l(o\T
THE BIOLOGY OF TAPINOMA SESSILE SAY, AN
IMPORTANT HOUSE-INFESTING ANT.*f
MARION R. SMITH,
A. and M. College, Mississippi.
INTRODUCTION.
The ant, Tapinoma sessile Say, a common and widely
distributed North American species, has been known to ento-
mologists since 1836, yet it has not been mentioned in literature
as an economic species until within comparatively recent
years.
The writer first became aware of the ant as a house pest
in 1921. Its importance as such was scarcely recognized by
hirjri until 1924 and 1925 when he found this species to be the
most important of all house infesting ants at Urbana, Illinois.
The ant was found in houses in nearly every block investigated
and in some blocks as high as 80 to 90 percent of the homes
were infested. Inquiries concerning the relative importance,
the biology, and the control of this ant were then sent to
entomologists in all sections of North America. Replies
received in response to the questionnaries showed the ant to
be a house infesting species in the following localities: California,
Nevada, District of Columbia, Maryland, Tennessee, and
Mississippi. The ant is very probably a pest in a number of
localities from which no reports are available. In California
this ant appears to be an especially serious house pest. Essig
in a letter stated that 50 percent of the trouble from house
infesting ants in the western section of that state was due to
this one species.
COMMON NAME.
This ant passed for many years without a common name
until Essig named it, the odorous ant, because of the unpleasant,
*An abstract of a thesis submitted in partial fulfillment of the requirements
for the degree of Doctor of Philosophy in Entomology in the Graduate School of
the University of Illinois, 1927.
(Contributions from the Entomological Laboratories of the University of
Illinois, No. 122.
307
308 Annals Entomological Society of America [Vol. XXI,
nauseating, .Tapinoma-like smell which it produces. This
rather descriptive name is objectionable in that there are other
Dolichoderinid ants having a similar odor, which might be
confused with this species. The writer would further restrict
the name, and call the species, the odorous house ant. In the
New England and North Central States, so far as the writer
is aware, there are no other Dolichoderinid house infesting
ants. In the Southern States east of the Mississippi River
species related to Tapinoma sessile Say are not common house
pests, excepting the Argentine ant, Iridomyrmex humilis Mayr,
an imported species. The writer fully realizes the name is
still open to objection in that there are a number of Dolicho-
derinid ants which are bad house pests in the Southwestern
States; however, for want of a better name the ant will be
referred to throughout this paper as the odorous house ant.
SYNONYMY AND DESCRIPTION.
The odorous house ant was described by Thomas Say as
Formica sessilis in the Boston Journal of Natural History,
Volume 1, page 287 for May, 1836, the description being
based on Indiana specimens. Say's specimens are now non-
existent. His descriptions, although possessing some very
salient characters is too brief and inadequate for an ant which
is so highly variable in color, size, and pubescence as is the
odorous house ant. The writer has redescribed the species
from specimens taken at Urbana, Illinois. He believes that
the specimens from which he has drawn his descriptions are
very similar to those of Say's since Indiana and Illinois are
contiguous.
Below is the synonymy of this species, followed by the
author's description of the ant.
Formica sessilis Say, Boston Jour. Nat. Hist., Vol. 1, p. 287 (1836) female and
worker.
Tapinoma sessilis Fred Smith, Cat. Hym. Brit. Mus., Vol. 6, p. 57 (1858).
Tapinoma sessile Mayr, Verb. Zool. hot. Ges. Wien., Vol. 36, p. 434 (1886);
Emery, Zool. Jahrb. Syst., Vol. 8, p. 332 (1895), female and male.
Tapinoma boreale Roger, Berl. Ent. Zeitschr., Vol. 7, p. 165 (1863), female and
worker; Mayr, Sitz. Akad. Wiss. Wien., Vol. 53, p. 397 (1866), worker.
Formica gracilis Buckley, Proc. Ent. Soc. Phila., Vol. 6, p. 158 (1866) worker,
female.
Formica parva Buckley, ibidem, Vol. 6, p. 159 (1866) worker.
1928] Smith: Biology of Tapinoma 309
Worker. Length, 2.39-3.19 mm. (Plate XVIII, Fig. 1).
Head oval, broader behind than in front, with faintly eniarginate
posterior border, rounded posterior angles and convex sides. Mandibles
with the teeth almost gradually and uniformly diminishing in size
from the apex to the superior border, the 3 or 4 apical teeth larger and
more distinct than the others. Eyes moderately convex, placed at a
distance from the mandibles equivalent to their greatest diameter.
Clypeus convex, the anterior border distinctly excised medianly, the
posterior border broadly rounded and extending for some distance
between the bases of the frontal carinas. Frontal area obsolete.
Antennal scapes surpassing the posterior angles of the head by almost
one-fourth their length. Thorax short and robust, anteriorly narrower
than the head. Pro-mesonotal and meso-epinotal sutures very distinct.
Viewed laterally, the pro- and mesonotum together form a rather long,
gentle arch, which terminates at the meso-epinotal constriction; from
the latter arises a short but gentle arch, which gradually fuses into the
straight, oblique, declivous surface of the epinotum. Petiole not
strongly developed, inclined forward and usually concealed by the
basal surface of the abdomen which is superimposed upon it. Gaster
subelliptical, broadest at the base and tapering apically; with four
distinct segments, the remaining segments concealed; basal surface of
the gaster with a wedge-shaped impression for the reception of the
petiole.
Body minutely shagreened, subopaque and slightly glossy. Mandibles
and anterior border of head more shining, the former with distinct
scattered punctures.
Hairs sparse, light yellowish, erect, confined to the mandibles,
clypeus, prosternum, coxas, and the ventral surface of the gaster and
dorsal surface of the fourth segment. Pubescence grayish, fine, yet
distinct, and closely appressed to the body, giving the body a general
pruinose tinge.
