ARGENTINE ANTS UPON A TEA TABLE. (ORIGINAL.)
U. S. DEPARTMENT OF AGRICULTURE,
BUREAU OF ENTOMOLOGY-BULLETIN No. 122.
L. 0. HOWARD, Entomologist and Chief of Bureau.
WILMON NEWELL, M.S.,
T. C. BARBER, B. S. A.
ISSUED JU'NE 26, 1913.
GOVERNMENT PRINTING OFFICE.
B UREA U OF ENTOMOLOGY.
L. 0. HOWARD, Entomologist and Chief of Bureau.
C. L. ALARLATT, Entomologist and Acting Chief in Absence of Chief.
R. S. CLIFTON, Executive Assistant.
W. F. TASTET, Chief Clerk.
F. H. CHITTENDEN, in charge of truck crop and stored product insect investigations.
A. D. HOPKINS, in charge of forest insect investigations. I
W. D. HUNTER, in charge of southern field crop insect investigations.
F. M. WEBSTER, in charge of cereal and forage insect investigations.
A. L. QUAINTANCE, in charge of deciduous fruit insect investigations.
E. F. PHILLIPS, in charge of bee culture.
D. M. ROGERS, in charge of preventing spread of moths, field work. I
ROLLA P. CURRIE, in charge of editorial work. .4
MABEL COLCORD, in charge of library.
SOUTHERN FIELD CROP INSECT INVESTIGATIONS.
W. D. HUNTER, in charge.
W. D. PIERCE, J. D. MITCHELL, G. D. SMITH, E. A. MCGREGOR, HARRY PINKUS,
B. R. COAD, G. N. WOLCOTT, W. A. THOMAS, R. W. MORELAND, C. E. HESTER,
engaged in cotton-boll weevil investigations.
F. C. BISHOPP, A. H. JENNINGS, H. P. WOOD, W. V. KING, engaged in tick investi-
A. C. MORGAN, G. A. RUNNER, S. E. CRUMB, D. C. PARMAN, engaged in tobacco insect
T. E. HOLLOWAY, E. R. BARBER, engaged in sugar cane insect investigations.
J. L. WEBB, engaged in rice insect investigations.
R. A. COOLEY, D. L. VAN DINE, A. F. CONRADI, C. C. KRUMBHAAR, collaborators.
LETTER OF TRANSMITTAL.
U. S. DEPARTMENT OF AGRICULTURE,
BUREAU OF ENTOMOLOGY,
Washington, D. C., January 2, 1913.
SIR: I have the honor to transmit herewith and to recommend
for publication as Bulletin No. 122, of the Bureau of Entomology,
a manuscript entitled "The Argentine Ant," by Mr. Wilmon Newell,
formerly a collaborator, and Mr. T. C. Barber, formerly an agent of
The Argentine ant is an imported pest of great importance. It
is unique among injurious insects of this country in the diversity of
the damage that it causes. It is not only a household pest of the
first rank, but it affects materially the interests of sugar planters,
orange growers, and others. The territory infested by this ant is
being rapidly extended. For all of these reasons it is important that
there be placed on record a full account of the studies that have been
conducted regarding it.
The work upon which this manuscript is based was begun by Mr.
Newell as secretary of the Louisiana State Crop Pest Commission.
Later Mr. Newell continued the work as a collaborator in this bureau,
and Mr. Barber, an agent of the bureau, but working under Mr.
Newell's direction, added to the results obtained.
L. 0. HOWARD,
Entomologist and Chief of Bureau.
Hon. JAMES WILSON,
Secretary of Agriculture.
Introduction.............. .... ... ................... .......--- .-.-- .- 9
General considerations .................................................... 10
History and distribution -..............................................----------------------------------------------.... 11
Introduction into Louisiana-........................................... 12
Present distribution in the Southern States...---...-.................. 14
Occurrence and distribution in California................................ -----------------------------15
Area of ultimate infestation.........--.-..--.-.-.-.....-..-..-....... 16
Common name.................... ..... ... ...-.....-.-.. ....-.... .. 18
M eansof dispersion-- ------...... -.................................................. 19
Natural spread ................... ...... ... ..... ... ... ....-....-- 19
F light ........................................................... 19
Dispersion by streams--.. ........................................... 20
Artificial dissemination.....---------------------------------- ----------... .. 20
Economic im portance...................................................... 22
Systematic position..................................................... 26
Description of the species- .--.- --.....---.....---.-.--...........- .. 27
Resemblance to other ants........................................... 30
M ethods of study.......................................................... 32
Establishing colonies for study........................................ 36
Life history............................................................. 38
The egg............................................................ 38
Period of incubation-- .............................................. 39
The larva ............................................................ 40
Duration of the larval stage- ....................................... 41
The pupa............................................................ 42
The worker pupa-....... .......................................... 42
The m ale pupa-................................................ 43
The queen pupa ................................................... 44
The callow or general stage ...-..-..... ...... ...-................. .. 45
Time required for complete development............................... 45
The adults......................................................... 46
The worker..................................................... 46
Length of life............................................... 47
The m ale .......................................................... 47
The queen .............................................. ...... 48
The virgin queen ............................................. 48
The deilated, or fertile, queen ................................ 49
The colony as a whole......--...--..- ..-. .. ....---....... ....... .... .. 51
Seasonal history ........................................................ 51
W inter colonies................................................. 51
Summer colonies...... ............................................. 52
Compound colonies or communities................................ 54
The colony as a whole-Continued.
General migration or dispersion................................
Migration to food supply...........................................
Nests or natural formicaries ....................
Underground nests ........................
Wet-weather nests or sheds................
Aversion to light................'...
Sense of smell........................
Sight.. .. .............. ........
Rate of travel.......................
.." .' :' :iii
Storage of food ............... ..... .......................
Relations with other Arthropoda.........................................
Coccidae and Aphididae.............. ............................
List of Coccidae and Aphididae attended by the Argentine ant......
Antagonism toward other insects.................................
The Argentine ant and the boll weevil........................
Beneficial aspects of the ant's activities........................
Sym biotic relations-.................................................
Natural enemies ............................................
Insects and spiders............................................ ..
Birds ............. ........ ..................................
Experiments with Pediculoides..................................
Experiments with fungous diseases................................
Low tem peratures....................................................
M ethods of repression....................................................
Experiments with repellents............................ .........
Corrosive sublimate and "ant tapes"..........................
Experiments with fumigants and contact insecticides..................
Experiments with poisons.....................................
Control of the ant in residences ..................................
Control of the ant in apiaries................. ..............
Control of the ant in orange groves -...... ............. -........------
Method of dissemination in the orange section .....................
Experiments in the orange groves-.......----.-----------.........................
Experiments with winter trap boxes..........................
. . . . - . -. - - -
. . . . . . . - -. - -
PLATE I. Argentine ants upon a tea table ........................... Frontispiece.
II. A small colony of Argentine ants as seen in one of the artificial for-
m icaries ..................................................... 32
III. "Formicarium," or special insectary, constructed and equipped for
the study of the Argentine ant................................. 36
IV. Immature stages of the Argentine ant............................. 40
V. Wet-weather nest or shed, erected by Argentine ants during rainy
weather- ................................................... .. 56
VI. Orange tree after exposure to Argentine ants for three seasons ....... 64
VII. Beehive on ant-proof hive stand, the latter resting upon a concrete
VIII. Orange orchard dying as a result of infestation by the Argentine ant. 92
IX. Batture of the Mississippi River 50 miles below New Orleans, over-
grown with willows and heavily infested by the Argentine ant.... 92
X. Siphon, pumping plant, and barrier ditch used in limiting the spread
of the Argentine ant ........................................... 92
XI. Bridges which the Argentine ant can not cross .................... 92
XII. Trap box and fumigating cover for destruction of Argentine ant
while in winter quarters.....................................------------------------------------.. 96
XIII. Orange grove in which campaign was waged against the Argentine
ant-appearance of the grove after recovery ..................... 96
FIo. 1. Map of Alabama, Mississippi, and Louisiana, showing counties in the
Southern States which are infested by the Argentine ant............
2. Distribution of the Argentine ant in California.......................
3. Injury to the stand of sugar cane by the sugar-cane mealy-bug
(Pseudococcus calceolariax), which is attended by the Argentine ant..
4. Sugar-cane mealy-bugs on sugar cane.............................
5. Covering constructed by the Argentine ant to protect the mealy-bugs..
6. The Argentine ant, adult forms.................................
7. Artificial formicary or cage used in studying the Argentine ant.....
8. Artificial formicary with parts assembled ready for use............
9. Entrance of artificial formicary shown in figures 7 and 8..............
10. Argentine ant removing pupa of sorghum midge from a head of sorghum.
11. Ant-proof hive stand, upturned, showing method of construction ....
12. Ant-proof hive stand, sectional view............................
13. Ant-proof hive stand, from above, showing construction..............
TIHE ARGENTINE ANT.
The Argentine ant (Iridomyrmex humilis Mayr), which is made the
subject of the present paper, is the first among the Formicidee to attain
the front rank among injurious insects in the United States. In its
field the Argentine ant is not excelled in destructiveness by even the
gipsy moth, the boll weevil, or the San Jose scale. Though this ant
is limited as yet to comparatively small areas, the observations and
experience of the authors fully convince them that future years will
see this insect steadily invading new territory and forcing its depre-
dations upon the inhabitants of all southern California and most of
the Gulf States.
The present paper aims to present, in as concise a manner as possi-
ble, the principal results of five years of almost constant observa-
tion and experiment by the senior author at Baton Rouge, La., and in
the orange-growing section of the same State, together with observa-
tions made by the junior author at New Orleans in connection with
his investigations of sugar-cane insects.
The junior author has prepared in their entirety the portions deal-
ing with the "Area of ultimate infestation," and the "Relation of the
ant to Coccidte and Aphididte," and to him is also to be credited the
important discovery that mating of the queens may occur within
the formicary or nest of the colony. The remainder of the paper,
except where otherwise noted, is compiled from the notes and records
of the senior author.
In the tedious work which accompanied the determination of the
ant's life history, from 1907 to 1910, much assistance was rendered
by the young men associated with the senior author in the work of
the Louisiana State Crop Pest Commission, particularly Messrs.
Harper Dean, A. H. Rosenfeld, G. A. Runner, M. S. Dougherty,
G. D. Smith, and R. C. Treherne.
The writers are under obligations to Dr. W. M. Wheeler, of the
Bussey Institution, Harvard University, for permission to use his
redescription of Iridomyrmex humilis and for his kindness in reviewing
the paragraphs upon "Systematic position" and "Resemblance to
Our thanks are also due to Messrs. R. S. Moore and John Meyer,
extensive orange growers of Louisiana, for their liberal cooperation
10 THE ARGENTINE ANT. /3
and assistance in experiments carried out in the infested orange :
Twenty years ago the Argentine ant was first noticed in New Or- i
leans, La., by Mr. Edward Foster, reference to whose interesting
account of the "Introduction of Iridomyrmex humilis Mayr into New
Orleans" will be found on a subsequent page. The species had
doubtless been introduced years before that time, but was gathering
strength and establishing itself for a considerable period before its l
numbers became sufficient to attract attention. Mr. Foster men-
tions it as occurring in 1891 in "fair numbers." Since then it has
increased from a few scattered and apparently insignificant speci-
mens to armies and hordes numbering myriads of individuals It
has spread from a few blocks on the water front of the Mississippi
River over practically the entire city, and has sent out vast numbers
of colonists for hundreds of miles along the railways and waterways '
radiating from New Orleans. These pioneers have succeeded in
founding scores of communities of more or less importance in the
smaller cities and towns. Each of these communities is in turn
furnishing its quota of migrants, and these are extending the affected
territory in all directions from the original source of infestation.
Thus, instead of the dispersion being from one source only, it is now
taking place from hundreds of different points. From an unknown
and little noticed insect this ant has developed into one of the fore-
most household pests in the world, and its ravages affect, directly or
indirectly, the majority of the crops grown in the South. Former
indifference to its movements has given way to concern at its approach,
which, in the orange belt at least, means heavy depreciation in the
value of property.
Continuous study for several years has served to enlighten us on
most of the salient features in the life history and economy of the
species. A considerable number of poisons and repellents have been
tested and have given good results. Methods of isolating, ditching,
and winter-trapping have been devised, and have proved their prac-
tical value in large experiments under field conditions.
Just how much territory this ant will ultimately infest we can not A
foretell with accuracy from the data at present available. It is
quite safe, however, to venture the opinion that the species will
eventually spread over a considerable portion of the Southern States-
certainly over all of the orange and sugar-cane belts, and perhaps over
all of the cotton belt. In California it is likely to cover the territory
corresponding in temperature to the belts mentioned for the South,
which will include the belts occupied by oranges and other tender
THE ARGENTINE ANT.
HISTORY AND DISTRIBUTION.
As stated on another page, this species was first described by Dr.
Gustav Mayr from specimens collected near Buenos Aires, in Argen-
tina. It is also included in the list of Argentine ants by Dr. Carlos
Berg.1 Its occurrence in the Argentine Republic is therefore unques-
tioned, and that Argentina is its native home is also borne out by the
fact that it does not appear to be generally a pest of importance in that
country. Dr. F. Lahille, of the Argentine department of agriculture,
in a letter to the senior author, states that it "is uncommon in
Buenos Aires and in Argentina generally, where it does not cause
annoyance or trouble of value." Mr. Arthur H. Rosenfeld, formerly
associated with the writers in entomological work in Louisiana and
now located at Tucuman, Argentina, writes that he has been unable
to find the species there. Rev. E. Wasmann, S. J., states that this
ant "is a native of Brazil and Argentina," and Rev. Albert Biever,
S. J., of Loyola College, New Orleans, whose careful studies of
this species are mentioned on other pages, has corresponded with
various priests in Brazil and Argentina, with the result that he finds
that this species is a serious pest in parts of Brazil and evidently in
Argentina also. For example, in a letter to Father Biever, Rev. J.
Ferol, S. J., of the Colegio del Salvador, Buenos Aires, writes:
The ants (Iridomyrmex humilis) of which your reverence makes mention are of no
utility whatsoever, but on the contrary are voracious and destructive. Of means
employed to destroy them the most effective, according to information given me, is
the use of an instrument and ingredient of which inclosed herein I send a prospectus
and instructions concerning its use and fVnctions.
Forel2 mentions its occurrence in collections from the States of Sao
Paulo and Rio Grande do Sul, in Brazil. Wheeler also mentions
its occurrence in that country. Dr. Lahille also states that the
Argentine ant occurs in Uruguay and is "especially common in
Mercedes and Montevideo," cities not far removed from Buenos Aires.
According to Stoll 4 and Wheeler5 the Argentine ant, after its
accidental introduction into the island of Madeira, entirely extermi-
nated another ant, Pheidole megacephala Fab., which was itself an
introduced species that had exterminated the native ants before it.
In 1907 M. N. Martins6 recorded the occurrence of this ant in
Lisbon and Oporto, Portugal, and gave a vivid account of its ravages
in those cities and their environs.
1 Enumeraci6n sistematica y sinondmica de los Formicidos Argentinos, Chflenos y Uruguayos. 1890.
2 Ameisen aus Sao Paulo (Brasilien), Paraguay, etc. Verhandlungen der k. k. zool.-bot. Ges. in Wien,
'Entoniological News, January, 1906, p. 24.
4Zaur Kenntnis der geographischen Verbreitung der Ameisen, Mitth. Schweiz. Ent. Ges., vol. 10, pp.
5 Ants: Their structure, development, and behavior, p. 154,1910.
6 Une fourmi terrible envahissant 1'Europe (Iridomyrmex humilis Mayr). Broteria Revista de Sciencias
Naturaes, vol. 6, pt. 1, pp. 101-102,1907.
THE ARGENTINE ANT.
In 1908 Prof. C. P. Lounsbury recognized this ant in Cape Town,
South Africa, where it had already become a household nuisance ana
had displayed its usual r6le of attending mealy-bugs and other insects.
The general belief in Cape Town, according to Prof. Lounsbury, was
that the pest had been introduced through the medium of forage,
large quantities of which were imported from Argentina during the
Boer War (1900-1902) and stored in Cape Town.
In July, 1910, the late Edwyn C. Reed, of Concepcion, Chile, in a
letter to the senior author, reported the occurrence of the species in
that country in large numbers.
In 1908 ants collected by Mr. J. Chester Bradley, of the University
of California, were identified as 1. humilis by Dr. W. M. Wheeler.
Immediately following this discovery Prof. C. W. Woodworth, of the
California Agricultural Experiment Station, visited the authors'
laboratory at Baton Rouge, La., for the purpose of becoming familiar
with the methods used in studying the insect and with the information
which had been gathered concerning it up to that time. On his
return to California he published a brief circular 1 concerning its
occurrence in that State.
From the foregoing it is readily seen that during the past few years
this ant has thoroughly established itself, as a nuisance of the first
order, on four continents, and, owing to the readiness with which it is
disseminated through the ordinary channels of commerce, there
seems little reason for supposing that it will not eventually invade
all of the semitropical countries of the globe.
INTRODUCTION INTO LOUISIANA.
As with most imported species, the original time and place at which.
a foothold was obtained by the Argentine ant in Louisiana must be
largely conjectural. However, we are able to conjecture with rather
strong circumstantial evidence to guide us. Not only does the tes-
timony of inhabitants indicate New Orleans to be the original starting
point of this species in the South, but its enormous numbers and the
extent to which it has exterminated other species of Formicidie con-
firm the opinion that it has been in New Orleans longer than else-
Mr. Edward Foster,2 of the editorial staff of the New Orleans
Daily Picayune, has given us the earliest record of its occurrence in
New Orleans. He noted it in 1891 in St. Charles Avenue, 9
squares from the river and 12 from Canal Street. It was then
1 The Argentine ant in California. Cal. Agr. Exp. Sta., Cir. 38, August. 1908.
2 The introduction of Iridomyrmex humilis into New Orleans. Journm, Econ. Ent., vol. 1, No. 5. pp.
289-293, October, 1908.
HISTORY AND DISTRIBUTION.
present in "fair numbers." At that date it was very scarce in
Audubon Park and below Canal Street, but was present in considerable
numbers between Magazine Street and the river.
"Five or six years later" he found it in St. Peters Avenue, near
St. Charles, but it was not abundant. This is about 40 squares
north and west from the point on St. Charles Avenue first referred to
by Mr. Foster.
In a personal letter to the senior author, Mr Foster writes as
I have known the species since 1891. At that time it was a rarity in Audubon Park,
but was very common in the section immediately above Canal Street. Below Canal
Street it was not at all plentiful. The boundary of the nuisance then was virtually
from Magazine Street to the river.- The coffee ships from Brazil, I understand, have
always landed about where the wharves are now situated (on the river front, adjoining
the area above mentioned), but from what we know of the spread of insect nuisances
the first batch of immigrants must have come in years before I came across their
Mr. E. S. G. Titus,' quoting Mr. E. Baker, former superintendent of
Audubon Park, states that in 1896 "they extended over but a small
area, reaching approximately from Southport docks to Carrollton
Avenue and from the river bank to Poplar Street," and that "in 1899
they were first noticed in Audubon Park." This area, from Southport
to Carrollton Avenue, is located about 5 or 6 miles northwest of the
area between Magazine Street and the river, noted by Foster to be
well infested as early as 1891. Mr. Baker, therefore, had not been
familiar with the original area of heavy infestation, but merely noted
the species after it had invaded the part of the town where he resided.
Mr. Titus's information that the species was first noted in Audubon
Park in 1899 was of course secured from citizens, who failed to note
the ant until it had reached prodigious numbers in the same place
that Foster had found it a "rarity" in 1891. The dissemination to
Audubon Park was undoubtedly from the heavily infested area
between Magazine Street and the wharves already referred to.
The distribution of the species in 1904, as given by Mr. Titus,2 was
Across the river in Algiers and adjoining small settlements; at West End, Spanish
Fort, and Milneburg, summer resorts on Lake. Ponchartrain; Bay St. Louis, Miss., a
summer resort between New Orleans and Mobile; along the Texas & Pacific Rail-
road at Donaldsonville, Cheneyville, and Alexandria; along the Southern Pacific at
Thibodeaux, Schriever, Houma, Berwick, Morgan City, Franklin, New Iberia, and
La Fayette, and at Opelousas.
There is every reason for supposing that this ant was introduced
into New Orleans by means of the coffee ships which have for years
1 Bul. 52, Bur. Ent., U. S. Dept. Agr., p. 79, 1905.
2 Ibid., p. 82.
THE ARGENTINE ANT.
passed back and fdrth between that city and Brazilian ports. This
view is supported by the fact that large numbers of the ants we
first noticed in the vicinity of the wharves where these ships unloaded
their cargoes and also by the fact that these ships have been the only
means of regular communication between New Orleans and the
countries in which the ant is indigenous. That this and other species
of ants are actually transported on ocean-going vessels has been fre-
quently observed. Thus in July, 1911, the senior author, while a
passenger on one of the largest coastwise vessels between New Or-
leans and New York, found colonies of this same ant occupying pro-
tected situations in the woodwork of the steamer. Dr. W. M. Wheeler
also writes us that while returning from Guatemala aboard a fruit
FIG. 1.-Map of Alabama, Mississippi, and Louisiana, showing counties in the Southern States which are
infested by the Argentine ant, according to the authors' records. (Original.)
steamer in January, 1912, he found it infested with another common
ant, Prenolepis longicornis Fab.
PRESENT DISTRIBUTION IN THE SOUTHERN STATES.
The area in the Southern States within which the Argentine ant
is known to occur at present extends from Montgomery, Ala., to
Lake Charles, La., a distance of about 380 miles east and west; and
from Delta, La., to the mouth of the Mississippi River, a distance of
about 250 miles north and south. (See fig. 1.) This section is not
uniformly infested, but contains a great number of infested areas of
more or less importance, ranging in size from many square miles of
HISTORY AND DISTRIBUTION.
occupied territory, as illustrated by the infestation at New Orleans,
to areas where the ants are so scarce that one not accustomed to their
habits would fail to discover them. The latter condition prevails at
present in Mobile, Ala. The only places remote from railroads
where they have been discovered are upon the banks of the Missis-
sippi River below infested localities. Their presence in such loca-
tions is easily accounted for by supposing that they have been carried
thither on driftwood, which, carrying numbers of ants from infested
places farther up the stream, has become stranded on the river banks,
thus establishing new foci. In all other cases the infested territory
is on a railroad, and usually on a main line running out from New
Orleans. For example, nearly every town along the Southern Pa-
cific Railway between New Orleans and Lake Charles is infested, and
the same statement applies to points on the Louisville & Nashville
Railroad between New Orleans and Mobile.
