The fascination of social insects
The social insects represent one of evolution's most magnificent, successful, and instructive developments. Ever since the behavior of ants, bees, wasps, and termites was first recorded in antiquity, these insects have exerted a powerful hold on our imaginations.
Three characteristics of social insects account for this interest. The first is the very habit of living in social groups. To biologists, this way of life represents a fascinating evolutionary innovation, yet it also poses a basic dilemma. Contrary to what we may have commonly learned, the essential history of life on Earth has not been the story of the rise and fall of dominant groups of animals like the dinosaurs. Instead, life's history has been the succession of what evolutionary biologists J. Maynard Smith and E. Szathmáry termed "major transitions" in evolution. Without any one of these transitions, living things today would be fundamentally different.
Two of these major transitions are the evolution of sexually reproducing organisms from those that reproduce asexually, and the evolution of multicellular from single-celled organisms. These transitions share a radical reorganization of living matter. In particular, at each transition, existing units coalesced to form larger units. In the process, the original units lost some or all of their power of independent reproduction, and the way genetic information is transmitted was changed. The social insects are the prime examples of the next major transition, from solitary organisms to social organisms. As a result of this change, workers of social insects have largely lost the power of reproducing independently, and genetic information has come to be primarily transmitted from generation to generation via the reproduction of the queens (and kings in termites). Why these workers have foregone their power of reproduction is a basic dilemma that insect sociality poses for biologists.
The second characteristic of social insects, which explains why they command attention, is their overwhelming numerical and ecological dominance. Ants, for example, occur from the Arctic tundra to the lower tip of South America. They swarm in diverse habitats, ranging from desert to rainforest, and from the depths of the soil to the heights of the rainforest canopy. The abundance and ubiquity of social insects give them an ecological importance that is unmatched among land-dwelling invertebrates.
The third and final fascinating characteristic of social insects is the way in which they perform work. Clearly, social insects carry out cooperative tasks, such as building nests, with results that are stunningly complex and precise. Termites build nests that are towering hills of red clay, with intricate internal architecture designed to maintain a cool, stable interior. The nests of honey bees house waxen combs composed of thousands of exquisitely arrayed hexagonal cells. Social wasps construct nests in which parallel tiers of cells are enclosed within a delicate paper globe.
These nest forms point to the ability of social insects to achieve, as a collective, impressive feats of architectural complexity. However, biologists have long puzzled over how social insects complete these complex tasks as a group when individual workers frequently strike us as inept. "It seems to me that in the matter of intellect the ant must be a strangely overrated thing," wrote Mark Twain after watching the fumbling meanderings of a worker carrying a grasshopper's leg back to its nest. The ant's seemingly unnecessary scaling of an obstacle was, Twain went on to say, "as bright a thing to do as it would be for me to carry a sack of flour from Heidelberg to Paris by way of Strasburg steeple." In this chapter, we first review some basic biology of social insects, then consider the three principal characteristics of social insects in turn.
An outline of social insect biology
Resources
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Organizations:International Isoptera Society. Web site:
International Union for the Study of Social Insects. Web site:
"Social Insects World Wide Web (SIWeb)" [cited April 1, 2003].
[Article by: Andrew F. G. Bourke, PhD]
