A Synopsis of Common and Economic Illinois Ants, 
with Keys to the Genera 
(Hymenoptera, Formicidae ) 
Herbert H. Ross, George L. Rotramel, and Wallace E. LaBerg 
TO THE ILLINOIS HOMEOWNER, gardener, 
or farmer, ants are probably the best known of all 
insects. They invade houses in search of food, hollow 
out house timbers to make nests, make mounds and 
bare spots in gardens and lawns, tend aphids that injure 
some of our crops, and the more pugnacious ones bite 
picnickers. However, ants that intrude upon our privacy 
are not the only ones living in Ilinois. Many live in 
the house, in the garden under stones, or in the soil, 
and they forage chiefly at night. Many other species 
inhabit woodlands, some living in the ground, others 
in rotten logs, and still others in dead trees. 
To date over 90 different kinds or species of ants 
have been taken in Illinois. Another 20 are known 
from neighboring states and will likely be found in 
Ilinois with further collecting. These midwestern ants 
are classified into genera and these are grouped into six 
large categories called subfamilies. A seventh subfamily 
s more southern and western in distribution. These 
seven subfamilies constitute the North American rep- 
resentatives of the family Formicidae, which contains 
several thousand different species in the entire world. 
Although superficially ants may look much alike, 
those belonging to different genera and species exhibit 
a remarkable number of differences in such characters 
as the shapes of the mandibles, sizes of the eyes, pro- 
jections on the body, and contours of various parts. 
These characters are most marked between the genera. 
The species within many genera are frequently difficult 
to diagnose, and many complexes have not yet been 
thoroughly studied. As a result, it is not practical to 
give identification characters for every species occurring 
in Illinois. The genera and certain of the common 
and economic species can be identified readily, and 
these are the units that are treated in this synopsis, 
intended as a useful guide to the householder, gardener, 
farmer, and hiker. 
LIFE HISTORY 
All ants are social insects living in colonies or nests, 
and they have evolved a highly developed social pattern 
This paper is published by authority of the State of Illinois, IRS 
Ch. 127, Par: 58:12: The authors are one-time colleagues in _ the 
Section of Faunistic Surveys and Insect Identification of the Illinois 
Natural History Survey. Dr. Herbert H. Ross was formerly Assistant 
Chief of the Survey and Head of that section, George L. Rotramel 
was formerly a Technical Assistant in that section, and Dr. Wallace E. 
LaBerge is a Taxonomist in that section. Dr. Ross is now Professor 
of Entomology, University of Georgia, Athens. Mr. Rotramel is com- 
pleting work for the Ph.D. degree in the Department of Entomology 
and Parasitology, University of California, Berkeley. 
COVER ILLUSTRATION: A worker of Polyergus lucidus, the pale slave-making ant. 
Ann Prickett. 
associated with the production and rearing of the youn; 
and the maintenance of the nest. 
Developmental Stages 
Ants belong to the large group of insects that hav 
four distinctive stages in the life history: (1) the eg 
(ii) the larva, (iii) the pupa, and (iv) the adult, th 
latter represented by males, females, and workers (Fis 
1). Typical males and females have well-develope 
wings and sexual organs; the workers are much smalle 
adult stages that lack wings and sexual organs an 
differ from the winged adults in many details < 
morphology. 
A typical ant nest centers around a queen, a fema 
that has been fertilized and lost its wings. The quee 
stays in the nest and lays eggs that hatch into larva 
The larvae are whitish, legless maggots, somewhat e¢ 
shaped but tapered toward the head end. They a 
completely helpless and must be moved about in tl 
nest and fed by the adult ants. When full grown, tl 
larvae transform into whitish pupae, the transformatic 
stage between larva and adult. Some larvae spin cocoo 
around themselves before pupating, but some do n¢ 
The pupae also are helpless. If the nest is badly di 
rupted, the workers will carry the larvae and pup 
out of the nest to hiding places in the soil or und 
stones. In nests with an active queen, the larvae usua 
develop into workers or certain workerlike forms. 
The eggs, larvae, and pupae are cared for by t 
workers, who handle the immature stages inside t 
nest and forage for food outside the nest. The work 
obtain enough food for themselves, the queen, and t 
growing larvae. Most of the larvae grow up to 
workers. When these workers are mature, they take 
their activities of foraging for food and feeding | 
queen and the larvae, collectively called the brood. 7 
development from egg to adult takes several weeks. 
Castes and Their Duties 
Depending on the’ species, a nest or colony 1 
consist of several hundred to many thousands of 
dividual ants, including a considerable number of diff 
ent forms or castes in addition to the queemumd 
commonest caste is called the worker, and these 0 
be of two sizes; the smaller are minor workers and 
larger are major workers. In the major worker 
head is considerably larger in proportion to the 
mainder of the body than in the minor worker. 
Drawn by Mrs. A 