OCCURRENCE AND DISTRIBUTION IN CALIFORNIA.
The first specimens of the Argentine ant observed in California
were collected in 1907 by Mr. J. Chester Bradley, at that time an
assistant in the entomological department of the University of Cal-
ifornia. The identity of the specimens was not established until
1908, when Dr. W. M. Wheeler found them to be Iridomyrmex humilis
As soon as the dangerous nature of the pest was known, Prof. C. W.
Woodworth took steps to make a study of the species along the same
lines as was being conducted in Louisiana at that time, and as a result
of his preliminary work he issued a warning circular 1 to the public
in August, 1908. In this circular he gave a brief outline of the
habits of the ant and reported the following localities as infested:
In the central portion of the State, East Oakland, Alameda, San
Francisco, San Jose, Cupertino, and a point near Campbell; in the
southern part of the State, Los Angeles, Azusa, and Upland.
In 1910 Prof. Woodworth published another small bulletin 2 giving
the results of his two years' study of the insect. In this paper the
infested territory was more clearly defined, and was estimated as
consisting of a total area of 5,000 acres. About twice the area was
reported infested in 1910 as in 1908, owing to the discovery of a few
new colonies and the natural spread of the ones first discovered.
Our information as to the extent of the infested area in California
(see fig. 2) has been obtained principally through the kind offices of
Mr. Ralph Benton, of the California Agricultural Experiment Station,
and Mr. P. E. Smith, of Santa Paula, Cal., as well as from the publi-
1 The Argentine ant in California. Cal. Exp. Sta. Cir. 38, Berkeley, Cal., August, 1908.
2 The control of the Argentine ant. Cal. Exp. Sta. Bul. 207, Berkeley, Cal., October, 1910.
THE ARGENTINE ANT.
cations by Prof. C. W. Woodworth, already referred to. All of t
persons agree that the following California points are infested:
meda, Azusa, Berkeley, Byron Hot Springs, Campbell, College I
Cupertino, Fruitvale, Los Angeles, Melrose, Oakland, Riverside,
Francisco, San Jose, Stockton, and Upland.
FIG. 2.-Distribution of the Argentine ant in California. From data furnished by Messrs. Ralph Benton
and P. E. Smith. (Original.)
AREA OF ULTIMATE INFESTATION.
Up to the present we have no exact data to indicate the final limit
of the area which may become infested by these ants. They appar-
ently thrive as well at Delta, La., at an elevation of 87 feet, as they,.
do near the mouth of the Mississippi River, 300 miles to the soutl
and almost at sea level. They seem to be little or not at all affected
HISTORY AND DISTRIBUTION.
by the variation in the amount of precipitation annually as between
different localities, for they seem to flourish as well at San Jose and
Los Angeles, Cal., with average annual rainfalls of 14.8 and 15.6
inches, respectively, as they do at New Orleans, La., where the aver-
age annual rainfall is 57.6 inches. The range of temperature to
which they have adapted themselves at different points does not
vary so greatly, but is nevertheless considerable. They have suc-
ceeded in establishing themselves at San Francisco, Cal., where the
mean annual surface temperature is 56 F., or 13 cooler than the
mean annual surface temperature at New Orleans, La.
If we assume that the Argentine ant is unable to persist in local-
ities where the mean annual temperature is below 55, we will find
that the isotherm of this temperature extends almost up to Columbus,
Ohio, and past St. Louis, Mo., and will include over one-third of the
United States, or more than 1,000,000 square miles. It is very
unlikely, however, that this neotropical species will be able to endure
the cold winters in the northern parts of this area. It will probably
be more nearly correct to assume that its advance will be checked
when it reaches the minimum isotherm of zero, or, in other words,
where the thermometer drops to zero or below during the average
winter. On constructing this isotherm we find that we have the
following area within the United States liable in the course of time
to infestation by the Argentine ant:
Starting at the Atlantic coast line; one-half of North Carolina,
one-half of South Carolina, one-half of Georgia, Florida, a portion of
Alabama, one-third of Mississippi, most of Louisiana, all of lower
Texas, a comer of New Mexico, one-half of Arizona, a little of Ne-
vada, practically all of California, and a coastal strip through Oregon
and Washington. This would extend the infestation into fourteen
States, more or less, and is undoubtedly a very conservative predic-
tion, as already the ant is established at one point, Delta, La., which
is above this line.
In spite of these considerations we are still in the dark as to the
altitudes.at which this insect will thrive, and it may be found later
that altitude will severely limit the distribution of this species, as it
does that of many other insects. Table I gives the elevation and
climatological data for a number of infested points in the United
States, and from this table it will be noted that the elevation of
points now infested varies from sea level to 338 feet.
The climatological data given in Table I are taken from Bulletin Q,
Weather Bureau of the United States Department of Agriculture,
1906, entitled "Climatology of the United States," by Alfred Judson
18 THE ARGENTINE ANT. -
TABLE I.-Data concerning various towns infested with the Argentine ant.
Mean Absolute mr Absolute MailJ
ame of ton Eleva- annual maximum ium minimum Wbi Wtp *i.
tion. temper- temper- ma.mu temper- .mnmum' lip 'i
nature. attire. mea ature. ti. .
Feet. F. F. aF. F. ". Ii ..a "I,
Montgomery, Ala .......... 196 66 107 90 -5 40 ..t
Mobile, Ala...... ....... ... 11 67 102 89 1 45 '. I
Vicksburg, Miss............ 229 65 101 90 1 42 ii ...
Meridian, Miss --------------............. 338 64 104 89 -6 38 i ii
Hattiesburg, Miss .......... 154 67 103 92 1 40 n
Biloxi, Miss ................ 24 67 100 88 1 43 .61. L ''
Alexandria, La............ ------------- 77 66 109 92 2 39 59 :OI.
Baton Rouge, La.......... ----------- 62 67 103 90 2 42 54. _i
Delta, La.................. 87 (i) (i) (i) (I) (1) (i)
Lake Charles, La........... 22 67 103 91 3 41L .I
New Iberia. La ............. 15 68 101 89 6 45 S.S '
New Orleans, La........... 8 69 102 88 7 48 57.: 6 i
Sacramento, Cal ........... 29 60 108 87 19 40 1g. .. -
San Francisco, Cal ----------......... 28 56 100 65 29 46 23,5li.
San Jose. Cal............... 95 58 104 .......... 18 ......... .-145 .
Los Angeles, Cal ............ 287 62 109 82 28 45 SI
'Records not available.
NOTE.-" Summer maximum, mean "=theaverage of the total maximums for June,:..
July, and August. "Winter minimum, mean "=the average of the total minimunm .,,:'..
for December, January, and February. ::
COMMON NAME. .....
The name "Argentine ant" was first used by the senior author for :
this species in 1908, when the public was on the point of accepting
the name "New Orleans ant." The permanent use of the latter
name would manifestly have been unjust to the Crescent City, for .
that city was in no way responsible for the introduction of the pest. ::
As stated on preceding pages, this ant was originally described from J
specimens collected in Argentina, South America, and up to the
present time we have no reasons for not believing that this is one, at
least, of the countries in which this ant is native. The naming of
this ant after the country from which it was first described is by no, :.;
means without precedent. Many other common insects, such as i
the San Jose scale, American cockroach, Colorado potato beetle, '
Mexican cotton-boll weevil, etc., have received their popular names l
in the same manner.
Various common names have been suggested from time to time,
among them "crazy ant," "tropical ant," "pernicious ant," etc.,
but all have the disadvantage of being as applicable to other species
as to Iridomyrmex humilis and none of them is distinctive.
The term "Argentine ant" has been readily accepted, alike by
entomologists and the press, is concise, and not likely to be confused '.
with similar names; hence we believe it to be as good a name as can
be adopted. ..
THE ARGENTINE ANT.
MEANS OF DISPERSION.
Under strictly natural conditions, the rate of dispersion of Argen-
tine ants is very slow. Owing to their intensely social habits they
spread but slowly from a locality until the number present becomes
excessive for the food supply or unless adverse conditions, such as
flooding, occur which compel them to seek fresh locations. They
will then spread in all directions, but will go little farther than is
necessary to give them sufficient foraging area to insure the food
required. However, if a large food supply is discovered at a con-
siderable distance from the colony, a heavy trail of workers will
soon be formed between the food and the nest, composed of many
thousands of tiny insects, each busy carrying a load of the coveted
material back to the nest or going out for another load. Sometimes
they will construct a new nest in the neighborhood of the food sup-
ply, and to this they will transport a number of pupae, larva, and
eggs from the parent nest. In the course of a day or so this new
colony will be thoroughly established, with a full supply of queens,
workers, and immature stages, and will then be capable of supporting
itself and increasing in numbers without assistance from the parent
Under normal conditions it is likely that the rate of spread does
not amount to more than a few hundred yards each year. When
food is plentiful, a well-traveled road or a paved street may restrict
the spread for a considerable period, but when any much-desired
food supply, such as the excretions of aphides or scale insects, is to be
reached, nothing short of running water proves an effective barrier.
It is possible, but scarcely probable, that the queens may aid the
natural dispersion by means of flight, but there are several reasons
why this is doubtful. One of them is that the flight itself is a very
uncertain event, as during the five years that these ants have been
studied in Louisiana only one general flight has been observed. It
has been established that the young queens can mate in the nest
without taking a marriage flight at all, and apparently this is what
usually takes place. Even should a fertilized winged queen fly or
be transported by the wind to any considerable distance from the
ant-infested territory, it is very doubtful whether any eggs she might
lay would ever hatch. The queen has never been observed assisting
in the slightest degree with the rearing of the young in the nest, nor
have we succeeded in getting eggs to hatch when they were not
cared for by the workers. As the workers are never winged, the
queen would necessarily be alone, and it would be very unlikely
20 THE ARGENTINE ANT. I.
.... ." E'. "* .. :E ...:iilH
"" ...":"..: .i;;..iia,,,ff
that the queen would develop the instinct of attending to and
for the eggs, larva, and pupa in succession for -several months .
Also, the queens are quite helpless and appear to be entirely incapar *-i
ble of defending themselves against other insects. The writer has ....
observed a queen ant being captured and bound by a minute spider,
considerably smaller in size than her own head, without making |
the least attempt to struggle. It therefore seems improbable that a& : *..i
defenceless queen could maintain herself in a hostile country for"""..
several months without the assistance of workers. il
Furthermore, we have several times kept Argentine ant queens
isolated in small nests, sometimes singly and sometimes in groups,
but have never yet succeeded in hatching eggs in these nests, or in i|
rearing larvae to the adult stage.
The fact that ditches of running water have proven sufficient bar- :
riers to prevent the spread of the species in orange groves appears to
disprove the theory that queens returning from the nuptial flight can, ,
without the assistance of workers, establish new colonies.
DISPERSION BY STREAMS.
As previously mentioned, driftwood is probably the most important |
agency in the natural dispersion of the Argentine ant. Along the
Mississippi River, below the infested territory, we find a considerable
number of larger or smaller colonies of the ants, and in places the
batture will be infested for miles, with practically no ants inside the |
levee. This can only be accounted for by ants floating down the
river upon driftwood from infested localities. The river banks are
covered with logs, more or less rotten, which have stranded during ..
high water. In the infested territory these logs are found full of
ants in all stages in enormous numbers. During high water some of
these logs drift and lodge alternately, gradually working down the
river, and distributing colonies in their wake.
The writer has several times seen complete colonies of ants on a
floating log, unable to escape. All that was required was a little
further rise of the water to start them down the river, with their
cargoes of ants.
ARTIFICIAL DISSEMINATION. ,?
Unquestionably the main distributing agent of the Argentine ant I
is man himself, by means of railway trains, boats, and other vehicles ;
which he controls and utilizes in the transportation of freight and ...
commodities of all kinds. The ants must necessarily have been intro-
duced to this country by means of ships, and railways have been the ":
I The "batture" is that land lying between the true bank of the river and the levee. The batture is
subject to overflow during high water, is ordinarily not cultivated, and is frequently overgrown with wil- '
lows. The batture is said to be "outside" the levee, while land protected by the levee from high water is "
said to be "inside" the levee. ,4j
MEANS OFP DISPERSION.
Principal means of dissemination since they succeeded in establishing
themselves. This is evident, as all the centers of infestation so far
discovered, with the exception of those down the Mississippi River,
the presence of which has just been explained, are located upon
railway lines; in the Southern States, upon main lines running out
of New Orleans.
The ants are easily transported in packing and freight of various
kinds. Large numbers of potted plants are shipped out of New
Orleans to-the surrounding country, and in many cases complete
colonies of ants are sent with them in the soil surrounding the roots.
Boxes and barrels of groceries, packing placed around fragile material
to prevent breakage, and shipments of household goods may all
contain queens and workers when shipped from infested points. The
writer has observed a queen and many workers inside an empty
passenger coach, which had been standing on the track for several
hours during a rainstorm.
The danger of promiscuous infestation is somewhat lessened by the
fact that it isnecessary for a queen ant to be transported with the workers
in order that a new colony may be founded. In a large series of ex-
periments conducted to determine this point we have never yet found
any indication that the workers were able to produce eggs, or to
reproduce their kind in any manner. Consequently large numbers
of workers may be scattered broadcast over uninfested territory and,
though they may live for a considerable time, they will ultimately
die out if a queen is not present. It is probably due to this fact that
these ants have not infested a great deal more territory than they
have during the past 10 years, as it is a certainty that thousands
of workers are being continually shipped from infested territory into
uninfested localities. At the same time the danger that fertile
queens will be transported is considerable, for we have frequently
found deflated queens foraging with the workers. The fertile queens
will "take up" with any workers of the species, and it is only necessary
for a queen and workers to be present in a new locality in order to
start a self-perpetuating infestation.
SSteamboats plying up and down rivers, carrying freight from
infested points, are responsible for spreading great numbers of ants.
For example, between New Orleans and Baton Rouge, La., there are
over a hundred steamboat landings. These are nearly all infested
by the Argentine ant, and probably the insects were first introduced
in the freight shipped direct to these points from New Orleans or
Baton Rouge. Many of the river steamboats are so heavily infested
by permanent colonies of this ant that the workers are almost as much
of a nuisance in the cook's galley as they are in culinary establishments
22 THE ARGENTINE ANT.
Up to the present time the Argentine ant has attracted most atten-
tion as a household pest. Particularly during rainy weather, when.
honeydew is scarce, the ants invade houses in myriads and drive the
housekeepers almost to distraction. Nearly everything which is ::
edible for human beings is attractive to them, and ceaseless attention
and strenuous effort are necessary to keep them out of pantry and
kitchen. The use of poisons and repellents must be continuous;
if there has been a little carelessness in this regard the foodstuffs '
become filled with countless numbers of ants in a very short time. "
Among the foodstuffs most eagerly sought may be mentioned :
honey, sirups, sugar, candy, cakes, cookies, jams, marmalades, pre-
serves, fruit juices, cream, olive oil, lard, egg (either raw or cooked),
fish (either fresh or canned), and various raw meats, such as chicken,
veal, mutton, pork, beef, etc. Corn meal is sometimes the object
of attack and wheat flour to a slight extent. N
Aside from their invasions of food the ants are household nuisances
generally. No comer or nook is safe from their explorations and the
discovery of something edible is quickly heralded in the nest, whence
come thousands of workers to carry away the plunder. In heavily
infested sections it is often necessary to place bedposts upon panes of
glass coated with vaseline or other repellent in order that the occu-
pant may sleep in peace. To have ants running all over one's person
is disagreeable enough, but what is more serious, they will not hesitate
to attack any part of the body where skin or membranes are tender
enough to be pierced by their mandibles.
Authentic cases are on record where it has been necessary to takei
babes from their cradles and repeatedly immerse them in water to J
rid them of the ants which crawled by hundreds over their bodies
and into their mouths and nostrils. We have even received reports
of infants being killed by the ants, but such reports we have not
verified. Such a thing is not, however, outside the realm of
In groceries and stores they are kept out of sirups, sugar, molasses,
and like products only with great difficulty. In restaurants and
confectionery shops the closest vigilance is required to keep the ants
out of the cakes, candies, ice cream, fruits, etc., as well as out of ice I
boxes, refrigerators,1 show cases, and windows. Meat in butchers'
shops is also a great attraction, and if left unprotected for even a
short time thousands of ants will be swarming over it.,
In nurseries and among ornamental plants the ants foster and
protect countless thousands of scale insects and plant lice, the excre-
tions of which furnish the choicest delicacy with which the ants
SThe temperature of the ordinary refrigerator is not low enough to deter the ants in their foraging.
regale themselves. This protective care results in rapid increase of
these insects, with resultant damage to the plants infested. In
florists' establishments the ants sometimes sever the petals of cut
flowers in their search for nectar.
Visits to flowers of various kinds seem a natural habit, and when
the ants do not find the nectar readily available they quickly cut
their way to it in all cases where the plant tissue is tender enough
to permit of it. In their attacks upon orange blossoms they are
particularly severe, as they sometimes eat their way into the fruit
buds even before the latter are fully open. The workers have also
been noticed regularly visiting the extra-floral nectaries of cotton
and other plants.
To truck growers the ants are very troublesome, owing to the
manner in which they remove certain garden seeds before they have
sprouted. Lettuce seed is especially subject to this attack, and in
infested districts the rows of lettuce seed are covered with corn meal,
which is also attractive to the ants. By the time the ants have
removed the meal the lettuce seeds will have sprouted. The ants
also assiduously attend plant lice on a number of vegetables, making
the latter unpleasant to handle. Cabbage heads are often found
through which plant lice and ants are completely distributed, the
cabbage leaves merely serving as divisions between layers of the
In the sugar-cane fields the ant again comes to the front, owing
to its fondness for the excretions of the sugar-cane mealy-bug,
Pseudococcus calceolaric. (See figs. 3, 4.) In order to protect
these insects from storms and enemies, the ants build protective
coverings and shelters over them and attend them constantly. (See
fig. 5.) As the result of these attentions the mealy-bugs thrive in
numbers and destructiveness to an extent which is impossible where
the ants are not present. Luckily the territory infested by the
mealy-bug is as yet very restricted, but this insect threatens to
become a serious problem in the future, owing to the manner in
which it destroys the eyes of "seed cane" after it is planted, prevent-
ing sprouting and thus injuring the stand. The vacant rows in a
field of cane, due to this injury, are shown in figure 3. The control of
this mealy-bug therefore resolves itself into the problem of controlling
In cornfields it can be easily noticed that aphides are several times
as numerous, and are also more generally distributed, in districts
infested by the Argentine ant than in the noninfested districts. The
ants are also found in great numbers attending plant lice upon cotton
plants, and in a cotton field at Baton Rouge, where these ants were
very numerous, it was noticed that the cotton aphides remained
during teeprin fteya hyaenral lotama
It is in th o
follows its introduction and s .aii
section depends to a coniealexetuothprscerabne
of the Argentine ant. The antalodecnserbeamgtoh,
fig crop by boringthogthrieefrioretrntecayed
of the ripening fig and tuneigteitro.I loasssi h
FIG. 3.-Injry to he stand of sgrcane by the ua-m el-u Peuoocsck~i) he
The ant is veritable plauimn oe eeadbeep
In the poul1try yadti n sa ps htms ercoe "
The ansfind the nests of stighn atclryatatvadi
perchance an egg be broken the ants will come :: :: :: : iiii ,"in schnu bes ha
thefol wllabndo hr est Te loo ad luis ro patill
incbtdebysaepriual ie yteatadwe h
egg r acin h okr wamoe h ongcik nsc
R numbers as to cause their death. Repellents which can be adapted
to such a case are rare, even pyrethrum powder being practically
ineffective. The only substance we have found which would at all
protect the sitting hens is zenoleum powder, liberally sprinkled
in the nest and among the hen's feathers from time to time
during the brooding period. The nests of many birds are
frequented, by the ants in the same way, and the number of
young birds destroyed in this manner must be considerable. The
ubiquitous English spar-
row, however, seems to :
flourish, as ever, in spite ...
'^ '. ., ,
of the ants.
Another form of injury, ::' '
though indirect, is due to N ''"
the antagonism which ex- .i :'
ists between the Argentine : ....
ant and other species of .,
ants, and which terminates . -
only with annihilation of : ;
the native species. As the .,
result of this, beneficial ".:,'
species of ants (such as the ; ;.
"fire ant," Solenopsisgemi- .'.. .,
nata, which destroys a con- . '', o
siderable number of boll . ,
weevils in their immature . '..:...
stages) are exterminated, ...
and their place is taken by
the infinitely more trouble- :.
some Argentine ant. .. :
It may presently be
found that the Argentine 4 r., .C
ant is an important agent :A. y
in the spread of disease.
The workers congregate in FIG. 4.-Sugar-cane mealy-bugs on sugar cane. (Original.)
great numbers around garbage pails, privies, etc., and are frequently
very hard to keep out of sick rooms, the odors seeming to attract them.
They have been watched busily carrying away the sputum of a negro
who was suffering from tuberculosis. There are many ways in
which it is possible for these ants to assist in the distribution of
various disease-producing organisms.
Rarely the activities of this ant take on a beneficial aspect. Father
Biever states that they have in many cases completely exterminated
the bedbugs in the hovels and tenements occupied by poor people in
the city of New Orleans. The same authority several years ago
26 THE ARGENTINE ANT. ./ ... ...
called attention to the scarcity of the common "chiggers" or so-.caI., ..
"red bugs" in parks and yards heavily infested by the ant, and this.j
latter observation has been verified by the junior author in the case-1 ,::::,S*
of Audubon Park, New Orleans. At Baton Rouge, however, the
senior author found the chiggerss" very abundant in premises heat- .
ily infested by the ants. The manner in which these ants destroy
the sorghum midge is described on following pages.
According to the classification adopted by Dr. W. M. Wheeler,'
the Argentine ant is placed in the subfamily Dolichoderinie, which
M 'A P.
FIG. 5.-Cering constructed by the Argentine ant to protect the mealy-bugs. (Original.) ....
is one of the five main subdivisions of the family Formicidie. The
Dolichoderinae are characterized by the cloacal orifice being slit-
shaped and ventrally located instead of being circular and termi-
nally located, as in the camponotine ants, by vestigial sting, by
single-segmented abdominal pedicel, by a much shortened or bell-
shaped gizzard (proventriculus), by the pupae being always naked
(not inclosed in cocoons), and usually by anal glands which produce
a secretion having a very offensive odor. In the case of the Argen-
tine ant, however, this odor is entirely lacking.
SAnts, thei r structure, development, and behavior, 1910.
