Worker Longevity in Harvester Ants (Pogonomyrmex)

Most studies of worker longevity in ants have been made in the laboratory (Haskins and Haskins 1980; Porter and Tschinkel 1982). In the field, increased energy expenditures, predation, and environmental fluctuations may all contribute to shorten the life of a worker ant. In the few existing studies of worker longevity conducted in the field, the lifespan of exterior workers was found to be extremely short. For example, Schmid-Hempel and Schmid- Hempel (1984) found that the half-life of Cataglyphis foragers, after they were marked, was only 6 days. In harvester ants of the genus Pogonomyrmex, the only existing field study of worker longevity demonstrated that the average life expectancy of foragers and defenders (ants emerging from the nest in response to a disturbance) of P. owyheei is 14 days (Porter & Jorgensen 1981). Here we show that these results for P. owyheei cannot necessarily be generalized to other species in the genus, and that longevity results for the exterior workers engaged in one activity, such as foraging, may not apply to exterior workers that do other tasks.