Introduction

Insects that live in colonies, ants, bees, wasps, and termites, have fascinated naturalists as well as poets for many years. “What is it that governs here? What is it that issues orders, foresees the future, elaborates plans, and preserves equilibrium?,” wrote Maeterlinck [230]. These, indeed, are puzzling questions. Every single insect in a social insect colony seems to have its own agenda, and yet an insect colony looks so organized. The seamless integration of all individual activities does not seem to require any supervisor. For example, Leafcutter ants (Atta) cut leaves from plants and trees to grow fungi. Workers forage for leaves hundreds of meters away from the nest, literally organizing highways to and from their foraging sites [174]. Weaver ant (Oecophylla) workers form chains of their own bodies, allowing them to cross wide gaps and pull stiff leaf edges together to form a nest. Several chains can join to form a bigger one over which workers run back and forth. Such chains create enough force to pull leaf edges together. When the leaves are in place, the ants connect both edges with a continuous thread of silk emitted by a mature larva held by a worker [172, 174]. In their moving phase, army ants (such as Eciton) organize impressive hunting raids, involving up to 200,000 workers, during which they collect thousands of prey (see chapter 2, section 2.2.3) [52, 269, 282]. In a social insect colony, a worker usually does not perform all tasks, but rather specializes in a set of tasks, according to its morphology, age, or chance. This division of labor among nestmates, whereby different activities are performed simultaneously by groups of specialized individuals, is believed to be more efficient than if tasks were performed sequentially by unspecialized individuals [188, 272]. In polymorphic species of ants, two (or more) physically different types of workers coexist. For example, in Pheidole species, minor workers are smaller and morphologically distinct from major workers.