1 .." : A s,. their: str ct.e .e eop e t .n: bea.o, 191.."-
The subfamily Dolichoderinie contains six North American genera:
Dolichoderus (Hypoclinea), Forelius, Tapinoma, Dorymyrmex, Lio-
metopum, and Iridomyrmex. Iridomyrmex is essentially tropical in
its distribution and only two species are known to occur in the United
States,1 the native Iridomyrmex analis Ern. Andr6, common in cotton
fields of the South, and the introduced species, Iridomyrmex humilis
Mayr, or Argentine ant.
DESCRIPTION OF THE SPECIES.
Three forms only of the adults are found in the colonies of the
Argentine ant, the females or queens, the workers, and the males.
(See fig. 6.) Major and minor workers do not occur, and no workers
seem to act in the capacity of soldiers or scouts more than others.
As previously noted, the species was first described as Hypoclinea
humilis by Dr. G. Mayr, in 1868, from workers collected in 1866 near
Buenos Aires in Argentina, the original description appearing in the
Annuario della Societa dei Naturalisti di Modena, volume 3, page
164. Following is Mayr's description of the species kindly fur-
nished by Dr. W. M. Wheeler, of the Bussey Institution, Harvard
University, from the original edition:
Operia: Long. 2.6 mm. Sordide ferruginea, micans, mandibularum parte apicali
flavescenti, abdomine nigrofusco, tarsis et nonnunquam tibiis testaceis; microscopic
adpresse pubescens; absque pilis abstantibus; subtilissime coriaceo-rugulosa, mandi-
bulls nitidis sublaevigatis punctis nonnullis; clypeus margin antico late baud pro-
funde emarginatus; thorax inter mesonotom et metanotum paulo et distinct con-
strictus, pronoto fornicato, mesonoto longitrorsum recto, transversim convexo, meta-
noto inermi longitrorsum fornicato, pronoto paulo altiori; petioli squama compressa
At the request of the senior author, Dr. Wheeler prepared the fol-
lowing redescription of the worker, and descriptions of the queen
and male, thus making a complete and comprehensive description
of the species:
Iridomyrmex humilis Mayr.
Worker: Length 2.2-2.6 mm.
Head oval, broader behind than in front, with its posterior margin slightly concave
in the middle. Eyes flattened, in front of the middle of the head. Mandibles with
two larger apical and several minute basal teeth. Clypeus short, convex in the mid-
dle, with broadly excised anterior margin. Frontal area and groove present but
rather indistinct. Antennal scapes extending about one-fourth their length beyond
the posterior corners of the head. Joints 1-5 and the terminal joint of the funiculus
distinctly longer than broad; remaining joints nearly as broad as long. Thorax slen-
der, narrower than the head; broadest through the pronotum which is convex, rounded
and nearly as long as broad. Mesonotum nearly as long as the pronotum, sloping,
laterally compressed, in profile evenly continuing the contour of the pronotum. Me-
' An undetermined species of Iridomyrmex, apparently introduced, has been found by Dr. W. M. Wheeler
in a greenhouse at Boston, Mass.
THE ARGENTINE ANT.
sodpinotal constriction rather deep, extending obliquely downward and backwa 'i
~~.. .. E:.... .'
each side. Epinotum short, nearly twice as high as long, convex on the sides: j
a short convex base, and a longer, flatter and more sloping declivity. Petiole f.1"
less than half as broad as the epinotum; its scale in profile, compressed, cuNg W
inclined forward, with flattened anterior and posterior surfaces and rather acute a :ir;e
seen from behind its border is entire and evenly rounded or even slightly prom&e4
upward in the middle. Gaster small. Legs rather slender.
Fio. 6.-The Argentine ant, adult forms: a, Adult male; at, head of male; at, petiole of male; b, waorbkem, .:
bl, head of worker; bU, petiole of worker; c, fertile queen; cl, head of queen: c2, petiole of queen. Ail
greatly enlarged. (Senior author's illustration.) I
Body minutely shagreened or coriaceous, subopaque and glossy; mandibles, clypetu ..-
and anterior border of the head more shining. Mandibles minutely and rather oIb" :
surely punctate. ii
Hairs few, suberect, yellowish, confined to the mandibles, clypeus, tip and lower"
surface of the gaster. Pubescence short and uniform, grayish, so that the body has a
slightly pruinose appearance. :i
Brown; thorax, scapes and legs somewhat paler; mandibles yellowish; apices of
the individual funicular joints blackish.
Female deflatedd): Length 4.5-5 mm.
Head, without the mandibles, but little longer than broad, with rather angular pos-
terior corners, straight, subparallel sides and straight posterior border. Eyes large and
rather convex. Mandibles and clypeus like that of the worker, scapes proportionally
shorter and stouter. Thorax large, as broad as the head, elongate elliptical, nearly
three times as long as broad. In profile the scutellum is very convex, projecting
above the meso- and epinotum. Epinotum with very short base and long abrupt
declivity. Petiolar node erect, more than half as broad as the epinotum. Gaster
elliptical, somewhat shorter and a little broader than the thorax. Legs slender.
Sculpture like that of the worker but more opaque; mandibles and clypeus also
Scattered hairs more numerous than in the worker and also present in small numbers
on the vertex, gula, mesonotum, prosternum, and fore coxae. There is also a row of
short hairs along the posterior margin of each gastric segment. Pubescence dis-
tinctly longer, more silky, and denser than in the worker.
Dark brown; antennae, legs and posterior margins of the gastric segments reddish;
mandibles, sutures of thorax and articulations of legs yellow.
Male: Length 2.8-3 mm.
Head much flattened; including the flattened eyes, as broad as long. Vertex and
ocelli prominent. Cheeks short. Mandibles small, overlapping, with a single, acu-
minate apical tooth. Anterior clypeal border straight. Antennae slender; scape
only between three and four times as long as broad; first funicular joint globose,
broader than any of the other joints; second joint much longer than the -cape; joints
3-5 growing successively shorter; joints 6-12 considerably shorter and more slender.
Thorax very robust, elliptical, broader than the head, which is over-arched by the
protruding, rounded mesonotum. Scutellum even more prominent than in the female.
Epinotum with subequal base and declivity, the former slightly convex, the latter
feebly concave, forming an angle with each other. Petiole small, its node with rather
blunt margin, slightly inclined forward. Gaster very small, elongate elliptical, with
small rounded external genital valves. Legs slender. Wings with a four-sided discal
cell and two well developed cubital cells. The costal margin is depressed or folded
in just proximally to the stigma.
Sculpture, pilosity and pubescence as in the worker; color more like that of the
female, except that the antennae, legs, mandibles and internal genitalia are pale,
sordid yellow. Wings smoky hyaline, with brown veins and stigma.
I. humilis belongs to a small group of neotropical species embracing also I. iniquus
Mayr, dispertitus Forel, keiteli Forel and melleus Wheeler. The workers of keileli and
melleus may be at once distinguished by their color, the former having a yellowish
.brown head and thorax and the remaining parts brownish yellow; the latter being
pale yellow with a blackish gaster and funiculus. In these and in L. iniquus and
dispertitus the mesoepinotal constriction is much deeper than in humilis and the meso-
and epinotum are of a different shape. The mesonotum in profile does not form a
continuous, even line with the pronotum and the epinotum is very protuberant and
almost conical. I. humilis represents a transition from the above group of species
to that of I. analis Em. Andr6, which is very common in the Southern States. This
species has a shorter, more robust thorax, more like that of Tapinoma, and much less
constricted in the mesoepinotal region.
The above description was drawn from a number of workers, males and females
taken from the same.nest in Baton Rouge, La., by Mr. Wilmon Newell. The types
described by Mayr were captured by Prof. P. de Strobel in the environs of Buenos
30 THE ARGENTINE ANT.
RESEMBLANCE TO OTHER ANTS. V.:
.. .. ...........
There is little difficulty in distinguishing Iridomyrmex ku ii ;4
Mayr from its nearest American relative, Iridomyrmex analis Ernm. ..
Andre. The latter species is quite common in cotton fields and other I
situations in the South, is much lighter in color than humilis, and I
possesses a very disagreeable odor which is entirely lacking in the
case of humilis. The clearly marked trails of the Argentine workers, I
when on their foraging expeditions or when moving from place to i|
place, have no counterpart in the case of analis, the workers, of which Jl
in large measure forage independently of each other. I. ana/i .:i
constructs inverted cone-shaped mounds or craters on the surface '
above the underground nests, while what little dirt is excavated by |
humilis is scattered about the entrance to the nest in promiscuous *
fashion, the ants evidently desiring to rid themselves of the exca-
vated pellets as expeditiously and conveniently as possible. The
wet-weather sheds" of the Argentine ant, constructed only during 't
or just after prolonged rainy spells, bear no resemblance whatever -
to the craters of analis; but on the contrary are more or less flat,
composed of fine particles of earth, unstable in structure and supported
by grass or leaves.
However, the superficial resemblance of I. humilis to several spe-
cies of other genera is even closer than to L. analis and is sufficient
to make positive identification of humilis well-nigh impossible ex-
cept by one skilled in detecting the characters used by myrmecolo-
gists for classification. Among the southern forms most likely to
be mistaken for L humilis, and vice versa, may be mentioned the
"crazy ant" (Prenolepis longicornis Fab.) and Dorymyrmex pynra-
micus Roger. The workers of both these species are of practically
the same size and color as those of humilis and the workers of all three
travel and forage in much the same way. Prenolepis is distinguished ,i
from I. humilis by its camponotine characters, particularly the shape
of the gizzard, by the cloacal orifice being round rather than slit-
shaped, and by the presence of stiff, erect hairs upon the body. Dory-
myrmex is easily distinguished by the conical or pointed elevation i
upon the epinotum (last dorsal segment of the thorax), a structure
that is entirely lacking in Iridomyrmex, the epinotum of which is *|
evenly convex. "I
The resemblance of L. humilis to still other species is sufficient to / 4
be confusing at times, but one can, by a process of eliminating certain -
easily observed characteristics, determine with reasonable probability
whether a colony of living ants belongs to this species or not. First : ::.i..y
to be noticed is the size of the ants under suspicion. The workers of '|
the Argentine ant are from 2.2 to 2.6 mm. in length, the largest indi- ;
vidual we have ever seen measuring 2.75 mm. If workers are more
than 3 mm. or less than 2 mm. in length, it may be safely concluded
that the ant under observation is of some other species. The Argen-
tine queen, however, is from 4.5 to 5 mm. in length. The color of
the Argentine ants-all adult forms-is a very deep brown, almost
approaching black, and the color is uniform over the entire body.
The possession of head and thorax of one color with abdomen of a
different color immediately eliminates a specimen from this species.
A colony containing workers of more than one size is also eliminated,
since all Argentine workers are of one size or caste. The fact that the
petiole or pedicel (connecting joint between the thorax and abdomen)
of L. humilis consists of only one segment readily distinguishes it from
the species of Solenopsis and other myrmicine ants. The pupae of
our species is never inclosed in cocoons, but always naked, with legs,
eyes, segments, etc., plainly visible. Argentine workers, when
crushed between the fingers, give no perceptible odor, and this readily
distinguishes them from their closest relative, L. analis, as well as
from their more remote relatives, the species of Tapinoma. The
Argentine worker does not possess a functional sting and does not
even attempt to sting. This again separates the workers from those
of a great many species, including Solenopsis, most of which sting
viciously upon the slightest provocation. Upon being disturbed,
particularly in the nest, some of the Argentine workers will attempt
to bite, but by far the great majority devote their energies to escaping
rapidly or to removing the larve and pupae to a place of safety.
What few do attempt to bite are not successful in piercing the skin
of one's hands owing to their weak jaws. It is only when reaching
tender places, such as the skin between the bases of the fingers for
example, that they are able to make their bites effective.
If, therefore, ants suspected of being Iridomyrmex humilis meet the
following qualifications, and in addition exhibit the habits already
described, there is a reasonable probability that they belong to this
species, and examples should be submitted to a specialist for exam-
Workers not over 3 mm. nor less than 2 mm. in length
Workers uniformly colored; deep brown, nearly black.
Workers of uniform size; no distinction as to caste.
Workers traveling in well-defined trails or lines to and from the nest.
Workers emitting no offensive odor when crushed.
Workers unable to sting and unable to bite effectively.
Pup'p not inclosed in cocoons.
Petiole or pedicel consisting of only one segment.
Petiole prolonged dorsally into a wedge-shaped scale, inclined slightly forward.
Epinotum devoid of a pointed or conical elevation.
Ocelli absent in workers, present in queens and males.
THE ARGENTINE ANT.
METHODS OF STUDY.
.. .. ". ... .
When the study of this ant was undertaken, two reqi a .ita ii..
themselves-a type of artificial formicary in which continp'.iu rnd.
rations could be made and individuals kept track of from i
egg deposition until the adult stage was reached, and
by which all individuals of a colony could be confined tknh
Space need not be taken to describe the types of artificial .
which were not successful. .. .......
The Janet cages proved successful only in the case of |i^
colonies, but in these the multiplicity of individuals made- l 60"
observations impossible. It may be remarked that this t
is excellent for studying the community life as a whole and f I
experiments with poisons or with parasitic fungi or bacteria :
Cages totally inclosed were not successful, for the reason 1 ,
ants, when deprived of the privilege of leaving their nest, failedtw
in a normal manner. ...
The cage finally adopted was, with modifications, the one det
by Sir John Lubbock on pages 2 and 3 of his classic work.1 'q
consists essentially of two glass plates containing between u
layer of pulverized earth in which the ants may burrow *t4
pleasure. Considerable difficulty was experienced in geting: '
glass plates the'proper distance apart; if too far apart the ants M>
make burrows which were not open to observation, and if too *
together insufficient room was afforded the queen in which to:t
and walk upright. As the queen is about twice as tall as the wcr
it seemed for a time that a suitable cage could not be constru
After repeated trials, however, it was found that if the space bet
the glass plates were made exactly 1.75 mmn. the queen would M(
sufficient room and the workers could not construct invisible Pga..
This type of cage and its supporting stand are well illustM
figures 7 and 8. Figure 7 shows the several parts of the cage; SiPI
cage proper, consisting of two plates of glass held uniformly 1.,
millimeters apart by strips of leather at all four edges, a door or ops
ing being left at one corner. (See fig. 9.) Old negatives, the fil
removed with caustic soda, have been found the most desirable:ii
making these cages, both because such glass is remarkably clear
free from imperfections and because it is of uniform thickness.
size of the cage may vary from 3t by 41 up to 8 by 10 inches or
larger. Leather was found more satisfactory for making the ei
of the cage than either glass or wood. The strip of leather betw
the glass margins is about I inch in width. 'It is extremely difkt
to find a strip of glass uniformly 1.75 millimeters thick and it ia M
'Avebury. Ants, bees, and wasps, 1881. ;
Bul. 122, Bureau of Entomology, U S Dept. of Agriculture.
'w w .. > '!
A SMALL COLONY OF ARGENTINE ANTS AS SEEN IN ONE OF THE ARTIFICIAL FORMICARIES.
E: > " "* .:." ,:.- . . i ." ; .:' : .." : '._ .' '.' .' .* .:' . : ^ ,, : : .'...J ,-, . ^ -. '-; '
I ..... :i :7,IA -, "ll 7... : W
,. . . _,:. ,:.: Z.
METHODS OF STUDY.
difficult to attach one piece of glass to another firmly. Wooden
strips present the disadvantage of quickly decaying and of warping,
no matter what glue or cement is used to hold them in position. Since
it is sometimes desirable to place moist earth in the cages, or to add
moisture from time to time, a waterproof cement is most desirable
for attaching the glass plates to the leather strip. The space between
the glass plates is filled with finely pulverized earth after completion
and drying of the cage, and in this the ants are permitted to burrow
and construct galleries as they please. (See Pl. II.)
The cage proper is supported on a platform (1) which in turn rests
firmly upon a standard (2) having a base (4). The platform must
have its upper surface perfectly level and it must remain so for an
FIG. 7.-Artificial formicary or cage used in studying the Argentine ant: 1, Supporting platform; 2, stand-
ard; 3, cage proper, made of glass and leather, containing earth; 4, base; 5, cover. (Senior author's
indefinite time, otherwise the ants will take up their abode between
the cage and platform rather than in the cage itself. The platform is
therefore made of two pieces of even, seasoned cypress 7 inch thick,
screwed together with numerous screws and with the grain of the
two pieces at right angles to each other. On this platform the cage
rests without fastenings of any kind. The cover (5) is constructed of
two pieces of cypress in the same manner as the platform, but in
addition has an iron handle attached to its upper surface and has a
piece of felt glued to its under surface, so that, when it is placed upon
the cage proper, all light is excluded except at the entrance. The
cover is of the same outside dimensions as the cage itself. To insure
the platform remaining level it is often necessary to make the base
34 THE ARGENTINE ANT.
of two pieces in the same manner as the platform, or to nail strips
across it at right angles to the grain. Both platform and base are
attached to the standard by long screws with heads countersunk.
Food is furnished by placing it on a piece of cardboard at any point
on the cover or platform. The base stands in running water, as
explained below. This type of cage permits the ants to leave their
nest within the cage and to forage over the platform, cover, and stand
in natural fashion, but their escape from the stand is prevented by the
very natural barrier of water, which they find when they approach the
bottom of the standard. It is not possible for them to conceal larvi
or eggs where the observer can not find them and they can not bring
FIG. 8.-Artificial formicary with parts assembled ready for use. (Senior author's illustration.)
in larve or pupae from outside sources to the annoyance and vexation
of the student.
While the ants are very fond of sweets, we have found that sweets
alone will not suffice for food indefinitely. Animal food is also
required, and we find that by supplying the colonies with a "balanced
ration" of honey and fresh beef or veal they will work in a perfectly
natural manner for many months without other food.
The problem of confining the ants to the cage and its stand was not
so easily solved. We first tried Sir John Lubbock's method of plac-
ing a moat of glycerine or water about the stand, but both liquids
METHODS OF STUDY. 35
dried too quickly and were effective for only a few hours. Recourse
was had to the proverbial chalk line without success. Bands or
ditches of kerosene, crude oil, tar, oils of sassafras and citronella, tree
tanglefoot, zenoleum, naphthaline, coal-tar disinfectants, whale-oil
soap, sharp-edged tin, and fur were all failures. Certain powerful
odors, such as those of zenoleum, sassafras, and citronella, act as
repellents temporarily, but after a few hours of evaporation are no
longer effective. Ordinarily these ants will not cross bands of cotton
tape which have been impregnated with a saturated solution of cor-
rosive sublimate and dried, but when attempting to leave an area to
which they have been confined by this means they are much more
persistent in crossing it.
Water with a film of whale-oil soap on it acted as a repellent for a
few hours only, while a film of kerosene upon water merely afforded
FIG. 9.-Entrance of artificial formicary shown in figures 7 and 8. (Senior author's illustration.)
a convenient floor upon which the ants could travel. The difficulty
in confining the workers with any liquid or mucilaginous substance
lies in the fact that they are exceedingly light,1 and sticky substances
shortly harden on the surface, so that the workers are supported.
The surface film of clear water is in fact almost strong enough to sup-
port a worker not loaded. It is not unusual to see an ant alternately
walking and swimming in crossing a narrow ditch of water which has
been standing for a few hours. Minute dust particles collecting upon
standing water shortly form a film upon which the workers pass with
ease. Perfectly fresh water therefore served to confine the colonies
to their cages, and at first our observations were made upon colonies
in cages which were standing in dishes of water. This, however,
necessitated frequent changing of the water, and observations were
often brought to an abrupt finish by other duties which prevented
the change of water in the vessels at the right time.
1 The average weight of one worker is 0.0002077 gram.
36 THE ARGENTINE ANT.
In February, 1908, the senior author constructed, on the grounds
of the Louisiana Experiment Station at Baton Rouge, a small build-
ing for the purpose of studying this ant more in detail. The building
was 10 by 30 feet and equipped with benches having upon them gal-
vanized iron trays 2 by 12 feet, 4 inches deep. In these trays the
cages were placed and by means of suitable connections running
water 2 inches in depth was kept passing through the trays day and
night. As the ants would not voluntarily enter running water this -
arrangement worked admirably. The interior arrangement of this
building is shown in Plate III. The iron trays and ant cages au
shown upon the right, with work tables, chemicals, etc., on the left.
The building was equipped with electric and extension lights for
night examinations, and a combined thermograph and hygrograph
recorded the temperature and humidity of the room at all times.
For convenience this building was referred to as the "formicarium."
Plenty of windows insured full ventilation at all seasons, and to avoid
abnormally high temperature in summer a second or accessory roof
was placed two feet above the main roof. This laboratory also
proved a convenient insectary for the rearing of other insects.
The Argentine ant possesses a marked proclivity for attacking all
insects which one has under observation, and all rearing experiments in
cages, no matter what the insect, must be protected from the ants.
The trays of running water therefore served to keep the ants away,
from general cage experiments as well as to confine them to the cages
in which they themselves were being studied.
ESTABLISHING COLONIES FOR STUDY.
To establish a colony in one of the artificial formicaries or cages is
comparatively easy. It is only necessary to secure a fertile queen
from some thriving outdoor colony and place her on the stand, first
placed in water, together with any desired number of workers which
have been captured by attracting them to a sweetened sponge or
piece of fresh meat. Any lot of workers will accept any queen and
vice versa. When queen and workers are thus placed upon the cage
and its stand, they usually, after a few hours, take up their abode,
in the nest proper. At first we experienced some difficulty in pre-
venting them from collecting beneath the stand, but it was presently
found that if a little dirt were removed from another colony and placed
in the entrance of the new formicary the ants would enter at once ad
adopt it as a suitable home. After the establishment of such colonies
the queen usually commences egg deposition in from 6 to 48 hours.
By establishing colonies in this manner, without immature stags
present, it is easy to observe the daily rate of egg deposition, the
incubation period of the eggs, and the duration of the larval and pupal
"FORMICARIUM," OR SPECIAL INSECTARY, CONSTRUCTED AND EQUIPPED FOR THE STUDY OF THE ARGENTINE ANT.
METHODS OF STUDY. 37
stages. In some of the records given below single individuals have
been kept under observation from deposition of the egg, through larval
and pupal stages, to the adult. In other cases the time from deposi-
tion of the first egg until hatching of the first larva was assumed to be
the period of incubation, date of hatching of first larva to formation
of first pupa the duration of the larval period, etc.
While these cages were invaluable in studying the life history of the
ants, the small amount of space available for them between the glass
plates made the number of ants they would contain very limited. For
the purpose of studying the general habits of large colonies of ants a
modification of the Janet cage was used. As its name implies, this cage
was invented by Mr. Charles Janet,1 and is described by him as follows:
The apparatus (an artificial horizontal nest of porous mineral substance) described
in this treatise gives, in reference to the raising of ants, remarkable results. Ants die
in a short time when placed where they can not receive sufficient moisture; but (and
this is the delicate point) this moisture must be maintained within certain limits.
