12.5. Success of eusocial insects

As we saw in the introduction to this chapter, social insects can attain numerical and ecological dominance in some regions. In Box 1.2 we describe some examples in which ants can become a nuisance by their dominance. Social insects tend to abundance at low latitudes and low elevations, and their activities are conspicuous in summer in temperate areas, or year-round in subtropical to tropical climates. As a generalization, the most abundant and dominant social insects are the most derived phylogenetically and have the most complex social organization.

Three qualities of social insects contribute to their competitive advantage, all of which derive from the caste system that allows multiple tasks to be performed. Firstly, the tasks of foraging, feeding the queen, caring for offspring, and maintenance of the nest can be per- formed simultaneously by different groups rather than sequentially as in solitary insects. Performing tasks in parallel means that one activity does not jeopardize another, thus the nest is not vulnerable to predators or parasites whilst foraging is taking place. Furthermore, individual errors have little or no consequence in parallel operations compared with those performed serially. Secondly, the ability of the colony to marshal all workers can overcome serious difficulties that a solitary insect cannot deal with, such as defense against a much larger or more numerous predator, or construction of a nest under unfavorable conditions. Thirdly, the specialization of function associated with castes allows some homeostatic regulation, including holding of food reserves in some castes (such as honeypot ants) or in developing larvae, and behavioral control of temperature and other microclimatic conditions within the nest. The ability to vary the proportion of individuals allocated to a particular caste allows appropriate distribution of community resources according to the differing demands of season and colony age. The widespread use of a variety of pheromones allows a high level of control to be exerted, even over millions of individuals. However, within this apparently rigid eusocial system, there is scope for a wide variety of different life histories to have evolved, from the nomadic army ants to the parasitic inquilines.

Chapter 12