ant

Introduction

ant, any of the 2,500 insect species constituting the family Formicidae of the order Hymenoptera, to which the bee and the wasp also belong. Like most members of the order, ants have a “wasp waist,” that is, the front part of the abdomen forms a narrow stalk, called the waist, or pedicel, that attaches to the thorax. The wings, when present, are also typical of the order; the small hind pair of wings is attached to the rear edge of the front pair. The head has two bent antennae, used both as organs of touch and as chemosensory organs. In most species there are two compound eyes. The jaws are of the biting type and in some species are used for defense. Some ants have stings, and some can spray poison from the end of the abdomen. Most ants are black, brown, red, or yellow. Metamorphosis is complete. A soft, legless, white larva hatches from the egg; in most species it is completely helpless and must be fed and carried by adults. In some species pupation occurs within a cocoon. Ants are cosmopolitan in distribution.

Classification

Ants are classified in the phylum Arthropoda, class Insecta, order Hymenoptera, family Formicidae.

Beneficial and Harmful

Ants as a group are beneficial to humans. Their tunneling mixes and aerates the soil, in some places replacing the activity of earthworms. Many species feed on small insects that are serious crop pests. House pests among the North American ants include the yellowish pharaoh ant, the little black ant, the odorous house ant, the Argentine ant of warm climates, and the black carpenter ant. Carpenter ants tunnel in wood but do not feed on it. The fire ant, which has a painful bite, is a serious pest to humans and livestock in many parts of the South.

Feeding Habits

Different species differ widely in their diets and may be carnivorous, herbivorous, or omnivorous. Members of some species eat honeydew from plants infested with aphids and certain other insects; others, called dairying ants, feed and protect the aphids and “milk” them by stroking. Harvester ants eat and store seeds; these sometimes sprout around the nest, leading to the erroneous belief that these ants cultivate their food. However, cultivation is practiced by certain ants that feed on fungi grown in the nest. Some of these, called leaf-cutter, or parasol, ants, carry large pieces of leaf to the nest, where the macerated leaf tissue is used as a growth medium for the fungus. Most leaf cutters are tropical, but the Texas leaf-cutting ant is a serious crop pest in North America. The army ants of the New World tropics and the driver ants of tropical Africa are carnivorous, nomadic species with no permanent nests. They travel like armies in long columns, overrunning and devouring animals that cannot flee their path; the African species even consume large mammals.

All species show some degree of social organization; many species nest in a system of tunnels, or galleries, in the soil, often under a dome, or hill, of excavated earth, sand, or debris. Mound-building ants may construct hills up to 5 ft (1.5 m) high. Other species nest in cavities in dead wood, in living plant tissue, or in papery nests attached to twigs or rocks; some invade buildings or ships. Colonies range in size from a few dozen to half a million or more individuals. Typically they include three castes: winged, fertile females, or queens; wingless, infertile females, or workers; and winged males. Those ordinarily seen are workers. In some colonies ants of the worker type may become soldiers or members of other specialized castes.

Whenever a generation of queens and males matures it leaves on a mating flight; shortly afterward the males die, and each fecundated queen returns to earth to establish a new colony. The queen then bites off or scrapes off her wings, excavates a chamber, and proceeds to lay eggs for the rest of her life (up to 15 years), fertilizing most of them with stored sperm. Females develop from fertilized and males from unfertilized eggs. The females become queens or workers, depending on the type of nutrition they receive. The first-generation larvae are fed by the queen with her saliva; all develop into workers, which enlarge the nest and care for the queen and the later generations. It is thought that the production of males by the queen and the rearing of new queens by the workers may be controlled by hormonal secretions of all the members of the colony. There are many variations on the basic pattern of new colony formation. In some species the queen cannot establish a colony herself and is adopted by workers of another colony. Slave-making ants raid the nests of other ant species and carry off larvae or pupae to serve as workers; in a few slave-making species the adults cannot feed themselves.

Bibliography

See publications of the U.S. Dept. of Agriculture; E. O. Wilson, Insect Societies (1971) and, with B. Holldobler, The Ants (1990); G. E. Ball, ed., Taxonomy, Phylogeny, and Zoogeography of Beetles and Ants (1985); J. H. Sudd and N. R. Franks, The Behavioural Ecology of Ants (1987); L. Keller and E. Gordon, The Lives of Ants (2009); M. W. Moffett, Adventures among Ants (2010); J. Choe, Secret Lives of Ants (2012).

See more Encyclopedia articles on: Zoology: Invertebrates