Contents

• Development
• Food
• Activities
• Ant Pests

ANT,

In most ant species, males remain winged throughout life, and females are winged until after mating. Certain wingless females, called workers, are usually infertile. The fertilized female becomes the queen of the colony, with the main function of laying eggs. The males die after mating, and the workers gather food, care for the young, and defend the colony. The nests of many species of ants commonly consist of chambers and galleries excavated under stones or logs or underground; some species construct their nests in mounds of earth and vegetable matter or in decayed trees.

The ant family contains more than 4500 described species, widely distributed in temperate and tropical countries. The ant body consists of head, thorax, and abdomen, with the abdomen articulated to the thorax by means of an abdominal pedicel, or stalk.

The four life stages of an ant are egg, larva, pupa, and adult. The minute white or yellowish eggs laid by the queen hatch in two to six weeks and develop into white larvae, or grubs. After feeding a few weeks to several months larvae become pupae, commonly but incorrectly called ant eggs. In some species the pupae are naked, and in others they are covered with cocoons spun from a substance that they secrete at the end of the larval stage. After the pupal stage, during which no food is taken, the adults appear. During development the immature ants are fed, cleaned, and attended by the adult workers. As in all insects with a complete metamorphosis, the ant has attained its full size when it leaves the pupa stage. Left to themselves, males generally die after fertilizing the queens in the nuptial flight, and queens and workers may live for several years. Queens of some species of the genus Formica are known to live longer than 15 years.

Ants are generally omnivorous; some species, however, eat only certain specialized foods. Most ants build some sort of nest and store food there. A few species have developed highly specialized agricultural or pastoral habits. Pogonomyrmex barbatus of the central U.S. and Mexico frequents fields of grass, harvesting and storing the grass seeds. Some species of the widely distributed harvester ants, which gather grain for food, have developed specialized workers, sometimes called soldiers, with enlarged jaws, and these soldiers do virtually nothing but crack the seeds for the other ants to eat. Ants of the genus Atta of the southeastern U.S. and tropical America cultivate inside their nests a species of fungus that is used as food by the colony. The tropical American species are called the leaf-cutting ants, as the workers cut off pieces of leaves, which are carried back to the nest and used to fertilize the fungus gardens.

Many ants eat a sweet fluid, called honeydew, that is excreted by aphids. Some species actually keep and protect the aphids and care for their eggs. Honeypot ants of the genus Myrmecocystus of the southwestern U.S. store honeydew, utilizing certain workers as living containers for the fluid. These workers are fed enormous quantities of honeydew; their bodies become so greatly distended that they are unable to crawl about. They remain motionless in the nest, disgorging droplets of food as required.

Many ants practice trophallaxis, an association which involves complex forms of reciprocal feeding and the exchange of chemical stimulation. While feeding the larvae, the worker ants obtain from the surface of the larvae’s bodies a salivary secretion that the workers eat avidly. The attraction of such metabolic products for the workers is considered to be the basis for the care of the young and for the organization and unity in the insect colony.

Colonies of ants usually establish one dwelling or nest. A few types, notably the army and driver ants of the subfamily Dorylinae, are nomadic with nesting phases. The nest of the doryline ants is an open mass formed by the clustered bodies of up to a few million workers hanging from the underside of a raised log or other surface and enclosing the queen and brood.. The activities of ant communities are characterized by a certain degree of division of labor, which in some cases involves a permanent functional differentiation among members of the colony. In certain harvester ants, for example, only the large-headed workers crack seeds. More frequently, however, the division of labor is a relative matter, as in most species of carpenter ants of the genus Campanotus. The largest workers of these species predominate in defense, the intermediate-size ones in foraging, and the smallest in brood-tending, but all castes are capable of all types of activity. In many species of campanotine and myrmecine ants, individual workers may be temporarily specialized for foraging or brood tending.

Like social insects in general, ants may be termed industrious, although colony activity varies from a high degree of intensity at certain times of the day (usually early morning and late afternoon, or early evening in nocturnal ants) to lethargy at other times, as through midday or in the early hours before dawn. Activity in Temperate Zone ants also varies seasonally, from a high level in midsummer to dormancy in winter. Lasting individual differences are present within the worker population of certain species; some are characteristically energetic while others are sluggish.

