18 
A, Atta cephalotes 
Fig. 23—Workers of leaf-cutting ants. 
Linnaeus; B, Trachymyrmex arizonensis Wheeler. (After Weber, 
courtesy of Science) 
11. Brachymyrmex Mayr 
The sole U.S. and Illinois species, B. depilis Emery, 
has minute workers 1.5-2.0 mm long that forage in the 
leaf litter of woods and meadows. These ants nest 
under stones or in the soil and are seldom seen without 
deliberate search. 
12. Acanthomyops Mayr 
“Of the nine U.S. species, only three are recorded 
from Illinois. The workers are 3.0-4.5 mm long and a 
medium shade of reddish brown. Normally these ants 
forage in leaf litter or underground, where they tend 
aphids and mealybugs, and are seldom seen except by 
a person digging in the garden. During the winter, 
however, entire colonies (including both workers and 
winged forms) frequently move to house foundations. 
If there is a break in the foundation, a colony of both 
workers and winged forms (Fig. 19) may move into the 
basement and take up residence under a loose brick or 
board. They do not raid through the house, but many 
persons find their company disconcerting. If the colony 
is disturbed, the ants emit a strong, citronellalike odor. 
When soil temperatures rise in spring, the ants will de- 
part along the path by which they entered. This winter 
habit has earned them the name of foundation ants. 
Formerly these ants were classified in the genus Lasius. 
13. Lasius Fabricius 
The seven Illinois species, all native, are among its 
commonest field and garden ants. In most of them the 
workers are dark brown, ranging in size from 2 to 4 mm. 
They actively search for food above ground and may 
enter houses and eat a variety of sweats and meats. They 
make large nests in soil or under covering objects, each 
nest containing up to 10,000 workers. 
Two cornfield ants, L. alienus Foerster and L. neont- 
ger Emery, are often found tending aphids on corn and 
other plants. L. neoniger is known to spread the virus 
causing barley yellow dwarf by its aphid-tending ac- 
tivities. 
14. Formica Linnaeus 
The dozen Illinois species of this genus, all natives, 
are the most commonly observed of our entire ant fauna. 
The workers are brownish black, sometimes with the 
head red, and range in length from 2.5 to 6.0 mm. They 
forage actively, often in the open, and are called side- 
walk ants. 
These ants nest in soil. Some species construct a nes 
entirely below the soil surface with an obscure entrance 
Others build large mounds over the nest, and each maj 
contain 100,000 workers. They are scavengers, predator 
on other insects, and nectar feeders. In Tllinois ther 
enter houses only sporadically and singly, and hence ar 
of no economic importance. If one disturbs them i 
the wild, however, they bite readily and inflict a painfu 
wound. 
Some species are “cuckoo” ants; that is, a youn 
queen uses a colony of another species to start her ow 
colony, first killing off the queen of the host species 
This results in temporary colonies of mixed workers. 
15. Camponotus Mayr 
The ants of this genus are the carpenter ants (Fis 
20). Eight native species occur in Illinois, including ov 
largest ants. Depending on the species, the workei 
may be all black, reddish brown, or tan and range 1 
length from 3 to 13 mm in the same nest. The large 
workers have heads disproportionately larger than tho: 
of smaller individuals; these large, big-headed worke 
are called majors, the small ones minors. They ten 
aphids, forage in columns, and are general scavenge! 
Most species of Camponotus nest in dead wood. | 
the wild they use logs, stumps, and the wood of standir 
dead trees. They also nest in timbers of houses, railing 
and poles, excavating tunnels by chewing out the soft 
wood between the harder annual rings of beams, sidin 
and other structures, weakening the wood and frequent 
causing extensive damage. The species most frequent 
encountered in buildings is C. pennsyluanicus DeGeer, 
large black species with long grayish or yellowish he 
on its upper surface. 
16. Polyergus Latreille 
These ants are the slave-making ants. Two nati 
species occur in Illinois; the workers of both are reddi 
brown and 6-8 mm long. The nest is 100-120 cm de 
in the soil and has an obscure opening. The workers 2 
out of the nest only when scouting or raiding; they | 
no foraging. 
On a raid the Polyergus workers attack a Formt 
nest and carry pupae of Formica workers back to t 
Polyergus nest. When these pupae develop and emet 
