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.
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