snails were dried and shipped in large quantities to the
Japanese homeland during the war. The price was equivalent to five
United States cents per pound."
As one seeks deeper into the reasons behind the importation and
consumption of the giant African snails by the Japanese, one fre-
quently finds that the presumed great medicinal properties of the
snails have provided the motivation. But this is not something in-
vented by the Japanese. Taylor (1900:428) not only discusses the pos-
sible curative powers of snails in ridding the body of tuberculosis but
recommends a method of puncturing the snail shell "to enable the
patient to suck the oozing liquor." Clapp (1902) similarly refers to
slugs in coconut milk as a cure for asthma. The use of helicine snails
in medicine has been traced by Cadart (1955) from the earliest times
right up to the present where it has been reported that the mucus of
Helix pomatia favors the action of penicillin. Hooper (1910) and
Read (1931) have given rather exhaustive and certainly most interest-
ing treatments of the use, by the Orientals, of snails and other ani-
mals in materia medica. An article in the April 19, 1936, issue of the
Osaka Mainichi Shinbun, translated by R. Urata and E. I. Naito
(Anon. 1936), discusses at length, with testimonials, the special cura-
tive powers with which snails are supposed to be endowed. The cura-
tive substance extracted from the snails is stated to be "Ishimoto
CONTROL THROUGH HUMAN USE	151
Negligin" which proves to be orthocalcium phosphate. This is per-
haps the "medicinal substance" which the Institute of Medicine in
Japan was reportedly extracting from the giant snails (Pangga
1949:342). This chemical is claimed to cure kidney disease, tubercu-
losis, anemia, diabetes, asthma, urticaria, circulatory disorders; to
improve constipation and hemorrhoids; to prevent influenza; to re-
store virility and vitality; to perpetuate beauty and clear the skin;
and to be recommended especially for those who sing a lot and those
in need of hormonal injections! The keynote for the entire article is
struck in the first paragraph with this sentence: ''Buying meat and
fish for your table is unnecessary, there will be no sickly person in
the house, doctors are kept away and it brings smiles to the home."
Tazawa (1934 et seq.}, especially, urged the cultivation of A. fulica
and made numerous recommendations for increasing production
and simplifying the task for raising the snails. Ri (1935), Kagiya
(1936), and Takamura (1936) made further suggestions in a whole
series of articles appearing in Nogyo Sekai ("Agricultural World").
The series (in which the giant snail was variously referred to as the
"edible snail," "land ear-snail," and "Shirafuji snail") was obviously
designed to promote the development of a "new industry" and
covered everything from a strictly zoological treatment (Taki 1935)
to an attempt to establish a convincing parallel with the edible heli-
cines of France (Kaibo 1935, Sato 1935).
With propaganda of this sort being turned out in agricultural
journals, newspapers, magazines, and the pamphlets of those promot-
ing snail sales, it is little wonder that within a few years A. fulica be-
came established in a number of new localities. The infestation in
the island of Maui in the Hawaiian Islands is unquestionably a result
of this advertising campaign. The Japanese importer there had not
only introduced A. fulica for "food or medicine," and had advertised
them in the papers in that manner, but had proved to be his own
best customer by consuming 425 of them himself (Pemberton 1938).
(Since he had reportedly sold only six other specimens since he had
obtained the original stock over a year previous to that time, it is
possible that he was eating them out of sheer necessity!) The infesta-
tion in Chichi Jima is another case in point. It was determined from
the older residents that sometime in 1937-38 a store owner in Chi-
chi Jima, by the name of Katsu Nishimura, brought back from Japan
some of these snails in the hopes that their broth would clear up the
tuberculosis he and one or both of his two children had contracted.
It might be recalled at this point that it was for precisely this same
reason that they were introduced into the island of Mauritius (Bosc
152	CONTROL THROUGH HUMAN USE
1803). Mr. Nishimura jealously guarded these snails and fed them
only the most choice food items. Only his closest friends received
some of the first batch of eggs. As expected, the containers were often
inadequate and there were early escapes. All too soon the population
build-up of the escapees took on the familiar pattern, and the people
on Chichi Jima found themselves plagued with a new pest. Charles
Washington, the oldest resident on that island, said that Nishimura
died of tuberculosis before the war and his two children were evacu-
ated to Japan. The story of the Pagan infestation runs essentially in
this same vein (Kondo 1950a, c).
In a strange sort of way, the giant snail, at first the apparent pre-
cious bearer of a medical panacea and then a cursed plague of the
vegetable and flower garden, turned out to be a salvation to the be-
sieged Japanese soldiers. Fishing could not be indulged in because of
a constant state of alert. Supplies were cut off, although often enough
there were sufficient stores of rice to last for a considerable period of
time. The only source of animal protein on the islands was the giant
snails, which in the meantime had become abundant. These then
provided that critical food item. In fact, it was stated that the com-
manding officer of the Japanese contingent on Chichi Jima insisted
that his men spend their rest period collecting these snails so that
they might be added to their store of food. There was found much
evidence in support of the assumption that these men "seeded" the
giant snails near their hundreds of small fortifications so that they
would have an easily obtainable protein item in the event of siege
(cf. Benthem Jutting 1952b:395).
It seems perfectly clear from the foregoing that there should exist
no reasonable doubt about the facts that the Japanese people actual-
ly have eaten the giant African snails, that the original purpose in
many cases for eating them was their supposed curative powers, that
the snails were introduced into uninfested areas with the intent that
they were to be eaten, and that not infrequently the exigencies of the
war made eating them a necessity. There still is uncertainty regard-
ing the extent to which the Japanese would under normal conditions
voluntarily select the giant snail as a food item of choice. In spite of
the praises sung in their "flavor," there is a great deal of evidence to
the effect that such claims were only to promote additional sales;
that is, they were apparently raised to sell and not raised to eat. Buy-
ers in turn sold them to still others. According to Esaki and Taka-
hashi (1942), some of these who got in early on the rapidly expanding
market, amassed a net profit of 2,000 yen in six months. These au-
thors have very beautifully summed up their opinions in this whole
CONTROL THROUGH HUMAN USE	153
matter in the following (translated): "It will first be necessary to
erase the name 'edible snail' to correct people's misbelief ... it is not
so tasteful, as can be ascertained if one tastes it. Even though it be
tasteful and rich in nourishment, Japanese are not used to eat snails,
demand will be very scarce, and it has no commercial value as food
material or canned food.... If difficulties in cooking and taste prob-
lem are ignored, it is certain that the snail will not be popularized
among Japanese, judging from the actual affairs in various places.
. . . Canning and other commercial enterprises are totally out of the
question." It is more than probable that today these statements re-
flect accurately a consensus among the Japanese people. It is signifi-
cant that Esaki had been asked to visit Koror Island and offer sug-
gestions for the control of the giant snail; he therefore was familiar
with the attempts to can the snails on that island.
The question immediately comes up as to whether or not other
peoples react in the same way. It has already been mentioned that the
Chinese in Singapore have been observed eating A. fulica. M. W. F.
Tweedie, director of the Raffles Museum and Library in Singapore,
corroborated this with the following statement (in litt. Dec. 19,
1949): "In the Japanese Internment Camp in Singapore the protein-
starved internees used them for food; they are said to be palatable,
suitably spiced, but rather tough. The trouble was that there were
not enough snails to go around." A. F. Caldwell of the University of
Malaya adds the following firsthand information (in litt. April 23,
1953): "During the Japanese occupation these snails were eaten by
the civilian internees after allowing the snails to empty the digestive
tract for a day or two. They taste somewhat like a piece of tough kid-
ney but the flavor is not so pronounced." H. A. A. M. Wirtz stated to
the author that while he was a prisoner of war in Singapore, he had
eaten many achatinas. He prepared them by breaking the shell, re-
moving the viscera, and cooking them for seven to ten minutes. Cook-
ing them longer made them tougher. If fat of any sort was available,
it was added to them. He claimed that he did not object to eating
them, although it was apparent that they were not relished. Garnadi
(1951) reports that because of the slime in the freshly prepared snails,
he found them less appetizing than dishes containing the dried
snails. According to him, Franssen (1936) considered the snails "very
tasty." Thomas (1949), in an apparently somewhat facetious vein,
makes the following comment, 'Tour photographs of the giant Acha-
tina snail made my mouth water, for here, undoubtedly, was my
1944 Christmas dinner in Singapore, looking every bit as succulent
as one of those specially fattened snails. . . . Three friends and I con-
154	CONTROL THROUGH HUMAN USE
sumed 40...." From the Hong Kong area, Herklots (1948) makes a
similar report: ''During the occupation these snails were certainly
eaten by the hungry Chinese and even after the war large specimens
could be seen for sale in the market. They are made into soup which
is said to be sweet and nutritious. A recipe worth trying is this one:
Remove snails from shells, stew in water, rub hard with ashes to re-
move the slime, wash and boil with lean pork. One of ray gardeners
who has been suffering from a chronic cough swears that he has been
permanently cured by eating these snails regularly." Additional first-
hand information on eating the giant snails in concentration camps
is offered by Kalshoven (1950). A letter from R. E. Dean of Hong-
Kong (Dec. 15, 1949), however, reports that the Chinese in that area
are no longer collecting the giant snail for consumption. According
to Vosburgh (1950), the Chinese in the coastal regions of Formosa
similarly do not eat these snails, although the aborigines in the inter-
ior eat them regularly with evident relish. These latter people are the
only ones other than the native West Africans known to eat the acha-
tinas from choice. It would be interesting to know whether develop-
ing an appetite for these snails is producing any appreciable effect
upon the snail population in that region. The people of the Philip-
pine Islands were also forced during the war years to collect and eat
the giant snails (Allan 1949) and they are reported as being offered
for sale in the Manila markets (Pangga 1950). There is no evidence
that this practice is being continued now although Talavera and
Faustino (1933) indicate that the freshwater snails Pila luzonica
Reeve and Vivipara burroughiana Lea are regularly consumed by
the poorer class of people in Manila. It is therefore possible that the
same class of people has more recently turned to eating A. fulica.
The Indonesians are known to eat aquatic snails; but they are preju-
diced against eating the giant snail, apparently because of its known
coprophagous habits (Garnadi 1951). The natives of New Guinea
have not so far shown "any great enthusiasm for the snail as a supple-
ment to other diet" (Harrison 1951, Allan 1949).
But the Micronesians seem to have gone one step further. It was
not a matter of lack of enthusiasm. It was downright antipathy which
often approached abhorrence, in every sense of the word. By far the
majority of the Micronesians, when asked if they had eaten or would
eat the giant snails, were most emphatic in their denial; in fact, it
seemed many times that the question had offended them, for they dis-
played an obvious resentment. One instance in particular stands out
in the mind of this investigator. The native skipper in the Truk
Islands was asked through an interpreter if he ate the giant snails. He
CONTROL THROUGH HUMAN USE	155
registered shock and surprise and then indulged in gesticulations
and denunciations which sounded like a mouth-filling Trukees oath.
Translation was not necessary. The question however was pressed
further with a ''Why not?" To this, no verbal answer was given. In-
stead, he indulged in a loud, protracted, agonizing demonstration of
intense reverse peristalsis that left the interrogator weak, convinced,
and without appetite. Even though his feelings were very negative
and very intense, his reactions probably reflect the general type of
response that most Micronesians, and incidentally most other peoples
of the world, would give to such an inquiry. An investigation into
the reasons for this almost automatic and seemingly inherent aver-
sion brought to light the following: (1) there is a natural abundance
of fish; (2) the Micronesians consider anything coming from the
ocean as being basically "clean" and conversely that land inverte-
brates (worms, slugs, snails, insects, etc.) are basically ''dirty''; (3) the
giant snails are extremely slimy and the slime is very tenacious and
repulsive; (4) the snails have been observed to feed on many un-
appetizing things, such as rotting vegetation, human feces, feces of
livestock, animal carcasses, including those of their own kind, etc.;
(5) when the snails are cooked, the so-called liver mass gives off an
acrid, offensive odor; (6) the natives are uncertain as to how to pre-
pare them even if they should become curious about eating them;
(7) and, finally, some have eaten them under semistarvation condi-
tions and have subsequently become sick—they reason from this that
the snails are probably poisonous.
Reputed Poisonous Properties There has been much talk but
little written on the presumed toxic nature of the giant snails as a
food item. It has been pointed out above that the death of Guamin-
ian dogs and cats has been blamed on the giant snails. Kondo (1950c)
writes that he heard in Guam, Saipan, and Pagan reports of deaths
following a snail dinner. His informant from Pagan offered the sug-
gestion that death of the Japanese soldiers was caused by insufficient
cooking of the snails. He said that they merely threw the snails upon
hot coals to broil and ate them without further preparation when
they seemed to be done. It was suggested that the copious slime was
the toxic factor and that they should have removed this through fre-
quent washings before they attempted to eat them. This conclusion
does not appear to be a safe one. Both van Weel (1948) and the au-
thor have sampled the slime with no untoward effects, although the
former did report that "one feels in the throat an itching, but no
more." This same sensation was experienced by the author only
when the raw "liver" mass was eaten, probably because of the power-
156	CONTROL THROUGH HUMAN USE
ful digestive juices it contains. It is likely that van Weel had some
contamination from that organ. Possibilities of an urticarial proper-
ty of the slime seem to have been dispelled by van Weel.
G. H. Halden of Millbrae, California, writes (in litt. Nov. 1, 1949)
that during his internment in the Philippine Islands, he and his wife
cooked and attempted to eat some of the giant African snails but a
physician companion warned against it. It was said that some of the
internees had eaten them and had become sick. The evidence that
the snails are poisonous is of course entirely circumstantial. Nausea
and regurgitation can be stimulated purely through auto-suggestion;
and with a natural repugnance for such things as snails, this would
not seem to be difficult, especially with plenty of time afterward to
contemplate what had been done in a fit of hunger. In times of stress,
the food that is eaten may be contaminated, partially spoiled, of
poor quality, or of insufficient and irregular quantity—any one of
which can precipitate a digestive upset. In attempting to find a
reason for such an upset, it is altogether easy to blame it on the most
novel and unusual thing that has been consumed. If snails had been
eaten, they would be elected on the spot. But there is another factor
involved. It is a well-known fact that rich food taken in any quan-
tity, especially after prolonged deprivation, may cause illness; and, as
indicated below, snail meat is rich indeed. Halden himself pointed
toward an explanation of this sort when he related that after a great
many months in a prison camp, he became ill upon drinking his first
glass of milk. Herklots (1948) supplies a bit of information which by
comparison is considerably more mild in its censure of the giant
snail. He writes, "... a friend who was interned in Borneo tells me
that those prisoners who ate these snails did not improve their phy-
sique in comparison with those that left this free food alone." It
might be facetiously added that worry over dire consequences could
explain the difference.
Quite aside from all these comments, however, there remains the
indisputable fact that other species of Achatina are eaten by choice
in great quantity and with impunity in West Africa. But again, these
people know how to prepare them. An insufficiently cooked snail
which had recently fed on contaminated or infectious material could
obviously provide a real threat. It has been suggested that cases of
helicine snail poisoning have resulted when the noxious contents of
the intestinal tract had not been allowed to pass before the snails
were prepared for consumption (Cadart 1955).
Experiments in Eating the Giant Snail    While in Chichi Jima,
it was decided by Kondo and the author that the gustatory qualities
CONTROL THROUGH HUMAN USE	157
of A. fulica should be determined through firsthand experience. The
shells of a dozen large achatinas were cracked with a hammer and the
soft parts were removed. The snails produced very little slime with
this treatment and seemed to remain surprisingly placid. The vis-
ceral mass was cut off, leaving the muscular foot and mantle. These
latter were dropped in salt water as they were prepared. They were
washed in several changes of fresh water (at least eight) and a half
gallon was used each time. Even the water used in the last washing
soon became as viscous as thin egg white; there seemed to be no end
to the slime. Finally, the foot of each was bisected and they were
placed, slime and all, in a pan of water seasoned with salt and
chopped onions. After boiling one and a half hours, they were still
tough and rubbery—like pickled limpets or clams. Another forty-five
minutes saw some improvement, for they could be cut with the edge
of a spoon with difficulty. The black pigment of the foot had boiled
out sufficiently to produce an unappetizing black broth. The aroma
issuing from the pan was reminiscent of a chicken freshly scalded for
plucking and it was not in the least associated with anything for con-
sumption. The gingerly initial taste of the broth convincingly
demonstrated the fact that one cannot determine by sniffing how a
thing will taste. Instead of hot feathers, it tasted more like a handful
of rich forest humus had been added to it. The snails had the con-
sistency of "tough mushrooms," if that can be imagined, and the
earthy flavor seemed to help this illusion. Mastication did not crush
and render soft the pieces of snail flesh, instead it merely split them
into smaller and smaller discreet, firm particles. The obvious "flat-
ness" in flavor seemed to be due to the lack of fats or oils, the addi-
tion of which might have helped considerably, as would other season-
ings, which unfortunately were not available for this experiment. A
number of recipes, originally designed for the Mediterranean heli-
cines, have recently been recommended by those who feel that the
giant snail will prove to be good eating (e.g., Garnadi 1951). They all
seem to have two things in common, viz., a pound of butter and half
the spice cupboard. Almost anything would be acceptable with its
own flavor so effectively disguised. It might be of interest to note
here that the Savorys' omnivorous dog, Patty, dashed to her dish in
great anticipation when the rest of the achatina stew was put there;
with her right paw cautiously curled under her, she took one sniff,
backed up, and retreated to the far corner to sulk.
Subsequent experimentation has shown that boiling the snails in
the shell for approximately five minutes and then dressing them pro-
duces a much less contracted and more tender morsel. The disadvan-
158	CONTROL THROUGH HUMAN USE
tage in this type of preparation, however, rests in the fact that the hot
hepatopancreas or "liver" imparts a pungent, acrid odor which to
the novice might prove more than discouraging. As will be shown
below, the hepatopancreas is the most nutritious part of the snail. To
solve the problem of an excessive amount of slime in the freshly pre-
pared snails, van Weel (1948) suggests soaking them for one to two
hours in a weak solution of vinegar, lemon juice, or grapefruit juice.
This he says "renders the snail hard at the same time, thus making it
more palatable." He does not recommend cooking them in brine.
The copious slime, on the other hand, was ingeniously and success-
fully utilized by H. A. A. M. Wirtz as a "binder" in the process of
making bread out of ground soybeans in a Japanese internment
camp in Singapore. One correspondent in all seriousness volunteered
the suggestion that the snails might be cleaned in a washing machine!
As an experiment in Saipan, Allie Jones pickled the African snails
in brine. Like the cooked snails, they proved edible but, by most
standards, not palatable. It should be mentioned at this point that
Jones was sent to Saipan, under the sponsorship of the Pacific Science
Board in 1949, to investigate the possibilities of making use of the
giant snail for human and poultry consumption. Before his experi-
ments were hardly more than under way, he sustained severe burns
in a most unfortunate accident. It is hoped that the projected re-
search will ultimately be completed. Apparently extensive experi-
ments of this sort were carried on in Japan by Shingo Tazawa; and
according to Esaki and Takahashi (1942), he "insisted that the snail
is rich in nourishment, good as a tonic, will give excellent dishes in
vinegar mixture, sesame bean-mash, bean-mash mixture, broiled
with soy, coquille or stew" and that "these dishes gained high praise
at experimental tasting eating parties." However, since Tazawa was
doing everything possible to promote the sales of the giant snails, his
reports were doubtless biased. As an interesting contrast, but without
qualifying evidence, Mahony (1955) states, "The snail is edible, but
when cooked and eaten it has a highly offensive odor and taste."
If commercial use of the giant African snail is to be made in the
future, it would seem at least at this time that it is as impractical as
it is unrealistic to presume there will be any extensive use of them as
an item of food for humans. The Micronesians will not eat them.
And it is sheer folly to assume that they can be "educated to eat
them." The same probably obtains for the other peoples of the
world who do not already customarily eat snails. Those who do eat
snails will not find the giant snails as acceptable as the edible heli-
cines unless some wholly new method of preparation can be devised.
CONTROL THROUGH HUMAN USE	159
Although there is need for exploring the possibilities of their use
directly in human consumption, it is not at all likely that anything
practicable will be discovered. Their use in curries or in the chow
mein type of dish is the most promising suggestion made so far. The
Japanese of course did eat them, but the reasons for it have been
shown to be temporary. The Chinese have eaten them and it is con-
ceivable that because of their naturally greater versatility in eating
and because meat of any sort is perennially a particularly scarce item
in China, there may be in the future some possibility of marketing
processed achatinas in that country. This needs and warrants ex-
ploration. It would seem, then, that any use to which the snails can
be put must be found in something other than human consumption.
           Food for Poultry  The fact that chickens and ducks will con-
sume achatinas has already been mentioned. This suggests in the
light of the present discussion that perhaps the giant snails can be
used for poultry feed. Van Weel (1948), Jones (1949), Pangga (1949),
and others urge this consideration. The possibility was explored to a
small extent by the author in Chichi Jima and inquiries were made
elsewhere. Small living snails were given to chickens with no success.
They occasionally would unenthusiastically pick at them but would
give up almost as soon as they started. Other observers in Micronesia
reported the same results. According to Garnadi (1951), Djaenoedin
(1942) had no better results even when the snail flesh was mixed with
coarse corn. On the other hand, van Weel (1948) found that chickens
would not reject well-crushed snails but that they would not take to
them as avidly as ducks invariably do. In Guam, Duane H. Kipp
(in litt. Aug. 4, 1956) reported that his chickens ate the giant snail
"raw, boiled, and roasted'' but "seemed to prefer them crushed and
boiled." Steven Haweis (in litt. Oct. 26, 1949) has recommended the
method used in the Dominican Republic; viz., the freshly killed en-
demic snails are pounded with corn meal before they are fed to the
chickens. The Formosan Chinese crush the large achatinas before
feeding them to their ducks (Vosburgh 1950). South (1926b), how-
ever, indicates that in Singapore the Chinese cooked the snails before
using them as duck feed.
It was decided to cook some of the snails before feeding them to
the chickens. The freshly boiled specimens were quite slimy and the
chickens were observed to be very slow to peck at them. The heavy
slime often discouraged them after an initial examining peck. As the
snails became somewhat dried out, the chickens would peck at them
more frequently though never enthusiastically. After many hours,
the cooked snails would be consumed. Kondo (1950c) observed
160	CONTROL THROUGH HUMAN USE
chickens in Guam feeding on the burned carcasses of large specimens
of A. fulica. Next, it was decided that boiled and dehydrated snails
should be tried. The brown, sun-dried pieces of snail did not elicit
even the slightest interest from the chickens, even at feeding time. Nor
did remoistening to form a soft, rich meal make any improvement in
its attractiveness. In the Seychelles Islands, the dehydrated achatinas
are reportedly used for poultry food; but there is no indication as to
how well they are received (Rees 1950). It is possible, however, that
a reasonably fine meal is made of the dehydrated snails and that this
is incorporated into the regular feed. Since chickens apparently do
not readily eat the giant snails, a method of this sort would seem to
be the only way in which they could be fed to chickens. A portion of
the achatina shell could also be ground up and combined with the
snail meal as an added source of calcium carbonate. In the proper
proportion, it would obviate the necessity of using oyster shell or
other calcareous substitutes (e.g., cf. Scholes 1945). But using snail
meal in chicken feed brings up some questions. Will it taint the eggs
or the flesh of the chickens? What does it contain in the way of essen-
tial nutrients? In what way will the chickens react to it? How does it
compare with other supplemental feeds? How dependable is the
source of supply?
As to the possibility of a snail diet imparting an off taste to eggs,
van Weel (1948) offers a negative answer with this statement: "No ill
flavour was observed in eggs of fowls, fed with Achatina." He has not
elaborated, however, on the extent of his experiments. It seems
reasonable that further experimentation will prove verifying on this
point. As an intresting sidelight, Taylor (1900:430) presents the be-
lief that the flavor of the flesh of sheep is improved when great num-
bers of snails are consumed in grazing. In contrast, some Chamorros
on Guam believe that when pigs are fed on a diet of giant snails, the
flesh acquires "a different and undesirable taste" (Kondo 1952).
Chemical Assay of Snail Meal  Determining the essential nu-
trients is going to be a more difficult problem. A start in this direc-
tion has been made with the reports of chemical analyses of van Weel
(1948), Mead (1950b) and Garnadi (1951). There is shown in Table
1 a comparison of the percentages that were found. Because the
tests were not equally extensive, the constituent chemicals compare
in only four instances. It seems clear from the figures that approxi-
mately three-fourths of the weight of the snail, exclusive of its shell,
consists of water (cf. Pelseneer 1935:15; Fischer 1941). The variation
in the amount of ash is not serious. But as gastropods are notoriously
lacking in fats, as such, it is not understood how van Weel and Gar-
CONTROL THROUGH HUMAN USE
161
nadi arrived at such comparatively high figures. The presence of
small amounts of fats in marine forms has been demonstrated by
Albrecht (1921 et seq.) and Struve and Kairies (1930). Biedermann
and Moritz (1899) actually showed that ingested fats were deposited
in the digestive gland. The "ether solutes" listed by Mead, however,
amount to scarcely more than a trace, as was earlier predicted. In fact,
it is this paucity of fats which makes it even more practical to con-
sider making use of snail meal; for it should not be necessary to run
the meal through a fat-removing process in order to insure against its
TABLE 1
chemical analyses of dehydrated Achatina fulica, exclusive of
shell, with percentages based on dry weight