Body deep brown to black; mandibles and appendages lighter,
especially the tibis and tarsi of the legs.
Dealated Female. Length, 3.75-4.29 mm. (Plate XVIII, Fig. 2).
Head, excluding the mandibles, subquadrate, about as broad as
long, widest posteriorly, with rounded posterior angles, faintly excised
posterior border and subparallel sides. Eyes large, rather convex,
placed at a distance from the mandibles equivalent to less than their
greatest diameter. Mandibles and clypeus similar to that of the
worker. Antennas proportionally stouter than in the worker, the
scapes surpassing the posterior corners of the head by almost one-fourth
their length. Thorax short and robust; through its greatest breadth
about as broad as the posterior region of the head. Mesonotum,
mesoparaptera and scutellum distinctly flattened dorsally, mesonotum
laterally with a distinct parapsidal furrow on each side. Basal surface
of the epinotum short, gently convex, not over one-half as long as the
oblique, declivous surface, into which it gradually merges. (Wings,
when present, of the same character as in the male). Scale of petiole
not highly developed, inclined forward and hidden beneath the basal
310 Annals Entomological Society of America [Vol. XXI,
surface of the gaster, which is somewhat superimposed upon it. Legs
of moderate size, distal ends of each tibia with a spur, that of the pro-
legs clearly pectinate. Gaster subelliptical, broadest basally .and
tapering apically, with four distinct segments dorsally, the others,
concealed; base of gaster with a wedge-shaped depression for the recep-
tion of the petiole.
Sculpturing similar to that of the worker.
Pilosity similar to that of the worker; the anterior border of the
clypeus with a long distinct hair on each side of the median excision.
Pubescence yellowish or grayish, according to the light, and longer and
more distinct over all parts of the body than on the worker, thus giving
the body a more subopaque, pruinose tinge.
Body varying from brown to almost black; thorax and appendages
lighter, especially the latter.
Alate Male. Length, 3.60-4.44 mm. (Plate XVIII, Fig. 3).
Head, excluding the mandibles, subquadrate, broader behind than
in front of the eyes, the posterior border faintly convex, the posterior
corners subangular. Mandibles with one large apical and several
subequal denticular. Maxillary palpi 6-segmented, labial palpi 4-seg-
mented, as in the worker and female. Clypeus moderately convex, the
anterior border with a faint central excision, the posterior border
broadly rounded and extending some distance between the frontal
carinse. Eyes elliptical, very large and strongly convex. Vertex
with 3 prominent ocelli, the distance between the two ocelli approx-
imately twice as great as that between one of the lateral and the median
ocellus. Antennas 1 3-segmented, the scapes surpassing the posterior
corners of the head by about one-fourth their length. Mesonotum
large, flattened dorsally, and with .a parapsidal furrow on each side, but
without Mayrian furrows. Wings sordid gray, thickly pilose, and with
ciliated margins, the veins yellowish-brown. Anterior pair of wings
each with a single closed discoidal cell, cubital cell, and radial cell, the
discoidal cell subquadrate. Epinotum with the base and declivity so
completely fusing that the limits of each are not definitely discernible,
the two forming a rather gentle, convex surface. Legs moderate in
size, the distal ends of each tibia with a spur. Petiole inclined forward,
but concealed for the most part by the base of the gaster which is super-
imposed upon it. Gaster elongate elliptical, with a wedge-shaped
impression at the base for the reception of the petiole. Genitalia
rather large and prominent, stipites large and subtriangular, the cerci
each with a tuft of hairs or cilia at their distal ends.
Pilosity resembling that of the worker and female, but different in
lacking hairs on the dorsum of the fourth segment, which are here con-
fined for the most part to the stipites of the genitalia and the cerci.
Body covered with dense, grayish pubescence, which is most discernible
on the appendages. In certain lights the pubescence of the body has a
slight, somewhat subopaque luster. The petiole is free of pubescence
and is therefore smooth and glabrous.
Body uniform deep brown to almost black; the mandibles and
appendages scarcely or not at all paler in color.
1928] Smith: Biology of Tapinoma 311
CLASSIFICATION.
The odorous house ant is a member of the subfamily
Dolichoderince, which in North America embraces seven genera.
The ants of this subfamily are characterized (1) by the presence
of a ventral, slit-shaped, cloacal orifice; (2) by the presence of
anal glands which produce a secretion having a rotten cocoanut
or nauseating Tapinoma-like odor; (3) by the presence of a
single-segmented abdominal pedicel, and (4) by the fact that
the pupae are not enclosed in cocoons.
1 The food of the ants of this family is small organisms,
supplemented by honeydew, and the floral, extrafloral and
glandular excretions of plants. A number of species are
important house pests: among these being, the Argentine ant,
Iridomyrmex humilis Mayr; the odorous house ant, Tapinoma
sessile Say; and the species, Tapinoma melanocephalum Fab-
ricius. The Argentine ant is without doubt, one of the worst
house infesting ants in the world.
Worker ants of the genus Tapinoma can be distinguished
from the workers of closely related genera in that the abdominal
pedicel bears a vestigial scale or petiole, which is overshadowed
by the base of the abdomen.
Only three species of Tapinoma are definitely known to
occur in North America, and all of these except one are native
species. The following key will suffice for the determination of
the workers.
KEY TO WORKERS OF THE NORTH AMERICAN SPECIES OF TAPINOMA.
1. Workers small, never measuring more than 1.5 mm. in length 2
Workers larger, measuring at least 2 mm. or more in length; color varying
from brown to black, appendages lighter; antennal scapes surpassing the
posterior corners of the head; most common species sessile Say
2. Antennal scapes surpassing the posterior corners of the head; head and
thorax very distinctly brown, mandibles, antennae and legs very pale
yellowish; imported species melanocephalum Fabr.
