N. Mark Collins/Oxford Scientific Films
No solitary termites exist. A colony may number from 100 to more than 1 million termites. Excluding the immature forms, called nymphs, a colony consists of several structurally differentiated forms living together as castes with different functions in community life. In socially advanced species, three principal castes exist: the reproductives, the soldiers, and the workers. Both the reproductives and the soldiers occur in two or three distinguishable forms, each specialized for a role in the division of labor in the colony. All forms comprise individuals of both sexes, but only in the reproductives do the sexual organs undergo complete development.
Among the reproductives are dark-colored males and females with fully developed wings and compound eyes. At maturity, they leave the parental nest in swarms. After the flight, they shed their wings and mate. A new colony is then established by a male and female who become primary reproductives, that is, the king and queen, whose sole occupation is the production of eggs. Termite kings and queens are longer-lived than other termites, and the queens are larger than other members of their colony. In certain tropical species, the king and queen live for ten years, and the queen grows to an enormous size, sometimes as much as 20,000 times the size of the worker. The abdomen becomes so distended with eggs that the queen is unable to move about. The eggs are laid at a prodigious rate that totals about 30,000 a day in some species. Most termite colonies have only one royal pair.
Apart from the reproductives, all castes are sterile and wingless and have whitish bodies. Typically, the workers constitute the most numerous caste and are the smallest of the adult forms. Workers build and provision the nest, tend the eggs, and feed and groom all the other inmates of the community. In some species, no true worker caste exists; undifferentiated nymphs do the work in the colonies of such species. All species have soldiers with greatly enlarged heads. The soldiers of certain species are equipped with huge jaws for defense of the colony; in some species, the soldiers have long snouts, from which they can eject a sticky, poisonous substance to envelop an enemy and render it helpless.
Caste differentiation was long believed to be hereditary, but investigations have since demonstrated that nymphs may develop into specialized forms as the need arises within the colony. Hormonelike substances secreted at the body surfaces of the royal pair serve to inhibit the production of primary reproductives. These substances, which are licked off by the workers in the process of grooming, are transmitted, probably with food, to other members of the colony. In the absence of these inhibitory exudates after the royal pair dies, nymphs at a particular stage in their molting cycle rapidly develop reproductive organs and become fertile. A similar process appears to operate in maintaining the required number of soldiers in the community.