	Mead
(1905b)*	Lot
At	van Weel
(1948)	Garnadi
(1951)	
Parts assayed 		Foot and	Visceral mass	All soft	All soft	
Per cent H2O before dehydra-
tion 		mantle
76.51	76.51	parts
80.2	parts
ca. 7%	
Ash  		11.18	10.72	17.7	10.0	
Calcium 		0.257	0.265			
Ether solutes ("fats") 		0.75	1.19	8.0	6 5	
Glycogen 				6 0		
Nitrogen. . .     .             ....	9 835	9.848			
"Nitrogen -free rest" 					30.5	
Phosphate (P2O5) 		11.78	35.34			
Phosphorus 		3.67	10.7			
Potassium 		2.75	3.35			
Protein 		60.95	60.99	55.6	53.0	
					
* Analyses made by Edwart L. Breazeale of the University of Arizona Agricultural Experiment Station,
Tucson, Arizona.
t Collected by Mr. and Mrs. Peter J. R. Hill, Koror, Palau Islands, and dehydrated there in a plant drier at
about 160° F. for 26 hrs.
becoming rancid in storage. The percentages of protein are all very
close, and together they vouch for the great value of snail meal as a
source of animal protein. The extremely low percentage of calcium
suggests that this important constituent is not accumulated to any
great extent in the mantle or elsewhere in the body, but is speedily
deposited in the shell. The whole problem of calcium metabolism in
Helix pomatia and H. aspersa is considerably elucidated by the de-
tailed work of Dexheimer (1951) and Wagge (1952), respectively. W.
Fernando (1946) first discovered galactogen in the albumen gland
and glycogeri in the albumen gland and reproductive cells of A. fuli-
ca. Van Weel found a significant amount of glycogen in his analysis
of the soft parts of this species. This carbohydrate has been demon-
strated in other gastropods (Creighton 1899, Levy 1890, Erhard 1912,
162
CONTROL THROUGH HUMAN USE
Leger 1924). The very high percentage of phosphate (and therefore
phosphorus), especially in the visceral mass, which consists largely of
the hepatopancreas or "liver," greatly increases the value of the snail
flesh as both a feed and a fertilizer. This finding lends support to
Leger's statement that the visceral mass of H. pomatia is its most
nutritious part and that therefore the snail should be eaten "in to to"
(cf. Table 3 and Moretti 1934). In no other constituent in A. fulica
is there any significant difference between the values found for the
visceral mass and the muscular mass.
TABLE 2
comparative chemical analyses of dehydrated Achatina fulica
from volcanic and coralline islands with
percentages based on dry weight*

		lot		
	B	C	D	
Origin (island) 		Koror	Ngannalk	Koror	
Type of soil 		Volcanic	Coralline	Volcanic	
Date collected 		3 Apr. 1950	25 Apr. 1950	27 Apr. 1950	
No. of specimens 		29	12	14	
Ash 					
Calcium 		0.26	0.25	.33	
Ether solutes 		0.75	Trace	Trace	
Nitrogen 		9.8	9.2	9.7	
Phosphate (P2O6) 		12.0	13.50	12.32	
Phosphorus 		4.0	5.36	5.38	
Potassium 		2.75	2.18	2.93	
Protein 		61.0	57.5	60.6	
Shell:
CaCO3 		98.7	99.0	98.9	
SiO2 		1.2	1.0	1.1	
				
* Collectors and analyses as for Lot A, Table 1, except dehydration was for 72 hrs.
In subsequent analyses, efforts were made to determine whether
major environmental differences produce any appreciable corre-
sponding differences in the values of the basic chemical constituents.
Specimens collected in areas of volcanic soil were compared with
those collected in areas of coralline soil. An examination of Table 2
will show that unless many other tests are run with essentially the
same results, the slight differences shown cannot be considered sig-
nificant. It is probable that at least a portion of the SiO2 in the pul-
verized shell analyses came from contamination with soil. But, on
the subject of variations, Brand (1932) made interesting discoveries
in checking the chemical composition of H. pomatia at various sea-
sons of the year. The variability which he found may help explain
CONTROL THROUGH HUMAN USE
163
why there is not closer agreement in the analyses of different investi-
gators. Table 3 has been drawn up to emphasize this point. Snails
often consume a fair amount of soil. Since the digestive tract is left
intact, and since the soil which it may contain will vary from place to
place in its chemical makeup, it is more than apparent that still
another variable enters the picture in this way.
Further contributions along this line have been made by Boycott
(1921), Vincent and Jullien (1941), and Janda (1951), who report on
TABLE 3
CHEMICAL ANALYSES OF Achatina fulica AND Helix pomatia
with percentages based on live weight

	Balland
(1898)	Brand
(1932)	Leger
(1932)	Garnadi
(1951)f	Mead
(19506)*	van Weel
(1948)	
Species 		H. po-
matia	H.po-
matia	H . pomatia	A. fu-
lica	A.fulica
	A. fu-
lica	
Parts assayed. . .	All soft
parts	All soft
parts	Foot	"Liver"	All soft
parts	Foot	Visc,
mass	All soft
parts	
Ash 		1.55	2-3.4	1.64	2.29	1.52	2.61	2.52	3.51	
Calcium 							.060	.062		
Ether solutes
("fats") 	
"Extractives" . . .	1.08
1 97	0.5	0.42
1.91	1.78
5.98	0.988	0.176	0.279	1.58	
Nitrogen 			1.5-2.0				2.31	2.31		
"Nitrogen-free
rest" 						4.63				
Glycogen 					0.842H				1.19	
Phosphate (P2O6)						2.77	8.30	
	
Phosphorus 							0.862	2.51		
Polysaccharides. .		1.5-2.8							
Potassium 							0.646	0.787		
Protein 		16.10		15.87	17.31	8.06	14.32	14.32	11	
Water 		79.30	80-84	80.16	72.64	84.7	76.51	76.51	80.2	
									
* Computed on basis of dry weight percentages,
t As a part of "extractives."
the presence of manganese in land mollusks (cf. Andre 1923), and
Fischer (1941), who states that under varying conditions the water
content of aquatic snails will go from 66 per cent, after prolonged ex-
posure to air, to an apparent optimum of 86-93 per cent. Chemical
studies of marine forms have been made by Albrecht (1921 et seq.}
and McCance and Shipp (1933), B. Bergeret of Yaounde, French
Cameroun, has announced (in litt. Dec. 25, 1953) that he has estab-
lished the nutritional value of Archachatina marginata and Archa-
chatina sp.
Dr. Y. W. Hes very kindly turned over to the author an unpub-
lished manuscript, dated August, 1951, containing a chemical analy-
sis of the "big shells" (>15 mm.), "small shells" (<15 mm.), and
164
CONTROL THROUGH HUMAN USE
"operculae" (i.e., epiphragms) of eastern Javanese specimens of A.
fulica. This analysis is probably the only one extant for the giant
snail; and it is for this reason that it has been reproduced, with per-
mission, in Table 4. A somewhat comparable analysis was made by
Turek (1933) on the shells of Cepaea nemoralis in which there were
found the following values: water 0.48 per cent, N 0.201 per cent,
SiO2 0.217 per cent, Fe 0.0014 per cent, Ca 38.88 per cent, Mg 0.0025
per cent, organic matter 1.36 per cent (of which 14.8 per cent was N),
P 0.0040 per cent, and conchiolin 1.21 per cent. In discussing the
shell of A. fulica, Garnadi (1951) states merely that it is made up
largely of CaCO3 with small amounts of CaP2O5 and MgCO3. Other
analyses of gastropod shells were reported upon by Clarke and
TABLE 4
chemical analysis of shells and epiphragms
OF Achatina fulica (Ex MS W. HES)

	Large Shells	Small Shells	Epiphragms	
Water (dried at 105° C.) 		0.2	0.3	1.4	
CO2 		39.6	39.8	36.7	
N 				0.4	
SiO2 		0.1	0.1	0.3	
Fe2O2+Al2O23 		Traces	0.1	0.2	
C2O 		54.6	53.7	50.1	
MgO 		0.3	0.2	0.8	
Organic matter 		5.0	4.9	9.7	
				