Antennal scapes not attaining the posterior corners of the head; general
color pale yellow, sometimes, however, with the dorsal surfaces of the
body brownish; native species, at present only recorded from the coast
of Florida litorale Wheeler
A species' which has been passing in literature for sometime
as Tapinoma pruinosus Roger was described by Roger in 1866
from Cuban specimens (Tapinoma pruinosum, Roger, Berl.
Ent. Zeitschr. Vol. 7, p. 165 (1866) ). Wheeler in his bulletin
on the ants of Cuba (Bull. Mus. Comp. Zool. Harvard, Vol. 54,
p. 497 1913) has shown that the ants which have been passing
312 Annals Entomological Society of America [Vol. XXI,
as Tapinoma pruinosus Roger are really Iridomyrmex pruinosus
(Roger), a species common to the United States as well as to
Cuba. The name Tapinoma pruinosus Roger is therefore
relegated to synonymy and the name Iridomyrmex pruinosus
(Roger) succeeds it.
On page 16 of this paper, the writer mentions a species of
ant which Wheeler described from Massachusetts as Bothrio-
myrmex dimmocki. Wheeler in remarking about the ant
mentions the fact that he was very much surprised to find a
species of Bothriomyrmex occurring in North America as no
species had been previously recorded for this country.
According to the opinion of Emery the ant should be
transferred to the genus Tapinoma (Emery, Bull. Soc. vaud.
Sci. Nat. Vol. 56, p. 19, 1925). Since the writer does not
posess Emery's paper he does not know what reasons the author
gives for such a change. To the writer it would appear that
Wheeler was correct in placing this species in the genus Bothrio-
myrmex as the workers which he described had 4 segmented
maxillary palpi and not 6 segmented as do the species of
Tapinoma. Wheeler does not mention whether the scale of
the abdominal pedicel of the workers was distinct or not; if it
was distinct, then the workers of this species would appear
unquestionably to belong to Bothriomyrmex, since the scale of
Tapinoma is vestigial. The writer has followed Wheeler for
the reasons stated and has therefore not considered dimmocki a
species of Tapinoma as Emery does.
METHODS OF CONDUCTING THE BIOLOGICAL STUDY.
Ants collected in the field, were brought to the laboratory
where they were etherized, counted, and placed in the cages
for observations. These plaster of Paris cages consisted of
two small, rectangular, intercommunicating chambers which
were covered by a small pane of glass upon which was a heavy
piece of carboard. The glass and cardboard not only pre-
vented the ants from escaping, but held in the moisture and
made the cages' dark. Food, consisting of nuts, meats, cooked
eggs, honey, and sugar, was placed in one of the compartments
of the cage as needed. Since the food would quickly mold it
was necessary to change it every other day. Observations on
the number of eggs laid from day to day and on the develop-
1928] Smith: Biology of Tapinoma 313
ment of the ants were recorded and compared with field observa-
tions.
In computing the development of the brood, it was necessary .
to assume that the first eggs laid were the first to hatch, and
that the first to hatch, were the first to pupate, etc. This
method, though open to some objections, is the only practical
means of ascertaining the life history of so complex a social
insect, inasmuch as it is constantly moving its eggs and brood
or even at times devouring them.
SEASONAL HISTORY.
Indoors in apartment houses, single residences, green-
houses, and other places where the temperature is optimum,
the workers " are active the year around, and very probably
breeding operations also take place continuously. Due to the
inaccessibility of such nests, no examinations could be made to
determine whether development of the brood was taking place
or not. Dealated females that were brought to the laboratory
in late fall and kept at a temperature of 70 degrees Fahrenheit,
or above, laid a few eggs, which took from twenty-two to
twenty-six days to hatch, and the larvag developing from, these
eggs made no satisfactory growth until spring.
Outdoors, on the other hand, the odorous house ant passes
the winter as workers, dealate females, and partly grown larvse.
Workers began foraging as early as March 7th. Egg laying
and uniform development of the brood were continuous pro-
cesses from late April till cold weather, approximately Novem-
ber 1st. After a dormant period from November till April,
the partly grown larva? appeared as workers during April,
thus requiring six to seven months for their complete life history.
For eggs laid from April to June, development of the workers
took place in from five to nine weeks. For eggs laid from June
to September development proceeded even faster than this,
requiring only six to seven weeks. No observations were made
on the development of the males and females.
Alate females have been observed by the writer and others
to appear at various dates ranging from June 17th to early
July, and males have been noted from June 10th to July 9th.
From the data available it appears that the males emerge a
short time before the females. Mating is believed to take
place both inside the nest and outside of it. That mating may
1928] Smith: Biology of Tapinoma 315
nests independently, but the writer has not been so fortunate
as to observe this. That young females of the current season
begin egg laying soon after fertilization has been proven by the
writer who kept such females in artificial nests and has obtained
eggs from them.
Since the breeding season lasts from April to November and
since the average time required for the development of the
worker in summer is seven weeks, four to five generations a
year is postulated.
DEVELOPMENT OF THE WORKER FROM EGG TO ADULT.
The egg of the odorous house ant is subelliptical in form,
pearly white in color, lustrous, and without markings. It
measures .24 by .39 mm. The egg membrane is thin and
easily ruptured. It is also of such a sticky nature that one
egg easily adheres to another. In the process of incubation the
egg gradually loses its luster, becomes more opaque, and
eventually the form of the developing embryo can be dis-
tinguished. Incubation requires from eleven to twenty-six
days according to the season of the year (Fig. 1).
The freshly hatched larva is scarcely larger than the egg.
As the larva grows its head becomes recurved ventrally, and a
peculiar protuberance can be noted on the superior surface of
the caudal end of the body. The body of the larva is distinctly
segmented and also somewhat yellowish in color. Beneath the
integument are small, scattered, white particles, probably
excretory products. When full grown the larva is rather plump,
being less distinctly segmented dorsally. The meconium is now
quite apparent. The head of the larva appears even more
recurved than formerly, and the caudal protuberance is very
clearly evident. The larva now measures .72 by 1.74 mm.
