any of approximately 10,000 species of insects (order Hymenoptera) that are social in habit and live together in organized colonies. Ants occur worldwide but are especially common in hot climates. They range in size from about 2 to 25 mm (about 0.08 to 1 inch). Their colour is usually yellow, brown, red, or black. A few genera (e.g., Pheidole of North America) have a metallic lustre.

Most ants live in nests, which may be located in the ground or under a rock or built above ground and made of twigs, sand, or gravel. Carpenter ants (Camponotus) are large, black ants common in North America that live in old logs and timbers. Some species live in trees or in the hollow stems of weeds. Tailor, or weaver, ants, found in the tropics of Africa (e.g., Tetramorium), make nests of leaves and similar materials held together with silk secreted by the larvae. Dolichoderus, a South American genus, glues together bits of animal feces for its nest. The widely distributed pharaoh ant (Monomarium pharaonis), a small yellowish insect living in houses, builds its nest outdoors when it occurs in warm climates. Army ants, of the subfamily Dorylinae, are nomadic and notorious for the destruction of plant and animal life in their path. The army ants of tropical America (Eciton), for example, travel in columns, eating insects and other invertebrates along the way. Periodically the colony rests for several days while the queen lays her eggs. As the colony travels, the growing larvae are carried along by the workers. Habits of the African driver ant (Dorylus) are similar. The red imported fire ant (Solenopsis invicta), introduced into Alabama from South America, had spread throughout the southern United States by the mid-1970s. It inflicts a painful sting and is considered a pest because of the large soil mounds associated with its nests. Effective, ecologically acceptable methods to control it are being sought.

The life cycle of the ant has four stages, including egg, larva, pupa, and adult, and spans a period of 8 to 10 weeks. The queen spends her life laying eggs. The workers are females and do the work of the colony, with larger individuals functioning as soldiers who defend the colony. At certain times of the year, many species produce winged males and queens that fly into the air, where they mate. The male dies soon afterward, and the fertilized queen establishes a new nest.

The food of ants consists of both plant and animal substances. Certain species, including those of the genus Formica, often eat the eggs and larvae of other ants or those of their own species. Some species eat the liquid secretions of plants. The honey ants (honey ant) (Camponotinae, Dolichoderinae) eat honeydew, a by-product of digestion secreted by certain aphids. The ant usually obtains the liquid by gently stroking the aphid's abdomen with its antennae. Some genera (Leptothorax) eat the honeydew that has fallen onto the surface of a leaf. The so-called Argentine ant (Iridomyrmex humilis) and the fire ant also eat honeydew. Harvester ants (Messor, Pogonomyrmex) store grass, seeds, or berries in the nest; whereas ants of the genus Trachymyrmex of South America eat only fungi, which they cultivate in their nests. The Tes leaf-cutting ant (Atta texana) is a pest that often strips the leaves from plants to provide nourishment for its fungus gardens.