Wheeler (1917, 1922), Boring (1872), Steel (1922), and Struve and
Kairies (1930). Stolkowski's more recent work (1951) especially
should be mentioned because of its detailed treatment and exhaus-
tive bibliography.
Vitamin Assay of Snail Meal Even though vitamin A is quite
susceptible to oxidation, especially in dehydration, a preliminary
assay for this vitamin was conducted in the nutrition laboratory of
the Univeristy of Arizona. The tests run by Mitchell G. Vavich of
that laboratory on the dehydrated material sent from Koror revealed
the presence of vitamin A in the dehydrated visceral mass to the ex-
tent of 5.4 Fg/g. For comparison, beef liver has 300-400 Fg/g. The
pro-vitamin carotene, not heat-labile at moderately high tempera-
tures, appeared in 10.3 Fg/g. These figures are low for animal tissue.
Analyses run on the dehydrated foot and mantle tissue brought still
lower values. These tests establish the fact that snail meal does not
provide a good source of vitamin A or carotene; and if it is to be
used as a food supplement, other sources must be depended upon for
CONTROL THROUGH HUMAN USE	165
these essential factors. It is of at least academic interest, however, to
report the presence of these factors even in small quantity. Projected
tests will determine the relative amounts in the live and freshly
killed snails. Vitamin b1 (thiamine) was found in only small amounts
by Roller (1941) who discovered it in the liver and whole animal of
active Helix pomatia in 0.3 Fg/g and 0.9 Fg/g, respectively. In the
dormant animal, the assays were negative. In contrast, vitamin B2
(riboflavin), in this species and in H. aspersa, was not only found in
considerably higher amounts, but the values actually increased dur-
ing hibernation. The amounts, expressed in terms of micrograms per
gram of the fresh tissue, are: hepatopancreas 16.3, kidney 7.0, muscle
1.4, and genital system 2.3 (Rafly and Ricart 1943). Hoar and Bar-
berie (1945) have shown that marine mollusk tissue is higher in vita-
min B2 than mammalian muscle and fish; and that drying, canning,
or salting the tissue may produce great losses of this vitamin, whereas
freezing and smoking do not. Destruction of "vitamin B" was earlier
demonstrated by Jones and Murphy (1926) in the dehydration of
oysters at temperatures as low as 40° C. In contrast, preliminary
chick feeding tests at the University of Arizona indicate that there is
no vitamin B deficiency when dehydrated giant African snail meal is
the only possible source of this vitamin complex (Mead 1959b).
The presence of vitamin C (ascorbic acid) in H. pomatia, in con-
siderably less quantity than in beef, was reported by Wenig and
Halacka (1948). Earlier, Marchi (1928a, b, 1929) and Random and
Portier (1923) found that this vitamin was present in a number of
marine mollusks; but Nespor and Wenig (1939), after finding it in
H. pomatia, concluded that it did not figure importantly in inverte-
brate metabolism. According to Meenakshi (1951), vitamin C in
A. fulica, as in other gastropods examined, is strangely concentrated
intracellularly toward the distal ends of the hepatopancreatic cells.
These several reports, plus such more comprehensive works as that
of Waisman and Elvehjem (1941), should stimulate in the near
future fairly exhaustive vitamin assays of A. fulica.
Amino Acid Assay of Snail Meal The discovery of a very high
protein content in the snail meal in turn has introduced the question
of the amino acid makeup of this protein. Preliminary amino acid
assays revealed the very significant fact that the essential amino acid
lysine was present in the dehydrated, pulverized snails to the extent
of 1 1/3 times that of whole chicken egg (Mead and Kemmerer 1953;
Anon. 1953d). The consistent deficiency of lysine in the common
sources of plant protein used as food supplements, such as cotton
seed meal, makes this discovery all the more important. In these
166	CONTROL THROUGH HUMAN USE
same preliminary tests, arginine was shown to be 2 1/3 times the rela-
tive amount found in whole egg; this amino acid, however, has not
been established as essential in normal nutrition. Other amino acids
were sufficiently high in concentration, as compared with whole egg,
to increase considerably the estimates of the value of snail meal as a
poultry and livestock supplemental feed. The variation in the assays
of snails collected in different environments suggests that a series of
experiments should be set up to determine, among other things,
what environmental conditions predispose the maximum production
of lysine. Sekine (1926) has not only demonstrated the presence of
lysine in the marine bivalve Meretrix meretrix but has determined
that it is almost 1f times the amount in meal made of the salmon,
Oncorhynchus mason.
It is not enough to demonstrate that certain amino acids are pres-
ent in desirable amounts. There still remains the question as to
whether or not growing animals will actually respond properly to a
diet in which the protein item consists largely or entirely of snail
meal. This properly implies that other growth-promoting factors,
not yet determined, would be allowed to come into effect under such
conditions. Just such investigations as these are currently in progress
at the University of Arizona, with day-old chicks as the experimental
animals. Attempts will be made to determine the most effective way
in which to incorporate the meal into chicken feed and to detect any
possible idiosyncrasy that the chickens might have to the snail meal.
In the chick feeding tests, a comparison will be made between snail
meal and other sources of animal protein, such as blood meal and
fish meal. A. F. Caldwell of the University of Malaya gives some
interesting information (in. litt. April 23, 1953) regarding the re-
sponse of ducks to a diet of snails. He states, "I did notice that the
addition of snails to the diet had a bearing on egg production; in dry
weather when the snails retreated to hide outs egg production fell,
but increased again as soon as they were given snails." H. A. A. M.
Wirtz of Java independently offered essentially identical informa-
tion. Along this same line, Fronda (1919) and Frigillana (1923) in
the Philippine Islands reported that when their experimental
chickens were fed ground and boiled snails (probably the freshwater
snails Vivipara and Pila according to Talavera and Faustino 1933),
there was a marked increase in the number and size of the eggs and
the weight of the chickens as compared to chickens on substitute
diets of copra meal, "palay" (unhulled rice), or cowpeas. Geseco
(1921) obtained similar results with ducks. Because the snails were
periodically difficult to obtain, Cruz (1932) attempted to find a sub-
CONTROL THROUGH HUMAN USE	167
stitute. On the basis of cost, shrimp meal was recommended. But
now that the people in the Philippines have a free source of A. fulica,
it is quite likely that giant African snail meal is currently being used.
          Food for Livestock  According to Kalshoven (1950), Djaenoe-
din (1942) has recommended that the giant snails be incorporated
into the daily rations of pigs. The value of fortifying their diet with
snail meal can be predicted on the basis of the present experiments
with chicks. The same goes for other livestock and pet feeds.
Wilson Savory of Chichi Jima stated that his pigs would take to
the live snails quite as readily as they would to the boiled and
chopped ones. In contrast, Frank L. Brown of Rota failed to per-
suade his pigs to eat the live snails, even after considerable fasting,
although they would eat them if they were cooked. Father H. F.
Costigan of Kolonia, Ponape, regularly fed his pigs on small cooked
achatinas left in the shell and mixed with other food. In Tinian, a
farmer was seen to feed his pigs boiled achatinas which had been
removed from the shells (Chamberlin 1952a). In no case were the
snails eaten avidly nor were the larger specimens consumed unless
they were crushed or removed from the shells.
Garnadi (1951) states that the surgeon of the Veterinary Institute
of Bogor determined that pigs put on a diet entirely of giant snails
lost weight but showed no signs of sickness.
          Fish Bait  Using the giant snails as salt-water fish bait in pre-
liminary experiments in Saipan did not prove encouraging (Jones
1949). Living edible European snails, however, are being used as
freshwater fish bait in the United States (Ingrain 1952). If the num-
bers sold for this purpose are any criterion, they must be good. The
raw flesh of the Philippine pond snail Pila luzonica Reeve is re-
portedly used as a bait for line fishing (Talavera and Faustino 1933).
          Fertilizer  In spite of the fact that primitive peoples all over
the world have made use of disintegrating animal flesh to replenish
the plant-growth-promoting constituents in depleted soils, the sur-
vey of the giant African snail problem in Micronesia failed to reveal
any extensive use of A. fulica for this purpose. The people of Chichi
Jima were the only ones observed at that time to be making direct
use of the giant snail in this manner. There they collected mostly the
small, thin-shelled snails in metal oil drums. These were allowed to
stand in the hot sun until the snails died and had reached a high
degree of putrefaction. These rotting, maggot-infested snails were
then scooped out, the shells were crushed, and the putrid, slimy,
odoriferous mess was added as a fertilizer to young vegetable plants.
The reason for the generally better quality of the crops in Chichi
168	CONTROL THROUGH HUMAN USE
Jima, as compared with other areas, rests at least in part in the use of
snail fertilizer. Its use in this case, however, introduced two pro-
nounced disadvantages. The inadequately covered oil drums per-
mitted escape of the fly maggots as a threat to public health, and the
addition of the crushed shells to the soil moved the soil pH even
more strongly in a basic direction. More recently, the latter disad-
vantage has been eliminated in the similar use of snail fertilizer in
Guam in that only the "liquor" is drawn off and diluted with ten
parts of water before being added to the soil (Peterson 1957b).
In areas where the soil is excessively acid, as is the case in humus
soils of forests, the alkalizing effect of adding crushed shells would of
course be desirable as far as most crops are concerned. But converse-
ly, coralline soils are already excessively basic and should not have
more calcareous material added to them. This suggests immediately
that if there is ever commercial use of the giant snails in fertilizers,
two different kinds should be made available—one with, and one
without shell fragments. One thing is certain, the thin, quickly
leached soils of tropical areas need enriching of some sort if they are
to be used for much more than two or three years. Where this is not
possible, the natives abandon the plot, burn off another portion of
the forested area and use that until the soil nutrients in turn are de-
pleted. All too often the abandoned land is soon taken over by
sword grass (Miscanthus) or some other noxious plant with little
chance, for a long time, of the land being recovered again for crops.
         Production of Snail Meal   The practicability of producing
fertilizer from the giant African snail is in most respects on a par
with that of producing the supplemental feeds. In both cases, it would
be desirable to dehydrate the snails and reduce them to a powder or
meal. In this form it could be stored and used when needed either as
a fertilizer or a feed supplement. The big question at this point is
not whether the snail meal has value in either of the categories. The
relatively high percentages of phosphate and lysine quickly answer
that question. The real question is: "How dependable is the source
of supply?" An examination of the reports in the literature and an
examination of an invading population would tend to convince one
that the snails are present in inexhaustible numbers. This is mislead-
ing. In any given area, irrespective of the abundance of the snails, an
intensive collecting campaign will remove in a relatively short time
so many snails that no further specimens can be found even with
diligent hunting. Experience has demonstrated over and over again,
however, that eradication is not thereby effected. In a year or two the
residual snail population builds up in appreciable numbers once
CONTROL THROUGH HUMAN USE	169
again (unless the phenomenon of population decline comes into the
picture, vide infra). This almost automatically suggests that perhaps
a system of ''harvesting" the snails could be set up wherein the col-
lecting could be rotated from one area to another on a long enough
program so that population recovery could take place before rehar-
vesting.
Let us assume that the island, or region of the mainland, and the
snail population are large enough for such a system of harvesting.
There still remains the problem of labor. Native help could be en-
listed. With the coconut tree actually or virtually wiped out on a
number of the Micronesian islands, and with no chance of reviving
trade in the Japanese-introduced sugar cane, the Micronesians in
many cases are hard put to find some means of providing for their
needs. In such areas, collecting and selling the ubiquitous giant
African snail could be a welcome source of native income. In some
other areas, however, attempting to enlist the help of the native
people would not be altogether easy, for the pay might not be suffi-
ciently high to arouse their interest. But in past times in a number of
areas where only a very modest bounty could be offered for the snails
during their initial build-up, considerable native help was obtained.
The "emergency" nature of the situation at that time and possible
elements of conscription may help explain the co-operation that was
obtained. In a regular program of harvesting the snails, however,
these persuasive factors would not be present. Nonetheless, since the
native people will be collecting the snails in their garden plots as the
most effective and most inexpensive means of controlling them, for a
modest fee they could be persuaded to bring them into a common
collecting place instead of trying to destroy them at an often even
greater expenditure of energy.
Let us suppose further that, through the means indicated, suffi-
cient snails are brought into a centrally located processing plant to
keep it in indefinite operation. There still must be worked out an
economically feasible processing program in which at least some of
the snails would be removed from their shells before they are de-
hydrated. Developing an economical method of dehydration, avoid-
ing chemical decomposition with excessively high temperatures,
avoiding maceration with insufficiently high temperatures, and
maintaining dehydration in storage, are only a few of the problems
which would have to be met. And even with these out of the way,
there still remains the problem of marketing the snail meal on a com-
mercial basis. This problem is sufficiently great in the minds of some
investigators to cause them to reject summarily the whole idea of
170	CONTROL THROUGH HUMAN USE
attempting to make use of the snail meal. They state: "With shipping
rates as high as they are, how can you ever hope to market snail meal
in this country at a price which will permit it to compete successfully
with other animal protein sources?" But it is not in this country
that the greatest critical shortage of animal protein food supple-
ments exists. Ironically enough, it is right in the areas where the
snails abound that there is the greatest need! As a case in point, in
Guam in 1949 eggs sold for $2.50 per dozen and chickens sold for
$3.00-4.00. The high cost and scarcity of imported chicken feeds
were given as two of the major reasons for these exorbitant prices.
Yet right on that island there are tons of giant snails, living, dying,
and going to waste. Marketing should be no problem there or in any
comparable area. The possibility of marketing the meal on a large
scale commercially not only seems remote, but the present need for it
is questionable. Local demand alone should take care of the supply.
In regions where lime is in demand, the achatina shells could be re-
duced in lime kilns as a by-product in the preparation of the snail
meal. The shells of Melania and Corbicula are apparently being used
in this manner in Malaysia (Benthem Jutting 1948:137).
It is a paradox indeed that these snails are forming from un-
wanted rotting and decaying materials a very rich source of protein
for which there is a continually growing need both as a poultry feed
supplement and a fertilizer, and yet next to no direct use is being
made of them. More than that, current methods of control call for
their destruction with no apparent thought given to their utilization.
There has been a definite hesitancy, on the part of many who are con-
cerned with the control of the giant snail, to prescribe any measure
which would in any way make, or even suggest, a use for the snails.
The reason for this undoubtedly rests in the fears reflected in the
words of the first major survey report coming out of the Pacific after
World War II, viz., "...if any persons found the snail a benefit,
others would be tempted to introduce it elsewhere, regardless of the
common good. It might, therefore, be unwise to try to develop uses
for it." (Townes 1946; cf. Rees 1950:586). It cannot be denied that
the warning is a sound one; but it has had an inordinate effect upon
subsequent control programs. There is considerable doubt in the
minds of some that any really appreciable spread of A. fulica would
result from finding a use for it. On the contrary, finding a use for it
could be responsible for reducing the population to the point where
the snails would practically cease to be a problem. It is the great mul-
tiplicity factor which largely causes them to be branded as a pest.
But, whether or not any use is found for them, the snails will con-
CONTROL THROUGH HUMAN USE	171
tinue to spread into new areas, in spite of all efforts to the contrary.
If they are going to spread, why not enlist the interest of man to
help keep their numbers down to the point where they are not a
serious problem? Man always has been at the head of the list of
known enemies of the giant snail. It is almost completely impossible
to try to teach man, in the recently invaded areas, to eat the snails;
but at least he can be taught to make indirect use of them toward his
own benefit. In this manner, the snail could be a blessing rather than
a curse (Mead 1953b, 1955b). Apropos of this, much attention is cur-
rently being given to various invertebrates as possible natural sources
of highly complex organic compounds, a development which holds
great promise for the fields of medicine and organic chemistry.
CHAPTER 9
CONTROL
THROUGH
LEGISLATIVE
ACTION
Ever since the very earliest stages in the spread of Achatina
fulica from its East African homeland, there have been various edicts
and decrees urging or demanding that the local people co-operate
in collecting the snail specimens and assist in preventing their spread
into uninfested areas. Some investigators (e.g., Corbett 1933) in addi-
tion suggested that all foreign plants be subject to inspection before
entering the country. By and large, these early measures were only
of transitory, if any, effect, largely through the fact that it requires
much more than regulations to stem the tide of this giant snail pest.
Forcible and effective quarantine regulations against A. fulica were
not promulgated until 1936. Early in May of that year, it was decided
by the Ministry of Agriculture and Forestry in Japan that this snail
had clearly earned for itself in Formosa the reputation of being a
serious pest. Forthwith there were set up emergency regulations which
permitted the confiscation not only of all specimens entering Japan,
but of all living specimens in the country at that time (Pemberton
et al. 1939, Esaki and Takahashi 1942). A concerted program of
propagandizing the imagined medicinal properties of these snails had
succeeded, in the years previous to that, in spreading them into many
areas. The thoroughness with which the regulations were carried out,
and probably to a lesser extent the severity of the winters in Japan,
together stamped out all sign of the giant snail. There is today no
evidence of its having become established in that country. This is the
172
CONTROL THROUGH LEGISLATIVE ACTION	173
only instance known where A. fulica has gained entrance to an area
and has been completely eliminated. It should be kept in mind,
however, that because these snails were cherished and coveted right
up to the time they were banned, they never actually became "estab-
lished" in the real sense of the word.
Such, unfortunately, is not the history of the Hawaiian infestation.
Two-year-old populations of the giant snail were discovered in both
Maui and Oahu in November, 1938 (Pemberton 1938, Mead 1949b).
Every effort was made to stamp out these infestations and, for a while,
it seemed that the snail had been eradicated. In fact, eradication was
announced by several prominent papers dealing with this subject.
But it was the same old story all over again. Live individuals were
continually found in the areas of the original infestation. Persistent
control measures (costing in excess of $200,000) coupled with stringent
quarantine regulations, with heavy penalties for people caught trans-
porting the snails or even having them in their possession, did succeed
in keeping the infestations pretty well corralled until 1951 (Fullaway
1943). In that year, a number of new loci were discovered, in both
Oahu and Maui, in some cases miles from the original site of infesta-
tion (Wong 1951). These discoveries have made intra-island quaran-
tines essentially impractical and have moved one government official
to state, "We simply do not have the money to resort to measures
approaching eradication. We have the snail in such quantities on
Oahu today and it is in so many places that it now becomes a matter
of individual control and not a possible function of the Government
—just like exotic weeds and insect pests in wide variety." Inter-island
quarantines, on the other hand, were successful in preventing the
spread of A. fulica to any of the other islands in the Hawaiian chain
for a period of twenty years. The discovery of established infestations
on the islands of Hawaii and Kauai in 1958, however, clearly dem-
onstrated once again that in spite of the best quarantine regulations
this pest may be able eventually to effect a breakthrough.
Shortly after the inception of the Trust Territory of the Pacific
Islands, a set of basic quarantine regulations was drawn up to limit
as much as possible any further spread of plant pests, including the
giant African snail (U.S. Navy 1950, Pemberton 1954). These have
provided the authority for the promulgation of numerous specific
quarantine regulations and controls, a general policy for which is dis-
cussed by Bryan (1949) and Cooley (1950) (cf. 1CCM 1947, 1948).
Subsequently, the Philippine government set up comparable regu-
lations imposing fines and/or imprisonment for offenders (Pangga
1947).
174	CONTROL THROUGH LEGISLATIVE ACTION
In the United States, California has had for a number of years
specific quarantine regulations covering the threat of introducing
snail pests. For over thirty years, that state has been battling foreign
snails at a cost of over $500,000. During this time, only one of four
introduced helicines, Theba pisana, is believed finally to be eradi-
cated (Armitage 1949) in spite of notes in the literature to the con-
trary (usbepq 1953). Finding as many as 3,000 specimens on a single
orange tree is a good index of the seriousness of the problem that this
species has presented (Gammon 1943). Attempts by the state to con-
trol two of the other helicines, Helix aspersa and Otala lac tea., have
been considered impractical because they have become too thorough-
ly established in many different areas (Messenger 1950). The fourth
helicine, Helix aperta, has a narrow but firm toehold in the San Diego
area. Concerted efforts are still being made to eradicate this snail.
Its habit of retreating deep underground for long periods of time,
however, has so far frustrated every attempt. California border and
port quarantine inspectors have for years periodically intercepted
shipments of these and other species of potentially harmful snails. For
example, in July, 1951, 122 cases of living H. aperta from Tunisia
were intercepted at one of California's border stations after passing
through New York as a port of entry (Messenger in litt. July 13, 1959).
Experience of this sort, coupled with considerably more experience
with introduced, pestiferous insects, mammals, and birds, has moved
such investigators in California as Storer (1931, 1934, 1949) and
Hanna (1939, 1948) to take an unequivocal stand against introduc-
tion of foreign animals. In fact, it was these two investigators who
were responsible for bringing to the attention of the proper author-
ities the fact that two specimens of the largest of all land snails,
Achatina achatina were to be found alive in California (Dickson 1946,
Hanna 1948, Mead 1949b). These two specimens and all their eggs
were quickly destroyed. But this incident in addition to the sudden
interception of about fifty live specimens of A. fulica during Cali-
fornia port inspection of war salvage material in 1947 (Messenger
1947) speedily put California's well-organized quarantine service in-
to high gear. And in spite of the fact that, since 1947, over ninety live
specimens of A. fulica have been intercepted in California ports, this
snail pest has never become established in the slightest, reports in the
literature to the contrary notwithstanding. Unfortunately, the cam-
paign in Southern California to eradicate O. lac tea in 1951 caused
many to believe that A. fulica had at last become established in Cali-
fornia, as newspapers referred to O. lac tea as the "African Snail" and
the "striped African Snail."
CONTROL THROUGH LEGISLATIVE ACTION	175
Not only has there been a redoubling of effort in California to
detect the possible presence of the giant snails in cargoes, but rigorous
steps are taken when the snails are found. The holds are fumigated
with methyl bromide or hydrocyanic gas. Infested war salvage equip-
ment, and such other equipment that can stand it, are treated with
KOH or NaOH in live steam (Messenger 1952). During the years
1949, 1950, and 1951, six, eight, and twelve interceptions, respectively,
were made in California ports (Messenger 1949-51). An explanation
for this increase, according to Messenger (in litt. July 8, 1952), is
found possibly in the fact that war salvage material from the Mariana
Islands was being obtained from areas deeper and deeper into the
bush where prolonged overgrowth with vegetation provided more
suitable retreats for the giant snails. In the years 1952 through 1958,
the interceptions were 5, 8, 0, 0, 0, 1, and 0, respectively (Messenger
1952-54, Messenger and Breech 1958). At this writing, there have
been reported no interceptions of A. fulica in California in 1959 and
1960. The reduction in interceptions undoubtedly finds its explana-
tion in the fact that there has been a commensurate reduction in,
and finally a virtual discontinuance of, the process of bringing war
salvage material into United States ports. To a much lesser extent,
the marked decline in the snail populations in the infested areas may
be having its effect.
Chapter 49 of the Arizona Code amply provides for measures to
meet the threat of introducing foreign snails. California and Arizona,
then, are the only two states which have quarantines so designed that
snails can be excluded. In contrast, before 1951, the federal quaran-
tine regulations lacked any provision for prohibiting the entry of
snails. These facts were pointed out by Mead (I949b, c, e) and the
danger inherent in such a setup was emphasized. With this, the U.S.
Public Health Service issued orders for its inspectors to assist the
usda plant quarantine inspectors in their attempts to intercept the
giant snail. Legally, however, this could not be enforced as the usphs
Regulation 71.156 provides only for an "animal . . . vector of human
disease or any . . . animal . . . capable of being a vector of human
disease." In addition to all the depredations of the giant snails, they
cannot so far be justly accused of being vectors of human disease.
Morgenstern (1949) most unfortunately was confused on this point.
The fact that the dying snails form potent sources for the breeding
of disease-carrying flies provided the only tangible connection with
public health, but this was so tenuous that it could not conceivably
be embraced by the existing regulations.
Photostat copies of Mead's article (1949b) were sent by the U.S.
176	CONTROL THROUGH LEGISLATIVE ACTION
Army to personnel in snail-infested areas in the Pacific islands in an
effort to reduce the spread of the snail in those areas and minimize
the chances of the snail's showing up on army equipment returned to
the States. Such steps as these could at best be only temporary expe-
dients. Interceptions of the giant African snails in other ports of the
United States added further emphasis to this point. After a single live
giant snail specimen was found in San Diego on a ship carrying war
surplus from Manila, a message of warning was sent ahead of the
north-bound ship to San Francisco, Portland, Seattle, and Vancouver.
The alerted inspectors in Vancouver found eight more snails in the
cargo; fortunately, all of the specimens were dead (Gardiner 1949,
Zuk 1949). Another ship carrying 8,000 tons of war salvage material
from the Pacific was found in Baltimore, Maryland, to be snail in-
fested. The inspectors sought and received the co-operation of the
importers, and recommendations to fumigate the entire cargo with
HCN gas were carried out (Brubaker 1950). But it cost the importers
$22,500! The giant snails were found on still another ship in that same
year of 1949 in Newark, New Jersey. An accidental fire brought a
quick solution to the problem by destroying the cargo—and the snails.
In 1950, snails were found in the cargo of a ship landing at New
Orleans, Louisiana, (cf. McCrory 1950). The following year, a ship-
load of scrap metal from Guam was similarly found infested with the
giant snail in Portland, Oregon, and was fumigated before it was
discharged (Burch 1951).
With the American public now informed (and in some cases, un-
fortunately, misinformed) by the publicity given in scientific journals,
magazines, and newspapers to the problem of the giant African snail,
definite steps were taken to set up legislation empowering the Depart-
ment of Agriculture to prohibit entry of this snail. Representative
Wingate Lucas, in response to the urging of the people of Texas, was
the first to start such action. On the basis of an original inquiry di-
rected to the author, it was decided by Lucas to introduce bill HR
6242 in the 81st Congress on September 27, 1949 and it was imme-
diately referred to the Committee on Agriculture. The wording of
the bill, however, was unfortunately such that only A. fulica would
be excluded. Any person acquainted in the slightest with the giant
African snails knows that any one of the many species in that big
group probably has the potentiality of becoming as serious a pest as
A. fulica. Immediate but unsuccessful attempts were made to obtain
a rewording of the bill (Mead 1950b:44). It was agreed by many that
the bill as it stood would at least meet the immediate problem at
hand. Others frankly feared the bill was a hasty outgrowth of a ''snail
panic" and that it would bring undesirable legislation (cf. Anon.
CONTROL THROUGH LEGISLATIVE ACTION	177
1949b). Nine months later (June 28, 1950), Representative Harold
D. Cooley, chairman of the Committee on Agriculture, released HR
6242 from committee without amendment. His Report No. 2363
carried an indorsement of approval both from his committee and
K. T. Hutchinson, assistant secretary of agriculture. After passing to
the Committee of the Whole House on the State of the Union, it was
read before the House and passed without amendment on July 27,
1950. The following day it was read before the Senate and referred
to the Committee on Agriculture and Forestry. Four months later
(November 29, 1950), Senator Elmer Thomas reported back to the
Senate from this committee and recommended (Report No. 2583)
that HR 6242 be passed without amendment. In spite of this recom-
mendation, Senator B. R. Maybank proposed an amendment (cf.
Cong. Rec. 96[12]: 16621) to this bill and it was passed by the Senate.
The title of the bill was changed to "An Act to Amend the Agricul-
tural Adjustment Act of 1938, as Amended, and to Prevent the Entry
of Giant Snails into the United States, and for Other Purposes." The
bill, in this hybridized form, quite understandably failed to receive
favorable action and died in the House during the last-minute rush
of the 81st Congress. This meant starting all over again.
This time, however, the author solicited the help of senate majority
leader E. W. McFarland as well as that of Representative Lucas. The
wording of the old bill was revised to include "any terrestrial or
fresh-water mollusk." It was introduced as S 1489 to the Senate on
May 15, 1951 by Senator McFarland and referred immediately to
the Committee on Agriculture and Forestry. On August 9, 1951,
Senator Ellender of this committee submitted a report (No. 628)
indicating that this bill had the approval of Secretary of Agriculture
C. F. Brannan and recommending that it be passed without amend-
ment. An identically worded bill was introduced as HR 4443 to the
House on June 13, 1951 by Representative Lucas and referred to
the Committee on Agriculture. Once again, Representative Cooley
of that committee reported back on the bill, recommending on August
7, 1951 that it be passed without amendment. His report (No. 800)
carried a message of approval from Acting Secretary of Agriculture
C. J. McCormick. The bill was read before the House on August 20,
1951 and passed without amendment. A week later, S 1489 came up
for reading in the Senate and it was agreed to substitute HR 4443
and to pass it without amendment. On September 12, 1951, HR 4443
was signed by both the Vice-President and the Speaker of the House.
Ten days later, it was signed by President Truman and became
Public Law 152 of the 82d Congress (cf. Smith 1951, Burch 1952b).
Under this new authority, the Secretary of Agriculture was em-
178	CONTROL THROUGH LEGISLATIVE ACTION
powered to draw up regulations controlling the entry of mollusks in
this country. Advice was sought from many persons, agencies, and
institutions during their preparation. Acting Secretary of Agriculture
K. T. Hutchinson published on July 25, 1952 a notice of the proposed
regulations and copies were sent to the sources of advice for criticism
and suggestions. The revised regulations were published by Acting
Secretary of Agriculture C. J. McCormick on October 22, 1952 and
became effective that date (Anon. 1953b). The following quotation
from McCormick (Cooley and McCormick 1951) explains how this
"snail legislation" will fit into the long-range plans of the Department
of Agriculture: "A study is now being made by the Interdepartmental
Committee on Pest Control of proposed legislation which would en-
compass a much wider field than is covered in HR 4448. This pro-
posed legislation will probably include provisions for control of such
plant pests as worms, insects, nematodes, slugs, and snails, any form
of protozoa, fungi, bacteria, or other living parasitic plants, any living
viruses, and similar or allied organisms, which can directly or in-
directly injure or cause disease in plants or parts thereof. It will
require considerable time to complete the studies which are being
made with respect to such legislation. . . ." The existing regulations,
however, will not just function in an interim fashion but will reveal
through actual application just what is really needed in the proposed
more extensive legislation.
With the assistance of the publications of Ling (1952, 1954) and
the FAO Plant Protection Bulletin, a cursory check was made of
abstracts of the plant quarantine regulations of somewhat over one
hundred governments. Slightly less than 3 per cent, that is, only three
governments, viz., the Republic of the Philippines, Union of South
Africa, and the United States of America (Anon. 1953b) were listed
as making specific mention of "mollusks" among the animals pro-
hibited or restricted. Less than 8 per cent of the total were listed as
having an "invertebrate" clause to cover agricultural pests other than
insects, thus technically embracing the mollusks. The countries in-
cluded were: Canada, Ceylon, Chile, Kenya, New Zealand, Sudan,
Trinidad and Tobago, and Uganda Protectorate. Nine other coun-
tries, the greater share of which are small island governments, had
vague, all-inclusive clauses which presumably would give them the
authority for excluding harmful mollusks (e.g., "and other small
animals," "organisms or other agents," 'living pests in any stage,"
"any object carrying an injurious pest," and so forth). But over 80
per cent of the governments listed had little more in their regulations
than the restriction and prohibition of certain specific pests and dis-
eases without any clause worded broadly enough, apparently, to pro-
CONTROL THROUGH  LEGISLATIVE ACTION	179
vide authority for the exclusion of harmful mollusks. It can be seen
from this survey that the vast majority of the governments have neither
given consideration to the problem of excluding molluscan pests,
actual or potential, nor prepared themselves for such an eventuality.
With respect to A. fulica, the quarantine picture is much less clear
in other countries. In England, Sir W. Wakefield especially has been
concerned about the threat of the giant snail in the colonies and has
brought the matter to the attention of Parliament (Anon. 1949d).
In Australia, T. H. Harrison (1951) reported that two interceptions
of A. fulica in Sidney taught them that their regulations were inad-
equate; hence there was passed Statutory Rule 1948, No. 92, which
authorizes the inspectors to follow produce to the warehouses if neces-
sary to intercept the snails. Quarantine inspection of imports is also
effective in Sarawak, according to Tom Harrisson of the Sarawak
Museum (in litt. Aug. 25, 1952). Internal quarantines on the other
hand present quite a different problem as indicated in Harrisson's
words, "Control within the country is quite impracticable as com-
munications are by water in thousands of small craft often carrying
leaf-thatch, vegetables, etc." In reports and correspondence, similar
reasons are given for the lack of specific quarantine regulations for
this snail in India, Indonesia, Malaya, and the Seychelles Islands.
Some (e.g., Anon. 1948c) have insisted that definite steps should
be taken in the infested areas to force the people to collect the snails
by hand and destroy them. Although large-scale collections of this
sort produce a discernible effect upon the snail population, they are
only ameliorative and transient, and most certainly do not warrant
the sizable expenditures of governmental funds that have been made
in past times—especially during snail population build-up. As the only
inexpensive means available of controlling the snails, the people
should be ''urged" to collect and destroy them in their own areas;
but attempting to exert force along this line through legislation would
be advisable in only the most unusual cases.
One thing is certain about quarantine regulations: Snails cannot
be legislated out of existence. At best, quarantines may delay indefi-
nitely the entry of the snail pest. The more carefully the quarantines
are thought through and carried out, the more effective will be the
barrier and delaying action. As in all good quarantines, even though
there is no guarantee of permanent exclusion of the pest, there is
provided more time—"borrowed time"—in which to develop more
effective controls and perhaps even eradicative measures that do not
now exist. In this way, external quarantines, and in some cases internal
quarantines, can be effective and practicable. Thus they warrant
serious consideration in any long-range planning.
CHAPTER  10
POPULATION
DECLINE
The phenomenon of population decline in Achatina fulica
was first reported upon by Green (1910c, 1911b) in Ceylon. At the
present stage of our investigations, the following words of Green seem
to be almost prognosticative: "A newly introduced pest usually in-
creases out of all due proportion during the first few years of its exist-
ence in a new country, after which it gradually reverts to more normal
conditions, There are already indications that this process is taking
place locally. The particular village [Halawegoda] in which the pest
is said to have originated, is at the present time not nearly so thickly
infested as are some of the neighbouring villages to which the pest
has since spread. A similar levelling process has apparently occurred
in other countries into which this snail has been introduced." In spite
of the early date in which these ideas were advanced, and the clarity
with which they were presented, the literature has been essentially
devoid of any reference to the phenomenon of population decline un-
til the past few years. In discussing the introduction of the giant toad
Bufo marinus, Townes (1946) significantly pointed out that the pop-
ulations of this predator dwindled after an initial build-up and that
the average size of the animal diminished. Williams (1951) learned
in Zanzibar that the several species of Achatina on that island years
ago caused damage to crops but that now the farmers pay little heed
to them.
It was the words of Green that persuaded the author in 1949 to
write to a number of investigators to inquire about the status quo
of the problem in the areas where A. fulica had been established the
longest. Although there were differences of opinion expressed in the
180
POPULATION DECLINE	181
response, even from different people in the same area, by far the ma-
jority indicated that there has been noticed in recent years a definite
reduction in the number of the snails and, therefore, in the problem
itself. Several people, apparently independently, observed that the
decline was noticeable in the older populations, but that the newer
populations were just as vigorous and damaging as the older popula-
tions had been in their early stages. A few reported conditions sug-
gesting an essential decimation of the snail population apparently
through the effect of some grossly adverse factor. Most of these reports
came from correspondents in Ceylon. In New Britain, however, G. S.
Dun (in litt. Nov. 5, 1951) stated that in Kavieng the giant snails used
to be very abundant, that recently they have decreased so in numbers
that vegetables can once again be grown, and that "high piles of
moribund snails" have been encountered.
Two main facts, then, came to the fore in these reports, viz., that
population decline in A. fulica is actually in process at least in some
areas, and that an unfavorable factor or combination of factors is
responsible for a catastrophic effect upon certain populations. It was
eminently apparent that a thorough investigation of the phenomenon
of population decline was needed. Because of the preponderance of
positive reports from Ceylon, because the infestation in that country
was over fifty years old, and because the majority of known predators
of this snail was in that country, a proposal was made to set up in
that area an extensive research project. This project was conducted
by the author under a grant (NSF-G519) from the National Science
Foundation, Washington, D.C., for a period of nine months in 1954.
A preliminary survey in Ceylon quickly verified the earlier reports
of population decline. In fact, populations were found in surprisingly
great variety. Some, such as those in Dambana and Balangoda, were
in the early fulminating stage. Others had been in progress for thirty
to fifty years and were either stabilized, declining, or apparently ex-
tinct. When all information was pieced together, a generalized pic-
ture of the population "life cycle" took shape. After firm, unobtrusive,
insidious establishment, the giant snail appears almost explosively
in great numbers. This is revealed by the fact that first announcements
of newly discovered populations are usually made in an urgent, al-
most frantic manner with descriptions depicting snails literally all
over the place. The numbers continue to build up despite control
measures in various combinations. The population then seems to
stabilize at a high level for an indefinite period of time. At this time,
poisoning campaigns in some cases paradoxically seem to favor further
build-up of the snail. Ultimately a gradual population decline takes
182	POPULATION DECLINE
place. Although there are subsequent periods of recrudescence, after
a certain stage the population rarely or perhaps never attains the
level of the first peak. With this progressive decline in numbers, there
is a concomitant decline in the average size of the individual snails
so that instead of a population of true "giant" forms from 4-6 inches,
they may be quite modest-appearing forms, ranging from 3-4 1/2 inches.
In some cases, however, the population may go into a sudden, un-
predictable, and pronounced slump with the result that live speci-
mens can be found only after prolonged hunting, or not at all. More
than a simple decline is obviously involved in these latter cases.
Somehow the decline has been augmented and intensified until ex-
tinction or near-extinction has occurred. Herein lies the very heart
of the problem of population control.
The problem of attempting to determine the causal factors in the
phenomenon of decline is not going to be an easy one; for it is an
ecological problem, and ecological problems are notoriously com-
plex. Several different areas of investigation have been suggested as
an approach to the problem. These are treated under separate head-
ings below.
Population Senility  Some investigators have attributed de-
cline in the populations of the giant snail to a mythical "population
senility." In so doing, they merely beg the question; for in effect they
have done nothing more than give an ambiguous term to the phe-
nomenon (Mead 1955b). To assume that all populations will eventu-
ally go into a state of senility and reduced vigor does not get to the
matter of causation.
Sterility  On some occasions in the past, investigators have en-
countered situations wherein, even with diligent hunting, not a
single mature snail specimen could be found in the gravid state. Both
Kondo and the author have examined snail populations in the Pacific
reflecting this characteristic (e.g., the Auluptagel population in the
Palau Islands). In attempting to find an explanation for this, some
have assumed that a physiological process of sterility had entered the
picture and was effecting a population decline through reduced
fecundity. The apparently favorable nature of the environmental
conditions, however, may have been misleading; for unsuspected fac-
tors may have been responsible for precipitating a perfectly normal,
temporary period of generalized reproductive inactivity.
There probably is a decline in the reproductive capacity of older
individuals in any population; but this, by itself, cannot explain
population decline. In the gigantic individuals, which may not neces-
sarily be gerontic, there is fair evidence of sterility. A correlation be-
POPULATION DECLINE	183
tween gigantism and sterility in mollusks has been emphasized by
Pfeffer (1928). This same correlation has been offered to explain the
fact that gigantic forms of A. fulica not infrequently appear in the
early sigmoid growth stage of the population, but quickly disappear,
never to be seen again. It perhaps is therefore relevant that Kondo
(1952) found gigantic individuals most prominently at the "fore-
front" of the Laguna population in Guam.
There has been found in neither the field nor the laboratory any
evidence of sterility through metazoan parasitism  (cf. Szidat 1941).
Starvation  Chamberlin (1952a) concluded in his ecological
study of A. fulica on Tinian that starvation was the main cause for
the great number of dead shells found on that island. Although this
same idea previously had been less positively expressed (Mead 1950b,
c), it would seem now, in view of the catholic appetite of this snail
and its faculty for withstanding for a long time complete lack of
food, that starvation could not possibly explain population decline
except in limited cases under most unusual circumstances. The same
reasoning would apply to the matter of nutritional deficiences, includ-
ing the very important calcium. As a contributory factor, starvation
could have its effect; but alone, it would not be generally decisive.
Exposure  Practically without exception, the investigators
who have made and reported upon a survey of the problem of the
giant African snail have emphasized the apparently high incidence of
death by exposure to direct sunlight. This point has been elaborated
upon above. Under the prevailing conditions in most infested areas,
it is not understandable how this factor could have anything more
than an incidental effect except in cases of severe overcrowding in
marginal areas. And even in the latter cases, the factor would be self-
limiting. The fact remains, however, that there appears to be an in-
ordinate amount of death by this means in some areas. As a possible
explanation, an unknown second factor may be contributing to their
general unthriftiness causing them to make a less vigorous, and there-
fore less effective, escape from adverse conditions.
Traumatic Breaks  Snails inhabiting rough, rocky terrain are
found in a high percentage of the cases to have shells which have been
broken and mended and broken and remended. The unsightly ap-
pearance of these snails has encouraged some observers to conclude
that they were unthrifty and hence were giving way to a population
decline. Later, it was suggested that some "other factor," such as a
genetic, a pathological, or a nutritional factor, was present to produce
the thin, brittle shells which in turn were more prone to fatal or
traumatic breaks. But whatever the explanation, the manifest ability
184	POPULATION DECLINE
to withstand even severe breaks and the high reproductive potential
in this species surely prevent traumatic breaks from producing a
decline effect upon the population. In fact, some of the most vigor-
ous populations examined in the Pacific islands were of this fragile,
broken-shell type.
Predators  Because the predators are the most tangible of the
unfavorable factors in the environment of the giant snail, they have
been seized upon by both the casual observer and the professional in-
vestigator as the most likely factors in effecting the observed decline.
The Indian glowworm, for example, is believed by many to be largely
if not entirely responsible for the fact that A. fulica is now not nearly
the pest that it used to be in the areas where this predator is endemic.
It is true that the glowworm is obviously more common in some in-
fested endemic areas than it ever could have been without the giant
snail. A distinction between cause and effect, however, has not been
made. Nonetheless, this predator and other predators believed to be
capable of holding A. fulica into at least a simulated state of popula-
tion decline have been used, and will continue to be used, as poten-
tial agents of biological control in non-endemic areas. That they will
accomplish their mission remains today a moot question indeed. But
irrespective of this point, there is still the fact that population decline
is manifesting itself in areas where predators are either unknown or
nonexistent. Undoubtedly the majority of investigators feel that
predators could have an appreciable augmenting effect in the phe-
nomenon of decline, but that predators, by themselves, are not re-
sponsible for the current widespread decline in the populations of
the giant snail.
Genetics  The subject of genetics and its possible relation to
the unthrifty nature of some giant snail populations, and therefore to
population decline, was first introduced by Mead and Kondo (1949).
Subsequent reports by these authors presented further evidence from
the field in support of a genetic rather than ecologic explanation for
some of the observed phenomena and emphasized the need for a
genetic study of this snail species. Variations in individuals, and in
populations in particular, were explained on the basis of possible
genetic origin. Some of these variations, such as the malformed speci-
mens (roughly in a 1:3 ratio!) in the Army Hill population in Sai-
pan, have been interpreted by some observers as indubitable signs of
population degeneration and decline. If the explanation is a genetic
one, as suggested above in the discussion of variations, then the vari-
ations would contribute to population decline only if they interfered
with the normal development of the population. As pointed out
POPULATION DECLINE	185
above, gigantic forms show signs of being reproductively sterile. A
genetic linkage between gigantism and sterility would have a quali-
tatively modifying effect upon the development of the population.
On the other hand, if the "climax type" in a normal-appearing popu-
lation possessed a reproductive inadequacy of genetic origin, there
would follow a quantitatively modifying effect upon the subsequent
development of the population. A population decline would be in-
evitable and proportional to the severity of the inadequacy. The in-
ferences are tempting in the extreme; for all observed phenomena in
the field can be explained plausibly through the medium of estab-
lished genetic principles. Unfortunately the entire subject, as it per-
tains to A. fulica, has proceeded scarcely beyond the purely specula-
tive stage.
Disease  Annandale (1919) in India was the first investigator
to report the belief that A. fulica was "subject to some kind of fatal
epidemic"; but he did not suggest that there was any connection be-
tween it and a general population decline. South (1926b) accepted
this report and listed the "fatal epidemic" as one of the controlling
factors in the biology of the giant snail.
Early in 1947, Daniel B. Langford, assistant entomologist of the
Trust Territory of the Pacific Islands, reported that many achatina
populations in the Pacific area seemed to be changing character; that
many of the individuals had thinner, more fragile, often badly dis-
torted, lighter-colored shells; and that reproduction and numbers of
individuals were noticeably reduced. This syndrome suggested to
him that a disease was present. ''Diseased'' specimens from Koror,
Palau Islands, were sent to investigators at the University of Hawaii
in the hopes that disease-producing agents would be found. The find-
ings were inconclusive. According to Langford, "diseased" specimens
were then introduced in the achatina populations in Oahu. When
these populations were examined by the author in January, 1955,
there was no tangible evidence of the described syndrome in any of
the specimens.
In January, 1949, Langford introduced from Koror "diseased"
specimens in the Anigua population, near Agafia, Guam. Kondo
(1950c) examined this population and determined that the typical
syndrome was present. The shells of specimens that had ben dead for
at least several months were compared with the specimens showing
the syndrome. There were striking differences. Kondo pointed out
that one might be tempted to conclude that the ''disease" had been
effectively introduced; but he emphasized that there was just as con-
vincing evidence that two genetically different types had interbred.
186	POPULATION DECLINE
It should be pointed out, however, that elsewhere in the Pacific
islands there were noted just as pronounced differences between the
ancestral shells and the living specimens. This suggests that perhaps
the so-called "diseased" specimens are nothing more than representa-
tives of a stage in the genetic evolution of the population. If this
reasoning is correct, and if the populations are genetically similar,
then probably the Anigua population would have appeared just the
same had Langford not introduced the Koror specimens. This also
would make more understandable the failure of the syndrome to
make its appearance in the Oahu populations.
The reports of Langford created the first wave of optimism in the
problem of the giant African snail. But this optimism was short-lived.
In addition to the failure of investigators to find any pathogens in
Hawaii, Lange (1947, 1950) early reported in his survey of the prob-
lem that he saw no evidence of an epizootic. He sent preserved speci-
mens to the author for examination; but the gross anatomy showed
no signs of pathology (Mead 19500:237). An examination of fifteen
of Langford's original "diseased" specimens from Koror revealed the
fact that, in spite of their nine months in Guam in open bell jars
without food or water, all but one was very much alive and apparent-
ly none the worse for the ordeal (Mead 1950b, c). During the summer
of 1949, many specimens from a number of different populations
were examined in the Pacific Islands. Instead of pathology, genetics
appeared to form a more logical basis for explaining the common
syndrome (Mead and Kondo 1949). With the announcement of these
findings, the hope of using a parasitic disease to control A. fulica was
virtually abandoned and renewed efforts were made to explore fur-
ther the possibilities of using predators as biological control agents.
That there actually exists a disease of A. fulica continued to re-
main very much a possibility. The reports of Annandale and South,
and the frequent reports from Ceylon reasserted that there was still
more to the story. An exhaustive check of the literature brought to
light the fact that practically nothing is known about gastropod
pathology. The works of Szabo and Szabo (1930 et seq.), despite their
ambitious titles, concern almost entirely anatomical anomalies and
gerontic changes. Fromming (1954a) makes the same type of contri-
bution. A presumed "contagious disease" of H. aspersa is reported
upon at length by Boycott and Oldham (1938); but although their
discussion is convincing, it is not conclusive. Aside from the fact that
no microbiological investigation was made, the factors of genetics
and nutrition were not adequately controlled. Muma (1954) states
that the tree snail Drymaeus dormani in Florida is subject to a dis-
POPULATION DECLINE	187
eased condition of possible bacterial origin which causes the snails to
turn a greenish color and die. Further work on this problem is cur-
rently in progress. Dr. C. Vago of the Station de Recherches Serici-
coles in Ales, France, writes (in litt. Mar. 23, 1955) that in the past
few years he has studied over ten different diseases of several species
of snails. His research so far has convinced him that a paracoli occa-
sionally goes into a highly virulent form and produces an epizootic
among the commercially raised helicines. Recently, one such epi-
zootic killed over 50,000 snails in "snail parks" where the snails are
raised in close confinement.
It was obvious at this point that investigating the possibility of dis-
ease being a causal agent in the decline of the giant snail population
in Ceylon would have to be essentially a pioneering work.
First of all, the extent and effects of predation had to be deter-
mined. This factor was announced early in the investigation as not
being decisive (Mead 1955b). By far the most effective predator was
the Indian glowworm. But this attacked only the smaller specimens
of A. fulica. It would be expected that any snails that escaped the
ravages of the glowworm during the first two months of their lives
would be too large to be attacked and, in the absence of other killing
factors, would eventually become gerontic individuals in a popula-
tion manifesting heterogeneity with respect to the size and age range
of its individuals. Yet in some areas where this predator was com-
monly encountered, the giant snail population was in a truly remark-
able state of homogeneity in that all individuals were clearly under
one and one-half years of age. In others, the snails were not over two
to three years of age. Older and larger individuals, which would be
immune to the attacks of the glowworm, were completely absent, al-
though their old, worn, dead shells were all too common. It was clear,
then, that something more than predation was operative. An epi-
zootic of decimating proportions, for example, or a chronic disease
that is aggravated with the increased age of the host, could definitely
produce the observed homogeneity in the population. Fitting into
this suggestion is the fact that in these same areas in Ceylon there was
a serious build-up of the snails in 1951 and such a sharp decline in
1952 that control measures were not undertaken. These populations
then had had one and one-half to two years to recover from the
decline—a period of time approximately equivalent to the age of the
average individual. As a further pertinent point, it should be borne
in mind that micro-organisms of disease, unlike predators, have the
reproductive capacity to produce quickly a catastrophic effect upon a
population (Mead 1955b).
188	POPULATION DECLINE
With epizootiological evidence building up in favor of the disease
hypothesis, a great many specimens were brought into the laboratory
to be dissected in the living state for a critical anatomical examina-
tion. The results were discouraging, for the viscera and the tissues in
general appeared within the range of normal in practically every case.
A break finally came with the advent of the summer rainy season. At
that time, snails were seen in great numbers during the day crawling
about in the rain. As they were being observed in the field, it was
noticed that one out of every two to three specimens had leukodermic
lesions on the tentacles and, occasionally, on the face and neck. Sure-
ly these were symptoms of disease. The gross anatomy of these speci-
mens was examined in the laboratory, but the findings were negative
as before. This suggested on the face of it that there was no visceral
phase of the disease. At this stage of the investigation, the syndrome
was described at the meetings of the Second Pan-Indian Ocean Science
Congress in Perth, Australia, in August, 1954. Subsequent histopatho-
logical examinations of the hepatopancreas and the kidney, however,
revealed pronounced differences between specimens manifesting
symptoms and specimens without discernible symptoms. Correspond-
ing changes in other elements of the viscera were suspected.
As more and more specimens were examined, a definite sequence of
progressive stages in the disease began to take shape. Leukodermia is
caused by the systematic destruction of melanophores in a small locus
in the dermis. The melanophores first appear fractured, then reduced
to a mass of granules, and finally disappear entirely. Because of con-
comitant tissue destruction and weakening in the dermis, the lesion
may become elevated into ridges, tuberculations, or horns; and as
the lesion enlarges, it may coalesce with adjacent lesions. Eventually
the tentacle becomes shortened and distorted and, finally, it may re-
main partially or completely invaginated. Occasionally the initial
lesions may diminish in size, but other lesions appear elsewhere on
the forepart of the body. It should be remembered that the severity
of the "liebespiel" is responsible for leaving pigmentless scars on the
surface of the body. Although they are clearly distinguishable from
leukodermic lesions, the lesions might easily be confused by the casual
observer.
As announced in the preliminary report of this disease (Mead
1956a), the whole epizootiologic picture is that of a chronic enzootic
disease of uncertain etiology, high incidence (35-68 per cent), and low
gastropod host specificity. Observations in the field and laboratory
suggest that the disease is spread through contact, that it is highly con-
tagious, and that the immunity is low. A great many natural factors in
POPULATION DECLINE	189
the environment favor the development of an epizootic. There charac-
teristically is a high moisture factor during the periods when the snails
are active; the traumatic breaks in the shells would allow additional
portals of entry for disease agents; the feeding habits of the snails in-
clude eating the substrate, consuming dying or dead individuals, and
mutual rasping of slime from the surface of the body; and their habit
of aggregating in moist, protected niches increases considerably the
element of physical contact.
In the areas in Hawaii where A. fulica abounds, certain terrestrial
arthropods, for example, the amphipod Orchestia platensis, the iso-
pods Porcellio laevis and Metoponorthus pruinosus and unidentified
collembolans, frequently have been seen at night crawling over the
extended achatina and apparently feeding on mucus on the surface of
the body. Their presence implicates them as possible agents of con-
tamination if not actual vectors. A transovarian mode of transmission,
however, still remains a strong possibility.
The various stress factors in the environment surely must provide
an aggravating influence, perhaps even to the extent of precipitating
an acute phase of the disease. Specimens kept for six months under
conditions demanding estivation showed a much slower rate of prog-
ress of the disease; and, although there were new lesions, in some in-
stances the old lesions appeared to be undergoing tissue repair with
irregular areas of excessive melanosis. Apropos of this, Ghose (1959)
has reported that tentacular regeneration in this species proceeds
much slower during estivation. The course of the symptoms moved
noticeably faster in specimens kept under conditions of high humid-
ity and abundant food, which encouraged prolonged periods of activ-
ity. The progress of the disease is clearly linked with metabolic rate.
From this point, the complications, implications, alternatives, and
speculative possibilities literally run out in all directions. Obviously,
a great deal of pioneering research is required to produce any sort of
conceptual perspective in this complex problem. As a good start in this
direction, a United States Public Health grant (E-1245 [C3]) has been
made in support of a projected investigation of the etiology and
pathology of this disease. The etiological research completed in Cey-
lon has essentially eliminated from further consideration protozoans,
malacogenous fungi, yeasts, and spirochetes. Hence, attention is being
focused on the bacteria and viruses.
Similar leukodermic lesions were found in specimens of A. fulica in
Singapore, Hong Kong, and Hawaii (cf. van Zwaluwenburg 1955). Be-
cause of the high rate of infectivity in the Ceylon populations, and be-
cause the snail infestations to the east of Ceylon undoubtedly were
190	POPULATION DECLINE
started by specimens from Ceylon, it has been provisionally assumed
that the disease has been carried with the snails and that similar symp-
toms mean the same etiology. There is evidence, however, suggesting
that different "strains" of the pathogen exist. For example, the in-
fected specimens in Hawaii show a conspicuous paucity of tubercula-
tions and an inordinately high incidence of large lesions, 3-6 mm. in
diameter, located at the base of the ocular tentacles (67 per cent of
positive individuals). Even in Ceylon, groups of infected specimens
from different populations displayed noticeably different tendencies
in their symptoms; in some, facial lesions were common, in others,
they were almost completely absent; in still others, the lesions were
conspicuously absent from the ventral tentacles. An explanation for
these differences conceivably cannot rest entirely with the pathogen;
for there must be differences in host response stemming from the dif-
ferent genetic make-up of the various populations. The difficulty in
distinguishing between possible strain difference and difference in
host response was most dramatically brought out in an experiment
wherein the pathogen was transferred from A. fulica to Limax flavus
to Helix aspersa. Out of 106 inoculated specimens of H. aspersa, 14.15
per cent were unmistakably positive; but the heretofore unobserved
symptoms in H. aspersa were vastly different from those of A. fulica
inasmuch as the leukodermia was generalized rather than localized
and the tentacles were atrophied rather than distorted.
From what was known of the distribution of the disease, it was as-
sumed that it would probably be found in all of the infestations east
of Ceylon and India (Mead 1956a). More recent support for this as-
sumption was obtained when specimens of A. fulica were collected in
Bangkok, Thailand, in December, 1957, and found to be diseased
(Mead 1958a, b). In contrast to the syndrome in the Hawaiian speci-
mens, however, leukodermia was much less pronounced and tubercu-
lation was severe. At that time, the only inkling we had regarding the
possible existence of the disease in the Pacific island specimens was a
casual remark of Chamberlin (1952b: 12) tucked away in a footnote,
viz., "Occasional individuals had pigmentless blotches on the skin but
examination of these showed no coincident anomalies." As good for-
tune would have it, the return trip from Thailand was routed through
Guam and it was possible to examine a number of giant snail speci-
mens in the vicinity of the military airport. These were found to have
the disease syndrome more nearly like that of the Thailand specimens
than the Hawaiian specimens. This information suggests strongly that
POPULATION DECLINE	191
all other Pacific island populations will be found to have the disease
in one form or another. It is of interest to note that A. J. Kohn, during
the 1957 Yale Seychelles expedition, found typical symptoms on speci-
mens collected on Hitadu Island of the Addu Atoll in the Maldive
Islands. On the other hand, Ghose (1960) failed to find any specimens
in India with discernible symptoms; but his field work seems to have
been quite limited. It is not known whether the disease occurs in the
East African achatinas; but it is felt that more than likely it does. Find-
ing a strikingly similar syndrome in the introduced achatinid Rumina
decollata in central Arizona (Mead 1959b) has precipitated the feel-
ing that the disease of the giant African snail is not unique, but one of a
whole class of diseases of varying pathogenicity found in many species
and in many parts of the world. It is a strong temptation to extrapolate
further to assume that it is these diseases which successfully hold most
snail populations in check and produce a major effect in population
fluctuations. Actually, it would be a paradox indeed if snails did not
have their own diseases. It is easy to predict that a number of snail
diseases will be found and reported upon in the next relatively few
years. When the effects of these are known, infinitely more will be
understood about establishing balance in invading populations.
After the etiological agent has been discovered, it will be impor-
tant to determine its affinity for forming different strains of varying
pathogenicity. An understanding of the pathology must be sought
at the histopathological level; but as Pan (1958) has emphasized, this
has as its prerequisite an understanding of the normal histology.
Thanks to the meticulous and exhaustive work of Ghose (1960), we
know now much about the gross anatomy, developmental anatomy,
and histology of A. fulica. Similarly, an understanding of the epi-
zootiology depends upon a rather considerable knowledge of the
ecology, and particularly of the population dynamics, of this impor-
tant species. We are less fortunate here; for although there have
been recorded many observations made at the time the invading
populations were at their fulminating stage, practically nothing is
known about the normal course of development of a population.
The field investigations of Mead and G. D. Butler, Jr., in Hawaii
are contributing to our knowledge in this respect; but considerably
more basic work is urgently needed.
So far, the epizootiological data recorded from examinations of the
unusually heavy population of snails in the Mahinui area of Oahu
since 1955 have given us our best, but by no means clear, conception
192	POPULATION DECLINE
of the course and effects of the disease on a relatively recently estab-
lished giant snail population. In January, 1955, the incidence of
the disease was 14.5 per cent and not a single specimen could be
classed as having "severe" symptoms. One hundred adult specimens
collected at random in August, 1957, indicated that the incidence
had increased to 57.0 per cent and specimens with advanced symp-
toms were common. Exactly one year later, the incidence had raised
to 68.6 per cent and the majority of the positive specimens had
prominent lesions. Throughout this period of time, the snail popu-
lation level remained essentially stable. In December, 1957, 400
specimens collected at random were measured, weighed, examined
to determine and record the presence and extent of disease symptoms,
and released in the area where they were collected. In the following
August, 132 (33 per cent) of these specimens were recovered and re-
examined. The new data demonstrated that in the intervening
months negative specimens had become positive and positive speci-
mens had either become more severe or had disappeared. In essence,
a far bigger population turnover had been taking place than was
ever suspected; and the high reproductive potential had apparently
insured the maintenance of the population load (Mead 1959b). This
information is compatible with the earlier conclusion that the disease
reduces life expectancy or, conversely, that age acts as a decisive
stress factor in the presence of the disease.
The disease, however, has not just been spreading from one
achatina to another; experimental evidence supports the assumption
that natural transmission has taken place between A. fulica and
Bradybaena similaris and Subulina octona in this area. These latter
two species were completely negative for symptoms in other areas
in Oahu which had not been invaded by Achatina.
Identical sampling techniques in the Mahinui population in
September, 1959, revealed the following facts: the incidence had
increased to an amazing 83.0 per cent; the vast majority of diseased
specimens were of the "severe" type with one or more large (5 mm.+)
leukodermic lesions; for the first time several specimens were found
to have multiple lesions (12+) on the exposed parts of the body;
and, also for the first time, there was a marked population decline.
There is good evidence that the disease becomes an increasingly
more effective limiting factor only after the snail population has
begun to level off following the sigmoid growth stage. Research is
being continued in the Mahinui area, but unfortunately the pred-
atory snail Euglandina has recently invaded the experimental site
as an incalculable variable.
POPULATION DECLINE	193
Multiple Factors  It is obvious that under natural conditions,
unfavorable environmental factors are mutually augmentative but
operate wholly independently. At any time in any one place, some
may be producing the maximum unfavorable effect while others are
temporarily ebbing or remaining neutral in their effect. But, as in
any other system of independently operating variables, there are
inevitable periods of synchronization. If a period of synchronization
is at a time when the unfavorable factors have reached their maxi-
mum intensity, then the effect upon the population will be most
severe. In some animal groups, this could mean local extermination,
particularly when man-made unfavorable factors are added to the
natural compliment.
Possible instances of this nature have been observed in Ceylon and
in the Pacific islands. A case in point is the population of A. fulica
at the Dodangoda post of the Godahene estate near Neboda, Ceylon.
In 1951, the giant snail was so abundant that the leguminous cover
crop Pueraria was almost completely denuded. A program of poison-
ing the snails with metaldehyde bait was immediately initiated. By
1952, the population of the snails had diminished to the point where
further poisoning was not considered necessary. By 1953, the snails
were scarcely in evidence and the local people literally ''forgot about
them" in that area. In 1954, the author made a lengthy and exhaus-
tive search of the area during the rainy season and in the rain. Not
a single live specimen could be found. Nor could any other snail
be found alive, including the ubiquitous and common Subulina
octona. Empty shells of A. fulica were there in abundance, but their
weathered condition indicated in every case that death had occurred
many months previous to that time. No predators were found; but
a large number of weathered but characteristically broken shells
near bandicoot burrows indicated that this mammalian predator had
been active in the past. More recently, the bandicoots had turned
to the large, rich seeds of the rubber plant for their food. With no
live snail specimens present, positive evidence of the disease was not
discoverable. However, it seemed more than significant that live
snails in the nearby Pettigola section of this estate had the highest
infectivity rate (64 per cent) that was found in Ceylon. Surely, then,
the chief unfavorable factors were poisoning, predation, and dis-
ease. Possible unfavorable meteorological conditions could not be
determined beyond the fact that rain had been unusually abundant
during the preceding months.
There appears to have occurred in that area virtual or actual ex-
tinction not only of A. fulica and other introduced snails but of
194	POPULATION DECLINE
the endemic snails as well. Cause for this cannot be laid wholly at
the feet of the poisoning program as their program was of such a
scale that it could not possibly have been eradicative. In the absence
of any further information, one can scarcely escape the plausibility
of the assumption that the disappearance of the snails was caused
by the compounding of unfavorable factors. But, more than a simple
summation of the unfavorable effects, there actually may be a syner-
gistic action in certain combinations of factors. If there is a formula
for producing an eradication of this snail pest, it probably will be
found in the realm of multiple unfavorable environmental factors.
CHAPTER  11
OUTLOOK
In this work so far, definite attempts have been made to
determine and evaluate the status of the several aspects of economic
malacology and the problem of the giant African snail in particular.
At this point, it will be well to look ahead and, on the basis of what
is known, to make prognostications which should indicate not only
where we are going but what we should be doing in the host of
problems presented by economically important snails.
Dispersal  A question of great concern in the outlook for the
problem of the giant African snail is, "Just how far can and will this
snail spread into the uninfested areas of the world?" First of all, we
know full well that we have in Achatina fulica an exceedingly hardy,
tenacious, variable, and adaptable molluscan pest with a high repro-
ductive potential and remarkably few natural enemies. Since the
limits of these faculties are not known in any case, the question at
hand, unfortunately, can be answered only in speculative terms.
Even so, information is available which forms a firm basis for spec-
ulation.
Finding A. fulica firmly entrenched in Ani Jima (lat. 27° 08' N.)
in the Bonin Islands is of real significance; for it is situated farther
north than any other known established population of this species,
with a possible exception suggested by the recent discovery of speci-
mens on Amami Oshima (lat. 28° 18' N.) in the Ryukyu Islands.
The well-established populations in Okinawa Jima of the Ryukyu
Islands are almost as far north (lat. 26° 03'-51' N.). Nuttonson (1952)
has established for the Ryukyu Islands the agro-climatic analogues
in the Northern Hemisphere. From these it can be stated flatly that
A. fulica could become established in the comparable areas of Flor-
ida, Alabama, Mississippi, and Louisiana. Because island climates
195
196	OUTLOOK
are characteristically more mild than continental climates at the
same latitude, it is to be expected that the northern and southern
frontiers of this species will be populations in islands which have
a subtropical-temperate climate. If, however, the giant snail adapts
itself as a greenhouse pest, it may become established in the more
temperate continental areas. Significantly, the populations in the
Bonin and Ryukyu Islands are vigorous and thriving. Further, the
winter climates in these islands and in the infested areas of Kauloon
in Hong Kong Colony, Amoy in China, and interior Formosa, are
considerably more vigorous than in some of the areas in East Africa
where A. fulica is endemic. This suggests that the snails have not yet
reached the threshold of minimum tolerance to cold.
From what we know, it is reasonable to assume that the giant snail
has the capacity to establish itself in all oceanic islands which have
an adequate cover of vegetation and fall between 30° north and 30°
south latitude. This embraces the greater share of Oceania and indi-
cates that such uninfested island groups as the Marshall, Gilbert,
Ellice, and Line, are vulnerable. Uninfested continental areas which
are tropical, subtropical, and, in some cases, subtropical-temperate
are similarly vulnerable. This includes northern and much of eastern
coastal Australia, as Harrison (1951) agrees. The most extensive of
the suitable but uninfested areas, however, are in the New World
where they form an essentially continuous belt from the Gulf States
of the United States south, through the West Indies and the lower
altitudes of Mexico, to the greater share of South America. That this
snail, so far as we know, has not yet become established in these vast
areas is almost a miracle, especially when one considers the general
inadequacy of plant quarantine regulations in the many countries
included. In fact, some investigators have been moved to suggest
that there is some basically intolerable factor in the tropics of the
New World which has kept this snail form becoming established.
Under the circumstances, however, it appears that it is merely a mat-
ter of time until these areas are invaded.
In the Pan-Indian Ocean area and in Indonesia, the giant snail
has already made considerable progress in its spread. It will continue
this spread until it is essentially ubiquitous. Australia, northern New
Zealand, southern Japan, and continental United States are periph-
eral areas about which there is considerable doubt because it is not
known to what extent A. fulica has the genetic capacity to form
populations of more hardy individuals. Masahiko Nakada of the
blight prevention section of the agriculture-forestry ministry in
Tokyo, however, predicted recently that the giant snails will make
OUTLOOK	197
their appearance in Kyushu, the south island of Japan, in the near
future.
In regions where there frequently occurs sudden lowering of the
temperature below 50° F., this snail probably will not permanently
establish itself except possibly in greenhouses and nurseries. On
the other hand, where temperatures are reduced gradually and are
not excessively low, it is not unlikely that the more hardy individ-
uals will bury themselves in the ground and survive, as they do in
the Bonin Islands. The inordinate sensitivity of this snail to higher
altitudes seems to stem not from the factor of cold alone but quite
likely from intolerance to a diurnal temperature fluctuation beyond
a point where, to survive, it normally would need a period of several
days to become conditioned physiologically. Of course, there may be
a barometric factor; but it is significant that snails are surviving
colder winter temperatures at sea level in Ani Jima than they can
at 5,000 feet altitude in Ceylon (Mead 1955b, 1957b). Green (1910b),
for example, reported that achatina specimens released at an altitude
of 4,000 feet in Ceylon died one by one without reproducing. Other
specimens released at an altitude of 6,600 feet in Masuri at the foot
of the Himalayas in central India similarly failed to establish them-
selves (Benson 1858). Reliable correspondents have indicated that
specimens have not been encountered much above 2,000 feet in
Mauritius and 3,300 feet in Java. This information correlates with
the findings of Pilsbry (1919:60) wherein achatinas were not found
above 1500 meters in Africa.
Although deserts would appear to be completely forbidding to
the establishment of this and other snail pests, it has been empha-
sized that in the cultivated areas of deserts conditions are surprisingly
suitable, as evidenced by the fact that several exotic terrestrial gas-
tropods have become established in the Sonoran Desert of southern
Arizona within the past few years (Mead 1952a, c, 1953, 1959a).
During the past ten years, the threat of establishing the snail in
the United States has come chiefly from ships carrying war salvage
from the Trust Territory of the Pacific Islands (Messenger 1952:252).
The interceptions of the snails have been discussed above under the
topic of quarantines. There is essentially no war salvage arriving
today in this country as remaining shipments are reportedly being
directed to Asia. Concurrent with the tapering-off of these shipments,
there has been a greater increase in the spread of the giant snail in
Hawaii. The threat, therefore, is still coming in from the west, with
the difference that it is now much closer to the United States, and
to California in particular. Fortunately, the recently enacted federal
198	OUTLOOK
quarantine regulations will provide a considerable buffer effect to
this threat. But there are no prospects of the threat becoming less
in the near future.
The actual threat that this snail presents to the agricultural state
of California has been much debated. Bequaert (1950b:74) has stated,
"It is, in my opinion, extremely doubtful that A. fulica could ever
become established in California or elsewhere in the continental
United States, to judge from the present distribution and the ecol-
ogy of this snail." In direct contrast, Mead (1949b, c] has stated, "It
would be especially bad in places like California, the Gulf states,
and the Southeastern states." On the other hand, Abbott (1949) has
stated, "Fortunately, the climate of that state [California] is not con-
sidered to be entirely ideal for the snail." The following year, he
modified his stand with, ". . . it is my opinion . . . that the southern
third of Florida is the only suitable area for its survival for any great
length of time." These differences of opinion are the natural out-
come of having to base predictions on woefully inadequate infor-
mation; and they underscore the advice Bequaert gives in the fol-
lowing words, ". . . controlled experiments, under strict supervision,
but under natural conditions in a presumably favorable area, are
called for in order to determine once and for all whether or not the
snail could survive the winter and reproduce freely in the United
States."
Let us assume for the moment that the only place in the United
States A. fulica could become established is the southern tip of
Florida. Let us assume further that at best only an unthrifty outpost
population of the giant snail, causing little local damage, could be-
come established. Nothing but a dim view could be taken of such
a situation; for the snail pest could use that beachhead as a spring-
board to start populations elsewhere in more favorable areas in the
western hemisphere. Cuba, being nearby, and having vast agricul-
tural areas and a fabulously rich mollusk fauna, would be partic-
ularly vulnerable. Aguayo (1950) has already sounded a word of
warning in that country.
Since man is the principal agent of dispersal of this snail pest,
any measure to check the spread will have to be aimed at man him-
self. Quarantine regulations have been set up for this purpose; and
for this purpose they should be maintained indefinitely. They are
far from being universally practicable; but in certain areas they
have been eminently successful. Keeping this snail out of California
in spite of the frequent interception of live specimens, and restrict-
OUTLOOK	199
ing it to the two originally infested islands of Oahu and Maui in
the Hawaiian Islands for a period of twenty years, are cases in point.
          Bionomics We know amazingly little about the biology and
ecology of the giant snails—far less than for any other agricultural
pest of comparable economic importance. We do not know how
long they live, how far they travel, how much heat or cold they can
tolerate, why they are limited by altitude, whether they can go into
true hibernation as well as estivation, why they move en masse out
of a favorable area into an apparently unfavorable one, how impor-
tant their own diseases are in regulating their numbers, what the
biological factor is that accounts for the tremendous vigor early in
the invasion of a new territory, or very much about literally a score
of other equally significant but unknown factors operative in their
existence. These thoughts bring out the obvious realization that just
as soon as comprehensive behavioral study can be made of these
snails, there will be not only an increase in the efficacy of the exist-
ing control measures but new and more effective means of control
can be conceived.
The unpublished thesis of Ghose (1960) gives us our most valu-
able contribution on the anatomy, histology, and embryology of
A. fulica. Hatai and Kato (1943) made detailed studies of the growth
and development of this species. Their ecological observations are
valuable, but as is the case in so many other reports based on field
observations of A. fulica, the bits of information amount to such a
pitifully small portion of the needed information that not even
speculation will pull the parts together into any sort of even vague
picture of the over-all ecology. The work of Takahashi (1942) gives
us more specific information on the movement of this snail within
a fairly limited area of a recently invaded compound; but like
Matsui's report (1942) on the total amount of movement of the giant
snail in a diurnal cycle, there apparently has been no translation
from the Japanese. Edelstam and Palmer (1950) and Palmer (1951)
of Sweden have made significant parallel studies with Helix pomatia;
but like all parallel studies, they are scarcely more than suggestive.
           Control  So far as is known, for over one hundred years erad-
icative measures of all types have been uniformly unsuccessful
throughout the areas of the world invaded by A. fulica. Even the
most intensive control programs, such as those in Oahu, Guam,
Koror, and Hong Kong, have proven in the long run only to have
impeded the spread of that snail pest. There has been, in fact, only
one case where a major land snail pest has been eradicated by man,
viz., Theba pisana in La Jolla, California. Basinger, who was in
200	OUTLOOK
charge of the control program, spared nothing in his efforts to erad-
icate this pest. After a few years, he stated (1923a), ". . . the vast
majority . . . have long ago been destroyed, but, when it conies to
extermination, it is much harder to get the remaining few than the
first hordes." Despite the fact that he thought he had virtually ac-
complished an eradication, as betrayed by the title of his article, it
took almost exactly 27 years more actually to accomplish it! And
during this time, almost unlimited manpower was made available
to the program through federal and state relief administrations. The
total cost of eradicating T. pisana and attempting to eradicate two
other helicine species came to over $500,000. To date, the other two
species are still very much at large (Messenger 1950). The factor of
"the irreducible minimum," which is the difference between control
and eradication, has plagued the program right from the beginning.
With many examples of expensive failures in the past, it is little
wonder that Green (1910c), South (1926b), Garnadi (1951), and
others have taken an unequivocal stand against "all out" measures
to eradicate A. fulica. Certainly their advice warrants serious consid-
eration if the infestation has become firmly established in a favorable
environment. If, on the other hand, the infestation is only in its
initial phase, or is in a marginally suitable environment, eradicative
measures should be undertaken. But in nearly every infestation, at
least some measure of control should be exercised. The big prob-
lem is: "What control measure, or combination of control measures,
should be used?" Naturally, the answer would vary according to
the circumstances involved; but in general, all practicable control
methods should be used where they are not mutually counteractive
(e.g., the introduction of predatory snails and the use of mollusci-
cides). Unfortunately, many of the control measures are relatively
expensive and they therefore are completely beyond the considera-
tion of most native peoples in the infested and potentially infested
areas. Under such circumstances, hand picking, the construction of
barriers, and other mechanical devices would have to be resorted to.
But these, like any other control measure, must be maintained in-
definitely. It is at this point that new difficulties arise. If after a few
weeks or months of attempting to control the snail there is little or
nothing in the way of tangible results, even the more fastidious
people tend to give up and let the snails take over. But what is worse,
peoples in many areas show a marked apathy, and even antipathy,
for making any attempt to help themselves in this problem. For
instance, R. E. Dean writes (in litt. Jan. 17, 1952) that in Hong Kong
the government offered snail bait free to the people, "but the re-
OUTLOOK	201
sponse was only lukewarm." The prevailing attitude among the
people in the Pacific islands is that all responsibility for controlling
the giant snail rests squarely upon the shoulders of the government.
If anything is done, then, the government must resort to force, in-
ducements through bounties, or government-supported large-scale
control programs. All of these measures in the past have proven at
best to be of only transient success.
Chemical control has been demonstrated many, many times to be
expensive and therefore practicable only on a small scale. In addi-
tion to the expense, tropical weather conditions in general are antag-
onistic to the use of molluscicides. Weather that is particularly fa-
vorable for snails is automatically unfavorable for chemical control
measures as the rain washes away the molluscicide and encourages
the growth of mold on snail baits; the high humidity favors recovery
from the paralyzing effect of metaldehyde; and the lack of sun
eliminates a killing factor that would ordinarily follow the para-
lyzing effect of the chemical. Dry weather is unfavorable to snails;
but they escape it, and any molluscicides put out at that time, by
going into estivation. But even beyond the expense and the weather,
the fact remains that the available molluscicides are far from satis-
factory in their effects. The tools of analysis devised by Basinger
(1935), Thomas (1944), and others; the increasing interest of the
bigger chemical companies in the development of new molluscicides;
and the continued research by a larger and larger group of investi-
gators, give us new hope that before long a truly effective, inexpen-
sive, safe, and easily used molluscicide will be developed. As it is
now, in the vast majority of the cases, after repeated chemical control
measures are finally discontinued, the giant snail population builds
up to the point where it is just as bad if not worse than it was before.
In some cases where population decline is taking place or where
there has been a fortuitous concomitancy of several control factors,
chemical control measures appear to be decisive. This suggests im-
mediately that there must be a better understanding of both the
phenomenon of decline and the effects of combining unfavorable
factors.
In the broadest sense, man is an agent of the biological control
of A. fulica because he is a natural controlling factor. Any hope of
making use of the snails on a commercial basis for human consump-
tion rests almost entirely with the native peoples who will readily
eat them, viz., the East Africans, the Chinese, and the Formosan
aborigines. These people have diets notoriously deficient in protein;
and it would seem on the face of it that the giant snails could provide
202	OUTLOOK
at least a partial answer to the problem. But in spite of the logic
involved, the chance is remote indeed that there will be even a
modest amount of commercial use of the snail for human consump-
tion in the foreseeable future. The possibility of there being more
use of the dried snail meal for poultry and livestock supplemental
feeds is becoming steadily greater with continued research. It is only
through the use of the snails in this manner that man will become
a steady, dependable source of "natural" control. Control of this sort
would be on an "individual" basis; and the program as a whole, as in
other types of biological control, would be self-sustaining. The single
greatest obstacle to this whole approach is the fact that it takes addi-
tional time and energy to prepare the snail meal. The native peoples,
first of all, have to be convinced that this is worthwhile; and, second,
they have to overcome their mutual loathing for handling the
slimy snails. Progress is bound to be slow in this aspect of control.
The other aspects of biological control are also in their infancy.
The prospects of using radiation-induced sterility of males as a suc-
cessful biological control weapon in insect control raises the highly
provocative question of its possible use in snail control (cf. Knipling
1955, Baumhover et al. 1959). Whatever the results of introducing
multiple predators of the giant snail in the Hawaiian Islands, they
are bound to be significant, particularly since in a number of in-
stances more than one species of predator has been released in the
same experimental area. Euglandina, and possibly the smaller or both
species of Gonaxis, will eventually become ubiquitous, spreading in
many cases as far as Achatina has, but in a shorter period of time.
The experimental island of Agiguan is only beginning to reveal its
complex ecological story (Mead 1956b). With both Gonaxis and the
phenomenon of population decline being variables in the current ex-
periments on that island, the results are almost certain to be mislead-
ing one way or the other. Quite unfortunately, however, the research
program on Agiguan Island was scheduled to be brought to a close in
1958 (Coolidge 1955).
Disease at last has entered the picture. Its presence provides the
most plausible explanation for the almost universally occurring de-
cline in the older populations. The nature of the pathology and the
etiology of the disease should be known in the near future. It is al-
most a certainty that the predatory snails Gonaxis, Euglandina, and
other predatory snails used in molluscan biological control, will be
found to be susceptible to the disease that has been discovered in
A. fulica. Ultimately, not one, but many diseases will be found and
considered in the light of biological control. Because of their affinity
OUTLOOK	203
for developing strains of variable pathogenicity, disease agents will
always have to be handled with respect and understanding in any
biological control program.
Decline  When A. fulica is in a pronounced state of popula-
tion decline, it ceases to be any more of a pest than some of the en-
demic snails. Determining accurately the causes for population de-
cline in A. fulica will provide a whole new perspective in the control
of this pest. When the entire story is known, it will undoubtedly be
found that there are many factors involved, the sum of several of
which will produce a decline. Probably the disease factor is the domi-
nant one.
Long ago, McCreery (1890) concluded that extinction was usually
brought about by a large number of small conditions. If man is ever
to eradicate the giant African snail on anything but the smallest scale,
he will do it through the use, augmentation, acceleration, and inten-
sification of the several factors, including disease, operative in pro-
ducing the decline. The discovery of the secret of population decline
in this and other species is of the very first importance, and research
in the future should be directed toward this end.
 