The larval stage occupies from thirteen to twenty-nine days
(Fig. 2). _
The prepupa is an almost exact replica of the full grown
larva except that the meconium is not evident, it having
been cast out just before the larva went into this stage. The
body is robust and very plump. The integument soon accquires
a much wrinkled, dry appearance. The prepupa measures
about 1.8 mm. in length. The prepupal stage requires from two
to three days.
316
'Annals Entomological Society of America [Vol. XXI,
The worker pupa when first formed is naked, white, .and
destitute of any color markings. It measures from 1.82 to
. 2.29 mm. in length. The head is directed ventrad, and the
appendages are borne very close to the ventral surface of the
body as in the usual manner. The eyes of the pupa begin to
show a faint brown in color in from two to three days, and in
from six to nine days not only are the eyes black but the mandi-
bles are brown and the body has accquired a sordid yellowish
tinge, the gaster being more infuscated and the head less so.
The pupal stage lasts from eight to twenty-five days, averaging
in midsummer about fourteen days (Fig. 3).
TABLE I.
The Maximum, Average, and Minimum Time Required for the Workers to
Develop from Egg to Adult at Various Seasons of the Year.
Maximum
Average
Minimum
Number
Season
Number
Number
Number
Specimens
Days
Days
Days
Observed
April- June Egg Stage
20
15
12
15
*Larval Stage
29
22
13
8
Prepupal Stage
Pupal Stage
18
13
6
35
Total Egg- to Adult. . . .
67
50
31
July-September Egg Stage .
16
12
11
28
Larval Stage
16
15
14
3
Prepupal Stage
3
2
2
7
Pupal Stage . . ....
25
13
8
Total Egg to Adult. . . .
60
42
35
Three days after emergence the gaster of the callow is
deeply infuscated, the head less so, and the thorax least of all.
The time required for the callow to attain full color in the life
history cages has ranged over wide limits, usually averaging
from less than a week to more than three weeks.
LENGTH OF LIFE OF THE VARIOUS CASTES.
Very little informations was obtained on the length of
adult life of the various castes. One female was kept eight
months,- the longest period observed, and was then accidentally
*This is the time required for the combined larval and prepupal stages.
1928] Smith: Biology of Tapinoma . 317
killed by crushing. Many of the females brought in from the
field died in a period of a few weeks to several months. Death
in many cases was due to unsatisfactory cage conditions, such
as the development of mold, etc. Workers appear to be as
hardy as females and lived equally long. In cages the males
on the other hand, are very short-lived, perishing within a week
or ten days. During confinement they seemed to have ex-
hausted themselves by running nervously about. Under natural
conditions the females probably live a number of years, as do
the workers, whereas the males perish within a few days after
emergence.
HARDINESS OF THE ANTS.
The hardiness of the ants is most remarkable. On a number
of occasions the writer has accidentally broken off appendages,
or even crushed the bodies of the female and workers, yet these
specimens lived and appeared to be little affected by the injuries.
Some females with considerably crushed abdomens have laid
eggs in spite of their injuries. In one case, two dealated
females without food or water, survived confinement in a jar for
a period of over two months.
THE EGG LAYING CAPACITY OF THE FEMALE.
Tapinoma sessile Say is remarkable in that there are so
many dealated females in each colony, in some nests as many as
two hundred, all apparently taking part in brood production.
The females, although considerably larger than the workers,
are not so much so as in other species. Females kept in life
history cages over a considerable period of time have laid only
a very small number of eggs. Sometimes an individual has
laid as many as twenty to thirty eggs a day, but when an egg
count was kept over a long period of time it was found that the
total number of eggs produced by each female was compara-
tively small; some averaged not over .03 eggs a day, whereas
the most prolific layers averaged only 1.78 eggs a day. Assum-
ing that a female begins egg laying in April and lays 1.78 eggs
per day up to the first of October, she will have laid only 350
eggs, a very small number. Although the records mentioned
above were obtained under artificial conditions, the writer
believes they closely approximate those in nature. The Small
size of the females and the great number in each nest very clearly
318
Annals Entomological Society of America [Vol. XXI,
indicate that the females are individually not large egg layers,
and that the flourishing condition of the colony is due to the
combined output of many females (Table 2).
REPRODUCTIVE ABILITY OF THE WORKERS.
Egg laying by the workers has been observed on three
different occasions, indicating a not uncommon habit of this
caste. A number of workers without a female, which were
confined in a cage on May 7th, laid twenty-one eggs by the
TABLE II.
The Total Number of Eggs Laid by Each Female, the Number of Days Each
Female Was Kept in Confinement, and the Estimated Number of
Eggs Produced a Day by Each.
Specimen
Number
Date Installed
in Cage
Date Cage
Discontinued
Total Number
of Eggs
Average No.
Eggs per Day
A
B
c
April 9
April 13
April 13
April 30
April 29
May 25
22
15
44 .
1.04
.19
1.04
D
April 26 ....
May 26..
40
1.30
E
June 11 ....
December 31. .
40
.20
F
G
H
I
June 22
August 22
September 5.. .
November 28
July 23
February 6.. . .
September 19..
July 8 . . . .
35
42
24
10
1.60
.22
1.78
.04
K
November 28.
December 11.
May 1
April 17
5
16
.03
1.12
L
December 11..
July 28
19
.08
14th of May. These eggs failed to hatch since the workers
died before the eggs had an opportunity to develop. Whether
more than one worker was laying is not known.
