In open, recently burned areas in northern Florida’s piney flatwoods, the Florida harvester ant, Pogonomyrmex badius, collects charcoal and deposits the pieces about the nest entrance. Out of 45 nests sampled, each nest had approximately 100g of charcoal spread about the nest entrance in a circle with a diameter of 65cm; this results in a well-covered circular area that makes the nests standout against surrounding habitat. Despite the extent to which these ants have been studied and the density of their charcoal deposits, there has been no comprehensive study addressing why these ants collect the charcoal. Moreover, since several other ant species including Pheidole morrisi and Trachymyrmex septentrionalis also have charcoal deposits around their nest entrances (although to a much lesser extent), the lack of information on this topic is surprising. A previous study (Gordon 1984)* had suggested that the harvester ants might use the charcoal to repel other ant species, by impregnating the charcoal with some type of chemical deterrent, but evidence for this was merely correlative circumstantial. This study investigates the validity of the chemical deterrence hypothesis using several different methods including behavioral assays and pitfall trapping. This study also investigates alternative hypotheses for why the harvester ants collect charcoal, including the increase of nest temperature and water/flooding regulation.
*Gordon, D. M. 1984. The harvester ant (Pogonomyrmex badius) midden: Refuse or boundary? Ecological Entomology 9:403–412
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