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INDEX
Ablattaria, 106
Abnormalities,   24-25,   32,   186;   see   also
Shell, malformed
Acclimatization, 31, 197
Acetaldehyde, 73, 80
Achatina achatina, 18, 115, 118, 119, 174
Achatina albopicta, 27, 50
Achatina in continental U.S., 4, 6, 18
Achatina craveni, 18, 50, 119
Achatina in Europe, 17-18
Achatina-free area, 45, 100, 116
Achatina fulica hamillei, 24, 109
Achatina panthera, 13, 132
Achatina rugosa, 26, 119
Achatina schweinfurthi, 125
Achatina stuhlmanni, 125
Achatina variegata, 118
Achatina zanzibarica, 50
Achatina zebra, 18, 21, 31, 124
Achatinella, 113
Activity, period of, 26-27, 33, 74-75; see
also Movement
Aerosol, 69, 71
Aethiopomyia, 120
Age  as   stress  factor,   187,   192;   see  also
Longevity
Agiguan, 12, 111, 117, 123, 128, 129, 130,
133-34, 139-41, 202
Agrihan,  13
Aguijan; see Agiguan
Air plant, 40
Alabama, 195
Alamagan, 13
Albizzia, 40
Aldrin, 91
A Ilium, 45
Alluaudinella, 120
Alocasia, 43
Alsophila, 43
Altitude, 31, 132, 197
Alum, 62-63
Aluminum sulphate, 63, 68, 82
Amami Oshiraa, 15, 195
Amaranthus, 40
Amaryllidaceae, 40
Amastridae,  113
Amino acid assay, 165-66
Ammonium alum, 63
Ammonium chloride, 68, 82
Ammonium sulphate, 68, 82
Ammonium sulphocyanide, 68
Amoy, 8, 9, 196
Ampalaya, 40
Amphibians, 102-5; see also Bufo marinus
Amphidromus, 6
Amphipoda, 189
Amyl acetate, 66, 71
Ananas, 46
Anastomus, 115
Anatomy, 191
Anemotaxis, 86, 101
Anguar, 14, 24
Ani Jima, 6, 7, 27, 195, 197
Annona, 47
Anomalous forms; see Shell, malformed
Ants, 105-6
"Ape," 43
Aphaereta, 118
Apple pomace, 71
Arachis, 46
Arakabesan, 14
Archachatina degneri, 28
Archachatina marginata, 18, 163
Archachatina ventricosa, 18, 119
Arginine,  166
Arianta, 125
Ariolimax, 125, 131, 147
Arion, 56, 106, 124
Arizona, 29, 175, 191, 197
A. fulica intercepted in, 4
Arrowroot, 40
Arsenicals, 63-66, 80, 89, 90
Artocarpus, 41, 44
Aruf; see Strophocheilus
Ascorbic acid, 165
Ash, 160-63
247
248
INDEX
 
