TERMITE

any of the cellulose-eating social insects that constitute the order Isoptera. Although they are referred to popularly as white ants, they are not closely related to ants, which are grouped with bees and wasps in a higher order of insects, the Hymenoptera. The social system of termites shows remarkable parallels with those of the Hymenoptera, but it has evolved independently. social, cellulose-eating insect of the order Isoptera, known also as the white ant, although it is not related to the true ants (order Hymenoptera). Most of the 1,900 species of termites are tropical in distribution, but the order has many representatives in temperate zones. In the Southern Hemisphere, termites reach the Cape Province of the Republic of South Africa, as well as Australia, New Zealand, and Tasmania; Northern Hemisphere species are found as far north as Maine and Vancouver in North America, the Atlantic coast of France in Europe, and South Korea and northern Japan in Asia. Man has introduced various species to areas outside their natural ranges by inadvertently carrying them in wooden articles. Termites probably evolved from roachlike ancestors and share many characteristics with the most primitive of living roaches, those of the genus Cryptocercus. Although the earliest fossil termites known are from the early Cretaceous Period (some 130,000,000 years ago), it is likely that they appeared much earlier, perhaps in the late Permian Period (about 230,000,000 years ago). Termites are small to medium-sized, usually soft-bodied insects that live in colonies with well-defined caste systems. Three castes are typicalreproductives, workers, and soldiers. Unlike hymenopterans, both sexes are present in equal numbers, although only the reproductives have fully developed sex organs. There is typically one pair of reproductives per colony, a queen and a king. These develop from winged dispersing individuals (alates) and have hard, pigmented bodies and compound eyes; after the dispersal flight the wings are shed. The king remains from 1 to 2 cm (0.4 to 0.8 inch) long, but once a queen starts laying eggs her abdomen enlarges, and she may eventually attain a length of 11 cm (more than 4 inches). Workers and soldiers are sterile. The workers constitute the most populous caste in most colonies. They are blind, pale, soft-bodied insects with mouthparts modified for chewing. The soldiers are also blind and, depending on species, use enlarged mandibles or chemical means to defend the nest. Termites live in nests either within wood or under the soil; these nests are sealed from the outside air to maintain high humidity, although ventilation pores may be constructed to facilitate diffusion of air through the nest. The most prominent nests are the termite mounds present in savanna habitats around the world. These may be domelike or conical; in Africa the mounds of the fungus-growing Macrotermes species may reach 9 m (29.5 feet) in height. In Australia the termite Amitermes meridionalis constructs wedge-shaped nests; the long axis of these nests is always set in a northsouth alignment. The outer wall of termites' large mounds is generally made of hardened soils; the internal galleries are constructed of carton, a combination of wood fragments and fecal matter that resembles cardboard. Some termites construct arboreal nests of carton; these nests are always connected to the soil by covered runways. Various invertebrates, as well as some lizards, snakes, and birds, may share a mound with the termite colony. Termitophiles, insects that cannot survive away from the nest of host termite species, are frequently found in termite nests. There are even certain termites, the inquilinous species, that can survive only within the nest of another termite speciestheir obligate hostand feed on the carton of the host species' nest; Incolitermes is even dependent on its host for exit holes during swarming. Swarming is the method by which new colonies are established. The alates develop at a certain time of year and exit the nest through tunnels prepared by the workers. The alates swarm when a combination of environmental factors is favourable. Emergence occurs simultaneously from colonies within a geographic neighbourhood, which may ensure that individuals from different colonies will have the opportunity to interbreed. The alates are weak fliers and, if not carried by the wind, will not disperse more than a few hundred yards. They shed their wings soon after the flight and pair with a member of the opposite sex. The pair dig a small nest and seal themselves within this nuptial chamber; only after they are sealed in do they mate. The queen, once fully developed, may lay 36,000 eggs a day for as long as 50 years. Termites are quite long-lived; workers and soldiers survive 2 to 5 years, while the reproductive pair in many advanced species may live for 60 to 70 years. Termites are hemimetabolous, undergoing a gradual metamorphosis through a series of nymphal molts, rather than showing distinct larval, pupal, and adult stages. In the early stages of a colony the nymphs all develop into workers and soldiers; only when a colony is well-established do the winged alates appear. Termites subsist on cellulose, a major structural material of plants. In order to digest this material they harbour various intestinal symbiotes. Primitive termites depend upon certain flagellate protozoans to break down the cellulose, while the more advanced termites (family Termitidae, comprising 1,413 species and some 75 percent of all termites) have a bacterial flora in the gut. Only the workers are able to feed themselves, and they are responsible for feeding the rest of the colony. Termites of the subfamily Macroterminae supplement their diet by farming the symbiotic fungus Termitomyces. They cultivate the fungus on combs of fecal material within the nest, and as the fungus grows it breaks down the combs into materials that the termites can utilize. These termites feed on both fungus and combs. Termites are frequently classed as pests. Although only 10 percent of the known species have destructive habits, these species may do great damage. Subterranean termiteswhich enter wooden structures through the ground, as they need to maintain contact with the soil's moistureare fairly easy to control; insecticides can be placed in trenches dug around the structure to be protected. Materials such as pressure-treated wood and reinforced concrete are impervious to termites and make safe foundations. Dry-wood termites (family Kalotermitidae), however, nest within the wood they feed on and are much more difficult to control; fumigation has proved to be the best technique. Additional reading K. Krishna and F.M. Weesner (eds.), Biology of Termites, 2 vol. (196970), an advanced treatise, dealing with the fundamental aspects of termite biology; S.H. Skaife, Dwellers in Darkness (1961), a popular account of termites for the informed layperson; W.V. Harris, Termites: Their Recognition and Control, 2nd ed. (1971); and T.E. Snyder, Our Enemy the Termite, rev. ed. (1948), two general works, with emphases on termite control. Kumar Krishna