Ants are black, brown, reddish, or yellowish and live in colonies. They have 6 legs, 2 elbowed antennae, and a constricted waist. Unlike wasps, the constriction includes the first few segments of the abdomen, the second of which has a raised node called a petiole (that term is also used for the stem of a leaf). The rest of the abdomen (the rounded hind part) is called the gaster. Ants have compound eyes and two powerful jaws (mandibles), which serve them just as hands serve humans.
Within each colony are several different types of ants (castes), each with a different job. Most of the ants we see are workers. Sometimes we see males and queens, which have wings for their mating flights.
Eggs, small grublike larvae, and pupae are often seen beneath upturned stones and other places where a colony is torn asunder.
Some familiar ants include:
- Acrobat ants (Crematogaster spp.), which have a heart-shaped abdomen. They eat aphids' honeydew, living and dead insects, protein from bird and other droppings, and sugary or meaty foods. Sometimes they build nests in people’s houses. When disturbed, acrobat ants raise up their abdomens and ooze pungent formic acid at their attacker. (The name “formic acid” comes from the Latin word for ant, formica.) There are about 30 species of acrobat ants in North America.
- The odorous house ant, Tapinoma sessile, is one of the species that commonly makes nests in people's kitchens, where their workers scavenge sweet or fatty foods, or foods rich with protein. They also eat insects. Outdoors, these hardy little ants may be found almost anywhere, but especially under rocks. Workers are less than 1/8 inch long. When squashed, these ants produce an unpleasant rancid or rotting smell, hence the common name.
- The eastern black carpenter ant (Camponotus pennsylvanicus) is large and named because it builds nest tunnels in already-decaying wood such as rotting logs. They do not eat wood; instead, they eat sugary and protein-rich substances provided to them by plants via extrafloral nectaries (nectar glands not positioned in flowers), plus honeydew (sweet excretions) of aphids and plant hoppers. They are also scavengers of dead insects and also eat live ones. They sometimes augment their central rotting-wood colony with additional nests in cracks and crannies of houses.
Similar insects: Velvet ants, other wingless wasps, and termites do not have elbowed antennae. Termites also do not have a constricted waist.