The Persistence of Role in Exterior Workers of the Harvester Ant, Pogonomyrmex Badius

The social organization ofan ant colony channels individuals into particular tasks, so that the colony continues to perform its tasks in a regular way. In other words, the colony is organized so that certain roles (sensu Osterand Wilson 1978), vital to its function, continue to be filled. The present study reports on role behavior in exterior workers of the harvester ant Pogonomyrmex badius. Three questions are addressed: 1) In P. badius, do particular groups of ants consistently do certain tasks? 2) Does the task performed by an ant depend on its age? Because P. badius workers live for about a year (Porter and Tschinkel 1982), marked individuals were observed for a longer time (up to four months) in the present study than in previous studies ofPogonomyrmex species (HiSlldobler 1976, Porter and Jorgensen 1981). 3) Does the task performed by an ant depend on its size? P. badius is the only polymorphic species in its genus. Since majors rarely emerged from the nest, only the role behavior of minor workers was considered in this study. However, even within the minor subcaste of P. badius, a greater size variation exists than in other Pogonomyrmex species. The relationship between size and role in P. badius minors is investigated. In the present study, the behavior of exterior workers is classified into a more detailed set oftasks than in previous studies ofthe genus. Foraging, i.e. food retrieval, is only one of five activities observed outside the nest. The classification of tasks used here is needed to explain other aspects of Pogonomyrmex behavior (Gordon 1983a