166 1%, and in Invasitermes spp. which live in the nests of other termites there is no soldier caste. The differentiation of the various castes and their maintenance in a fixed ratio to each other are complex phenomena, controlled by the interaction of pheromonal, nutritional, hormonal, and perhaps other factors (see Chapter 21, Section 7). A colony matures (i.e., begins producing winged reproductives) after several years, but it continues to increase in size after this time. It is obviously difficult to estimate the number of individuals in mature colonies, but in the lower termites the figure is usually several hundred or thousands, while in the higher termites it may be several million.

Two other methods of colony foundation are known. In some species, in which the nest is a rather diffuse structure, groups of individuals may become more or less isolated from the rest of the colony. In these groups neotenics differentiate, and the group becomes independent of the parent colony. This is described as budding. The foundation of new colonies by deliberate social fragmentation (sociotomy) has been reported for a few species. In this situation many individuals of all castes (often including the original royal pair) emerge from the parent colony and march to a new location. The original colony then becomes headed by neotenics.

Termite nests exhibit a wide range of form, the complexity of which parallels approximately the phylogeny of the order. In the primitive Kalotermitidae and Termopsidae the nest is simply a series of cavities and tunnels excavated in wood. Few partitions are constructed by these termites, and there is no differentiation of the nest into specific regions. In other lower termites the nest may be in wood or subterranean, but even in the former situation contact with the ground is maintained by a series of tunnels. This ensures that the humidity of the nest remains high. Most Hodotermitidae build completely subterranean nests, in which the beginnings of specialization are seen. Food is stored in chambers immediately below the surface of the ground. The main chamber, which is considerably subdivided by both horizontal and vertical walls, is several feet below the surface. However, in nests of this family there is no chamber specifically for the royal pair. Nests of Rhinotermitidae may be entirely in soil or in wood or in both of these media. In a few Hodotermitidae, some Rhinotermitidae in the genus Coptotermes, and many Termitidae epigeous (above-ground) nests are constructed (Figure 7.8), though it should be emphasized that even in these species a considerable portion of the nest may be subterranean. In the simplest epigeous nests little differentiation occurs between the peripheral and internal parts, which comprise a mass of interconnecting, uniform chambers; the royal chamber is either absent or located in the subterranean part of the nest. In more complex nests the above-ground component comprises a thick peripheral wall enclosed within which is the habitacle (nursery) and surrounding food chambers. The royal chamber is usually located near the base of the structure.

A major problem for all social insects is maintenance of a suitable nest climate. Regulation of relative humidity, temperature, and carbon dioxide concentration occurs (Korb, 2003). For termites that live in wetter regions humidity regulation is not a serious problem, and the relative humidity within the nest is generally 96% to 99%. In termites from regions with long dry spells various behavioral adaptations ensure the well-being of a colony. The commonest of these is for the termites to move more deeply into the ground where the moisture content is greater. Other species behave like honey bees and regurgitate saliva or crop contents onto the walls of the nest, especially in the nursery region. Some species burrow deeply into the ground to the level of the water table and bring moisture-laden particles up into the nest area.

Temperature is also regulated in some termite nests to a remarkable degree. To some extent this is facilitated by the location of the nests in wood and soil, which serve as excellent

FIGURE 7.8. Mature nest of Bellicositermes natalensis (Termitidae). [After P.-P. Grassé (ed.), 1949, Traité de Zoologie, Vol. IX. By permission of Masson, Paris.]

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