Ashes, 66, 70, 91
Asplenium, 41
Atrophy of organs, 28
Attractants, 66, 71, 73, 86
Auluptagel, 14, 117
Australia, 179, 196
Australorbis, 123
Autofertilization, 22
Averrhoa, 41, 42
Babelthaup, 14
Baboon, 122
Bacteria, 123, 178, 187, 189
Bait paints, 64-65
Bait requirements, 85, 87
Bait shelters, 77, 87
Banana peel, 64, 78
Bananas, 18, 19, 40-41
Bandicoot, 122, 193
Banyan, 59
Barium fluosilicate, 66
Barium sulphocyanide, 68
Barometric factor, 197; see also Altitude
Barriers, 92-94, 200
Bdeogale, 122
Beach morning-glory, 41
Beach populations; see Populations, beach
Beans, 41
Beetles, 106-13; see also under genus and
family
Bengal, 7, 9
Benzene hexachloride (BHC), 67
Betel pepper, 41, 52
Biological control, 32, 102-45, 201-3
evaluation of, 136-45
Bionomics, 199
Biotic potential; see Reproductivity
Birds, 32, 60, 89, 113-16, 121
Bird's-nest-fern, 41
Birgus latro; see Coconut crab
Biscuit baits, 76, 81
Bismarck Archipelago, 6
Blimbing, 41
Blood, 25
Boehmeria, 46
Bone flour, 68
Bonin Islands, 6, 31, 55, 135, 195-96; see
also  Ani  Jima;   Chichi  Jima;   Haha
Jima;   Higashi   Shima;   Muko   Jima;
Ototo Jima
Borax, 68
Bordeaux mixture, 67, 69, 82
Bothriembryon, 118
Bougainvillea, 41
Bounties, 98, 169, 179
Bradybaena similaris, 51, 56, 135, 142, 192
Bran, wheat, 64, 65, 66, 71, 76, 81, 82, 86;
see also Rice bran; Rice husk
Brassica, 42
Breadfruit, 41
Breaking plants, 52
Breaks in shell; see Shell, traumatic breaks
Brick baits, 64, 77-78, 88
Brontispa; see Coconut beetles
Brush Barrier, 94
Bryophyllum, 40
Buffer areas, 96
Bufo marinus, 60, 102-5, 111, 180
Bulimulus, 28, 105
Bulinus, 124
Burhinus, 115
Burma, 7, 11
Burning-over, 94-95, 168
Burning snails, 100
Burtoa, 119
Bush hen, 115
Bush turkey, 115
Butyraldehyde, 80
Cabbage, 42
Cacao, 34, 42, 50, 52, 70, 94
Cactus, 42, 52
Caladium, 45
Calcium, 22, 33-34, 39, 99, 161-64, 170; see
also Shell, calcium, source of
Calcium arsenate, 63-65, 66, 75, 76, 84, 87,
88
Calcium arsenate-bran baits, 63, 71, 87-88
Calcium arsenate-lime-cement bait, 64—65,
78, 88, 90, 133
Calcium carbide, 68
Calcium carbonate in baits, 66,68,70, 78, 83
Calcium cyanide, 68
Calcium fluosilicate, 82
California, 134, 174-75, 176, 198
Calophyllum, 42
Calopogonium, 50
Calosoma, 106
Camellia, 48
Canna, 40, 42
Cannibalism, 57, 88, 101, 126-27, 131, 139,
140, 142, 189
Canning snails, 147, 150, 153
Capsicum, 42
Carabus, 106
Carambola, 42
Carbolic acid, 68, 81, 82
Carbon dioxide, 164
Carbon disulfide, 67, 72, 91
Carica, 45
INDEX
249
 