Some ants, especially those in the genus Formica, are capable of learning to find their way through fairly complex mazes, and they normally utilize this ability in establishing individual foraging routes from the nest. The learning capacity of ants is rigidly limited, however, and in contrast to mammalian learning is stereotyped and restricted. The complexities of ant organization that seem so remarkable to humans are actually a series of simple cues and responses.

In foraging from the nest, some ants, including the army and the driver ants, operate in definite columns following chemical trails; others vary in the individual use of cues, for example, the direction and plane of polarization of light. Many ants function only through subterranean galleries, many are strictly arboreal, but commonly the species range both above and below the surface of the earth. Communication among ants is highly efficient and is conducted mainly through tactual and chemical means, although some species exhibit vibratory and even auditory processes. Typically a “finder” ant arouses the colony, and excited nestmates may be influenced in their direction of progress from the nest by one means or another, according to species. For example, in the diminutive reddish-yellow Pharaoh ant, Monomorium pharaonis, common in kitchens, the excited finder in returning to the nest incidentally releases a track of chemical secretion that directs others to the food. Usually the excitement of the finder is greater when larger concentrations of food are discovered, and thus correspondingly greater numbers of nestmates are stimulated to forage.

The nests of many ants are inhabited by various beetles and other insects called myrmecophiles, or ant lovers, which are continuous residents; such insects range from definite parasites to somewhat beneficial types. Many ants live as temporary or permanent social parasites in the colonies of other ant species. The Amazon ant, Polyergus breviceps, carries out forays against other ants and brings back to the home nest some of the unconsumed brood to serve as slaves when they are mature. These slave ants perform the work of the Amazon colony, including excavation and brood-tending. Other slave-making ants include the sanguinary ant, F. sanguinea.

In the U.S., one of the most harmful pests among the ants is the black imported fire ant, Solenopsis richteri, a small stinging ant of the subfamily Myrmicinae that was introduced accidentally from South America, presumably at Mobile, Ala. The large mound communities of this pest disrupt mechanized farming and damage crops. The tiny black ant, M. minimum, and its close relative, the sugar ant, infest households in the U.S. In the northern states the carpenter ant, C. pennsylvannicus, is another common intruder around dwellings. Ants of this species usually gnaw out the galleries and chambers of their nests in wood initially infested by beetles. Also common in the north is the pavement ant, Tetramorium caespitum, native to the Near East but now cosmopolitan. The bulldog ant, which is indigenous to Australia, has large workers more than 2.5 cm (1 in) in length. These ants have a formidable sting and often build mounds of considerable height.

Most widely known of the American army ants is the tropical species Eciton burchelli, the workers of which include the major, or soldier, type. The major has huge hook-shaped mandibles and a potent sting. Each day colonies of this species organize a swarm raid that may have a front almost 14 m (more than 45 ft) wide and that advances at a rate of about 30 cm (12 in) a minute. These ants capture, tear, and carry back to their bivouac any insect or other arthropod, such as roaches and tarantulas, that cannot escape them. At times, nestling birds, cornered snakes, or other small animals are killed by stinging. Driver ants in the African genus Dorylus carry out comparable swarm raids, which usually begin in the early evening. Many arthropods and other prey are captured and torn up. Small forest mammals or domestic stock that are cornered in pens and unable to escape the ants are sometimes included in the kill.

The economic significance of ants is difficult to judge. Thus the carpenter ants, which must be considered destructive to wood, actually may contribute to forest economy by hastening the breakdown and recycling of timber previously infested by other insects. Also, the many ants that gather seeds are destructive to agriculture when they become excessively numerous around grain fields or storage centers, but normally their presence may favor good production by opposing the increase of injurious parasitic beetles. Ants such as aphid-tending species of Lasius are frequent pests around lawns and gardens; however, the great benefit of these and other ants in aerating and mixing the soil must also be considered. Further, important contributions to forest economy in tropical and subtropical areas may be made by the predatory driver or army ants; they are highly effective exterminators of other, more damaging, insects and are not always unwelcome in human dwellings.      

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