The apparatus invented up to the present do not solve this difficulty. Furthermore,
they do not lend themselves easily to observation, nor do they permit one to withdraw
with ease specimens when needed. The artificial nest is formed of a block of plaster,
or any other porous substance, which has hollowed out of it a certain number of small
cells, placed one after the other and communicating. These cells are covered with an
opaque slab designed to keep the cells dark between the periods of observation. A cup
of water placed at the end of the block allows it to absorb moisture. The cell nearest
this cup is the dampest, and the one farthest away the driest. I leave this last always
light so that it resembles, for the breeding under observation, a space outside of the
nest. If the water-cell has been kept top moist, the ants go into the cell farthest away,
that is to say the driest. When, on the contrary, the apparatus becomes too dry the
ants return to the walls of the cell containing the water, which is always damper than
the other parts of the nest. They can thus choose for themselves the part of the nest
presenting the degree of moisture which suits them best.
The chief modification adopted was the use of a five-celled cage
instead of one of four cells, as described by Janet. Also, the ants
were not inclosed within the cage, but were allowed to enter or leave
at will. To permit of this the Janet cages were placed upon plat-
forms, which stood in running water. These platforms were consid-
erably larger than the cages, and this gave the workers quite an area
to forage over, simulating natural conditions quite closely. The food
was placed upon the platform, outside the nest, and the workers thus
had to carry it in and feed the larvae in the same manner in which it
was done outdoors. These cages had sufficient capacity for many
thousands of ants. They were used for observing the behavior of
large colonies and for the purpose of noting the effects of poisons
and various control measures.
'Studies on ants. Note 2. Apparatus for the raising and observation of ants and other small animals
which require a moist atmosphere. Extract Ann. Ent. Soc. France, Mar. 10, 1893; vol. 62, pp. 467-482,
figs. 11-12. (Translated by Miss A. O'Conor.)
THE ARGENTINE ANT.
(P1. IV, A.)
The egg is elliptical, pearly white, lustrous, without markings, and
the membrane is extremely thin and delicate. The surface is some-
what mucilaginous, so that when eggs come in contact they adhere
to each other. This enables the workers to handle them en masse and
also permits of their being deposited upon the walls or ceilings of the
The average size is 0.3 mm. long by 0.2 mm. wide. The largest egg
encountered while measuring a series was 0.34 mm. long by 0.24 mm. 4
wide, and the smallest 0.27 mm. by 0.187 mm.
As time for hatching approaches the luster fades and the surface
takes on a dull appearance. This is not sufficiently pronounced and
uniform, however, to be taken as a safe guide to immediate hatching.
When the embryo takes on the larval shape the membrane not infre-
quently adapts itself in a way to the general contour of the inclosed
embryo, thus making it very difficult to distinguish between the eggs
and the newly-hatched larvae.
In the large Janet style cages the workers seem to take elaborate care
of the eggs in order to secure for them just the requisite amount of
humidity. Frequently they will be shifted several times in the course
of the day, first being stored in one corner, then moved to the center
of the compartment, afterwards carried to another compartment, and
perhaps finally stuck to the glass ceiling. Sometimes the eggs are
separated from the larvae and pupae; at other times they will be stored
together in apparently hopeless confusion.
The care of the eggs by the workers seems essential to complete
embryonic development. Eggs deposited in test tubes by isolated
queens have gone through a portion of 'the embryonic development,
but we have not been successful in getting them to hatch. This may
be due in part to the ease with which the delicate embryos are injured
in handling and to the fact that when placed on glass the condensing
moisture may retard or stop development.
The queen appears to act merely as an egg-producing machine, and
once the egg has been deposited she pays no further attention to it.
The act of oviposition has been observed several times and does not
occupy more than a few seconds of time. An attendant ant appears
to be anxiously watching for the appearance of the egg, and it is
immediately picked up and rushed off to the nearest "egg pile,"
sometimes before it has time to touch the floor of the nest.
Attempts to get fertilized queens, unattended by workers, to
deposit eggs and rear the resulting larvae to maturity have been
unsuccessful. Such queens stop laying a few days after their isola-
tion and seemingly pay no attention to what few eggs they do deposit.
LIFE HISTORY. 39
Eggs are deposited at all seasons of the year. The large majority
of them are produced during the summer, but a few are laid in warm
spells during the winter months. The rate of deposition has not been
determined, but one queen under observation in a cage deposited
at the rate of 30 eggs per day, now and then suspending oviposition
for several days at a time.
In outdoor colonies oviposition ceases when the daily mean tem-
perature drops below 65 F., but is usually begun again when the
mean temperature rises above this point, regardless of the time of the
No indication has been found of workers depbsiting eggs, even in
colonies that were queenless for long periods; neither did queenless
colonies ever rear queens from the eggs and larvae present in the nest
at the time queenlessness occurred.
PERIOD OF INCUBATION.
The period of incubation varies with the season of the year, and
in proportion as the temperature remains high or low. The shortest
incubation period observed has been 12 days, the longest 55 days,
and the average is about 28 days. The longer periods are doubtless
accounted for by the entire suspension of embryonic development
during cool weather, and it is not impossible that the viability of
eggs may be entirely destroyed by a temperature as low as 25 or
30 F., but on this point more data are needed.
The period of incubation has been determined, ordinarily, by
placing a queen and workers, but no immature stages, in an artificial
formicary and then noting the time from deposition of the first egg
to appearance of the first larva. This period was assumed to be the
real period required for incubation. In other cases single groups of
eggs have been kept under constant observation throughout the
entire period of incubation. The following table shows the variation
in development at different seasons, together with the average daily
mean temperatures prevailing:
TABLE II.-Duration of the egg stage of the Argentine ant at different seasons-worker.
Record No. From- To- Days.1 tempera- mean
F. Pr cent.
1 ........................................... IOct. 1,1907 N ov. 15,1907 45 () ..........
3 ........................................... Dec. 22,1907 Feb. 14,1908 55 (-)
4 ............... ........................... Mar. 14,1908 Apr. 9,1908 27 70.3 70.2
6 ........................................... M ay 1.1908 May 23,1908 23 74 68.9
7 ........................................... July 20,1908 Aug. 10.1908 22 81 82.9
8 ........................................... July 25,1908 Aug. 12,1908 19 81 81.5
12 ........................................... June 30,1908 July 18,1908 19 81.1 74.9
14 ........................................... July 24,1909 Aug. 5,1909 12 82.5 78.8
1 Average days, 27.8.
2 Cages kept in office; record of exact temperatures not available. The balance of the records were made
in the "formicarium" and the recording instruments kept in the same room with the cages; hence the
temperature and humidity records are correct for the exact location of the eggs under observation.
40 THE ARGENTINE ANT.
(PI. IV, B, C.)
The larva when first hatched is not distinguishable from the egg
without the assistance of a magnifying glass. For a time after
hatching the body is considerably curved, the cephalic end being
almost in touch with the caudal end, but as development progreases
the larva assumes more and more of a straight form. The curvature .
is not entirely lost, however. *1
A recently hatched larva, measured with the compound microscope .
and eyepiece micrometer, was 0.49 mm. long by 0.32 wide. The fully
grown larvae (workers) average 1.7 mm. long by 0.66 mm. wide. The
largest one under our observation measured 1.87 mm. by 0.765 mm.
With the exception of slight constrictions of the body, the larvae
are incapable of motion, thus being entirely helpless and relying
altogether upon the ministrations of the attendant workers. The
latter, however, perform their duties faithfully, and care for their
charges with the greatest solicitude. They feed and groom the
young larvae continually. and transport them from place to place
whenever necessary. In case of danger their first instinct appears to
be to remove the young to a place of safety, and they readily sacrifice
their own lives in order to accomplish this.
The larvae are fei often by the attending workers upon regurgitated
and presumably predigested food. There is nothing in the appear-
ance or actions of the workers which do the feeding to indicate that
they are different from those which perform other duties, or that
they are assigned to the particular and exclusive duty of being nurses.
The feeding of the larvae has several times been observed under a
magnifying glass, and is as follows: The larva ordinarily lies upon
its side or back. The attending worker approaches from any con-
venient direction, usually from one side or from the direction in which
the head of the larva lies, and, spreading her mandibles, places them
over the mouth parts of the larva, which are slightly extruded. The
tongue of the worker is also in contact with the larval mouth. While
the worker holds the body and mandibles stationary a drop of light-
colored, almost transparent fluid appears upon her tongue. This
fluid disappears within the mouth of the larva, but it can not be ascer-
tained to what extent the larval mouth parts are moved during the
operation, as they are obscured from view by the mandibles and head
of the attending worker. Slight constrictions of the larval abdomen
during feeding are sometimes noticeable, at other times not. The
time required for feeding a single larva varies from 3 to 30 seconds,
depending doubtless on the hunger of the "baby." The workers
Bul. 122, Bureau of Entomology, U. S. Dept. of Agriculture.
IMMATURE STAGES OF THE ARGENTINE ANT. (ORIGINAL.)
A, eggs; B. larva[ and worker pupa; C, ]arvae, more enlarged: D. pupa, of workers: at center,
male pupa. All enlarged. (Senior author'sillusitration.)
LIFE f HISTORY.
Sproffer food to, or at least inspect, each larva, for the worker doing
the feeding will place her mandibles to the mouth of one larva after
another, feeding those which seem to require it.
Both larvae and pupae are groomed or licked with the tongues of the
workers; thus they are ever kept in a state of absolute cleanliness.
The most pronounced increase in size of the larvae occurs during the
first five days after hatching. As is the case with other ants, nothing
is voided from the alimentary canal during the larval period, the
undigested portions of the food being retained in the stomach, the
latter having no open connection with the intestine. As the larva
reaches its full growth this meconium, or mass of undigested material,
becomes quite large and is distinctly visible as a dark object in the
posterior portion of the body. At about this time communication is
established between stomach and intestine and the meconium is
voided. The larva then enters the prepupal or semipupal stage.
While the insect in this stage is not very different in appearance from
a full-grown larva, close examination shows a number of slight differ-
ences. Aside from the absence of the meconium, the cephalic and
thoracic regions become markedly smooth and shining, with segmen-
tation very indistinct, while the segmentation in the abdominal
region is, if anything, more pronounced than before. The line of
demarkation between abdomen and thorax is now in evidence, but
without any very noticeable constriction. The mouth parts are
protruded more than in the larva. The difference in appearance
between larval and prepupal stages is not great but is sufficient to
enable one to predict, with reasonable accuracy, the approaching
transformation to the pupal stage proper.
In the later portion of the larval stage we have first been able to
distinguish between the males and workers. The male larvae grow
to a somewhat larger size than do the worker larvae, and it is thus
possible to predict with some degree of certainty which of grown
larvae will transform to males and which to workers. In all other
respects, however, they are apparently alike. The larval stage of the
queen is unknown to us.
DURATION OF THE LARVAL STAGE.
The duration of the larval period has been determined by observa-
tion in the artificial nests in the same manner as the incubation period
The following table shows the duration of the larval period at dif-
42 THE ARGENTINE ANT.
TABLE III.-Duration of larval stage of the Argentine ant at different seasos-I
Record No. From- To- Days.' tempera- mean
1--------------------Nov. 16,1907 Jan. 15,1908 61 52. 2
I............................................ Nov. 16,1907 Jan. 15,1908 61 52.2 .........
6............................................ Feb. 5,1908 Apr. 1,1908 57 62.2 71.9
8............ ..........................do............o do ....... 57 62.2 .71.9
10.......................................... Feb. 15,1908 Mar. 28,1908 43 62 72
3........................................... Feb. 29,1908 Mar. 26,1908 27 67 73
9............................................ Apr. 10,1908 Apr. 24,1908 15 76.6 75.3
7 ............................................ Apr. 12,1908 Apr. 25,1908 14 76.1 75.2
2............................................ July 19,1908 Aug. 1,1908 14 80.5 82
11 ........................................... Aug. 13,1908 Aug. 27,1908 15 81.7 71.7
4 ............................................ Sept. 4,1908 Sept. 14,1908 11 81.1 73.6
SAverage days, 31.4.
When the pupal stage is reached by the young ant all doubt is
removed as to the sex of the individual, for one can tell at a glance
which pupae will transform into adult workers, which to males, and
which to queens. The pupae of these three forms are easily distin-
guishable and will be discussed in the order named.
THE WORKER PUPA.
(P1. IV, B, D.)
The worker pupa immediately after transformation from the larval
stage is pure white, without markings, except that the compound eyes
are prominent as jet-black spots upon the head. The pupa is
slightly larger than the grown larva, the average length being about
2 mm. The head is by far the most prominent portion. A pupa
measuring 2.04 mm. in length was found to have a head 1.19 mm. in
length (dorso-ventral diameter), while the thorax and abdomen
measured 0.51 and 0.561 mm., respectively.
As time for transformation to adult approaches the pupa changes to
a creamy color, then through a light brown to a dark brown, the latter
shade being almost as dark as the body color of mature workers. The
time of these changes varies with the duration of the pupal stage, but
the following record of changes in color of a pupa which occupied a
full 20 days from larva to adult (callow), is near the average:
First to seventeenth day-Pupa pure white, except compound eyes.
Eighteenth day-Turned to a light creamy yellow.
Nineteenth day-Became a light brown.
Twentieth day-The brown color deepened.
Twenty-first day-Reached general stage.
LIFE HISTORY. 43
In some colonies there is more or less of an indistinct sorting of the
immature stages, pupae being placed in one portion of the nest and
larvae in another. This tendency is not perceptible in many colonies
and is usually most noticeable in very large colonies.
The duration of the pupal stage has been determined in the manner
already described for the incubation and larval periods. The range
of pupal development is shown in the following table:
TABLE IV.-Duration of pupal stage of the Argentine ant, individual workers. 1908-9.
Record No. From- To- Days.' tempera- mean
0 F. Per cent.
1 ............................................ Jan. 21,1908 Feb. 14,1908 25 56.5 68.3
2 ................- ........................... ---- Mar. 14,1908 Mar. 27,1908 14 67.5 71.8
5 ...........................-................ Mar. 26,1908 Apr. 11,1908 17 73.8 68.9
6 ............................................ Mar. 30,1908 Apr. 14,1908 16 73.8 70.2
3.... .... -.....-- ........... ..... ..--. Apr. 5,1908 Apr. 15,1908 11 76 73.5
10 -................................- .........-..... do ....... Apr. 18,1908 14 76.3 74
7- ........................................... . do....... Apr. 20,1908 16 76.7 74
8 ..............--................-...-........- .. Apr. 8,1908 Apr. 23,1908 16 76.6 74.5
9 ............................................ Apr. 25,1908 May 13,1908 19 71 63.5
11 ........................................... ..... do.. .- May 14,1908 20. 71.2 61.4
4 ..............-----...........................-- .. Aug. 1,1908 Aug. 11,1908 11 82.2 80
12 ........................................... Aug. 6,1908 Aug. 16,19 6 11 83 74.8
13 .............. ............................ Aug. 10,1908 Aug. 20,1908 11 82.8 70.7
14 ..................................... ..... Aug. 28,1908 Sept. 7,1908 it 81.4 71
19 .... --............-.......................... Apr. 5,1909 Apr. 28,1909 24 70.1 68.4
21 ........................................... June 13,1909 June 22,1909 10 82.75 68.75
22 ........................................... June 24,1909 July 6,1909 12.1 84.08 76.08
1 Average days, 15.
THE MALE PUPA.
(PI. IV, at center.)
The male pupa is fully 50 per cent larger than the worker pupa and
has, by comparison, an enormous thorax. The male pupae vary in
length from 2.78 to 3.23 mm., with an average length of 3.04 mm.1
As the average length of the thorax alone is 1.19 mm., it is at once
seen what a relatively large part of the body it constitutes. The male
pupa is shown in the center of Plate IV.
When first transformed from the larval stage the male pupa is pure
white, with exception of the compound eyes, which are faintly tinged
with brown. Gradually the color of the compound eyes deepens and
the ocelli become visible as minute dark spots upon the head. The
male pupa, like the worker pupa, passes through gradations of creamy
yellow, light brown, and dark brown to almost black before transform-
ing- to the adult stage. The color reached by the male pupa just prior
to transformation is much deeper than that attained by worker pupae.
The males are assisted in their transformation to the adult stage by
I From measurements of 10 specimens by Mr. Arthur H. Rosenfeld.
THE ARGENTINE ANT.
the workers, and the pupal skin, or at least a portion of it, is worked
backward to the tip of the abdomen and there shed entirely. Within
a few hours after transformation the wings of the male become fully
expanded. The following table shows the duration of the male pupal
stage at different seasons.
TABLE V.-Duration of pupal stage of the Argentine ant, individual males, 1908.
Record No. From- To- Days.' tempera- mean
1...................................................... Apr. 11 May 191 73.6 69.8
2..................................................... Apr. 14 M ay 4 20J 73.6 6 .6
3 ...................................................... ... do.... ..do.... 20 73. 6 f6t 6
4...................................................... Apr. 17 M ay 10 24 72.3 67.3
7 .................. ...... ........................... ...do ... ..do.... 24 72.3 67.3
8.. .................................................... Apr. 18 M ay 11 24 72.2 66.7
9 .............................. ....................... ...do .... May 13 26 72.8 66.5
5 ...................................................... Apr. 20 ...do .... 24 71.8 65.8-
6 ...................................................... Sept. 24 Oct. 21 28 70.5 67.8
SAverage days, 23j.
The normal time of appearance of the male pupr is in the spring,
but the appearance of a relatively small number in autumn is not
uncommon. During April and May they are usually abundant,
gradually disappearing in the latter part of May and early June.
Only in one case have they been observed in midsummer, when three
or four male pupae were found at Baton Rouge, July 24, 1909, in a
huge nest which contained thousands of immature stages.
THE QUEEN PUPA.
The pupa which is to become a queen is readily distinguished from
the male or worker pupa by its size, as it is considerably larger than
the male and more than twice as large as the worker pupa. The
whole body is more uniformly developed than in the case of the male
pupa. The head and thorax are not nearly so large in proportion to
the rest of the body, the abdomen is much larger, and the dividing
line between head and thorax is much more distinct. Apart from its
size the queen pupa is readily recognized by the presence of the promi-
nent wing pads.
Queen pupae have been found only during April and May. The
duration of this stage has not been worked out, as we have not been
fortunate enough to secure larvae which would transform into queen
pupae in our cages. Considerable numbers of these pupas have, how-
ever, been collected in the field by the junior author and have been
reared to the adult stage in the artificial formicaries, observations on
them extending over a period of two weeks. The queen pupal stage
seems to occupy relatively more time than is required for the worker
pupal stage, but the gradual change in color from pure white to
brown is about the same. It seems probable that the queen pupal
stage extends over three or four weeks, depending upon the prevailing
temperature. As many as 35 queen pupae were collected from one
colony in Audubon Park, New Orleans, La., on April 29, 1910; hence
there is every reason for believing that the virgin queens are reared in
Reasoning from what is known concerning the development of
queens in the case of such insects as the honey bee, one would expect
to find the queen ant developed from the same kind of an egg that
produces the worker and that the queen would be developed as a result
of special food given to the female larva. It is possible that the diet
furnished to our colonies in confinement did not contain the requisite
materials out of which the workers could elaborate a food suitable
for rearing queens, and this may account for their failure ever to appear
in the artificial formicaries, no matter how populous the latter were.
THE CALLOW OR GENERAL STAGE.
During the last few hours of the pupal stage, in all forms, the legs,
mouth parts, and antennae become more prominent and the pupa is
assisted in its transformation by the workers, who attempt to
straighten out the legs and antennae. We are convinced that there
is a very thin transparent membrane or skin surrounding the pupa,
which is shed at time of transformation, but its existence is difficult
to establish satisfactorily.
Immediately after transformation the young ant is colorless, almost
transparent, but is otherwise identical in appearance with fully
mature specimens. To this stage, following the custom of some
authors, we apply the term "callow." The callow is at first very
clumsy and walks with uncertain steps and staggering gait, reminding
one much of a worker bee just emerged from the brood comb. During
this stage the workers seem still to feel a responsibility for the cal-
low's welfare, for when the colony is disturbed the allows, like larvae
and pupae, are unceremoniously grabbed up by the workers and
hustled to a place of safety.
The body of the callow deepens in color quite rapidly and in from
48 to 72 hours after transformation from the pupa becomes indistin-
guishable from that of other adults.
TIME REQUIRED FOR COMPLETE DEVELOPMENT.
By adding together the minimum periods required for the develop-
ment of worker eggs, larvae, and pupae, as given in Tables II, III,
and IV, we find that at least 33 days are required for development
THE ARGENTINE ANT.
from egg to adult, and in a similar manner addition of the maximum
periods gives 141 days as the maximum time required.
From the tables also it is seen that the average period of incuba-
tion of the eggs is 28 days, for development of the larvae 31 days,
and for maturing and transformation of pupa to adult 15 days.
By adding together these averages we arrive at 74 days as the average
period of development. This, of course, can not be termed the time
required for the development of a generation, since workers do not
reproduce, and the term "generation" can be used only in referring
to the succession of queens.
The time required for complete development of males is, of course,
still unknown, for male larvae could not, in their earlier stages of
growth, be distinguished from the worker larvae; while the larval
form of the queen is still unknown.
There are only three adult forms in the case of this ant, namely,
the queen, male, and worker. Of the immature forms there are three,
egg, larva, and pupa, of each the queen, male, and worker. There is
hardly sufficient difference between the virgin queen and the deflated
queen after fertilization to justify considering them as distinct
forms. A complete colony may therefore consist of a queen and
.workers only, of queens and workers, or of a queen (or queens),
males, and workers. With each of these combinations may be asso-
ciated any one or more of the three immature stages, corresponding
to each of the three adult forms, or nine immature stages in all.
Plate II shows a colony consisting of 1 queen, about 100 workers,
and about 20 eggs, with no larvae, pupwe, or males present. For a
technical description of these adult forms the reader is referred to
other pages. The following descriptions are general in their nature:
The worker measures from 2.25 to 2.75 mm. in length and is well
illustrated at b, figure 6. As with the queen, the abdomen extends
to about the tarsi of the hind legs when the worker is active or engaged
in feeding. The abdomen is capable of considerable distension, and
when the worker is fully engorged with sirup or other liquid its
chitinous plates are forced apart, rendering the connecting mem-
branes distinctly visible. The writer has often noticed workers
returning from their attendance upon plant lice with abdomens so
distended that they looked like little drops of silvery liquid. Par-
ticularly is this appearance presented when the returning workers
are viewed with a strong light beyond them.