Caroline Islands, 7; see also Ponape; Truk
Islands; Yap
Carotene, 164
Carrots, 42
Casein glue, 76
Cassava, 42, 52
Cassia, 44
Cassowary, 115
Cats, 89, 105, 122-23
Cedar oil emulsion, 68
Celebes, 10
Cement in baits, 64, 77, 78, 87
Cenobita perlatus; see Hermit crab
Centropus, 114-15
Centrosema, 44, 50
Cepaea, 50, 164
Cereus, 42
Ceylon, 8, 10, 11, 18, 19, 24, 26, 32, 34, 50,
51, 53, 54, 103, 107, 109, 114, 115, 122,
181, 187-89, 193, 197
Charcoal, 66
Chemical assay, 160-65
Chemical control, 61-91, 201
evaluation of, 84-91
Chichi Jima, 6, 7,  19, 26, 27,  116,  149,
151-52
Chick feeding tests, 165-66
Chickens,  89,  104,  105,  113, 114,  159-60,
165-66; see also Poultry feed
Chili peppers, 42, 52
China, 8
Chloral hydrate, 68
Chlorcresylic acid, 68, 83
Chlordane, 67, 91
Chloropidae, 118
Cinders, 66
Circumstantial evidence, 59-60
Citrullus, 45
Citrus, 42, 50, 66, 67, 70, 7l, 84, 99, 114,
118, 132
Civet cat, 122
Clean culture, 95
Clearing, 95
Climbing; see Secretive habits;  Trees as
refuge
Clove oil emulsion, 68
Coal tar, 67
Cockroaches, 31, 55, 104-5
Coconut, 36, 42, 52, 59, 104, 126
Coconut beetles, 104-5, 117, 126
Coconut crab, 105, 117, 126, 140, 141
Coconut fiber, 63, 67, 70
Coconut meal, 71
Coffee, l, 42, 50, 52, 65, 92
Coir, 70, 94
Cold, tolerance to, ll, 27, 30-31, 196, 197
Coleus, 43
Collembola, 189
Colophotia, 108
Color; see Shell, color, variation in
Commensalism; see Symbiosis
Commercial use; see Snails in commerce
Comoro Islands, 13
Competition, 13, 33, 53, 132
Conchiolin, 164; see also Periostracum
Contact poisons, 68-69, 82
Control and religion, 20
Control
biological, 32, 102-45, 201-3
chemical, 61-91, 201
general, 201-3
human use as, 100, 146-71, 201-2
legislative, 172-79
mechanical devices as, 92-lOl, 200
radiation, 202
Copper acetoarsenate, 69
Copper benzoate, 69
Copper carbonate, 68, 69
Copper chloride, 69
Copper chromate, 69
Copper compounds, 69-70; see also Bor-
deaux mixture; Paris green
Copper cyanide, 69
Copper ferrocyanide, 69
Copper sulphate, 66, 67, 68, 69-70, 72, 73,
82, 90-91, 99
Copper sulphocyanide, 68
Copra, 67
Coprophagy, 55-57, 154, 155
Coral in baits, 65
Corbicula, 170
Corn, 43, 51, 60
Corn meal, 71, 77
Corona, 53, 70
Corrosive sublimate, 68, 70, 83, 89
Corrugated iron, 93
Cosmos, 43
Cotton, 43, 50
Cover crops, 44, 49, 50
Cow pea, 43
Crabs, 116-18; see also Coconut crab; Her-
mit crab
Crag, 658, 70
Creolin, 82
Creosote, 68, 70, 82, 83, 92
Crinum, 40, 45
Cross fertilization, 22
Crotalaria, 44
Cruciferae, 49
Crude oil, 83
250
INDEX
 
