Bring out your dead: quantifying corpse removal in Bombus terrestris, an annual eusocial insect

Abstract

Corpse removal is a hygienic behaviour involved in reducing the spread of parasites and disease. It is found in social insects such as honeybees, wasps, ants and termites, insect societies that experience high populations and dense living conditions that are ideal for the spread of contagion. Previous studies on corpse removal have focused on perennial species that produce thousands of workers, a life history that may incur a greater need for hygienic behaviours. However, whether and how corpse removal occurs in annual species of social insect, which may experience different selection pressures for this behaviour, remains largely unknown. Here the corpse removal behaviour of the bumblebee Bombus terrestris was investigated by artificially adding larval and adult corpses into colonies. Larvae were removed more rapidly than adults, with adult corpses eliciting significantly more antennating and biting behaviours. Workers that removed larval corpses were significantly more specialized than the worker population at large, but this was not the case for workers that removed adult corpses. Workers that were previously observed spending more time inactive were slightly, but significantly less likely to perform corpse removal. Size did not affect whether a worker removed corpses, but workers that removed larvae were significantly larger than those that removed adult corpses. Finally, infecting larvae with the virulent parasite Nosema bombi did not elicit prophylactic removal. Our results provide the first quantification of corpse removal in an annual social insect and set the scene for comparative analyses of this important behaviour across social insect life histories.