As would naturally be expected in the case of so small a creature,
the weight of a single worker is very small. To determine it, 1,000
workers, freshly captured and killed with cyanid fumes, were care-
fully counted and weighed on an analytical balance. The thousand
insects weighed 0.2077 gram, which gave the average weight of each
worker as 0.0002077 gram, or two-tenths of a milligram.
As already stated, there is only one caste among the workers. In
a large colony there seems to be something of a division of labor,
certain ones engaging in foraging, others in nursing, and still others
in excavating or sanitary work. However, any individual worker
can assume the duties of any other, and does do so when exigencies
demand. Worker allows, barely hardened into mature adults, go
forth in search of food and the hardened veterans of many months'
service seem to make as efficient nurses as even the youngest.
LENGTH OF LIFE.
The workers are particularly long lived. A colony of about 70
workers was made queenless and broodless on July 8, 1908. By
October 10 the number of workers had become reduced to about 40,
and some of the original ones survived until February 25, 1909, a
period of 64 months. As this colony was queenless, the workers in
it were not under normal conditions. With a queen present it is
ordinarily impossible to ascertain the length of life of individual
workers, owing to the constant maturing of young. However, in
one case we had opportunity to observe the survival of workers with
queen present and with immature stages absent. A colony started
on October 10, 1908, proved to have an infertile, deflated queen
and was kept under observation to see how long the workers would
survive. The last of these died on July 22, 1909, having lived for 9
months and 12 days after their capture. Their age at the time they
were confined in the cage on October 10 was, of course, unknown; but
it appears safe to conclude that under normal conditions the workers
not infrequently live to an age of at least 10 or 12 months.
Mr. G. D. Smith was successful in keeping a queen and several
workers for more than two months, during which time they had no
food other than that which may have been contained in the drinking
water furnished them. During this period of prolonged fasting the
queen even deposited eggs, some of which hatched into larvae.
The appearance of the adult male is illustrated at a, figure 6. The
males average about 2.8 to 3 mm. in length. The most noticeable
feature about them is the manner in which the thorax is enormously
developed. The abdomen is relatively small and the head short
THE ARGENTINE ANT.
and blunt. The shape of the head alone permits distinction betwear.e 1
the male and virgin (winged) queen without the aid of a glass. h I
The normal time of appearance of the males, of course, follows the
appearance of the male pupae, usually in the spring, but a few appear
in the fall. They are plentiful in the colonies during the latter part
of April and May, and numbers are still to be found in June. After
the beginning of July, however, they vanish, and are very seldom al
seen during the hot months of the summer. A few are occasionally .
found during October, November, and December, and in one case
a few males were found in a colony as late as January.
The males are essentially drones, and never exhibit any indications
of industry or usefulness beyond their special function.
THE QUEEN. .... "
Adult queens are found in two forms, the winged and the wingless
or deflated. The former is the virgin queen and the latter the fertile
or egg-laying queen.
THE VIRGIN QUEEN. '
When the queen reaches maturity she possesses long narrow wings '
which are rather opaque, gray in color, with the veins and stigma '
pale brown. In other respects she does not differ in appearance .
from the deflated queen, described on page 49. The wings are i
retained until after the queen has mated. Mating may take place .
during the nuptial flight in spring, but under some circumstances
occurs within the nest without any flight being made. In the latter
case the queen loses her wings shortly after fertilization and assumes
her egg-laying duties in the home nest along with the older queens I
The earliest date at which we were able to find virgin queens in the i
outdoor colonies was April 1. Normally the first spring appearance
of males precedes the first appearance of virgin queens by about 1
Probably owing to the extreme shortness of the winged stage,
winged queens are very hard to find in the outdoor nests. Although
they must exist in large numbers every spring, they have been col-
lected only occasionally. Most of our observations have been made A;
upon specimens reared from pupae in artificial nests. J
An enormous and general flight of males and virgin queens was j|
observed at Baton Rouge, La., in the spring of 1908, when large num-
bers of both sexes were captured in butterfly nets. On the other ,
hand, during the spring of 1910 and that of 1911 no general flight
was observed at New Orleans, La., although close watch was kept for
one. Considerable numbers of males were seen flying around the i
city electric lights, and individual males were found flying aimlessly I
. LIFE HISTORY.
in various localities, but no queens were found with them, and no
flight took place that could compare with the one noted at Baton
Rouge in 1908.
At the same time a large number of queen pupse transformed into
winged queens in a large Janet style nest in the laboratory at Audu-
bon Park, New Orleans, La. About an equal number of males were
also present in the same nest, which the junior author watched
closely for a flight. Nothing of the kind took place. On two occa-
sions all ants were driven out of the nest-workers, males, and queens-
to see if they could be induced to fly, but after wandering around for
a time they all returned to the nest. The males could be seen actively
pursuing the young queens inside of the nest, and although copulation
was never actually observed, it must have taken place. In the course
of time all the queens lost their wings and commenced to lay an
enormous number of eggs. These eggs hatched, and finally developed
into workers, proving that they were fertile. The males all died one
by one, the last one disappearing when about two months old. It is
therefore evident that the nuptial flight is not a necessity.
Under natural conditions the tendency toward a general flight may
be partially controlled by the comparative numbers of males and
young queens in the nests and colonies. The weather conditions
about flying time may also exercise a very important influence upon
-the flying impulse; cool, cloudy, and rainy weather tending to
restrain the inclination to flight, and warm, clear weather encouraging
it. The severity of infestation may also be an important factor, as
the ants would be more likely to fly in crowded communities than in
localities where they are comparatively scarce.
The males are much more given to flight than the virgin queens.
In the formicarium at Baton Rouge males were often found flying
during their season, and seemed to have no preference as to time of
flight. They were found flying on cloudy days as well as on clear
ones and as frequently at night as in the day.
THE DEFLATED, OR FERTILE, QUEEN.
The deflated queen is illustrated at c, figure 6. The deiilated
queen measures from 4.5 to 5 mm. in length, and queens measuring
6 mm. in length are not uncommon. It should be remarked here that
during egg-laying periods the abdomen is much larger and longer
than shown in the drawing. Normally the abdomen extends well beyond
the tarsi of the hind legs. Unfortunately, a drawing can not show
the delicate silky pubescence of the queen's body, and in life she is a
far more beautiful creature than one would imagine from the drawing,
correct though the latter is in anatomical detail.
50 THE ARGENTINE ANT. "*
The credit for first discovering and recognizing the queens of
species seems to belong to Mr. E. Baker, formerly superintendentV:
Audubon Park, New Orleans, and Prof. R. E. Blouin, formerly fiE ;l
charge of the Audubon Park Experiment Station. i
The rate at which the queen deposits eggs varies with the prevyi-
ing temperature, and egg deposition is suspended entirely at low tiam-
peratures. In the artificial formicaries, already described, the num.r 9!
her of eggs laid each day varied from 1 or 2 to as many as 50 or 60.
Thirty per day is not far from the normal number in warm weather, .
when the food supply is abundant. It appears probable, however, -'
that the queens deposit much more rapidly in large colonies, although
from the nature of the case this can not be verified by direct observa-
tion. Egg deposition becomes very slow, or ceases entirely, in the
artificial formicaries when the daily mean temperature falls below
Practically all queens under observation have shown a disposition
to suspend egg deposition entirely for longer or shorter periods, even .I1
when the occurrence of such periods can not be accounted for by low ...
Fertile queens confined in test tubes without accompanying
workers will often deposit a few eggs upon the walls of the tubes, but
we have been totally unable to get colonies established by confining .
queens in artificial formicaries without workers accompanying them." -!
This failure has not been due to any need of workers to feed or care
for the queen, since she can feed herself from a supply of honey or
sugar as readily as can a worker. Ordinarily she attends to her own
toilet, and it is doubtful whether she is in reality "attended" by the
workers in the sense that queen bees are attended.
Fertile queens do not confine themselves to the formicaries, either
natural or artificial. Isolated deflated queens are not infrequently
found wandering about buildings by themselves, and while the queens
in artificial formicaries ordinarily stay within the nest proper, they
have at times been seen outside of it. The finding of deflated queens
wandering about, coupled with the fact that workers readily accept a
queen from any source, seems to indicate that new colonies mayr
sometimes be established in nature by workers associating with such
The length of life of the queen has never been determined, but. ,
there is no doubt that it extends over several years. Observations
have been carried on with the same queen for considerably over a year.
The number of queens that may be found in a colony varies from
one to several in the summer nests, and may reach into the hundreds ...
in the large winter colonies. Queens never show the least hostility
to each other or to the workers. _
THE COLONY AS A WHOLE.
In the laboratory at Baton Rouge it was our custom to put all sur-
plus queens into one colony, kept for the purpose, and leave them there
until wanted. As many as several dozen queens were sometimes in
this colony at once, all living peaceably together, and with the num-
ber of queens sometimes exceeding the number of workers.
Queens will frequently leave the nests with the workers, and will be
observed in the foraging trails. Ten queens were collected in 30 min-
utes from a large trail of workers at New Orleans, La., during Jan-
uary, 1911. These were quite remote from the nearest nest. Any
colony will immediately accept a strange queen without hesitation,
and it is probable that a constant interchange of queens takes place
between different colonies.
THE COLONY AS A WHOLE.
In size the colonies may vary from a dozen to many thousands of
individuals and the number of queens present in a colony may vary
from one to many hundreds. Although the Argentine ant is particu-
larly aggressive and a hard fighter when coming in contact with most
other species of ants, there is no apparent antagonism between sepa-
rate colonies of its own kind. In fact, in heavily infested areas the work-
ers and queens are so intermingled that the individuality of colonies
is entirely lost sight of and all colonies appear to become part and
parcel of one enormous community. In this respect the species may
be said to have a more perfect social organization than even the honey
bees, colonies of which are very distinct and the individuals of which
usually repel with alacrity any visitor from another colony.
In order to connect the scattered and individual life histories
already given into one united whole it may be well to take a glance at
the changes which occur in the ant colonies with the different seasons.
The tendency of the Argentine ants to segregate into large winter
colonies is very pronounced, and during the winter small colonies
are very scarce, while nearly every protected situation will reveal
the presence of enormous colonies. The stages which are represented
in the nest are queens, workers, eggs, larvawe, and worker pupae.
During cold weather very few changes occur. The egg and larval
periods are very much lengthened compared to the summer rate of
development. The workers themselves move very little, and a large
colony will subsist upon a small supply of food for long periods.
During warmn days heavy trails of workers emerge from the nests
and carry back anything available for food. Except for this the ants
may be considered as almost in hibernation during the winter months.
THE ARGENTINE ANT.
When the temperature falls as low as 60 F. the ants bee. oS 9
sluggish, and foraging is largely suspended. At from 50 to 55 1.
there is practically no foraging, and when this temperature is reached:i"......
within the nest all adult ants become inactive, moving only occasion-
ally, and even then with apparent difficulty. Activity is not strictly I
limited by these temperatures, however. On one occasion we found
workers foraging in a building the interior of which was at 43 F. :
but the colony itself was outside the building and at a higher tem-rn ,
perature. Very few refrigerators are cold enough to keep out these
invaders when the outside temperature is warm enough for them to
forage normally. On the very hottest days of summer they will
enter refrigerators and even crawl into the ice chamber itself in order i
to reach some much-desired delicacy. ..
The most ideal location for the large winter colonies is in piles of 0
decomposing vegetable matter. This material gives off a large quan-
tity of heat during the process of rotting and consequently furnishes
the ants with automatically heated apartments. In the same manner
in which the ants seek optimum humidity conditions during the
summer months, so they will regulate their location to preserve an
even temperature in their nests in the winter. In cold weather they
will carry the young stages toward the center of the piles, while in
warmer weather they will be found near the surface.
Of course all the ants are not able to find ideal locations for the
winter months, and great numbers have to locate themselves as well
as they can. In open fields great numbers will be found under large
ridges, or along ditch banks, particularly those which have a southern
exposure. Many will burrow into the ground at the bases of large
trees, where their tunnels and galleries will sometimes attain a depth
of 12 to 14 inches.
Under Louisiana conditions the winter colonies are in evidence
during the months of December, January, and February. The segre-
gating tendency becomes marked during November, and the "divis-
ional migration" normally occurs in February, but may not take
place until March if the spring is cold and wet.
As soon as the weather gets warmer in the spring and food becomes
abundant the large winter colonies break up into a great number of
smaller colonies. These usually consist of one or more queens and a
- considerable number of workers, and they establish themselves ii
any good location where a supply of food is available. In places
where food is exceptionally abundant these summer colonies will still 4
remain very strong in numbers. Under large magnolia or oak trees,
for example, colonies with 10 or 20 queens and many thousand
workers are nearly always present. .
THE COLONY AS A WHOLE.
A short time after the "divisional migration" has taken place in the
early part of March, the large amount of food brought in by the
workers, acting in conjunction with the warmer temperature, appears
to stimulate the queens to lay great numbers of eggs. Most of the
young stages carried through the winter or which have slowly matured
during winter have by this time transformed into workers, so that
the colonies consist of many workers, with comparatively few imma-
ture stages other than the eggs. Hatching takes place during the latter
half of March, and the larvae resulting from these eggs, after develop-
ing, transform into three classes of pupae, viz, queen, male, and
worker. Of these the male pupae preponderate, with the workers a
close second and queen pupae a very poor third. The male pupae
appear in great numbers several days before the queen pupae appear,
which may possibly indicate a slightly longer larval period for the
queens than for the males.
The adult winged males appear during the latter part of April and
in May, and are in evidence in the nests until the beginning of June,
when they begin to disappear. The winged queens appear a few days
later. For some reason the winged queens are extraordinarily diffi-
cult to find in the nests, although their large size and long narrow
wings should make them very conspicuous. However, only three
winged queens have as yet been located in the nests under natural
conditions in Louisiana. Fortunately the queen pupae are not so
difficult to discover, and a considerable number have been reared to
the adult stage in Janet style nests in the laboratory, where most of
our observations upon this stage have been made.
The appearance of the winged queens and males may or may not
be followed by a nuptial flight. In either case, after the queens have
become fertile they lose their wings and immediately start laying
great numbers of eggs. These eggs develop into workers, with the
exception of a few eggs which are laid in the late autumn and develop
into males. It thus follows that the most rapid and conspicuous
increase in numbers occurs during July, August, and September,
when the eggs laid by the army of young queens complete their life
history and transform into adult workers.
From then on to late in the fall the history of the colonies is very
similar and devoid of incident. The numerical strength of the ants
is constantly on the increase, and it is probable that the greatest
natural dispersion occurs during the fall months, after the nests
have been excessively crowded by the activity and increase of the
During the latter part of October and in November the nights
begin to get cool and we find the first inclination toward the form-
ation of the winter colonies. The nests in exposed open situations
are gradually deserted, and strong colonies accumulate in well-
54 THE ARGENTINE ANT.
protected situations. This becomes more pronounced during li'
latter part of November, and in the beginning of December we i
that the winter colonies with which we began are once more restoredl.
and that large united colonies are the rule, with small colonies the :::;i
COMPOUND COLONIES OR COMMUNITIES.
Mention should not be omitted of the pronounced manner in which ,
the social habit is extended beyond the limits of the individual nest
or formicary. During the summer season of activity, and in heavily '
infested areas, communication between adjacent colonies is corn-
monly observed. Not only the workers, but even fertile queens,
travel from one colony to another. So closely are adjacent colonies
associated in their activities that one can not do otherwise than con-
sider a heavily infested area as one enormous "compound colony" or
Four distinct types of migration are exhibited by these ants,
without including the long trips which they take in columns to and
from the nests in search of food.
GENERAL MIGRATION OR DISPERSION.
By general migration is meant the slow but steady spread of the
ants from infested points into adjacent uninfested territory. This is
practically continuous, and while under natural conditions it may
amount to only a few hundred feet per year it is greatly accelerated
by artificial dissemination of the ants by man and his agencies.
MIGRATION TO FOOD SUPPLY.
When the supply of food becomes scarce in the immediate vicinity
of a colony and a plentiful supply is discovered at a distance by the
foraging workers, movement of the colony in toto to the neighbor-
hood of the latter is not infrequent. Trees or plants harboring large
numbers of scale insects are invariably surrounded by many populous
colonies and the housewife who grows careless, permitting the ants
to get food in plenty within her domicile, is soon repaid by having
the premises overrun with the pests. One can easily note this form
of migration by keeping a constant supply of honey or sirup in one ,
place for several days and providing a suitable nesting place--such
as a decaying log-near it. The latter is shortly occupied by one or -_
more colonies. :
Concentrating migration takes place within the infested territory J
and consists of the coming together of a large number of smaller colo-
nies to form a single large colony. This migration occurs under
THE COLONY AS A WHOLE.
f various adverse conditions. During floods the ants will concentrate
in great numbers upon elevated ground, or many colonies will carry
S their young stages up the same tree in order to get protection from
the rising water. The most pronounced concentration, however,
occurs at the approach of cold weather in the fall, when large numbers
of colonies concentrate at one point to form the large winter colonies,
often consisting of hundreds of queens and many thousands of work-
ers. These colonies are fully described elsewhere.
Divisional migration is the opposite of concentrating migration,
and is always in evidence after a large number of ants have conce>-
trated at one place. It is most conspicuous in the spring, when the
large winter colonies break up into a great number of smaller ones.
These small colonies usually consist of one or more queens and a sup-
ply of workers. They distribute themselves in all directions from the
large colony, and locate in any place which affords suitable protec-
tion and an available food supply.
NESTS OR NATURAL FORMICARIES.
Almost any place seems to be suitable for the location of nests of
the Argentine ant, provided that light and water may be sufficiently
excluded. Some of the situations in which they have been found
are within hollow trees, beneath the rough bark of growing trees,
in forks of trees, in rubbish and compost heaps, in decaying logs and
timbers, beneath boxes and boards, under and in brick foundations,
in stored household goods, beneath shingles on roofs, in rolls of wrap-
ping paper, between walls of dwellings, in flowerpots, in piles of
brick and stove wood, in garbage cans, in bags of sugar, in birds'
nests, in discarded tin cans, in moss packing about the roots of nur-
sery stock, and in straw packing containing glassware or china, in
beehives with colonies of bees, under discarded tin roofing, around
the roots of cotton, corn, sugar cane, and other growing crops, in
railway cars, in various places on river steamboats and ocean-going
vessels, in old clothes, under street-car tracks, under brick and con-
crete pavements, in greenhouse benches, inside the husks of roasting
ears, inside of cotton bolls, in hollow iron electric-light posts, in the
cracks and crevices in telephone and telegraph poles, and in the cinder
ballast of railroad tracks.
Most of the situations named are used as permanent nesting places
so long as weather conditions do not force the ants to find more
suitable quarters. With the advent of unfavorable conditions the
ants move their colonies with alacrity.
56 THE ARGENTINE ANT. k .i:
: .5 .. .. .
Many permanent nests are located in the tops of trees, m: I
branches, or in places where borers or termites have been k_
In rot ten logs the ants will nearly always utilize old borer or term.
tunnels for their nests, but do not appear to do any boring for theai4 ....
The facility with which entire colonies move is sometimes am .M.. I
If a nest is disturbed the workers will frequently move all stages i ...
'1 11.. .. :i; .:.; .! .:; : i..!ii
establish another nest in a fresh location in the course of a very f" :: i
UNDERGROUND NESTS. ... ..;. .
The ants seldom burrow to any great depth in the ground. fThe
exceptions to this occur during hot, dry weather in the sum er W*: i;^^
during particularly cold spells in the winter. In the dry spells thfYl .^^
evidently work downward in an endeavor to secure sufficient hn- ..::
midity for the young, while'in the wintertime they sometimes al:'e, i'
deep into the soil for the sake of protection from the cold. '...in ......
deepest burrows which we have measured have been 14 inchren :I:
depth, but they usually average from 4 to 10 inches? under norm"'i"t"i:sl
conditions. These deep burrows are usually located at the foot of 3*. !!
tree trunks, or under the ridges in cane, cotton, or corn fields. .
Under more favorable circumstances, however, the underground ||
galleries average from 1 to 4 inches in depth. In summer time .th s
ants appear to do as little excavating as possible and seem to limit. ,
their efforts to excluding light and water. When the nests aem' -:-i
i" ... .....'.." P.."i
located above ground, under boxes, boards, stones, etc., very little
soil is used, and this is utilized in closing holes, etc., to keep out J:
light and drafts. ,:
_.... :i::.. "||..
WET-WEATHER NESTS OR SHEDS. e . ,...
... ...... ...':
In wet situations or after heavy rains, when the ground has become: ."IA
soaked with water, the ants construct curious honeycombed structures.,
around the bases of tree trunks. These are made of a great number 1`:':
of fine, loose particles of soil, usually supported by grass stems or 5
loose leaves. They vary from one-half inch to as much as 5 inches ;$|
in height, and sometimes cover an area of several square feet. They
are built with great rapidity by the workers, and are extremely fril, :
falling in at the lightest touch. As a result of this weakness these :A!1
nests disappear after a few days of dry weather, or are washed away:
by showers. They consist of a maze of covered galleries, in which'
large numbers of the larvae and pupae are placed. Their purpose |
appears to be to afford protection to the young stages until the .
ground gets dry enough for the underground galleries to be 4
reoccupied, or they may be used to dry and "air" stages which..
have become wet, the loose construction permitting a liberal circula- :
tion of the air through the walls and ceilings. (See PI. V.)
.. . ........ ... ..
Bul. 122, Bureau of Entomology, U. S. Dept. of Agriculture.
I.e g ii~Tr ^
WET-WEATHER NEST OR SHED, ERECTED BY ARGENTINE ANTS DURING RAINY WEATHER.
THE ARGENTINE ANT.
AVERSION TO LIGHT.
The ants demonstrate in many ways their dislike of light, or at
least their aversion to it. Their nests are always located in dark
places, the ants are active all night, and their immature stages are never
exposed to light except for brief periods in emergencies. If the
opaque cover is removed from the top of an artificial ant nest for a
considerable time, all the ants will come out and will refuse to return
until the cover is replaced. Several experiments were made at
Baton Rouge, La., in 1909, using different colored glasses for cage
covers, but the ants were not satisfied unless the cover was absolutely
opaque. While they will go anywhere into daylight in search of
food, they will cover over as thoroughly as possible, with their
protective "sheds," the colonies of scale insects, mealy-bugs, and
aphides which they habitually frequent.
SENSE OF SMELL.
