Ants
(click on image to enlarge.)
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.
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.
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.
DAMAGE AND CONCERNS
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.
Columbia Encyclopedia,
Sixth Edition, Copyright (c) 2004.
