The adaptive nature of non-food collection for the Florida harvester ant, Pogonomyrmex badius

1. Many animals forage for non-food objects, such as nesting materials. In many organisms, the depots of such objects can be expansive, and are not intuitively adaptive. This study empirically explores varying theories for why these depots exist in the Florida harvester ant, Pogonomyrmex badius. 2. The Florida harvester ant, like its western congeners, collects and deposits large quantities of non-food objects around its nest entrance. The vast majority of objects sampled from colonies in this study population were charcoal pieces whereas most western species collect pebbles. 3. Objects in these depots can number in the millions, suggesting a large cost to this behaviour and strengthening an adaptationist argument. 4. Many hypotheses have been suggested for these depots, including temperature and water modification and territoriality. No evidence was found to support the results of a previous study which found that charcoal depots deter other ant species. 5. The depots do not appear to affect soil hydrology, but do slightly increase soil temperature at the very top of the nest. In an attempt to estimate the seasonal fitness of colonies with and without charcoal depots, no statistical difference was detected in sexual investment between treatment groups. 6. These results suggest that the charcoal depots may be selectively advantageous through temperature modification, but may serve alternate functions that are species and habitat specific.