The workers exhibit a very keen sense of smell by the manner
in which they locate certain foods. Meat which is wrapped in heavy
wrapping paper will attract thousands of the insects, and they will
work their way through the various folds and crevices of the paper
in a surprising manner until they reach the meat itself. The workers
readily secure entrance into the ordinary Mason or glass fruit jar,
if one omits placing beneath the cover the rubber ring or gasket.
No matter how tightly the cover is screwed on, the workers follow
the spiral threading between cover and glass until the interior is
Another illustration of the sense of smell is seen in the readiness
with which trails are restored when broken or disturbed. If a line
of ants be moving across a floor in a circuitous line, for example,
and all ants be swept from the floor with a broom, the next on-coming
workers will follow exactly the original course. This may be repeated
indefinitely and the trail will always be established in the original
location. If, however, some strong-smelling substance, like oil of
citronella or kerosene, be placed upon the trail the ants become
confused at once and by their aimless wandering about show plainly
that they can not locate the original pathway.
While the Argentine ants are extremely sensitive to light, it is
doubtful if they possess the sense of sight. The action of light can
generally be described as exerting a repelling influence upon them
and they avoid it as much as they can. That they do not use eyesight
in locating food substances has long been recognized. Their trails
58 THE ARGENTINE ANT.
will frequently encircle the spot which they ultimately hope to attain. }
They will never attempt to avoid a hand threatening from any 7
direction as a spider will do, but will continue going ahead until i
their antenna touch the obstacle. The manner in which they
religiously follow their trails and the'confusion which results when i
these trails are destroyed proves that they do not trust to a sense of
sight in traveling. This is illustrated again by the fact that they are
active all night in the darkest situations.
The sense of hearing in these insects is not acute, even if indeed it I
be developed at all. The ants are not disturbed by ordinary noises,
such as talking or working about the nests. If, however, one emits
a loud shout within a few inches of the formicary, or fires a pistol s
near it, the ants are thrown into the confusion and excitement
characteristic of them when disturbed. It seems not impossible
that in such cases they have detected actual vibrations of the surface
on which they are located, due to the action of the sound waves.
Strangely enough, in situations where loud noises and vibrations are .
of constant occurrence, the ants become accustomed to them. Thus
at New Iberia, La., we found ant colonies between and under the
ties of a railroad track over which many trains passed daily.
Cannibalism in any form is extremely rare in the case of this
species, and true cannibalism has not yet been observed. The only
thing at all approaching it was observed in the case of a colony kept
in our formicarium, the workers of which developed a habit of eating
the eggs as fast as they were deposited by the queen. This, colony
was established in an artificial formicary on November 27, 1907, and
from that time until the early part of July, 1908, larvae were reared
more or less continuously and in the usual numbers. In July it was
noticed that the number of immature stages became steadily smaller,
and on July 28 a quick removal of the cover from the cage disclosed
several workers in the act of eating eggs. Thinking that this might
be due to lack of sufficient food of an animal nature fresh meat was
at once furnished the colony and was thereafter kept continually
accessible. In spite of this the egg-eating habit continued until
November 5, 1908, all eggs being eaten within a few hours after their
deposition by the queen. By this time the number of workers in the
colony had been reduced to six, and by November 11 the queen and
remaining workers were dead, the colony having apparently been
exterminated through lack of any maturing workers to replace those
dying from old age and accident.
All adult members of the colony keep themselves scrupulously
clean, after the manner of most hymenopterous insects. Workers
divest their bodies and legs of foreign matter by persistent rubbing
of the body and antennae with their legs, while the tarsi are cleaned
by pulling them between the mandibles. At times we have seen the
workers assisting each other in these operations, particularly when
some gummy or adhesive substance became attached to the head and
mandibles. On one occasion the senior author observed one worker
industriously cleaning the mandibles of a companion. During this
operation, which lasted for several minutes, the worker receiving the
kindly ministrations stood with her head well raised, mandibles
extended, and feet firmly braced, while the teeth of her mandibles
were thoroughly cleaned by those of her sister.
The queen is occasionally cleaned and groomed by the workers,
but for the most part she attends to her own toilet, being nearly as
skillful and dextrous at the task as are the workers themselves.
Larvae and pupae are groomed from time to time, this grooming being
done with the tongues of the workers.
Dead adults or larvae are not tolerated within the colony and are
removed immediately. Dead adults are also invariably removed
from the vicinity of any food supply which the ants are visiting.
Decaying animal matter is not tolerated in near proximity to the
nests. If the ants are unable to remove it bodily they will carry
particles of earth with which to bury it, much after the manner
adopted by honey bees in covering with propolis any dead animal
which they can not remove from their hives. The following example
will serve to illustrate this habit: A small minnow, recently dead,
was placed near the entrance of one of the artificial formicaries. It
was immediately covered with workers, and in the course of a few
hours all the soft portions had been torn apart and carried into the
formicary, little remaining except the bones and skin. On the fol-
lowing day another fresh minnow was given the same colony. While
this was torn apart the same as the first one, it did not receive nearly
as much attention. When a third minnow was given the colony the
workers paid no attention to it, having evidently had fish "a plenty."
As soon as it commenced to decay the workers brought particles of
trash and dirt from their nest and piled these up around the minnow.
This work they continued for three days, by the end of which time
the remains of the minnow were completely buried. Decaying fruit
left near the artificial nests was treated in the same manner.
RATE OF TRAVEL.
One of our associates, Mr. G. D. Smith, made some interesting
experiments to determine how rapidly the workers travel both in
going to food and in returning from it with their loads. Sirup was
60 THE ARGENTINE ANT.
placed on the comparatively smooth floor of an infested building,
and when the ants were visiting it in large numbers a distance ef :
6 inches was measured off on one of the principal "trails." The rate i:X
of travel of individuals over this 6 inches was then noted. Mr. Smith
found that the average time required to travel the 6 inches when.
going to the food supply was 124 seconds, or at the rate of 29 inches :
per minute. When returning from the food, presumably with their
stomachs filled with sirup, the average time required to travel the
6 inches was 21 seconds, or at the rate of 17 inches per minute. The
rapidity with which the foraging ants can travel (29 inches a minute,
or 145 feet per hour) explains their ability to keep thoroughly
patroled all of the walls, furniture, and other contents of a building
within their reach. It explains at the same time the reason for their
so quickly locating food supplies left accessible to them.
The rate of travel over horizontal polished surfaces is, however,
much greater than that cited above. On a tiled floor or on the top
of a glass showcase their speed is two or three times as great as that
just given. In fact, it is almost impossible to capture the workers
on a tiled floor, so rapidly do they move. This same degree of speed
is not attained on vertical polished surfaces, such as window panes.
STORAGE OF FOOD. ,A.:
Only to a very small extent do the workers of this species provision
their nests for future emergencies. They are given to carrying let-
tuce seed, and perhaps other seeds, into their colonies at times, but 4
the bulk of these seed are used up in a short time, and in a few days all
have disappeared. Apparently the desire to carry in a full supply of
any desirable food is the cause for this storage, rather than any fixed
instinct toward providing the colony with permanent stores. In like
manner, when the ants have access to large amounts of granulated
sugar, the granules are carried into the nest and deposited in various
parts of the galleries, there being no place set aside, apparently, as a
granary or storehouse. Like the seeds above mentioned, the supply
of sugar is consumed within a few hours or a few days after its
acquisition. Particles of meat are deposited in the galleries in simi-
lar manner, often to be neglected until they are too dry to be of much
service. Even when dried, however, they seem to furnish a relish or
variation in the diet, as workers may be seen, from time to time, .
rasping off small shreds with their mandibles and then masticating
these with apparent enjoyment.
Liquid food, such as honeydew, sirup, etc., is not deposited any-
where in the nest, and if any liquid food is kept in reserve at all it is "
merely that which is retained in the stomachs of the workers. Appar-
RELATIONS WITH OTHER ARTHROPODA.
ently liquid food is consumed soon after being brought into the for-
micary, as evidenced by the following observation:
Some fresh honey was placed upon the food table of an artificial
formicary, and when the first worker was observed to leave the honey
the top of the formicary was removed and her actions observed.
Upon entering the colony she was met by three other workers, all
of which placed their mandibles to hers. As she regurgitated the
liquid they sipped it up. When one of these workers had received a
sufficient quantity she retired and another took her place, as many
as four or five workers sometimes feeding at once. The foraging
worker in this manner supplied about 15 others with food, after
which, her supply being apparently exhausted, she left the group of
assembled feeders and went her way, leaving some of them hungry
and still unsatisfied.
RELATIONS WITH OTHER ARTHROPODA.
S It may be said in general that the Argentine ant will not tolerate
the presence of other species of ants within its domains. There are
a few exceptions to this rule. In 1908 Mr. G. A. Runner and the
junior author found a small colony of Monomorium minimum Buck-
ley living in the same tree stump with a colony of Argentine ants at
Baton Rouge. The Monomorium colony possessed a number of young
stages and appeared to be unmolested by the Argentine ants. The
following season, however, the Argentine ants were in full possession
of the stump, and no trace of Monomorium could be found. During
the same summer another small colony of M. minimum was noticed
living in a fig tree in territory heavily infested with the Argentine
ant. This was also at Baton Rouge. This colony was observed for
several weeks, but finally died out, though it could not be determined
whether the Argentine ants were responsible for its annihilation.
In another case a log was split open, disclosing vigorous colonies
of both Iridomyrmex humilis and M. minimum. Whether the ants
were occupying the same chambers or whether the nests were in
close but disconnected chambers could not be ascertained, but the
Monomorium workers were seen to pick up and carry away the larvae
of humilis with as much solicitude as they did their own. Just what
relationship obtains between these two species we have not been
able to determine, but certain it is that humilis tolerates this small
species to a much greater extent than it does any other ant. At
Baton Rouge Monomorium minimum still seems to maintain its
normal abundance, and this certainly can not be said of any other
species of ant.
: ,, :::': gj.
62 THE ARGENTINE ANT. ..
An account of the methods used by the Argentine ants in over- .i
coming other species of ants was published by the senior author'
in the Journal of Economic Entomology....:
Prof. W. M. Wheeler, in Entomological News for January, 1906,
gives an interesting account of the way in which this species obtained
a foothold in Madeira and supplanted another introduced species,
Pheidole megacephala Fabr.
COCCID1E AND APHIDIDIE.
The liquid excretions of the various species of scale insects and
aphides form one of the chief sources of food for the Argentine ant.
The large variety of trees and plants in the South gives support to a
great number of coccids and plant lice, and these insects in turn
yield sustenance to myriads of ants. In return for this food supply
the ants shelter and protect these insects, with the result that the
latter increase beyond all customary proportions. As the result of A
this symbiotic manner of living we find that a comparatively small
area of land frequently supports enormous numbers of ants, scale.
insects, and aphides, while the plants themselves become so severely
infested that some of them are killed and many more seriously
All through the summer months, and also during warm days in-
winter, heavy streams of ants can be seen ascending and descending
the trees and plants; the ascending ants empty, the descending ones
heavily laden with the liquid excretion which they have obtained
from the various scale insects and plant lice. During the summer
this activity is well-nigh endless, and the ant trails can be observed
at all hours of the day and night. All scales and aphides are closely
attended, but some species appear to attract more of the ants than j
do others. The large unarmored scales and the plant lice appear to
be the chief favorites, the mealy-bugs, however, following them very
closely in this regard.
Aside from protecting the aphides and scale insects from ladybird
beetles and constructing earthen shelters over them, the ants only
rarely foster them directly. In one case only have insects of this
character been actually found in the ants' nests. In January, 1909,
Mr. G. D. Smith, in excavating an underground colony at Baton
Rouge, found a number of barnacle scales, Ceroplastes cirripediformia
Comst., on tree roots which passed through the formicary. 'These
scale insects were full grown and vigorous. At this season of the
year no live scales of this species could be found above ground. It
may be remarked in passing that this is one of the species to which d
the ants are very attentive during the summer and autumn months.
1 Notes on the Habits of the Argentine or "New Orleans" Ant, Iridomyramez humilis Mayr. Wilmon .
Newell, Journ. Econ. Ent., vol. 1, no. 1, pp. 21-34, 1908. .
RELATIONS WITH OTHER ARTHROPODA.
SWorkers are often seen carrying plant lice and scale insects, and
this fact, coupled with the observed phenomenal spread of scales in
ant-infested territory, brings one inevitably to the conclusion that
the workers carry and establish these pests upon new growth and
upon new host plants.
During March, 1910, a considerable number of adult female scale
insects were found embedded in a band of "tree sticky" placed around
a magnolia tree to repel the ants. This band was located 4 feet from
the ground. The scale insects were a species of Odonaspis 1 which
is found upon Bermuda grass close to the surface of the ground.
There was apparently no other way for these insects to get up the
tree except through the transporting agencies of the ants.
On sugar cane the ants have frequently been seen carrying around
small sugar-cane mealy-bugs. They do not appear to pick them up
unless they are rudely disturbed or frightened, but the fact remains
that they have been seen transporting them. Experiments made by
the junior author showed that the ants would pay no attention to the
larval mealy-bugs until after the latter had commenced to feed on the
canes and produce exudations. The following three paragraphs are
quoted from our notes:
Placed a piece of paper on which were about 2,000 "seed mealy-bugs" across a
strong ant trail, and weighted it down flat, so that the ants could not get underneath
it. At first the ants were bewildered at losing their trail, and ran over the paper in
all directions. They absolutely refused to notice the young mealy-bugs, and after a
while reestablished their trail across the paper, and commenced traveling the same
as before, The mealy-bugs were swarming directly across the trail, but the ants paid
no attention to them.
This seems to indicate that the ants have no dealings with the mealy-bugs until
they begin to secrete the juices from the cane stalks. These young mealy-bugs had
never fed, being taken directly from the tube in which they were hatched. Thus
they would probably not have excreted any liquid. At the same time the ants did
not show any hostility toward them.
The eggs are out of reach of the ants when they are enveloped in the egg mass, as
the waxy covering appears to entangle the feet of the ants, being slightly sticky and
adhesive. The egg stage and young larval stages are therefore removed from the
sphere of the ants' influence.
Even though the actual transportation of plant lice, aphides, and
mealy-bugs by the ants may not assume much economic importance,
there is, nevertheless, no doubt that the ants assist these insects
greatly in other ways. They build shelters over them, these consist-
ing of fine particles of earth, protecting them from storms and hin-
dering the attacks of parasites. These shelters have been noticed
in many different localities. In Bulletin 52, Bureau of Entomology,
Mr. E. S. G. Titus gives an illustration of a large shed built by the ants
over the surface of a persimmon, protecting a number of Florida wax
scales (Ceroplastes floridensis Comst.). These sheds are also present
I Determined by Mr. E. R. Saascer.
in great numbers on sugar cane, Johnson grass, willows, and 4,
and, in fact, in all places where a number of coccids or plant liei
exposed to the weather. :
The stimulation resulting from the attentions of the ants b
collecting the sweet liquids appears to have the effect of rea
encouraging the numerical increase of the aphidids and oe*
During the summer of 1910 the junior author reared several gems
tions of sugar-cane mealy-bugs on sugar cane planted in large ,:,)
One-half of these pots were isolated from the Argentine ants, wb
to the others they were allowed free access. The mealy-bugs gr
and multiplied in both lots of cane, but there was great differ
between the thriftiness of the isolated and nonisolated insects. In f
pots to which the ants had access the mealy-bugs multiplied so fe
that finally they almost smothered out the sugar cane with tub
cottony egg masses. In the isolated pots, while the mealy-tb
increased in numbers, they were not nearly so numerous or heattih
looking as in the ant-infested pots. At the end of two monthbit
number of mealy-bugs in the ant-infested pots probably excem
the number of mealy-bugs in the isolated pots to the extent E
least five to one. !
That the same conditions exist in the cane fields is shown by ,
number of mealy-bugs which can be found in the fields infested .
the Argentine ant as compared to their scarcity in fields not iWle
by the ant. Only one field under the latter conditions has betiaff
covered as yet, but it has been watched closely for two years. I
mealy-bugs have never become sufficiently numerous to attract
attention of the working hands, and they can be found only w..
considerable difficulty. On the other hand, in the fields wherl
mealy-bugs and ants are associated the former have becomei
numerous that the white cottony egg masses can be easily oberv
from the road while driving through the fields. -
The same thing holds true with scale insects generally. :;il
orange groves invasion by the ants is followed by a rapid in.reas
scale insects, particularly the chaff scale (Parlatoria pergand Co
and various species of Lecanium. So rapidly do these scales inr
that, unless prompt measures are taken against the ants, the ser
year of infestation shows a severe curtailment of the crop, sand:
fourth or fifth year witnesses the death of many of the trees. :i.
rapid decline of orange trees under conditions of heavy ant infesi
is well illustrated by Plate VI, which shows a tree after exvposux
attacks of the ants and chaff scales for three seasons. 'l
The ants constantly attend the citrus white fly (Aleyrode:
R. & H.), and a marked increase in this injurious pest always i
panies ant infestation.
THE ARGENTINE ANT.
Bul. 122, Bureau of Entomology, U. S. Dept. of Agriculture.
ORANGE TREE AFTER EXPOSURE TO ARGENTINE ANTS FOR THREE SEASONS. (ORIGINAL.)
RELATIONS WITH OTHER ARTHROPODA.
During a period of 18 months 48 species of scale insects have been
collected in Audubon Park, New Orleans, all of which are attended
by the Argentine ant. Many of these species, however, are visited
sparingly, and are evidently regarded as sources of food when the
more popular species fail to furnish a sufficient amount for the needs
of the ants. A few species are particularly favored by the ants, and
S the trees and plants upon which they occur are always crowded with
large numbers of the workers.
Among these favored species may be mentioned the Magnolia scale
(Neolecanium cornuparvum Thro), which is found upon the various
magnolia trees. This scale is very large and unarmored, and the
young scales appear in great numbers during February and March.
As this is the period during which the ants have the greatest difficulty
in securing sufficient food it naturally follows that they concentrate
upon the magnolia trees in immense numbers, and the soil at the
bases of the trees is turned into gigantic ant nests. During June and
July this scale is brought under control by the larva of a small black
ladybeetle, and the number of ants in the magnolia trees falls off
greatly. By this time, however, an abundance of scale insects and
plant lice of many different species can be found everywhere, and the
ants do not have to place such dependence upon the magnolia scale.
Another species which attracts great numbers of workers is the soft
scale (Coccus hesperidum L.). This species has been collected upon
a variety of plants in Audubon Park, among which may be mentioned
the orange, banana, Camellia japonica, coral tree, cocoa tree, rubber
trees, myrtle, and maidenhair ferns. This scale can be found in all
stages at almost any time of the year, and is always heavily attended
Other important scale insects from the Argentine ant's point of
view are the sugar-cane mealy-bug (Pseudococcus calceolaria Mask.),
the two barnacle scales (Ceroplastes cirripediformis Comst. and
C.floridensis Comst.), and the black scale (Saissetia olese Bern.). The
last three species are found upon a variety of plants.
A complete list of the scale insects and aphides which this ant
attends would comprise a check list of these species for the entire
ant-infested territory. The following list, however, includes the
more important species upon various plants and crops which are the
most eagerly sought after by the ants. Most of the determinations
have been made at Washington, D. C., through the courtesy of
Messrs. E. R. Sasscer, J. G. Sanders, and Theo. Pergande. So far as
possible the species most attractive to the ants have been placed
nearest the host plants, and they follow in order of preference within
66 THE ARGENTINE ANT.
LIST OF COCCIDE AND APHIDIDiE ATTENDED BY THE ARGENTINE ANT. i
Upon bamboos: Asterolecanium bambusn Bdv., Odonaspis secret Ckll., Odonaspi "
Upon banana: Coccus hesperidum L., Chrysomphalus aonidum L. o
Upon cotton: Aphis gossypii Glov. V
Upon corn: Undetermined aphis (probably Aphis maidis Fitch). i
Upon figs: Pseudococcus citri Risso, Lecaniodiaspis sp., Aspidiotus camellia Sign.
Upon hickory, elm, hackberry, and various shade trees: Pseudococcus sp., Ceroplaatea
cirripediformis Comst., Ceroplastes floridensis Comst., Chionaspis longiloba Cooley, -
Chionaspis americana Johnson.
Upon magnolias: Neolecanium cornuparvum Thro, Aspidiotus camelliie Sign., Tourney-
ella turgida Ckll.
Upon mulberries: Chrysomphalus tenebricosus Comst.
Upon oaks: Kermes galliformis Riley, Eulecanium caryx Fitch, Eulecanium quer-
cifex Fitch, various aphidids.
Upon orange: Coccus hesperidum L., Parlatoria pergandii Comst., Lepidosaphes beckii
Newm., Lepidosaphes gloverii Pack., Chrysomphalus aonidum L., Aphis gossypii '
Glov.; also the white fly, Aleyrodes citri R. & H. .
Upon palms and other ornamentals: Coccus hesperidum L., Eucalymnatus tessellatus
Sign., Aspidiotus latanix Sign., Aspidiotus hedere Vail., Chrysomphalus dictyospermii
Upon peach, pear, and other fruits: Aspidiotus perniciosus Comst., Aulacaspis penta-
gona Targ., various aphidids.
Upon persimmons: Ceroplastes cirripediformis Comst., Eulecanium corni Bouch6, Pulvi-
naria vitis L.
Upon strawberry: Aphisforbesi Weed.
Upon sugar cane: Pseudococcus calceolaria Mask., Aphis gossypii Glov.
Upon sweet gum: Cryptophyllaspis liquidambaris Kotinsky.
Upon various shrubs: Coccus hesperidum L., Saissetia olea Bern., Pulvinaria cupanta
Ckll., Aspidiotus latanix Sign., Chrysomphalus aonidum L.
Upon willows: Eulecanium nigrofasciatum Perg., Pseudococcus sp. (near citri), Chion-
aspis salicis-nigre Walsh, Aspidiotus perniciosus Comst., various undetermined
In considering the remarkable increase in scale insects and aphidids
which invariably accompanies heavy infestation by this ant one can
not avoid taking into account the persistence with which the ants
drive away ladybird beetles which attempt to prey upon the insects
fostered by the ants. So thoroughly are the Coccid&e and Aphididse
protected in this manner that it is rare that a ladybird can be found
at all on the infested trees. The only exceptions to this rule thus
far noted are a species of Pentilia, a few specimens of which the
senior author found in an infested orange grove below New Orleans,
and the coccinellid mentioned before as preying upon the magnolia
ANTAGONISM TOWARD OTHER INSECTS.
