What are Social Insects?

Social insects, the ants, social bees, social wasps, and termites, dominate the environment in most terrestrial habitats. From Ellesmere Island in the north to Tierra del Fuego in the south, from the heights of the Himalayas to the Dead Sea Valley, social insects occur, and predominate. For example, in rain forests near Manaus, ants and termites form about 30 percent of animal biomass and all the social insects together are 80 percent of total insect biomass (Fittkau and Klinge, 1973).

Social insects make up an absolute majority of all insects combined in the celebrated forest canopy fogging samples collected in Peru by Terry Erwin of the Smithsonian Institution (Erwin, 1982; see Wilson, 1990). With some 750000 described species of insects (Arnett, 1985), of which 13000 are social insects, 2% of the described species comprise much more than half the biomass. As Wilson (1990:3) observed: "social insects are at the ecological center".

These facts translate into ecological dominance. Ants and termites in particular swarm at every level of the forest, humus, and soil. Together they turn more of the soil than earthworms. And leaf-cutter ants are the dominant herbivores in tropical forests: the earth excavated by a single 6½ year old nest of Atta sexdens weighed approximately 40000 kg, and this young colony was estimated to have gathered 5892 kg of leaves (Wilson, 1971: 47). The seeds of 35% of all herbaceous plants are estimated to be dispersed by ants (Beattie, 1985). Ants are the foremost predators and scavenge in excess of 90 percent of all dead insects and other arthropods. Social insects, in particular bees, are the foremost pollinators as well, and 30% of all human food comes from bee-pollinated species (O'Toole, 1993). Borror et al. (1989) estimate the total value of the annual yield of insect-pollinated crops in the United States alone at $19 billion, with up to 97% of crops such as red clover pollinated by honeybees and bumble bees. It follows, and has been well documented, that the diversity of social insects is crucial to the health of most terrestrial ecosystems.

These considerations suggest a central role for social insects in biodiversity inventory. Less than 2% of the described animal species, the social insects, need be sampled to profile the ecologically most central part of a given ecosystem. Social insects, by virtue of their great abundance, are also the easiest of all animals to sample. Of equal importance, they can be collected in all seasons, because their colonies are perennial and continuously active. It is not necessary to wait for the occasional emergence of adult forms, the equivalent of the fruits or flowers required in most plant taxonomy. Consequently, social insects are superbly suited both to rapid inventories to establish hot spots and to longterm population studies of relevance to ecology and conservation biology. Just for example, a patch of tropical forest consisting of two trees and 11 vines yielded 79 species of ants belonging to 30 genera (Tobin, 1994).

Special attention to social insects will not only rapidly yield crucial data on an ecosystem, but such data may also be brought rapidly into useable form. Social insects have occupied much attention by systematists, and the basic outlines of their taxonomy are understood, and accessible. Studies centered on social insects have a wealth of taxonomic resources to draw upon. Basic keys and catalogs exist, or are nearing completion, for all the groups (ants: Bolton, 1994, 1995; social bees: Michener, 1990; Richards, 1968; social wasps: Archer, 1989; Das and Gupta, 1989; Richards, 1978a&b; termites: Ernst and Araujo, 1986; Snyder, 1949). Increasingly, pertinent information is being made available over the Internet (Porter, 1993; antbase.org). The potential for quick production of accurate biodiversity data is clear.