Crushing, 97, 99, 100
Cryolite, 70
Cuba, 198
Cucumber, 43
Cucumis, 43, 45
Cucurbita, 46, 47
Cucurbitaceae, 43, 49
Cunimene 2243, 70
Cupric oxide, 69
Cuttings, 49
Cycles toma, 123
DDT, 70, 91
Dadap, 42, 44, 96
Damage, indirect, 52-54, 116
Damage to plants, 39-49
evaluation, 49-52
Damaster, 111-12
Daucus, 42
Dead  snails and  disease, 55-57;  see also
Health factor
Debris accumulation, 20, 57-58, 94, 95-96,
101
Decline, 98, 141, 145, 169, 175, 180-94, 201,
202, 203
Deguelia, 44
Dehydration, 74, 75; see also Desiccation
Deroceras, 53, 56, 62, 63, 68, 69, 79, 80, 81,
83, 106, 124,
Derris, 68
Deserts, 197
Desiccation, 28, 29, 31, 86, 96, 186; see also
Dehydration
Desmodium, 44, 50
Diaphanes, 107, 109
Dichlorobenzene, 68
Dieldrin, 71, 91
Diethylparanitrophenyl thiophosphate, 84
Digestive gland; see Hepatopancreas
Diluents, 66, 71
Dinitro-o-cyclohexylphenol, 84
Dioscorea, 49
Discomyza, 120
Disease, 139, 142, 144-45, 185-94, 202-3
incidence of, 188, 192, 193
plant, 53
Dispersal, 4-16, 170-71, 195-99
effect of lime on, 33
map, 5
Distribution; see Dispersal
Diurnal  temperature fluctuation, 31,  197
Dogs, 89-90, 105
Drilus, 106, 109, 110, 112
Drowning, resistance to, 6,14, 19, 32, 97-98,
100
Drymaeus, 120, 132, 186
Dublon, 7
Duck farmers, 9, 11, 114
Duck feed, 11, 16, 17, 32, 114, 159, 166; see
also Poultry feed
Ducks, 113-14, 159, 166
Earthworms, 89, 140
East Borneo, 10, 97
Eating snails, experiments in, 156-59; see
also Human consumption
Ecological chain reactions, 53, 104-5, 117,
137,   140-44;  see  also  Environmental
interrelationships
Economic status, 36-60
Edentulina, 112, 127, 128, 129, 130
Edible snails, 146-59
Egg laying, snail, 21-24
Egg production, poultry, effect of snails on,
166
Eggplant, 43
Eggs, snail, attacked, 103, 104, 105, 106, 108,
119, 136
Egilomen, 131
Elaeis, 45
Elephant ear, 43
Ellice Islands, 196
Embryology, 191, 199
Endodontidae, 113
Endrin, 91
Engine oil, 68
Environmental conditions, optimum, 29, 87
Environmental  interrelationships,  53,   87,
104-5, 117, 134, 140-42; see also Eco-
logical  chain reactions;  Molluscicides
and environment
illustrated, 137
Eobania, 106
Epidemic; see Epizootic
Epiphragm, 27, 31, 164
Epizootic,  145,  185,  186,  187-89; see also
Disease
Epizootiology, 188, 191-92; see also Disease
Eradication, 26, 98, 168, 173, 194, 199-200,
203; see also Extermination; Extinction
Erosion, 53, 96
Erythrina; see Dadap
Escape reaction, 34-35
Estivation, 20, 25-27, 28, 30, 38, 87, 95, 140,
142, 189
Ether solutes; see Fats
Ethylene chlorohydrin, 69
Ethylene dibromide, 72, 91
Etiology, 188, 189, 190, 202
INDEX
251
 
Euglandina, 132, 134-35, 138, 142, 144, 192,
202
Euphorbiaceae, 43
Evaporation in environment, 29
Exaggerated accounts, 36-37, 60
Excrement; see Coprophagy
Experimental island, qualifications, 127-28
Exposure; see Sunlight
Extermination, 139-40, 193; see also Eradi-
cation; Extinction
Extinction, 181-82, 193-94, 203; see also
Eradication; Extermination
Factors favoring dispersal, 17-35
Fats, 160-63
Feces; see Coprophagy
Fefan, 7
Fences, 92-94
Ferns, 43
Ferrous sulphate, 72, 83
Fertilizer, 55, 162, 167-68, 170
Fish bait, 167
Fish oil emulsion, 82
Flame thrower, 95
Flies,   118-20,   144;   see   also   Mosquitoes
breeding in shells; Myiasis; and under
genus and family
in dead snails, 55, 101, 103, 104, 105, 118-
20
vectors of disease, 55-56, 120
Flooding, 32, 87, 98
Flordia, 195, 198
Flower gardens, 43, 49, 60, 93, 98, 114
Flukes, 56-57, 108, 135
Food; see Human use; Starvation
Food as environmental factor, 29, 33, 39,
189
Form; see Shell, form, variation in
Formosa, 8, 11, 14, 15, 196
Fossaria, 135
Frogs, 102, 103
Fruits, general, 52, 60
Fumigation, 67, 72, 80, 90, 91, 175, 176
Fungi, 123-24, 178, 189
Fungicides, 70
Fungous diseases, 53
Galactogen, 161
Gammexane, 72
Gardens; see Flower gardens
Gasoline, 68, 82
Genetics, 25, 142-43, 184-86, 190, 196
Geostilbia, 105
Gerontic changes, 182, 186
Ghana, 105, 122, 147-48
Giant South American snail; see Stropho-
cheilus
Giant specimens, 24, 182-83, 185
Gilbert Islands, 196
Gliricidia, 44, 96
Glowworms, 32, 106-9, 113, 120, 144, 184,
187; see also Lamprophorus
Glycogen, 161, 163
Goats, 123, 140
Gonaxis kibweziensis, 12, 111, 112, 117, 127,
128, 129, 130, 131, 133,  134, 135, 136,
138, 139, 140, 141, 142, 143, 144, 202
reproductivity, 4
Gonaxis quadr Hater alls, 134, 202
Gonaxis vulcani, 135
Gossypium, 43
Gourd, 43
Grains, 51
Grasses, 43, 51
Greenhouses, 196, 197
Greenol, 70
Ground glass, 63
Guam, 12, 24, 54, 59-60, 93, 102, 109, 123,
134, 190, 199
Gulella, 105, 130, 135
Gynandropsis, 44
HCH, 72
HETP, 69
Haha Jima, 6, 7, 19
Hand collecting, 92, 94, 996, 98-100, 169,
179, 200
"Haole koa," 44
Haplotrema, 138
Hardiness, 28-32
Harvesting snails, 169
Hawaii, island of, 9, 135, 173
Hawaiian Islands, 4, 24, 102, 110, 133, 189,
197,   202;   see   also   Hawaii;   Kauai;
Lanai; Maui; Oahu
infestation, 8-9, 173
Health factor, 55-57, 58, 98, 100, 101, 104,
105, 119, 168, 175
Health hazard, molluscicides, 88-90
Helicella, 106, 130, 131
Heliculture, 146-47, 151, 187
Helix aperta, 95, 174
Helix aspersa, 29, 51, 63, 66, 67, 70, 71, 73,
74, 79, 81, 84, 88, 99, 106, 114, 130-31,
138, 161, 165, 174, 186, 190
Helix desertorum, 28
Helix pisana; see Theba pisana
Helix pomatia, 25, 56, 150, 161-63, 165, 199
Helix spiriplana, 21
Hellebore, 82
252
INDEX
 