The Argentine ant is strongly antagonistic to nearly all forms of
insect life, with the exception of the Coccida3 and Aphididve. The
amount of damage it is able to inflict upon other insects, however, is
governed by the strength, fleetness, structure, or habits of the
RELATIONS WITH OTHER ARTHROPODA.
insect attacked. Thus it is able to destroy house flies, butterflies,
mosquitoes, etc., only when the latter are hurt or disabled, as
under ordinary conditions they are much too swift for the ants to
catch. In the same manner nearly all forms of beetles are strong
enough to escape from the ants when caught,, and their external
covering is so hard that the ants can make no impression upon it;
but an injured beetle of any kind is very quickly overcome by the
numbers of the ants, and his body is finally cleaned out of the shell
piecemeal. Newly emerged adult beetles of many species are often
captured by the ants before their chitinous integument has hardened,
and they are then an easy prey.
Cutworms and hairless caterpillars found upon the surface of the
ground are destroyed in great numbers; but the ants will not burrow
into the ground after hidden cutworms, and most hairy caterpillars
appear to be invulnerable to them. Web-spinning caterpillars are
also safe from their attacks, and the spiny, mealy projections sur-
rounding coccinellid or ladybeetle larvae appear to protect these
latter very effectively. Insects and other small related animals which
the ants can meet upon even terms are, however, almost always over-
come; not so much on account of the individual valor of the Argen-
tine ants as by reason of their overpowering numbers.
Nests of the social wasps, Polistes sp., which were brought into our
laboratory as food supplies for cultures of Pediculoides, were quickly
found by foraging workers, and the latter soon killed and removed
all of the wasp larvae and pupae that could be reached. Many of the
cells in the comb of Polistes were entirely or partially open so that
the ants had ready access to the insects inside. As the prey in this
case was too large to be handled by individual ants, as many as two
or three dozen would unite in removing a single wasp pupa or larva.
Even the adult wasps, just emerging from the cells, were set upon by
the ants before they had attained sufficient strength to escape by
flight. More and more of the ants would get on these adult wasps
until the latter were helpless and were dragged away, still alive, by
scores of the worker ants. So anxious were the ants to get at these
wasps that when the latter were placed on top of a fruit jar standing
in a tray of water the ants swam the 3 inches of fresh water, climbed
the glass sides of the jar, and continued their attacks as before; nor
could they be made to desist until oil of sassafras was placed upon
The nests of mud-dauber wasps, Pelopeus sp., were also brought
into the laboratory for the same use as the Polistes. The mud-
dauber larvae were of course inaccessible to the ants, but parasitic
flies1 which emerged from these were seized by the ants as fast as
SIdentified by Mr. C. H. Tyler Townsend as a species of Pachyophthalmus.
68 THE ARGENTINE ANT. "
" ... l iii i
they emerged and were summarily disposed of in the same manner
as were the Polistes. Invariably the flies were seized before enough "
time had elapsed for their wings to expand and dry, and only a very
small percentage of them escaped the ants.
Cockroaches are esteemed a great delicacy by these ants, and while
the workers are not able to capture uninjured roaches, they attack
in great numbers any roach so unlucky as to be injured. Dead cock-
roaches are also eagerly visited by the ants and all soft parts removed. .
It seems almost retribution that one of the few natural enemies of the
Argentine ant should itself be a larval cockroach (Thyrsocera cinct a
Burm.), mention of which is made on a following page.
THE ARGENTINE ANT AND THE BOLL WEEVIL..
Prior to the advent of the boll weevil in the territory infested by the
Argentine ant there was considerable speculation as to whether so
combative an ant might not prove to be an insect of some value in
protecting the cotton crop against weevil ravages. Any hopes of this
kind which were entertained have not thus far been realized. In one
rather unimportant respect the ants seem to annoy the boll weevils.
At Baton Rouge the Louisiana Experiment Station had afew small plats
of cotton, aggregating less than an acre, within the city limits and in a
section where the Argentine ants were exceedingly abundant. The
plats were bordered on one side by the Louisiana State University
campus, with its large oak trees sheltering hundreds of ant colonies,
and on the other side by the batture of the Mississippi River, which
was likewise a seething mass of ant colonies. The ground in the cotton
plats was therefore heavily infested by the ants, and when this field
also became infested by the boll weevil the outcome was watched with
considerable interest. During September, 1909, it was found that
the ants, in their steady patrol of the plants while attending cotton
lice, worried the adult boll weevils considerably. Whenever an ant
encountered a boll weevil it would nip the legs of the latter, usually
causing the weevil to fly to another plant or drop to the ground. In
no case were the ants found killing fully matured weevils, though in a
few instances they did attack and kill unhardened weevils which had
just issued from infested squares. The great abundance of ants in
these plats evidently resulted in many of the weevils being driven off,
for something of a top crop was produced in the fall of 1909. It is
worthy of note in this connection that the heavy, ant infestation
obtaining in these plats will not be duplicated in large cotton fields
for many years to come, if, indeed, such will ever be the case. Condi-
tions in large cotton areas are not such as to attract the Argentine ant
in numbers. It was also of interest to note that the presence of the
ants in these particular plats resulted in an abnormally heavy infesta-
RELATIONS WITH OTHER ARTHROPODA. 69
tion of the plants by the "cotton louse," Aphis gossypii Glov.,
throughout the entire growing season.
Were the jaws of the Argentine ant powerful enough to pierce the
cotton squares so that they could remove the boll-weevil larvae, and
were they so inclined, they might be of substantial service in destroy-
ing this pest. However, repeated experiments made by the senior
author proved conclusively that the ants would not do this. The
following experiment will serve as an illustration of those carried out:
On July 10, 1908, three weevil-infested squares were placed on the
food table of an Argentine-ant colony in the insectary at Baton Rouge.
The workers crawled over them constantly for three hours, but made
no attempt to bite into them and evidently did not suspect the pres-
ence of food inside of them. Afterwards the weevil larva) were re-
moved from the squares and placed, alive and uninjured, on the food
table. The ants attacked them, hesitatingly at first and then with
avidity, and in the course of a minute one large weevil larva was
dragged an inch across the food table, vertically another inch, and
into the vestibule of the nest. Another lot of weevil-infested squares
was placed on a board inside the insectary where the ants had been
securing other food for several days. The squares were left here for
five hours, during which time the ants crawled over them constantly,
but made no effort to open them. The ends of the squares were then
broken off so that the ants could enter them if they chose. None
entered. Presently some of the Weevil larvae wriggled themselves
completely out of the squares and they were then attacked by the ants
and dragged away.
These and similar experiments lead one to the conclusion that the
Argentine ant will never be of material value as an enemy of the boll
weevil. In fact, in this respect it can not hope to approach in effi-
ciency the common native fire ant, Solenopsis geminata Fab.
BENEFICIAL ASPECTS OF THE ANT'S ACTIVITIES.
In some few cases the predatory habits of the ant take on a bene-
ficial aspect. In the summer of 1908 Mr. R. C. Treherne was associ-
ated with us in the investigation of the sorghum midge (Diplosis)
Contarinia sorghicola Coq. In the course of his work Mr. Treherne
placed heads of sorghum, milo maize, etc., min cages for the purpose of
rearing the adult midges. In a very short time he found that the
Argentine ants were invading the cages and were carrying away the
adult midges almost as fast as they emerged. (See fig. 10, from draw-
ing by Mr. Treherne.Y To continue the observations it was necessary
to isolate the cages over trays of water or oil. For the purpose of
more closely observing the capture of the midges by the ants, about
200 of the former were placed inside a large glass bell jar. The jar was
raised a trifle at its lower edge by the insertion of a match. In the
70 THE ARGENTINE ANT.'
course of three minutes two Argentine workers had found their way
into the jar and each had captured an adult midge. Other workers i
soon followed. In about 15 minutes fully three-fourths of the flies
had been captured and at the end of 30 minutes all had been either
captured and carried away or were in possession of workers. The -
first midges captured were quickly carried to the ants' nest, but pres-
ently the workers seemed less appreciative of their prizes and spent
much more time in playing with them, although in but few cases were
the midges relinquished. Occasionally a midge would succeed in
taking flight after a worker had taken hold of it; in such cases worker
and midge tumbled to the floor, but without the midge being released. 6
That the workers were unable to see the midges was made evident
many times over in this experi-
ment, for workers repeatedly passed
) within one-sixteenth of an inch of
their prey without even changing
the direction of travel. Only when
the worker touched the midge with
her antenna could she locate the
S Later on it was found that the
ants thoroughly patrolled the sor-
,j ghum heads in the field and not only
captured the mindges as they were
emerging from their pupal cases be-
tween the glumes but also removed
the pupa themselves. That this
S ant is by far the most important
P natural enemy of the sorghum midge
s in southern Louisiana there can be
FIG. 10.-Argentine ant removing the pupa of a no doubt,1 but its services in this
sorghum midge from between the glumes of a regard do not begin to expiate its
sorghum head. (Original.) i
many other crimes.
The Argentine ant is a persistent enemy of the white ants, or
termites, and will capture and kill them at every opportunity. Espe-
cially during the mating season of the termites every male and queen
that falls to earth is quickly set upon by the ants. The latter cut
off their wings, and frequently also legs and antennae, and then bear
them away, still alive, to their nests. Wherever colonies of termites
are accidentally exposed the ants soon destroy them, carrying away
all stages. Not infrequently one finds the Argentine ant colonies
domiciled in the old termite galleries in logs and timbers, the assump-
tion being that the ants had first destroyed the termite colonies and
then taken possession of their domiciles. When winged termites were
I Dean, Harper, Bul. 85, Part IV, rev., Bar. Ent., U. S. Dept. Agr., p. 57,1911.
RtLATIONS WITH dTHEtR ARTHROPODA.
furnished to the ants in our artificial formicaries the wings were
quickly amputated, although the termite itself was not always carried
into the formicary, possibly because, in such cases, the ants were
already bountifully supplied with animal food.
The Rev. Albert Biever, of New Orleans, whose observations on
the Argentine ant are elsewhere mentioned, is authority for the
statement that these ants have in many cases entirely exterminated
the bedbugs in the houses of many of the poorer people in New
Father Biever also states that in some sections of the city the
"red bug," or chigger, has entirely disappeared with the advent of
the ants. The junior author's observations in Audubon Park, New
Orleans, are of similar nature, the chiggers being entirely absent
where once they were a plague. At the same time the senior author
till retains some very unpleasant memories of daily attacks by
chiggers on premises in Baton Rouge which were heavily infested
by the ants. We are thus unable, as yet, to state with certainty
that the ants always destroy these annoying pests.
The attitude of the Argentine ant toward other species of ants has
already been discussed and its action in destroying other ants takes
on either a beneficial or injurious aspect according to whether the
annihilated ant is itself one of beneficial or injurious nature.
The relationships which exist between the Argentine ant and those
insects or other creatures which it tolerates in its nests or in the
near vicinity can not be considered as symbiosis, yet mention of these
may be permissible at this point. Despite the hostility which these
ants exhibit toward most insects which are not directly of service
to them, a few instances have been noted in which other insects and
crustaceans were permitted to live in close proximity to their nests,
or even within the nests themselves.
Certain staphylinid beetles have frequently been found in decayed
logs which were full of Argentine ants. Efforts have been made to
keep some of these beetles in the artificial formicaries along with
colonies of the ant under observation, but the results have been
variable. In experiments of this kind made by the junior author
the beetles were invariably set upon by the ants in the formicary
and either killed or driven out. In similar experiments by the
senior author no apparent attention was paid to the beetles, so far
as could be observed, and they were tolerated in the formicary for a
week or longer, after which they evidently left of their own accord.
On August 17, 1909, a large ant nest was discovered in Baton
Rouge under a large dry-goods box. About 20'specimens of "spittle
THE ARGENTINE ANT.
insects" (family Cercopidae) were also present in the same newt, .:*
attached to straws of grass. These were apparently protected from
the ants by the wet, sticky secretion which surrounded them. This
is the only instance, however, in which the presence of these insects :
has been recorded in the colonies. :
Sowbugs (Oniscida) apparently go among the Argentine ants with I
impunity. These little crustaceans are often found in the ant
nest, especially if they are located under boards or boxes in moist
places. There does not appear to be any relationship existing, and
the ants are apparently indifferent to their presence.
With the exception of two species of mites, which are true inquilines
in the ant colonies, the Argentine ant does not pay much attention
to the majority of mites and spiders. Mention is made on a later
page of certain spiders which prey upon the ants to a limited extent. -
The cattle tick (Margaropus annulatus Say) flourishes with undi-
minished vigor in the ant-infested region, and the same may be said
of the "red mite" of the orange and the red spider of ornamental
plants (Tetranychus bimaculatus Harv.).
Only two true inquilines, both mites, have thus far been found in
the colonies of the Argentine ant. These were first discovered at
Baton Rouge by the senior author in 1908, and were subsequently
found in various localities and in nests of various kinds, usually in
those located in masses of decaying vegetation or litter. Soon after
they were first found specimens were sent to Dr. L. 0. Howard, who
submitted them to Mr. Nathan Banks, of the Bureau of Entomology.
Mr. Banks found them to be new, and his descriptions of them were
published in the Journal of Economic Entomology, volume 1, pages
263 and 264 (1908), together with notes on their habits, by the senior
As compared with most injurious insects which reach great abun-
dance the Argentine ant is remarkably free from natural enemies,
and very few of these have been noted during the course of our inves-
tigations, while even these few are of little importance. No true
parasites of this ant have been observed, and apparently the only
enemies are predatory ones.
INSECTS AND SPIDERS..
In 1909 Mr. Harper Dean observed a small cockroach capturing I
Argentine ant workers in a room in Baton Rouge, La. This insect
from time to time caught up and ate workers which were traveling
about the floor. The cockroach was captured and sent to the Bureau
of Entomology, where it was identified by Mr. A. N. Caudell as a
nymph of Thyrsocera cincta Burm., a species occurring in the south-
ern United States, Mexico, and Central America. A similar habit by
individuals of this species was subsequently observed by the senior
author on one or two occasions, but the number of ants destroyed
by this insect is certainly inappreciable.
A jumping spider of the family Attidae was seen to capture a few
workers, and various species of the cobweb weavers (Theridiidae) had
the habit of reposing beneath the stands supporting our artificial
formicaries and there depleting the colonies under observation. In
fact, -so persistent were they that it was necessary to examine the
stands daily and destroy these spiders. Among the most abundant of
these was one which was identified by the late Prof. B. H. Guilbeau, of
the Louisiana State University, as Theridiuni tepidariorumn. Spiders
of this family were not observed destroying ants in outdoor colonies,
but it is possible that they do so.
On one occasion Mr. G. A. Runner observed an English sparrow
industriously picking up the Argentine workers from a trail which
crossed a wide roadway at Baton Rouge. This habit is not, how-
ever, a common one with this bird.
The flicker or yellowhammer, Colaptes auratus, has often been seen
industriously digging up shallow ant nests in lawns and grass plats,
evidently for the purpose of obtaining the pupae and larvae, and
should doubtless be credited with being the most important natural
enemy which this ant has in the South. Our knowledge of the extent
to which native birds subsist upon these ants is very limited as yet,
and the subject is one well worth more complete investigation than
we have been able to give it.
EXPERIMENTS WITH PEDICULOIDES.
The idea of finding some parasite which would destroy the ants
naturally suggested itself early in our investigations. Owing to the
readiness with which the small parasitic mite, Pediculoides ventricosus
Newp., parasitizes the larvae of wasps and beetles whenever it can
obtain access to them it was thought worth while to see if this para-
site could be successfully used against the ant. For our experiments
we first reared enormous colonies of these mites on living wasp larvae
and thereafter placed these infested larvae in the formicaries, where
they could be closely observed. The following experiment will illus-
trate the results obtained:
For the experiment we selected a large populous ant colony which
was domiciled in a plaster of Paris Janet cage of several chambers.
74 THE ARGENTINE ANT. ;
All immature stages of the ant were present in abundance. On March ......
14 the cover to one of the living chambers was raised and one of the i
mite-infested larvae was dropped in among the workers and larvae in
the formicary. The workers set to work immediately to kill the ,
hundreds of mites. The larval mites were picked up in the workers'
mandibles, chewed a bit and then thrown aside. Adult mites were
seized by the legs and vigorously pulled until they released their hold
on the wasp larvae, after which the workers would crush them in their
mandibles. However, the subsequent developments were entirely
unexpected. A worker was seen to mount the wasp larva, eagerly
destroying mites and becoming at the same time covered with a dozen
or more of the mite larvae. Within a minute the. worker desisted
from destruction of the mites about her and turned her attention to
the ones on her body, trying to dislodge them by rubbing head and
abdomen with her legs. Failing thus to get rid of them, she resorted
to various gymnastic performances, such as jumping and rolling over.
Soon afterwards her movements became slow and feeble and finally
ceased entirely, it being evident that she had either been killed or
paralyzed by the bites of the larval mites. Observations were sus-
pended until March 18, when it was found that the adults and larv :
of Pediculoides were greatly reduced in numbers. No mites could be
seen on any of the ant larvae or pupae, and all of the latter had been
removed from the chamber where the mites were introduced.
The workers in leaving the cage to forage were compelled to pass
through the infested chamber, but in doing so they made the widest
possible detour about the mite-infested material. This status of
affairs continued for some time, the mites gradually decreasing in
numbers until by April 28 they had all disappeared. On this date
cultures of the mite were again introduced into the colony, but in
much greater quantities than before. A spoonful of mite-infested
wasp larvae was placed in each chamber of the formicary. The ants
did not this time attempt to kill the mites, but inside of two minutes
after the introduction of the latter the colony had completely deserted
the formicary, taking with it all eggs, larvae, and pupae. Not being
able to find other suitable quarters on account of the water surround-
ing the formicary, the ants on the following day decided to return to
the nest. They attempted to remove the Pediculoides, but the mor-
tality among the workers was heavy, many being carried out at the
entrance. On the following day the number of dead workers was too .
great for removal, and many of them remained in the cage. The con- :
tinual warfare against the mites continued for several days, the ant
colony becoming by May 6 severely depleted in workers as well as IA
in larvae, some of which were killed by the mites. At the same time
it was evident that the Pediculoides were being destroyed much more
rapidly than they could increase. After May 6 the ant colony ap- .
peared to recover slowly. By July 22 the colony had completely
resumed its normal condition and the mites had been exterminated.
That the Pediculoides could live and breed upon the ant larvae was
established by placing the latter in a glass dish which was isolated
from all workers and permitting them to become infested. On them
the Pediculoides grew and increased as well, apparently, as on wasp
and other larvae. Such enormous cultures of the mite as were intro-
duced into the ant colonies in these experiments could not possibly
occur in nature, and it seems a safe conclusion that this parasite can
make no headway against the ant under normal conditions.
EXPERIMENTS WITH FUNGOUS DISEASES.
During 1909, at Baton Rouge, several experiments were made in
the attempt to inoculate the ants and their larvae with the chinch-bug
fungus, Sporotrichum globuliferum. Cultures were prepared from
beef extract and corn meal, sterilized at a pressure of 18 pounds per
square inch for 30 minutes at a temperature of 256 F., and these
were then inoculated with the fungus from a dead beetle. After these
cultures had been stored for about a week in a dark, damp place,
they all showed a heavy white layer of fungous growth over the sur-
face, and this layer was used in the experiments.
Large quantities of this fungus were placed in Janet cages which
contained strong and healthy colonies of ants with many immature
stages. For a short time the workers would busy themselves carry-
ing out the fungus and dropping it over the side of the cage support,
but after a time they apparently became accustomed to its presence.
It grew and increased inside the apartments in which the ants and their
young stages were domiciled until it formed a heavy white mass over
nearly everything, but in not a single instance was an ant or a young
stage observed which appeared to be in the least inconvenienced by it.
As a number of dead ants were found covered with fungi the
various organisms on them were isolated and cultures made. The
principal fungi obtained were Aspergillus and Penicillium. Cul-
tures of these were also introduced into the ant colonies, but without
effect. It Was therefore concluded that they were purely sapro-
phytic on the dead ants on which they were found.
Attempts were also made to infect colonies with Bacillus larve,
the germ causing the disease among honey bees known as American
foul brood. Owing to the fact that this bacillus attacks the larval
stages of the honey bee, and considering the similarity of ant and bee
larvae, it was thought that this disease might attack the larval stages
of the ant. The experiments were made in a locality where the ant
infestation was very heavy but where honey bees were not kept.
Honey was thoroughly mixed with broken and mashed brood combs
containing bee larvae badly infected with foul brood, and this honey
76 THE ARGENTINE ANT. ?
was then fed in abundance to foraging workers. Subsequent exami-.
nation of the colonies receiving this infected material failed to show
any indication of the disease.
No attempt was made to experiment with this disease under labora- i
tory conditions, on account of the danger of accidentally infecting
honey bees in the neighborhood.
The winter temperatures experienced at Baton Rouge, La., seemed.'
not to produce any appreciable mortality among the ants. During
the winter of 1909-10 a colony at Baton Rouge was kept out of doors
all winter with no other protection than the plaster of Paris walls of
the cage in which it was confined. This colony successfully with-
stood a temperature of 22 F., the lowest temperature recorded
during the winter. It is safe to assume that in their underground
nests and in well-protected situations they can withstand a much
lower degree of cold than this.
Heavy rains appear to be the only meteorological phenomena
which produce any appreciable effect upon the Argentine ants, but
even in this connection it is worthy of note that the most heavily
infested sections at present are within regions of exceedingly heavy
After sudden severe rainstorms it was noticed that the ditches and
drains at Baton Rouge and New Orleans contained thousands of the
dead ants, evidently washed from trees and ground before they could
reach a place of safety. The sudden rising of flood waters over low-
lands would appear to destroy many colonies and the larva in them,
yet, strange to say, the batture along the Mississippi River, which is
annually covered for several weeks with several feet of water, con-
tinues to be an area of approximately maximum infestation. So
facile are the ants in migrating to higher grounds or in ascending
trees, taking with them all larvae and pupae, that it is likely that the
mortality from this source is much less than would be expected.
The mere destruction of foraging workers by rains does not effect any
appreciable diminution in the rate of increase, since, if the colonies
themselves remain unharmed, the deposition of eggs and the rearing
of more workers continues unabated.
METHODS OF REPRESSION.
It is as a household pest that the Argentine ant has forced itself
most into prominence, particularly in the infested cities and towns,
although it is doubtful if the financial loss due to its inroads in this
METHODS OF REPRESSION.
F respect even begins to compare with the losses suffered by the florists,
bee keepers, and orange growers. Early in the course of our studies
we undertook experiments looking to the development of measures
by which householders could obtain some relief from this pest.
A successful campaign against the Argentine ant is by no means
devoid of work, but the control measures thus far devised are no
more cumbersome or expensive than those employed in the warfare
against many other insects, and their intelligent eniploymnent is found
well worth the while in reduced annoyance from this pest.
