Is a Corpse a Corpse? Spatial Aspects of Necrophoresis in the Western Harvester Ant, Pogonomyrmex occidentalis

Disease poses a threat to any society, and this threat is amplified for societies persisting in cramped quarters over extended periods of time. Highly social (eusocial) insects actively combat the danger of pathogen proliferation with a myriad of tactics, one of which is necrophoresis or the removal of corpses from the nest. This study examines the spatial patterns of the corpse depositions of several wild colonies of the western harvester ant, Pogonmyrmex occidentalis. These colonies were presented with nestmate as well as non-nestmate corpses to discern if this type of waste could be treated categorically. Specialized areas for corpse disposal, reported in the literature as " ant graveyards " were not observed, suggesting that observations of such accumulations in the species may be an artifact of laboratory conditions. Non-nestmate corpses were carried further away from the nest than were nestmate corpses, presumably reducing the chance of introduction of foreign pathogens to the colony. Factors external to the nest mound, such as slope and nearby neighbors, had no detectable effect on these depositions and failed to result in anything other than rather uniform dispersal of this particular waste. These findings shed light on the intricacies of a set of behaviors that are critical to the notable ecological success of these organisms. Research in recent years has increased our understanding of necrophoresis, but much remains to be discovered. Corpse removal is proving to be a dynamic activity in the world of eusocial insects, and investigation of this disease mitigation tactic, along with other such tactics employed by eusocial insects will aid in our understanding of topics such as immunity, division of labor, polyethism, and even the evolution of sociality itself.