The most complete record is that of Cage 9 in which seven-
teen workers were confined on May 6th. Between this date
and May 19th they laid a total of forty-five eggs. On May 31st
small larvae were observed for the first time and on July 10th
a prepupa appeared, which was almost immediately destroyed
by the ants before it had a chance to pupate. July 13th
another prepupa appeared which met a similar fate. Judging
from the size of the prepupas the writer feels that if these had
been allowed to pass into the pupal and adult stages they
would have formed workers. Although this is somewhat con-
trary to general expectation it is by no means impossible or
1928] Smith: Biology of Tapinoma 319
improbable, for Tanner and Reichenbach, experimenting with
other species of ants, have succeeded in rearing worker ants
from worker eggs. The writer believes that the workers of
Tapinoma sessile Say and other ants lay eggs more frequently
than is usually supposed and that the eggs may at times develop
into castes other than males.
A number of writers contend that when workers lay eggs,
the brood developing from these eggs take longer to reach
maturity than the brood reared from female eggs. From the
present data it would appear that their contention is correct.
With some of the eggs just mentioned the incubation period
was twenty-three days, and the larval stage forty-one to forty-
two days. If three days be allowed the brood for the pre-
pupal, and fourteen days for the pupal stage (the time required
by the brood reared from female eggs) then it would have taken
the workers from eighty-one to eighty-two days to attain
maturity, or a period of eleven to twelve weeks as compared
with five to nine weeks for workers produced from female eggs.
Superficially the eggs of the workers appeared larger and
more elongate than those laid by the females, but the writer
cannot be sure of this statement for he did not measure or
otherwise carefully study the eggs, due to their scarcity and the
fact that he was anxious to have them incubate successfully.
NESTING SITES.
Probably no ant surpasses the odorous house ant in the
diversity of its nesting sites. These ants nest in the soil beneath
stones, boards, leaves, or other rubbish; under the bark of
rotten logs and stumps; and also in cavities in the stems of
elder (probably those made by the caterpillar, Achatodes zece
Harris). Sturtevant found the odorous house ant nesting in
the galls made by the wasp, Amphibolips confluens Harris
that were lying on the ground beneath an oak tree. Essig
stated in a letter that the ants nest in bird's nests, rubbish, and
trees. In addition the writer has found them nesting in houses
in Urbana, Illinois. The type of soil or the altitude has ap-
parently little to do with the choice of their nesting sites.
The ants have been found to nest all the way from sea level to
heights of over 10,000 feet, and from nests located in boggy or
swampy localities to sandy areas along the sea coast or to
higher and drier locations inland. A study of the nesting sites
320 Annals Entomological Society of America [Vol. .XXI,.
of this species has revealed two facts: (1) their lack of perma-
nency; and (2) their shallowness. Some of the nests are located
at the surface of the soil or only slightly beneath it. The nests
are most commonly found in the soil beneath stones, rubbish,
boards or any such refuse.
RELATION TO CLIMATIC CONDITIONS.
The odorous house ant is evidently acclimated to a wide
range of temperature and humidity, since it is distributed from
Canada to Mexico. At Urbana, Illinois, the workers have not
"been noted foraging outdoors at a temperature below 50 degrees
Fahrenheit. At this temperature the ants appeared as if
numbed by the cold and moved at a slow gait, as compared
with their usually quick method of scurrying along. Workers
however, have been observed to enter refrigerators and get
into the ice compartments where the temperature must certainly
have been below" 50 degrees Fahrenheit. The ants do not like
to cross water and if possible avoid doing so ; but once in the
water, due to the lightness of their bodies, they can float on
the surface film, and in their violent struggles usually manage
to propel themselves to one side and crawl out. Many colonies
have escaped from the writer by crossing a slow stream of water
which surrounded their nest. Rain, by washing their favorite
food, honey-dew, from the foliage of plants, ' often causes the
ants to invade homes; in fact, many housekeepers state that
the ants are worst immediately after a rain. The writer has
seen workers foraging in his yard when a wind storm was in
progress, which was so violent as to blow aphids from trees.
The aphids referred to were the box elder louse, Periphyllus
negundinis Thos. That the ants can stand considerable heat
is shown by the fact that they often construct nests under
small piles of leaves or in compost heaps where the temperature
is undoubtedly very high.
RELATION TO OTHER ORGANISMS.
RELATION TO HONEY-DEW EXCRETING FORMS.
Few ants excel the odorous house ant in its honey-dew
loving habits. It is an aphidicolous and coccidicolous species
par excellence and deserves to be ranked with such ants as the
corn field ant, Lasius niger. var. americanus Emery, the honey
1918] Smith: Biology of Tapinoma 321
ant, Prenolepis imparis Say, and other such honey-dew loving
species.
The writer has very commonly witnessed the workers of
this species stroking with their antennae, the box elder louse
and obtaining from them the much sought honey-dew. The
ants also showed a keen interest in mealy-bugs, especially
individuals of the species Pseudococcus maritimus Ehrh. which
they attempted to pick up and carry away when the .writer
sought to take specimens of the mealy bugs from the trunk of
box elder trees. The workers of the odorous house ant may
also distribute plant lice and other honey-dew excreting forms.
On two occasions they have been seen carrying live box elder
lice in their mouths and also a species of Macrosiphum, common
on raspberry. A list of some of the insects with which this
ant has been found associated is given below :
Aphididce: Periphyllus negundinis Thos. on box elder;
Chaitophorus viminalis Monell on American aspen and quaking
aspen trees; Aphis viburnicola Gill, on Viburnum opulus L. ;
Aphis sp. on Englemanns Ivy; Anuraphis cardui Linn, on
plum; Aphis sp. on burdock; Aphis rumicis Linn, on Viburnum
opulus L. ; Aphis helianthi Monell on sunflower; Neothomasia
populicola (Thos.) on cottonwood; Myzus cerasi on cherry;
Macrosiphum solanifollia Ashm. on rose and raspberry; 'Aphis
pseudobrassicce, Davis on turnips and Chaitophorus delicata
Walker on an undetermined host.
