Nest usurpation and sequential nest occupation in the digger wasp Crabro monticola (Hymenoptera: Sphecidae)

Abstract

Females of Crabro monticola regularly abandoned the nests which they had been provisioning, sometimes for no apparent reason, sometimes because the nest had been entered in their absence by a conspecific usurper. After giving up her nest, a female had the option of digging a new nest or entering an already constructed burrow and usurping it from its owner, if it were occupied. Both options were exercised by members of the population. The result was that individual nests were held by as many as six different females over the course of 26 days. Each female occupied 2.2 nests on the average during the study. The adaptive advantages of nest usurpation and burrow switching are unclear. Nest usurpation attempts never resulted in joint occupation of a burrow in this species. Therefore, whatever its benefits, the entering strategy can evolve even if it does not lead to joint defense of a nest by its "communal" occupants.