The organization of work in social insect colonies

A social insect colony operates without any central control; no one is in charge, and no colony member directs the behavior of another. A worker cannot assess the needs of the colony. How do individual workers, using fairly simple, local information, in the aggregate produce the behavior of colonies? The dynamics of colony behavior results in task allocation [1]. Colonies perform various tasks, such as foraging, care of the young, and nest construction. As environmental conditions and colony needs change, so do the numbers of workers engaged in each task. For example, when more food is available or there are more larvae to feed, more foragers may work to collect food. Task allocation is the process that adjusts the numbers of workers engaged in each task in a way appropriate to the current situation. I study task allocation in harvester ants (Pogonomyrmex barbatus) [2]. Inside the nest, ants care for the brood (the preadult forms: eggs, larvae, and pupae); process and store seeds; construct and maintain chambers; and simply stand around doing nothing. The ants that work outside the nest are a distinct group, apparently older than the interior workers. I divide the behavior I see outside the nest into four tasks: foraging, searching for and retrieving food; patrolling, assessing food supply and the presence of foragers from neighboring colonies; midden work, sorting the colony refuse pile or midden; and nest maintenance work, the construction and clearing of chambers inside the underground nest. Tasks are interdependent; numbers engaged in one task depend on numbers engaged in another [3,4]. Ants switch tasks, though not all transitions are possible. In harvester ants, task switching funnels ants into foraging and away from tasks inside the nest [4]. An ant’s decision whether to perform a task depends, first, on cues about the physical state of the environment: for example, if part of the nest is damaged, more ants do nest maintenance work to repair it. Task decisions also depend on social cues arising from interactions with other ants. Workers from different task groups meet as they come in and out of the nest. The rate at which one ant encounters others influences its task decisions. The pattern of interactions among ants as they move around can be seen as a kind of ad hoc, dynamical network [5,6]. Task allocation is the process that adjusts the numbers of workers engaged in each task in a way appropriate to the current situation. DEBORAH M. GORDON