Coccidce: Lecanium sp. on box elder; Kermes sp. on water
oak; Chionaspis furfur a (Fitch) on apple; Saissetia hemisphcerica
(Targ.) on lemon and olive; Coccus hesperidum Linn, on orange;
Pseudococcus citri (Risso) on Dracaeena plant, the rice paper
plant, lemon and coleus; and Pseudococcus maritimus (Ehrh.)
on box elder.
Membracidce: Entylia sinuata Fabr. on sunflower.
RELATION TO OTHER ANTS.
During the period of two years devoted to the study of
this ant, the writer failed to observe any fight or animosity on
the part of Tapinoma sessile Say toward any other native
species which it encountered. The odorous house ant is
extremely common at Urbana, Illinois, and its nests are situated
near those of other species, yet the ants do not seem to fight.
When the odorous house ant. encounters another species, each
322 Annals Entomological Society of America [Vol. XXI,
seems to sense the other's presence and they therefore avoid
one another. On one occasion the odorous house ant and
the corn field ant, Lasius niger var. americanus Emery, were
found foraging in a kitchen at the same time, yet the two
species did not intermingle. The tiny thief ant, Solenopsis
molesta Say, and the ant, Strumigenys pulchella Emery, have
been found to live with this ant in what appeared to be com-
pound nests. The tiny thief ant is known to feed on the brood
of other species of ants and the species of Strumigenys are sus-
pected of the same habit.
King (1897) has found mixed colonies of the odorous house
ant and the following species: Formica fusca var. subsericea
Say, Lasius flavus subsp. nearcticus Wheeler, and Lasius niger.
var. americanus Emery.
Wood worth (1910) appears to be the only observer who has
seen the odorous house ant in conflict with another species;
namely, the ubiquitous Argentine ant, Iridomyrmex humilis
Mayr. The latter species is noted for its pugnacity toward all
ants it encounters except a few small species such as the tiny
black ant, Monomorium minimum Buckley, and Pharaoh's ant,
Monomorium pharaonis Linn. Wood worth has the following to
say concerning the conflicts between the Argentine ant and the
odorous house ant : ' ' This odor is produced by a liquid secretion
(speaking of the ejections from the anal glands) which can
be ejected from the abdomen as an appreciable drop, and
which is used in its contest with the Argentine species. As
long as the supply of the secretion lasts the Tapinoma has no
difficulty in keeping the Argentine ant off, but after having
put four or five Argentines out of the combat in this way
finally the Tapinoma is put to rout and the Argentines are
invariably victorious, because they always attack in sufficient
numbers. We have observed many battles between these
species and the Tapinoma is always driven away from its feeding
ground and its home despoiled."
If there is any animosity exhibited by individuals of one
colony of Tapinoma sessile Say towards those of another colony,
the writer has not witnessed it. He has mixed colonies arti-
ficially in the laboratory and has also seen alien colonies combine
of their own accord.
Wheeler (1916) described a species of ant, Bothriomyrmex
dimmocki, from Massachusetts, which he states may be a
1928] Smith: Biology of Tapinoma 323
temporary parasite on the odorous house ant, like its cogener,
B. atlantis Forel, of Tunis is on Tapinoma nigerrimum Nyl.
The female of B. atlantis Forel after descending from her
nuptial flight is pulled into the nest of T. nigerrimum Nyl., by
the workers of that species. She soon crawls on the back of
the nigerrimum female and decapitates her. After the death
of the nigerrimum female, the workers of that species accept
the B. atlantis female and rear the brood she produces. Eventu-
ally all the nigerrimum workers die and the colony then becomes
a pure one of B. atlantis.
RELATION TO MYRMECOPHILES AND OTHER NEST INMATES.
In the nests of the odorous house ant, Mann (1911) has
found the little cricket, Myrmecophila oregonensis Bruner, and
also a little wingless wasp, Isobrachium myrmecophilum Ashm.
"Ashmead states that the genus (Isobrachium) is parasitic
upon the ants or other myrmecophilous Coleoptera," according
to Mann who writes further, "the latter being so rare in the
nests of Tapinoma, it is probable that Isobrachium is a parasite
on the ant itself." The crickets, M. manni Schimmer and
nebracensis Lugger, have also been taken in the nests of this ant.
The following species of Coleoptera, most of which are rove
beetles (Staphylinidce) , have also been taken from the nests of
the odorous house ant by Mann, Wheeler, and others: Zyras
tapinomatis Mann, Myrmoecia lugubris Casey, Nototaphra
lauta Casey, Connophron longipenne Casey, and Myrmedonia sp.
The writer has found in the nests of the odorous house ant
an unidentified species of spring tail (Collembola), termites
(Isoptera), and sow bugs, Armadillidium vulgare (Latr.). In
the laboratory a species of book lice thought to be Troctes
divinatoria (Muller) appeared in the cages and fed on the'
dead bodies of the ants and other refuse. Neither were the
ants observed to attack the lice nor the lice to trouble the ants.
RELATION TO PREDATORS.
The only animals known to feed on the odorous house ants
are birds and toads. - A winged male of this ant was taken
from the stomach of a toad, Bufo sp., at Anna, Illinois, by a
member of the Illinois State Natural History Survey. The
following list of the species of birds known to feed on the
324 Annals Entomological Society of America [Vol. XXI,
odorous house ant was sent to the writer by the United States
Bureau of Biological Survey: the pigeon hawk, Falco columbarius
Linn; the American magpie, Pica pica hudsonia (Sabine) ; the
Bartramian sandpiper, Bartramia longicauda Bechet; the chim-
ney swift, Chaetura pelagica Linn. ; the crow, Corvus brachy-
rhynchos brachyrhynchos Brehm; and the red shafted flicker,
Colaptes cafer collaris (Vigors). Bryant (1914) mentions that
the western meadowlark, Sturnella neglecta neglecta Audubon,
feeds on this species of ant and the writer has observed the Eng-
lish sparrow, Passus domesticus Linn, doing the same thing.
