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The Squirrel Botfly

by Jason Ross, Wildlife Biologist

Tree squirrels have relatively few diseases and parasites. However, one important parasite affecting squirrels in Mississippi and the Southeast is the larval stage of the warble botfly. Commonly known as "wolves, heel flies, warbles, or grubs", this skin parasite (Cuterebra emasculator) produces unsightly, bloody swellings. Usually 3-5 nodules, the swellings tend to concentrate around the front shoulder and chest areas of the infected squirrel.

Little is known regarding the botfly life cycle. It is believed that eggs deposited on surrounding vegetation hatch into infective larva that parasitize the host squirrel.

Larval occurrence is seasonal and appears to fluctuate annually in intensity. Past infestation rates up to 50% have been reported in Mississippi. As the larva develop and begin to pupate, small (one inch or smaller), dark brown, spiny "grubs" emerge from the swollen areas. Prevalence of infestation seems to be highest in east-central counties and in upland areas with lighter soils. The larval swellings begin in August with the "grubs" generally emerging by mid October. Although unsightly, these infestations do not affect human consumption beyond normal raw meat cooking precautions. To ensure that harvested squirrel carcasses are not wasted by uninformed hunters, the season opener for Mississippi squirrel hunters generally reflects the post-emergent period for this common rodent parasite.

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