Introduction

The ability to recruit group members to new sources of food, to defend the territory, or to protect the group against enemies are crucial to the success of social species across the animal kingdom. This ability is one of the most important factors behind the extraordinary ecological dominance of social insects in so many habitats. Recruitment brings nestmates to the place and task required.

Recruitment signals are commonly pheromones, in part because the taxa that show the most development of recruitment behaviours are those most reliant on pheromones (Table 7.1), but also because pheromones enable mass recruitment to tasks. ‘Call to arms’ pheromones for collective defence are also common in social insects (Chapter 8). New nest site finding and colony moving are also often pheromone mediated (Fig. 7.1). Even elaborate nest building may be organised this way (Section 7.3.2).

The coordinated activity of social insect colonies puts them at a pinnacle of biological complexity, but although hundreds of thousands, even millions, of individuals may be involved, activity is not commanded from the centre: perhaps the complexity is possible precisely because of this. Instead, the social integration and assembly of colony-level patterns come from simple interactions between individuals and individual responses to local conditions, largely mediated by pheromones (Section 7.3) (Traniello & Robson 1995; Bonabeau et al. 1997).

The range of recruitment tasks mediated by pheromones in social insects is illustrated by African weaver ants (Oecophylla longinoda), which have the most complex set of signals yet identified in ants (Hölldobler & Wilson 1978).