RELATION TO PLANTS.
The odorous house ant not only visits plants for the purpose
of attending insects but for the purpose of visiting also the
floral and extrafloral nectaries and other glandular excretions.
The workers have very commonly been seen lapping up exudates
on the buds of peonies. This habit apparently causes the buds
to dry out to such an extent that the flowers developing there-
from are smaller and in many cases malformed. Dietz (1926)
states that the black lawn ant, Formica fusca var. subsericea
Say, can spread peony bud wilt by means of the workers crawl-
ing from infected to non-infected buds, while visiting the buds
for the much sought exudates. If this be true in case of the
lawn ant, it should also apply for the odorous house ant, for
it, like the lawn ant, is a persistent visitor of peony buds.
Davis of New York (1922) states that he has seen workers of
this species visiting the glands at the base of the leaves of
Populus grandidentata Michx. The writer has seen this ant in
attendance on the glands of castor bean plants.
During 1926 the writer found a fungus, Laboulbenia formi-
carium Thaxter, infecting several species of ants in Urbana,
Illinois, namely: Formica fusca var. argentea Wheeler, F.
neogagates Emery; Lasius niger var. neoniger Emery, and F.
pallide fulva schaufussi var. incerta Emery. Although the
odorous house ant was present on the same blocks as the
species mentioned above, this ant was not found to be infested
with the fungus.
In the laboratory, colonies of the odorous house ant were
'often choked out by luxuriant growths of the bread mold,
Rhizopus nigricans Ehrh., and a species of Aspergillus. These
molds arose from foods that were allowed to remain in the
1928] Smith: Biology of Tapinoma 325
cages too long, thriving best where there was considerable
excess moisture. The writer did not find the ants outdoors to
be affected by any sort of fungus and he doubts if they ever are.
FOOD.
The food of the odorous house ant under normal conditions
is largely honey-dew, supplemented by the flesh of organisms
and the juices of fruits. The ants are also very fond of the
floral and extrafloral secretions of plants. In the laboratory
cages the ants occasionally fed on their brood. It is presumed
that under outdoor conditions this seldom, if ever, happens.
When the ants enter houses they are almost omnivorous but
seem to show a slight preference for sweets. In a number of
homes in Urbana, Illinois, the ants have been known to cut
through paraffine in order to reach jelly and preserves in
containers. They have been noted to infest the following
foods: honey, sugar, preserves, pies, custards, marmalades,
cooked and uncooked beef, fish, raw and fried liver, boiled and
mashed potatoes, stewed prunes, cheese, milk, ice cream, and
ripe fruits.
SIZE OF COLONIES.
The colonies of this ant show a wide variation in size, perhaps
due to their age. The smallest colony observed contained only
four dealated females and about one hundred workers. The
largest colony noted was estimated to contain about ten thou-
sand individuals, including brood and adults. An average
colony may be expected to contain between two thousand and
five thousand specimens.
One of the most striking characteristics of the colonies of
this ant is the unusually large number of dealate females, all of
which no doubt take part in reproduction. The females,
unlike those of the honey bee, are most amiable toward one
another.
From observations that have been made it is believed that
the sexed-forms are not produced in any but the older and
stronger colonies. Although many nests have been examined
sexed-forms have been found only in the larger and more
flourishing colonies, which were very probably from four to
five years of age (Table 3).
326
Annals Entomological Society of America [Vol. XXI,
GENERAL HABITS OF THE WORKERS.
The workers of the odorous house ant are strikingly slender
and graceful in appearance. When alarmed they run with a
rapid, erratic, jerky sort of pace and oftentimes with the
caudal end of their abdomen slightly elevated. When a nest is
disturbed it is only a few seconds until the ants are running
everywhere in a somewhat helter-skelter manner.
The workers are splendid foragers, who seek food by night
as well as by day. Very seldom are they seen foraging singly
but are ordinarily observed trailing along in a file from their
TABLE III.
The Size of the Colonies and the Types of Castes and Immature Stages in the
Nest at Various Periods During the Year.
Total No.
Dealate
Male
Female
Worker
Date
Individuals
Males
Females
Pupae
Pupa?
Pupae
Larvas
Eggs
Apr. 1-25
104
4
X
Apr. 8-26
. p
X
X
Apr. 12-26
p
X
X
Apr. 25-26
?
X
X
X
June 1 1-25
?
15
X
X
X
June 6-26
?
X
X
X
X
X
X
X
June 27-25
6,000-8,000
X
*x
X
X
X
X
X
Aug. 22-25
3,000-4,000
X
X
X
X
Sept. 5-25
10,000
240
X
X
X
Nov. 10-25
?
X
X
X
X
x Form present.
* Alate and Dealate Females.
NOTE. Workers are not mentioned in Table because they are present all the
year and comprise the largest percentage of individuals in the nest.
nest to the source of food supply. The ants seldom have to
travel over thirty to fifty feet to find food, and for this reason
their trails are generally not long. Their foraging activities
take them into every conceivable sort of place, such as garbage
cans, commodes, dirty linens, pantries, sinks, refrigerators, and
other places too numerous to mention. Like their cogeners,
the Argentine ants, the odorous house ants are prying little
busybodies, eternally poking their antennas into everything.
1928] Smith: Biology of Tapinoma 327
FEEDING HABITS OF THE WORKERS.
When hungry the ants eat very greedily. The writer found
that a worker will feed from three to five minutes before she
seems satisfied. During this time her gaster gradually en-
larged until the chitinous segments stood out like small islands
between the intersegmental membranes.