Studies of the ant's life history early developed the fact that per-
manent relief can be obtained only by actual destruction of the ants
themselves. The use of repellents only serves to permit the contin-
ued increase of the pests and to postpone the time when more laborious
methods of warfare must be adopted. Not only is it necessary to
kill the ants outright, but it is also necessary to adopt means which
will kill the queens. It is hardly necessary to call attention to the
difference between killing ants and the usual insects with which we
have to contend. If one kills a female gipsy moth or boll weevil, for
example, possible future progeny of that particular individual is made
impossible. Such is not the case when one destroys a worker ant,
for the rate of increase and the development of future generations are
in no way interfered with. This is true for the reason that the workers
take no part in reproduction, all eggs being deposited by the queens.
That the destruction of foraging workers does not materially affect
the domestic economy of the colony or retard the rate of increase by
reducing the available food supply is shown by repeated observations
upon the number of foragers required to keep the colony supplied with
food. In the artificial formicaries counts were made of the number
of workers going out for food during periods varying from five hours
to several days, and in no case did the number of foraging workers
out at one time exceed more than 1 per cent of the number of indi-
viduals in the colony. From this we naturally conclude that less than
1 per cent of the workers can keep the remainder, including the queen,
and immature stages, supplied with food. These observations were
made in cases where the food supply was only a few inches from the
nest and was always in abundance. In times of food scarcity, and
when it is necessary for the workers to travel considerable distances in
order to reach a food supply, a larger percentage would have to engage
in foraging. Observations by the junior author upon a large number
of field colonies leads him to the conclusion that even under the most
adverse conditions not more than 10 per cent of the workers are
required for foraging. Under normal outdoor conditions the food
supply is abundant and at such times it is very doubtful whether more
than 2 per cent of the workers are ever engaged in foraging at any one
time. The futility of destroying the foraging workers is therefore
THE ARGENTINE ANT.
self-evident, for the number of workers leaving a colony during any
given period is little if any greater than the number reaching maturity'
within the colony during the same period. i
In spite of these facts repellents are very desirable and their use is,
under most conditions, absolutely imperative in the protection of
foodstuffs, such as sugars, candies, cakes, molasses, honey, vegetable i!
oils, fresh meats, etc.
EXPERIMENTS WITH REPELLENTS.
Our first experiments consisted in testing the various substances
which had been used in successfully repelling other species of ants.
Experience with artificial formicaries and with the hives of honey
bees very quickly showed that water would deter the workers for only
a short time. In our first experiments with colonies kept under
observation the nests were placed on platforms supported above trays
of water. As soon as the water had stood for a few hours minute
dust particles, settling from the air, formed a very thin, almost imper-
ceptible scum on it, and this the workers traversed with ease. A
scum which, when viewed by reflected light, is barely perceptible to
the eye will support the workers. When such standing water was
removed and fresh substituted for it the ants would plunge into it as
before, evidently expecting the scum to be there still. Instead of
drowning, as might be expected, the workers merely swam, or crawled
upon the bottom of the tray until they reached the edge or the wooden
support of the nest, when they proceeded to crawl out. Workers
thrown into water can readily crawl up one's finger or up a stick if it
is brought near them. The senior author has observed workers
which had accidentally fallen into a glass decanter three-fourths full
of water gain a foothold on the smooth glass sides and crawl out suc-
cessfully, feet up and body down, on the wet glass. The workers will
apparently not enter fresh water voluntarily, but evidence indicates
that they will sometimes do so in the attempt to reach their nests or
to reach some much-desired food supply. When running over a film
of oil or dust upon the water the feet and legs do not get wet, but
when the film breaks through, as sometimes happens, the worker
swims with her legs and a portion of the body submerged. Running
water, such as a stream in a ditch or trough, seems to be a successful
repellent, but the practical uses of such a stream are very limited.
The use of running water as barriers to prevent the spread of infesta-
tion in orange groves is more fully described upon a subsequent page.
Sir John Lubbock in his book, "Ants, Bees and Wasps," describes
bands of fur which kept the ants within his artificial formicaries.
The kind of fur used by Sir John Lubbock is not specified, but the
finest we were able to secure was that from an ordinary "cottontail"
rabbit. With this the following experiment was made:
METHODS OF REPRESSION.
Two devices were prepared, each consisting of a small wooden box
nailed to the top of a rounded 2-inch stake about 2 feet in length.
Around the support (stake) of one box a roll of the fur was tightly
placed, arranged so that the hairs projected downward and so that the
ants would have to crawl "against" them in going up the stake.
Fur was not placed upon the other device. The latter was stuck in
the ground and a supply of honey placed in the box. The ants
visited the honey at once and as fast as they removed it the supply
was renewed. This continued for several days, when this device was
removed and the one with the fur was put in its place, also with honey
in the box. The interruption of the "trail" confused the ants for a
little, but within a minute's time they were going up the new device
and working their way persistently among the hairs of the fur. In
a short time they were able to get through it, when they continued to
the food supply at the top and removed it as before. The workers
were forced to make their way slowly through the fur, wrestling in
turn with the hairs in their way, but at most the fur did no more than
delay them a little; it did not repel them in the least.
Various experiments were made with certain proprietary and coal-
tar disinfectants for protecting food supplies from the ants. Wood-
work rubbed or painted with these substances was not crossed by the
workers during periods of from 2 to 48 hours after the applications,
but none of these substances was effective for more than two days.
Oil of citronella seemed more distasteful to the ants and they would
not cross woodwork treated with it as long as the odor remained.
Evaporation of this oil is, however, quite rapid.
The use of zenoleum powder was found quite effective. Sprinkled
heavily on the floors of infested houses it killed many of the workers
with which it came in contact and answered fairly well for breaking
up trails and causing the workers to seek food elsewhere. It was
also found of some service in keeping ants out of the nests of sitting
Pine tar was not effective. In an attempt to feed honey to bees in
the open air the feeder was supported on a stick around which were
placed two separate bands of fresh pine tar. The feeder was placed
out in the afternoon and by 6 o'clock the next morning the ants had
crossed both bands of tar and the honey was black with them. To
stop them, two fresh bands of tar were applied. Within 30 minutes
the ants which were trying to get out of the feeder had forced their
way into the tar in sufficient numbers to form a bridge and over this
the ants were soon passing freely to and fro, despite the strong odor
of the tar itself.
The following experiment proved the inefficiency of tobacco dust:
In the middle of a large iron pan with flat bottom was placed a dish
of honey. This dish was surrounded by a layer of tobacco dust from
THE ARGENTINE ANT.
1 to 2 inches wide and thick enough to obscure entirely the bottom.
the pan. This arrangement was made at 2 p. m., and by 5 p. m. 4
ants were crossing the tobacco dust and getting the honey with':
much facility as they would have crossed an equal amount of soft di
The experiment was repeated, finely powdered sulphur being subi
tuted for the tobacco. The sulphur was not crossed so quickly as]
tobacco dust, but within 24 hours the ants were crossing it fre4
On one occasion the senior author planted a small lettuce bed, a.
thinking to protect the seeds until they germinated, he spread on0
the surface of the bed a layer of tobacco dust covered in turn by
layer of powdered sulphur. The ants got the seeds.
Tree tanglefoot, when placed about the trunks of trees up whi
the ants were traveling, checked them for periods varying from a fa
hours to three or four days. However, a more dilute form of tb
material, used with much success in the gipsy moth work in Maa
chusetts by Mr. D. M. Rogers, has recently been tested by the jui
author with the result that in one case it kept the ants off the trees%
as much as two weeks without being renewed. There is therefore:
possibility that this special form of tanglefoot may have a use in U
protection of trees.
Kerosene acts as a repellent until the odor has largely disappears
but a film of kerosene on water only affords a good floor for the an
to travel on.
Various devices in the form of inverted troughs of tin or othi
smooth surfaces have been tried without success.
Crude petroleum, of all the liquids tested, has proved to be U
most effective repellent. When placed in dishes supporting the ke
of tables, benches, etc., it will continue to repel the ants even aftef.
great amount of dust and trash has accumulated in it.' Its a
indoors, owing to its oily nature and disagreeable odor, is of couzq
impracticable. Out of doors it is useful for giving temporary P$
section to such food materials as sugars, molasses, honey, etc. -'
CORROSIVE SUBLIMATE AND 9ANT TAPES." 'i
The only repellent found to possess any merit (aside from sweet"
arsenical solutions, described below) was dry corrosive sublime
Woodwork or cloth which has been treated with a saturated wai
solution of corrosive sublimate and allowed to dry will not be cross
by the ants while any of the sublimate remains. This fact is utU_
in a practical way by soaking ordinary cotton tape about 1 inch
in the corrosive sublimate solution, wringing it out, and then d
it. When this "ant tape" is fastened around the legs of tables,
of shelves, etc., the ants will not cross it for many months, prove
only that it is not allowed to get wet. The explanation of thhi3;
markable action of the sublimate may be found in the exa
METHODS OF REPRESSION.
0P irritating effect which it has on tender membranes and surfaces.
The finely powdered sublimate and the minute crystals when inhaled
cause a severe irritation of the throat and nostrils, giving rise to
sneezing and nasal discharges. The continued or careless handling of
freshly made ant tape will often have the same effect. It seems not
improbable that the sublimate particles may have something of an
irritating effect upon the sensory organs of the ants. The ants are
quick to detect and avoid corrosive sublimate even when it is in solu-
tion and mixed with other substances. All attempts to poison them
with this substance have been ineffectual, for they can not be induced
to partake of their most favorite foods when the latter contain the
poison in as weak a proportion as 1 to 500.
In some of the tests made by the senior author the corrosive subli-
mate tape has been found to retain its efficiency for over 11 months in
rooms where, except when the temperature was too low for insect
activity, workers could be seen at all hours of the day and night.
Our method of preparing the tape is first to heat corrosive sublimate
and water in a porcelain or granite-ware vessel until the maximum
amount is dissolved. This solution is allowed to cool to ordinary
temperatures, filtered, and ordinary cotton or binding tape is soaked
in it for several hours. The. tape is then removed and pinned upon a
wall to dry, after which it is ready for use. It is very important that
no iron, tin, or steel come in contact with the solution, or with the
tape itself after being prepared. The tape is effective for only a short
time when used on metal surfaces. The extremely poisonous nature of
corrosive sublimate must be continually kept in mind, both in the
preparation of the solutions and tape and in the use of the tape itself.
With this tape it is a comparatively easy matter so to isolate dining
tables, kitchen cabinets, refrigerators, etc., as to protect all food
supplies in the ordinary residence. The same method is constantly
S used by confectioners in infested sections for the protection of their
S candy cases and supplies.
EXPERIMENTS WITH FUMIGANTS AND CONTACT INSECTICIDES.
Following the announcement by Mr. R. S. Woglum,' of the Bureau
of Entomology, in September, 1908, that he had succeeded in
destroying colonies of other ants with a solution of potassium
cyanid, considerable interest was aroused in the question as to
whether the same method could be used with success against the
Argentine ant. The senior author conducted a number of experi-
ments at Baton Rouge to determine this point, among which the
following illustrates the results obtained:
I Los Angeles Times, Los Angeles, Cal., Sept. 20,1908.
. THE ARGENTINE ANT.
A solution of potassium cyanid was made at the strength of
1 ounce of 98 per cent cyanid to 1 gallon of water. The site selected
for the experiment was the area surrounding a few small cotton
plants which were heavily infested with the cotton louse, Aphs
gossypii Glov. Around the plants the earth was literally honey-
combed by numerous small colonies of the Argentine ant, the workers
of which were in constant attendance upon the aphides. The
experiment was made at 11 a. m. on a bright day, with the tempera-
ture at about 77 F., when the workers were busily visiting the lice
and foraging elsewhere for food and when the activities of the colonies
were at about a maximum. The solution was sprayed onto the
trails of traveling ants and the ground itself was sprayed until
thoroughly wet with the solution. By the time the spraying was
completed the odor of the cyanid was so strong as to affect the
operator. In spite of this the solution did not immediately kill the
workers with which it came in contact, but they appeared to suc-
cumb within about five minutes after the spraying. Five hours
after the spraying the odor of cyanid was still very strong and the
number of dead workers on the surface of the ground fully equaled,
or exceeded, the number of living ones in sight at the time of spraying.
Many live workers were busily engaged in carrying away the dead.
The ground was examined and thousands of living ants in all stages-
workers, pupae, larvae, and eggs-were found less than half an inch
below the surface. Two days later the area was again examined
and the ant colonies were apparently as populous as ever. This
and other experiments seemed to demonstrate the impracticability
of using this solution for destruction of the colonies, particularly as
the earth would have to be treated with a sufficient amount of the
solution to saturate it thoroughly to a depth of several inches. This
would probably destroy all vegetation, would be expensive, and
would involve the risk of injury to or loss of life by the operator and
others. For species constructing compact nests having single or
few openings the solution is doubtless effective but, owing to the
multitudinous openings and galleries of the Argentine ant nest,
destruction could be accomplished only by the use of enormous
quantities of the solution.
The resistance of this species to hydrocyanic-acid gas was well
illustrated in experiments made in attempting to fumigate the
winter trap-boxes in orange groves. These trap-boxes are described
more in detail on pages 95-96. They were about 2 feet wide, 2 feet
high, and 3 feet long, made of rough lumber and filled with decaying
cottonseed and hay. During the winter months these boxes con-
tained enormous colonies. For fumigating them to destroy these
colonies galvanized-iron covers were made (see Plate XII) which
would fit over them easily. A 6-inch hole was made in the top of each
"**.,, i iii2 i
"'" .':! :: :
; .. .=ii|
METHODS OF REPRESSION.
cover-box for the introduction of the chemicals used in fumigating.
Just beneath this opening, which could be closed practically air-tight,
was placed the usual earthenware crock for holding sulphuric acid
and water. Experimental fumigation of these boxes was commenced
with a charge of I ounce of 98 per cent potassium cyanid and the
requisite amounts of water and sulphuric acid. This strength was
found not to kill any ants in the box except those which were actually
outside the packing at the time of fumigation. Gradually this
charge was increased until as much as 4 ounces of cyanid were used
at a time in the inclosed space of 22 cubic feet. Even at this strength,
which corresponded to 18 ounces of cyanid per 100 cubic feet, ants
more than 8 inches from the outside of the box were not affected by a
confinement of four hours. In later experiments an iron rod was
used to make holes all through the contents of the box and the same
charge used as before, 18 ounces of cyanid per 100 cubic feet. After
the gas had been confined for five hours the boxes were examined
and it was found that only those within a couple of inches of the
perforations were killed. Larger charges could not be used, simply
because the cover-box would not contain a generator of sufficient
capacity. Even had a charge heavy enough for effective results
been found its cost would have been prohibitive in practical field
Experiments were accordingly undertaken with bisulphid of
carbon for destruction of the ants in the boxes. Holes were made to
the very bottom of the contents, bisulphid poured into these, and
the metal cover placed over the box, its lower edges afterwards
being mounded up with dirt. One-half pound of bisulphid, used in
this manner and confined by the metal cover-box for five hours,
destroyed all ants, and all stages, in the boxes. Mention is made
of the use of this fumigant on page 96.
Other experiments made with the bisulphid of carbon showed
it to be the most available fumigant for the destruction of colonies
in accessible situations.
When colonies are so situated that they can be fumigated with
bisulphid nothing is more effective for their destruction, but the
difficulty of applying this measure lies in the situation of colonies
in all sorts of inaccessible places (see list of nesting places, p. 55)
and to the fact that in heavily infested areas the galleries of one
nest are practically continuous with those of others, affording many
ants the opportunity of escaping from the fumes.
Such substances as hot water, kerosene, crude oil, etc., will, of
course, destroy the ants sprayed with them and often it is quite
practicable to use these substances for the destruction of colonies
that are discovered by turning over boards, pieces of wood, piles
of trash, etc.
84 THE ARGENTINE ANT.
Many preparations have been sold throughout the infested sections 1
for the purpose of destroying the ants. In nearly all cases these..^^
have been merely fluids which would kill the ants when coming '.,
in contact with them and the directions have stipulated that the ants i
should be sprayed with the solutions when on their foraging trails. I I
In view of the foregoing statements relative to the small proportion I
of workers foraging at any one time it is not at all remarkable that j
such preparations have always yielded nothing but disappointment,
even though enormous numbers of foraging workers Were destroyed
by their use. *I
EXPERIMENTS WITH POISONS.
The use of poisons is generally the first measure suggested for the
destruction of an injurious insect, and experiments along this line 1
were begun by the senior author early in the course of his investiga-
tions. An appreciation of the salient features in the life history of
the pest soon emphasized the futility of using a poison which would i
destroy the workers only. Any poison, to affect the rate of produc-
tion or to exterminate the species, must be one which will destroy the
fertile queens and the immature stages, all of which are located within
the nest and are supplied with food by the workers.
No way could be devised by which poison could be administered to
the queens and larvae except by having the workers carry it to them
from sources of supply outside the nest itself. The problem therefore
resolved itself into the search for some poison which would be fatal,
but which at the same time would act so slowly within the workers'
stomachs that they could transport it to the colony and there feed it
to the inmates before perishing themselves.
Some small measure of success attended our experiments in this
line but, incidentally, another and much more valuable use for poison-
ous mixtures was discovered.
Arsenate of lead, containing but little arsenic in soluble form,
naturally suggested itself as the most promising substance for the
purpose. Accordingly it was tried in various experiments, of which ,
the following will serve to illustrate the results obtained:
A mixture was made of 1 part pulverized sugar, 1 part paste
arsenate of lead, and 2 parts of honey. The ants carried this away ,
rapidly and on August 11 exhausted the entire amount that had been -
untouched. An examination of the nest was then made and it was
found to be entirely deserted; the colony had moved away, taking
with it all immature stages. That this action had been taken to get .... ;
outside the sphere of danger from the poison there can be little doubt, ....
for this colony had occupied the same spot for many weeks, despite
the fact that it had been frequently dug open for examination and .I.
METHODS OF REPRESSION.
had been entirely submerged at times during hard rains. No dead
ants were found in the empty nest; any such, if present, were taken
away at or before the time of vacating the formicary. The ants will
not tolerate dead within their living chambers, the cadavers always
being removed expeditiously and often to a considerable distance.
This makes it extremely difficult to tell, by examination of a colony
in nature, how many of the individuals have been killed by any poison
fed to the workers. The action of the colony in moving outside the
zone of danger was observed in, many subsequent experiments in
which poisoned food was used, and tlis gave us the clue to the use of
sweetened arsenical mixtures as repellents for driving the colonies
away from infested situations. The same phenomenon, improperly
understood, has been responsible for the conclusion, arrived at by
several experimenters, that the use of such mixtures was actually
exterminating the ants, their absence after use of the poison being
ascribed to their death and not to their migration to a safer place.
That the mixtures containing lead arsenate, such as those just
described, do destroy the individuals within the nest and that their
continued consumption by the ants would result in extermination if
the colony did not move away from them, were established by experi-
ments made with colonies kept in artificial formicaries where migra-
tion from the poison was made impossible. In one such experiment
a small amount of the mixture last described (1 part lead arsenate
paste, 1 part pulverized sugar, and 2 parts honey) was kept constantly
on the food table of a colony in the formicarium. On the same table,
but a short distance from it, food not poisoned was also kept at all
times. The workers from this colony therefore had their choice
between poisoned and nonpoisoned food. A few workers died each
day, the larvae all succumbing a few days after inauguration of the
experiment. At the end of about 20 days the colony seemed demor-
alized and discouraged, the queen ceased to lay, and the workers did
not work with their accustomed activity. At the end of 44 days all
individuals were dead, the queen having lived until near the end of
Many solutions and mixtures containing white arsenic (arsenic
trioxid) were tested in various ways and the one which gave by far
the best results was made by combining one-fourth gram of arsenic
trioxid with 20 grams of granulated sugar in 100 cc. of water.1 When
placed in a small dish anywhere within the foraging range of a colony
this preparation would be greedily taken for a few hours, after which
the ants would not touch it as long as it remained in the same position.
When the dish was moved a few feet away or placed in another part
I To give warning of its dangerous nature it is well to add to this mixture sufficient confectioner's color
paste to dye it a brilliant red or green. Fruit juices, as of raspberry or similar fruits, may be added to
accomplish the same end.
86 THE ARGENTINE ANT. AI
of the same room and "rediscovered" by the workers they seemed not '
to recognize its dangerous nature and would take it as before. After' i
a few experiences of this kind the colony would move away from the II
vicinity. Only in rare instances were these migrations actually wit- 4
nessed, as they seemed usually to take place during the night. A
solution containing more than one-fourth of 1 per cent of arsenic did
not give as good results for, in such cases, many of the workers died
while sipping up the poison or on their way to the colony. Thus the
poisonous nature of the substance was more quickly detected by the
ants and work on it was stopped proportionately sooner. In all cases
the ants removed the dead and dying from along their trails and from.
the vicinity of the poisoned mixture.
A number of experiments were made to determine whether or not
the ants could distinguish between poisoned and nonpoisoned foods,
with the result that they evidently could not do so; this perhaps being
the reason that they moved their colonies away from the vicinity.
One of these experiments was as follows:
On July 9 a fruit jar containing honey was placed on the floor of a
small shed, where the ants had been very abundant for weeks. By
the following day all honey had been removed by the workers and more
was placed in the jar. Between the 9th and the 12th the jar was
replenished several times, the ants during this time carrying away
more than a half pint of honey. At noon on July 12 a small glass.
vessel containing a mixture composed of one-half of 1 per cent of
arsenic and 20 per cent of sugar was placed about 3 inches from the
honey jar. The ants commenced taking this solution at once, and
in the course of five minutes the vessel was black with them. At 4
p. m. on the same day they were still working with undiminished
vigor on both the honey and the poisoned solution. At 8 a. m. on
July 13 there were only about one-fourth as many ants visiting the
jars as on the previous day. They were still working on both the
honey and the solution and many dead ants lay about. At noon of
the same day very few were visiting the vessels, but many were
engaged in carrying away the dead bodies of their erstwhile sisters.
A few were still taking the arsenic solution, but it was evident that the
ants did not know which of the food supplies was destroying them.
At 2 p. m. on July 14 only two workers were in the vicinity of the ves-
sels and neither of these was feeding. On July 15 all ants, both alive
and dead, were gone, and not a single worker could be found in the
building. Plenty of the nonpoisoned honey still remained in the jar.
On July 16 and 17, also, no ants were to be found in the shed, even
though heavy rainstorms in the meantime drove them indoors in
many other buildings and decreased their available outdoor food sup-
ply. This experiment and many others demonstrated not only the
effect of the poison in driving the ants from the vicinity, but also that