Helminths, 120-21
Hepatopancreas, 122, 123, 155-56, 158, 161-
63, 165, 188
Heptaldehyde, 80
Hermaphroditism, 21
Hermit crab, 7, 116-17, 140
Herpestes; see Mongoose
Hevea; see Rubber
Hexachlorocyclohexane, 72
Hexaethyl tetraphosphate, 69
Hexaldehyde, 80
Hibernation, 25-27, 30, 165
Hibiscus, 44, 45
Hiding; see Secretive habits
Higashi Shima, 7, 116
Hippelates, 118
Histology, 191
Histopathology, 188, 191
Hog bristles, 83
Homing instinct, 33
Honey in baits, 65, 76
Hong Kong, 9, 27, 189, 196, 199, 200
Host response, 190
Host-specificity, 131, 145
Hot water, 99
Human consumption,  12, 13, 146-59; see
also Human use
Human use, 18, 100, 146-71, 201-2
Humidity, 29, 30, 33, 39, 74, 75, 87, 189;
see also Moisture
Hydration, 28
Hydration cycle, 26, 35
Hydrocyanic acid gas, 67, 72,90,91,175, 176
Immunity, 188
Importation, 147
Incidence, disease, 188, 192, 193
India, 8, 9, 11, 24, 39, 191, 197
Indifference to snail problem, 39
Indigofera, 44
Indirect damage, 52-54, 116
Indonesia,  9-10,   103,   196;  see also  East
Borneo; Java
Insecticides, general, 91, 144
Interceptions; see Port interceptions
Intermediate hosts, 56, 135
Introduction; see also Dispersal
intentional, 17-18, 151-52, 185
unintentional, 18-19
Ipomoea, 41, 47
Iron, 164
Ishimoto negligin, 150-51
Isodrin, 91
Isolan, 72, 88
Isopoda, 189
Jackal, 122
Jak, 44
Japan, 8, 11, 172-73, 196-97
Jatropha, 141
Java, 9-10, 18, 24, 38, 99, 103, 108, 197
Johnsonia, 118, 120
Jungle crow, 32, 114-15
Kainite, 69
Kalutara snail, 8
Kauai, 9, 135, 144, 173
Kerosene emulsion, 71, 72
Khas khas, 83
Koror, 14, 24, 93, 150, 185, 199
Kusaie, 7
Lack of food and water; see Dehydration;
Desiccation; Estivation; Starvation
Lagenaria, 43
Lamprophorus, 106-9, 112, 144, 184, 187;
see also Glowworms
Lampyris, 106
"Lamtoro," 45
Lanai, 9
Laportea, 48
Large-scale farming, 96
Latex, 47, 51
Lead arsenate, 65, 76
Lead sulphocyanide, 68
Leaf analysis, 34
Legislation, 176-78
Leguminosae, 44, 49-50
Lesions, 142, 188-92
Lettuce, 44
Leucaena, 44
Leucodermia; see Lesions
Light,  33;  see also Sunlight;   Ultraviolet
Liliaceae, 45
Limax, 190
Lime; see also Calcium
in baits, 63, 64, 65, 66, 67, 69, 72-73, 77,
78, 82, 84, 86, 90
Limicolaria, 21, 50, 125
Line Islands, 196
Linseed oil, 79
Liver; see Hepatopancreas
Livestock feed, 166, 167, 202
Lizards; see Varanus
Longevity, 21, 140; see also Age as stress
factor
Loss of flesh, 32, 115
Loss of shell; see Shell, loss of
Louisiana, 176, 195
Luciola, 106, 107, 108
Luffa, 49
INDEX
253
 
Lycopersicon, 48
Lymnaea, 135
Lysine, 165-66
Madagascar, 13, 15, 103
Magnesium, 164
Magnesium fluosilicate, 82
Malakal, 14
Malathion, 91
Malaya, 7, 11, 13, 15, 16, 29, 38, 114
Maldive Islands, 11, 191
Malungay, 45
"Mamaki," 46
Mammals, 121-23
Man
agent of dispersal, 17-21, 57, 58, 170
influence on environment, 20, 57
Manganese, 163
Manihot, 42
Mariaella, 51
Mariana Islands, 11-13, 15, 175; see also
Agiguan; Guam; Rota; Saipan; Tinian
Marshall Islands, 4, 6, 196
Maryland, 18, 176
Materia medica; see Medicine, use of snails
for
Maui, 8-9, 109, 111, 133, 134, 135, 151, 173,
199
Mauritius, 8, 9, 13, 15, 18, 103, 133, 197
Mechanical devices in control, 92-101, 200
Medicine, use of snails for, 6, 7, 8, 13, 148,
150-52, 154, 171
Megapodius, 115
Megaselia, 118, 119
Melania, 170
Melanophores, 188
Melanosis, 189
Melittobia, 118
Melons, 45, 116
Mercuric chloride; see Corrosive sublimate
Meretrix, 166
Meta; see Metaldehyde
Metaldehyde, 64, 65, 66, 67, 69, 71, 72, 73-
80, 8i, 84, 86, 87-88, 89,144,193
baits, 76-80, 87-88
dust, 78-80, 88, 90
spray, 78-80, 88, 90
Methyl alcohol, 64
Methyl bromide, 72, 80, 91, 175
Metoponorthus, 189
Mexico, 196
Mice, 121
Micronesia,  8, 38, 55,   103,  104; see also
under particular island
Micro-organisms, 123-25, 144-45, 187; see
also Bacteria; Fungi; Protozoa; Spiro-
chetes; Viruses
Migration; see Movement
Migration cycle, 34-35
Milax, 63, 68, 69, 70, 80, 81, 82, 84, 106
Milk, 79
Mimosa, 44, 94
Miscanthus, 168
Mississippi, 195
Mites, 7
Moen, 7
Moisture, 86, 87; see also Humidity
Mokil, 7
Molasses, 64, 76, 81
Molluscicides and environment, 80, 86-87,
99-100, 101, 144, 201
Molluscicides as supplemental measure, 94
Moluccas Islands, 10
Momordica, 40
Mongoose, 112, 122
Monitor lizard; see Varanus
Montanoa, 45
Morinda, 45
Moringa, 45
Mosquitoes breeding in shells, 57
Movement, 34-35, 199; see also Activity,
period of; Anemotaxis; Homing in-
stinct; Migration cycle
Mucus, 32, 75, 150, 155-56, 158, 189
Muko Jima, 7
Multiple factors, 193-94, 201, 203
Multiple predators, 143-44, 202
Musa; see Bananas
Mustard solution, 68
Mutualism; see Symbiosis
Mydaea, 119
Myiasis, 119
Myxomatosis, 145
Naphthalene, 68, 80, 82, 83
Natalina, 135
Natural enemies, paucity of, 32-33
Nematodes, 56, 120-21, 178
New Britain, 6, 13, 134
New Caledonia, 4, 130
New Guinea, 13, 130, 135
New Ireland, 6, 13
New Jersey, 176
New Zealand, 196
Nicoria, 126
Nicotiana, 48; see also Tobacco
Nicotine sulphate, 67, 68, 69, 82
Nitrogen, 161-64
Nocturnal habits, 27, 29, 33, 59
North Borneo, 13, 100
254
INDEX
 
Nuisance factor, 54-55, 58
Nurseries, 50, 197
Oahu, 8-9, 108,  109, 110-12, 130, 133-34,
135, 142, 173, 185-86, 191-92, 199
Oceania, 196
Ochromusca, 119
Ocypode, 117
Ogasawara Gunto; see Bonin Islands
Oil of lemon, 68
Oil palm, 45, 50, 60
Oil of tar emulsion, 68
Okinawa, 7, 8, 14, 15, 135, 195
Okra, 45
Oleacina, 135
Omazene, 70
Omphalotropis, 140
Onion, 45, 52
Opeas, 103, 105
Opuntia, 42
Orange pulp, 66
Orchestia, 189
Orchids, 45, 78, 83, 90
Oregon, 176
Ornamentals, 49
Orthocalcium phosphate, 151
Oryctes; see Coconut beetles
Oryza, 46
Otala lactea, 6, 28, 174
Ototo Jima, 7
Ouagapia, 130
Outlook, 195-203
Oxychilus cellarius, 79, 129, 130, 131
Oxystyla, 21
Pachyrhizus, 41
Paddy crab, 117
Pagan, 13
Pakistan, 9
Palau Islands,  14, 15, 116, 134, 135, 150;
see also Anguar; Auluptagel; Koror
Paludestrina, 28
Panaga, 120
Pandanus, 12, 45, 52
Papaw; see Papaya
Papaya, 45-46, 50, 51, 52, 60, 72, 78
Paraffin, 76
Paraffin oil, 77
Paralaoma, 131
Paraldehyde, SO
Parathion, 81, 91
Paris green, 65, 76, 81, 82, 88
Parkia, 44
Parmarion, 51
Partula,33, 113
Paryphanta, 129, 132
Passiflora, 46
Passion flower, 46
Pathology; see Disease; Syndrome
"Patola," 49
Peanut, 46, 51
Peleliu, 14
Penicillin, 150
Penite, 65
Pepper, 46, 51
Pericyclocera, 119
Periostracum, 24; see also Conchiolin
Phalaenopsis, 45
Phaseolus, 41
Pheidologeton, 105
Phenol, 68, 81, 82
Philippine Islands, 14, 24, 135, 173
Phoridae, 118-20
Phosphate, 161-64
Phosphorus, 161-64
Phytalus, 103
Pigs, 105, 122, 160, 167
Pila, 154, 166, 167
Pineapple, 46, 52
Pingelap, 7
Piper, 41, 46
Pipturus, 46
Pisang; see Bananas
Planorbis, 106
Plant damage; see Damage to plants
Plant debris; see Debris accumulation
Plant diseases, 53
Plantain, 40-41
Plaster of Paris, 76, 81
Poisonous properties; see Toxic factor
Polygyra, 95
Polysaccharides, 163
Ponape, 7, 103, 134
Population dynamics, 142-43, 191, 192
Population evolution, 25, 39, 95, 98, 141,
142-43, 181-82, 185-86, 191
Population senility, 98, 182
Population variation, 181, 187
Populations
acid soils, 34
beach, 29, 83, 116, 117
coralline islands, 33, 162
diseased, 187, 192
volcanic islands, 162
Porcellio, 189
Port interceptions
Baltimore, 176
California, 174-75, 176
New Orleans, 176
Newark, 176
INDEX
255
 
Portland, 176
Vancouver, 176
Potassium, 161-63
Potassium aluminum sulphate, 62-63
Potassium antimonyl tartrate, 84, 90
Potassium bichromate, 68
Potassium cyanide, 81
Potassium-magnesium chlorosulphate, 69
Potassium permanganate, 68, 81, 82
Potassium sulphocyanide, 68
Potassium xanthogenate, 68
Poultry feed, 15, 159-60, 162, 166, 170, 202,
see also Chickens; Duck feed
Predator-free period, 108
Predator-prey differential, 131, 138-40, 142
Predators, general, 143-44, 184, 187, 202;
see also Biological control; and under
specific type
Prey-specificity, 131
Productivity; see Reproductivity
Prophysaon, 56
Propionaldehyde, 80
Protection
of baits, 77, 87
by shell, 32
Protein, 58, 147, 161-63, 170
Protozoa, 123-24, 178, 189
Pueraria, 44, 50, 193
Pumpkin, 46
Pygmy specimens, 24
Pyrethrum, 82
Pyrophyllite, 78
Quarantines, 11, 19, 172-79, 198
Queltehue, 115
Rabbits, 121, 145
Radish, 46
Ramie, 46
Rana, 103
Raphanus, 46
Rasping shells, 34, 57
Rat problems, 54-55, 122; see also Rats
Rats, 57, 60, 104, 105, 112, 117, 121-22, 140,
141; see also Rat problem
Rattan, 94
Regeneration, 32, 115, 189
Regulations, quarantine; see Quarantines
Repellents, 64, 73, 82-83, 85, 94
Reproductivity, 21-24, 140, 145, 192
Reptiles, 125-26
Reunion, 13, 14
Rhea, 115
Rhodiatox, 84
Rhysota, 33
Rhytida, 129-30, 131, 135
Riboflavin, 165
Rice, 46, 51, 52
Rice bran, 66, 71, 77, 78, 88
Rice husk, 71, 78
Riouw Archipelago, 10, 18
Road hazard, 54
Robber crab; see Coconut crab
Romalum, 7
Roses, 46
Rota, 11, 12, 100, 103, 116, 134
Rotenone, 84
Rubber, 34, 38, 47, 51, 60
Rubber-crude oil solution, 83
Rumina decollata, 21, 106, 191
Ryukyu Islands, 15, 195-96; see also Amami
Oshima; Okinawa
Saccharum; see Sugar cane
Saipan, 11, 12, 54, 102, 134
Salt, tolerance to, 29
Salvia, 43
Sand, 63, 78
Sarawak, 15
Sarcophaga, 118-20
Sarcophagidae, 118-20
Sargus, 120
Sawdust, 66, 70, 71, 78, 81, 83, 94
Scaevola, 47
Scaphinotus, 111
Scarabaeidae, 113
Scavenging, 20, 57-58, 60
Sciomyzidae, 118-20
Sciurus, 122
Secretive habits, 19, 26-27, 31, 59, 95
Seedlings, 49
Senility, 98, 182
Sesame, 50
Sexual maturity, 22
Seychelles, 15, 133
Sheep, 160
Shell
calcium, source of, 34, 57,  160, 162-64
chemical analysis, 162-64
color, variation in, 24, 25
distribution, effect of lime on, 33
form, variation in, 24-25
loss of, 32
malformed, 24-25, 32, 184; see also Ab-
normalities
mosquitoes breeding in, 57
protection, 32
rasping, 34, 57
size, variation in, 24, 182
traumatic breaks, 31-32, 183-84, 189
256
INDEX
 
Shell—Continued
variability, 24-25, 142-43, 184; see also
Variability, environmental influence
on
effect of lime on, 33
influence of diet on, 25
Shifting cultivation, 100, 168
Shrew, 121, 123
Silicate clay, 78
Silicon dioxide, 162, 164
Singapore, 8, 10, 15, 17, 189
Sisal, 50
Size; see Shell, size, variation in
Slime; see Mucus
Slugs, 56, 178; see also under genus
Slugs, snails, comparison, 64, 73, 76, 85
Snail-free period, 38
Snail meal, 160-71
Snails
in commerce, 146-47, 150-51, 152, 153,
158-59, 169-70
as food; see Human consumption; Hu-
man use
predatory, 126-36; see also Edentulina;
Euglandina; Gonaxis
preparation of, 147-48, 149, 153, 154, 155,
157-58
Snakes, 123, 126
Soap solution, 83
Sodium arsenate, 65
Sodium arsenite, 65, 89
Sodium carbonate, 68, 82
Sodium chloride, 83, 99
Sodium dinitro-orthocresylate, 83
Sodium fluoaluminate, 70
Sodium fluoride, 82, 83
Sodium fluosilicate, 64, 75, 76, 83, 88
Sodium hydroxide, 68, 82
Sodium hyposulphite, 68
Sodium nitrate, 68, 83
Sodium silicofluoride, 68
Sodium sulphocyanide, 68
Soil
acid, 34, 53
alkalizing, 34, 53, 168
consumption of, 57, 163
coralline, 33, 168
eggs and adults in, 19
erosion, 50, 53, 96
leaching, 96, 168
lime supply, 33
and molluscicides, 65, 66, 73, 78, 83, 87,
90-91
nitrogen, 50
nutrients, 96
Solanum, 43
Solenopsis, 105
Soot, 84
Soursop, 47
South America, 196
South Pacific, 4
Spinophora, 120
Spirochetes, 123, 189
Squash, 47
Squirrel, 122
Staple crops, 47, 52
Starvation, 28, 29, 142, 183, 186
Sterility, 131, 182-83
radiation, 202
Stomach poisons, miscellaneous, 84
Strains, pathogens, 190, 191
Strangesta, 129, 130-31, 136
Stratiomyidae, 120
Streptaxis; see Gonaxis
Stress, 189
Strophocheilus, 1, 65, 92, 148
Strychnine sulphate, 84
Submersion,  tolerance  to;  see Drowning,
resistance to
Subulina octona, 56, 135, 192, 193
Sugar in baits, 64, 65, 76, 81, 84, 86
Sugar cane, 47, 51, 53, 59, 103
Sulphocyanides, 84
Sulphur, 68, 73, 82
Sumatra, 10
Suncus, 123
Sunlight, 29, 74, 75, 86, 87, 93, 96, 101, 105,
183; see also Light
Sweet potato, 12, 47, 52, 59
Sword grass, 168
Symbiosis, 124-25
Symptomatology; see Disease; Syndrome
Syndrome, 185-92; see also Disease
Synergism, 91, 194
Taboo, 20
Tahitian spinach, 49
Tanglefoot, 82
Tapeworms, 56
Taro, 48, 52
Tartar emetic, 84, 90
Tea, 34, 48, 52, 53
Teakwood, 48
Tectona, 48
Tefflus, 110-13, 129, 133, 144
Temperature, 28, 29, 31, 33, 39, 75, 87, 197
fluctuation, 31, 197
Tephrosia, 44
Tetanoceridae, 120
Thailand, 15, 190
INDEX
257
 
Theba pisana, 50, 63, 64, 67, 69, 72, 83, 95,
99, 113, 114, 147, 174, 199-200
Theobroma, 42
Thermophilum, 111
Thespesia, 48
Thiamine, 165
Thiourea, 68
Ticks, 125
Tinian, 11, 12, 38, 103, 134
Toads; see Bufo marinus
Tobacco, 44, 48, 52, 60
Tobacco dust, 68, 82, 83
Tomato, 48
Torenia, 43
Toxic factor
in consumption by cannibal snails, 131,
142
in   consumption  of giant   toad,  59-60,
104-5
in human consumption of snails, 155-56
Toxicant, requirements, 86-87
Toxicology, 61-91
Transmission, 188-89
Traps, 100-101
Trauma, 31-32
Traumatic   breaks;   see   Shell,   traumatic
breaks
Tree nettle, 48, 52
Trees as refuge, 26-27
Triodopsis, 106, 123, 147
Truk Islands, 7, 19, 134
Tuberculosis, 13, 150, 151, 152
Turkeys, 114
Turtle, 126
Ultraviolet, 96
Uman, 7
Uncultivated plants, 49
United States, 176, 195, 196, 197
Unjust charges, 59-60
"Upo," 43
Urukthapel, 14
Valeraldehyde, 80
Vancouver, 176
Vanda, 45
Varanus, 104-5, 125-26, 140
Variability, environmental influence on,
25, 162-63, 166; see alsp Shell, varia-
bility
Varicella, 135
Vectors, 55-57, 189
plant diseases, 53
Vegetable sponge, 49
Vegetables, 48, 49, 98, 114
Ventridens, 106
Veratrum, 82
Veronicella, 102, 103
Vetiveria, 83
Victaphanta, 129
Vietnam, 16
Vigna, 43
Viruses, 178, 189
Vitamin A, 164
Vitamin assay, 164-65
Vitamin B, 165
Vitamin C, 165
Vivipara, 6, 154, 166
Wandolleckia, 118-19
War salvage, 19, 174-76, 197
Warfarin, 54, 84, 122
Water content, 25, 160, 161, 163, 164
Water loss; see Dehydration; Desiccation
Watermelon, 116
Weed killers, 65, 83, 96
Weeds, 49
West Indies, 4, 196
Wheat, 51; see also Bran, wheat
White arsenic, 66
White oil emulsion, 67
Whitewash
poisoned, 64-65, 84
snails eating off houses, 54
Wind, 35; see also Anemotaxis
Wire cages, 94
Wire screen, 93
Xanthosoma, 49
Xerarionta, 28
Yam, 49, 52
Yam bean, 41
Yap, 4, 7, 103
Yeasts, 123, 189
Zea, 42
Zinc, 83, 93
Zinnia, 49
Zonitidae, 113
Zonitoides, 53
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