Workers have often been observed regurgitating food to the
female or to other workers. They also feed their larvae in this
manner but never with solid particles as do some of the primitive
ants.
NURSING DUTIES OF THE WORKERS.
The workers are good nurses as well as foragers. Whether
there is any particular division of labor among them, the writer
does not know, since the individuals are practically all the
same size (monomorphic) and indistinguishable. Recently
emerged individuals (callows) show considerable interest in
the brood and will attempt to pick up the brood and carry it
away when the nest is disturbed. The dealated females seem
to- show little interest in the brood, leaving their care to the
workers, when these are present in sufficient numbers. The
workers show considerable attention to the female and to the
brood, around which they cluster. Since the pupae of this
ant has no cocoon covering it, the assistance of the worker for
its removal at emergence is not necessary. The writer has,
however, noted a worker removing the meconium from a larva
which was preparing to enter the prepupal stage. Workers
are continually seen licking the brood, the females, or other
workers.
ACKNOWLEDGMENTS.
The writer wishes to express his gratitude to Dr. C. L.
Metcalf for his unfailing interest and guidance in the work and
in the preparation of this paper. He is also grateful to Dr.
W. P. Hayes, Dr. R. D. Glasgow, and Dr. W. V. Balduf for
their valuable aid and many helpful suggestions. The writer
is also indebted to the United States Bureau -of Biological
Survey and the Illinois State Natural History Survey for
furnishing valuable data, and to Dr. W. E. Britton, Mr. J. R.
Horton, and Mr. S. A. Rohwer for the loan of specimens.
Mr. P. W. Mason kindly determined the plant lice for the
author.
328 Annals Entomological Society of America [Vol. XXI,
SUMMARY.
1. Tapinoma sessile Say, a native North American ant, is
of considerable economic importance as a house pest not only
in Urbana, Illinois, but in localities in California, Nevada,
District of Columbia, Maryland, and Mississippi.
2. The synonymy and a redescription of the species is
given in this paper. The immature stages of the ant are also
described.
3. The common name, the odorous house ant, is applied to
the species for the first time.
4. The ants overwinter outdoors as dealate females,
workers, and larvae. Workers begin foraging as early as
March 7th. Egg laying and the uniform development of the
brood begins in late April and continues until cold weather in
the fall or approximately November 1st. The overwintering
larvas attain maturity in April, having required from six to
seven months to attain maturity. From April through June
workers can be produced in from five to nine weeks, whereas
during the period July through September they require only
six to seven weeks to attain maturity. Four to five generations
of workers a year are postulated.
5. Alate females were observed at various dates ranging
from June 17th to early July. Males appeared from June 10th
to July 9th. Only large and strong colonies seem capable of
producing sexed-forms. Mating probably takes place both in
and outside of the nest.
6. Colonies range from a hundred to ten thousand indi-
viduals. The average colony contains from two thousand to
five thousand individuals, many of which are dealated females;
one colony contained' over two hundred dealated females.
7. Some of the workers lay eggs. The brood reared from
such eggs attained the prepupal stage before they were eaten
by the workers. It is believed that if they had attained maturity
the adults would have been workers. Development of -brood
from worker eggs apparently takes longer than the develop-
ment of brood from female eggs.
8. The ants show a wide diversity in their nesting habits.
Nests have been found in houses; under the bark of logs and
stumps; in galls on plants; in stems of plants; under debris; and
in the soil.
1928] Smith: Biology of Tapinoma 329
9. The species is apparently eurythermal in disposition as
it is found throughout most of North America from the sands of
the seashore to heights of over ten thousand feet and from
boggy locations to perfectly dry inland spots. Workers have
been seen foraging at temperatures as low as fifty degrees
Fahrenheit.
10. The natural food of the ants is honey-dew, supple-
mented by the flesh of organisms. In houses they feed on
fruits, vegetables, meats and sweets, but seem to show a prefer-
ence for sweets.
11. A list of the species of plant lice, scale insects, mealy-
bugs, tree hopper, etc., which they are known to attend is given
in this paper.
12. A number of beetles, wasps, crickets, spring tails,
termites, book lice and other insects have been found living in
association with the ants.
13. A species of toad and eight species of birds are known
to feed on the ants.
BIBLIOGRAPHY.
Bryant, H. C. 1914. Univ. of Cal. Pub. Zool., 11: 21-24.
Davis, W. T. 1922. Bull. Bklyn. Ent. Soc., 17:2.
Dietz, H. F. 1926. Insect Pest Survey, 6: 122-123.
Doten, S. B. 1910. Nev. Agr. Expt. Sta. Bull., 73.5: 43-44.
Emery, C. 1912. Genera Insectorum, 137: 40.
Essig, E. O. 1926. Insects of Western North America. McMillan Co., N. Y.,
pp. 863-864.
King, G. B. 1896. Entomological News, 7: 169.
Mann, W. M. 1911. Psyche, 18: 29.
Reichenbach, H. 1902. Biol. Centrabl., 22: 461-465.
Say, Thos. 1836. Boston Jour. Nat. Hist., 1: 287.
Tanner, J. E. 1892. Trinidad Field Naturalist's Club, 1: 123-127.
Wheeler, W. M. 1910. Ants, Their Structure, Development and Behaviour. Co-
lumbia Univ. Press, N. Y., pp. 45.
1913. Bull. Mus. Comp. Zool., Harvard, 54: 497.
1915. Bull. Amer. Mus. Nat. Hist., 34: 417-418.
Woodworth, C. W. 1919. Univ. Cal. Publ., 207: 70-71.
ANNALS E. S. A.
VOL. XXI, PLATE XVIII.
Marion R. Smith
Tapinoma sessile Say.
Fig. 1. Worker, greatly enlarged.
Fig. 2. Dealated female, greatly enlarged.
Fig. 3. Alate male, greatly enlarged.
330
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