Kleptoparasitism and phoresy in the Diptera

Spiders, dung-feeding scarabs, social, and prey-storing insects provide pre dictable and concentrated sources of food for a variety of thief flies (kle ptoparasites) and their larvae. Whenever waiting in the vicinity of the "ho st" for an opportunity to exploit its resources is more energy efficient an d less dangerous than foraging among hosts, a number of intimate relationsh ips between the fly and host may evolve. In extreme cases, flies may become long-term phoretic associates that travel with hosts even while the latter is in flight. The behaviors and ecologies of kleptoparasitic Diptera are r eviewed with special attention paid to the adaptations of Sphaeroceridae ph oretic upon Scarabaeidae. The mating systems of kleptoparasitic flies are i nfluenced by the type of resource that is stolen; flies associated with pre dators are mostly female, while those found on scarabs are of both sexes. T hese differences are discussed in terms of mate location, sperm competition , and mate choice.