Termite colonies are composed of three castes; the reproductives (kings and queens), the soldiers, and the workers. The kings and queens are sexually mature termites, with compound eyes and fully developed wings. The workers and soldiers lack wings and compound eyes. Sexually mature termites, or reproductives, are produced in large numbers during certain seasons and leave the colony in a swarm. They are poor fliers, and most are eaten by birds and other animals.
When the surviving termites settle, their wings break off along a weakened seam at the base. They then form pairs, each of which establishes a new colony. A couple excavates a chamber in wood or soil, in which they mate; they remain permanently paired, and the queen eventually produces as many as 30,000 eggs per day. Two or three weeks after mating, the young nymphs hatch and are fed on liquid secreted by the parents and on fecal wastes, from which they obtain the protozoan or bacterial symbionts essential for life.
The caste into which the young termite, or nymph, develops is dependent upon the amount of growth-inhibiting substance (a pheromone) passed to it during feeding and grooming. The pheromone is secreted by the reproductives and, when present in a high enough concentration, prevents the development of nymphs into reproductives. (A large colony may have several pairs of reproductives.) As more workers and soldiers are added, since they do not produce the pheromone, its concentration in the colony is correspondingly decreased. Therefore when the colony reaches a certain size, some of the nymphs begin to develop into reproductives, which then produce pheromones. This phenomenon also occurs if the original reproductives die. The increase in the pheromone level prevents the maturation of additional nymphs into reproductives; these remaining nymphs then become workers. In a similar way, the appearance of soldiers appears to inhibit the production of more soldiers.
In some families of termites, no workers develop, and the nymphs perform worker functions, which include feeding the royal couple, the soldiers, and the very young nymphs; caring for the eggs; grooming the queen; constructing and repairing the nest; and foraging for food. The soldiers have heads as large as the rest of the body and equipped with strong mandibles used in defense of the colony. They attack any intruders to the colony and stand guard at the entrances, in some species closing the entrances by putting their heads in the holes. Soldiers of certain species squirt a sticky, poisonous secretion at enemies.