Large numbers of males of the bee Centris pallida Fox have been observed patrolling areas in which females are emerging. Males locate specific sites at which a buried bee is about to emerge and dig down to meet the other individual, male or female. If it is a female, mating is initiated when she scrambles into the excavation pit created by the male. Males fight intensely with one another for possession of digging sites and for unburied virgin females. Experiments indicate that males locate conspecifics beneath the surface on the basis of extremely non-specific olfactory cues; they are capable of locating buried honey bees and other insects. The evolution of digging behaviour is traced to selection favouring males that are first to reach a virgin female which will mate just once in her lifetime. A number of examples are given of other insects that have evolved similar abilities, apparently in response to similar selection pressures.