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Bot Fly

Cuterebra sp.

Cuterebra bot fly photo © by Mike Plagens

This specimen was captured with a net near the summit of a small hill top in the Dripping Springs Mountains, Pinal Co., Arizona, USA.

Cuterebridae -- Bot Fly Family

Male bot flies are frequent hilltoppers - they fly to and establish territories at the summits of small mountains and hills in the Arizona Desert. This is a means of establishing rank and finding receptive females. Several different species are frequent on hilltops from mid spring through fall.

Few observers can study the life history of these insects without cringing with disgust. The idea of a large maggot living beneath the skin of a warm-blooded mammal seemingly reversing an established order between higher and lower organisms is hard to accept. Our perceptions of course are biased.

Harris' Antelope Squirrels are frequent hosts of these flies in the Sonoran Desert. Through binoculars most squirrels will be seen with thumb-sized warbles or scars on their flanks caused by the large maggot below the skin. The flies lay their eggs in the nesting area and the small maggots tunnel into the skin to begin the infection. Occasionally these flies will lay eggs in pet bedding areas resulting in incipient infections of dogs or cats (follow link below for more info). Normally these hosts are not well suited to the fly's biology and the maggot dies before developing in which case a secondary infection can occur at the wound site. Just for a reminder - there are tropical species of bot flies that parasitize humans! When the maggot is fully grown it pops out of the skin, pupates within the nesting material and later ecloses as an adult fly - one that could be mistaken for a horse fly. As adults they are harmless and do not bite.

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Copyright Michael J. Plagens, 1999-2009