MSD Manual

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Professional Version

Spider Flies/New Forest Flies


Charles M. Hendrix

, DVM, PhD, Department of Pathobiology, College of Veterinary Medicine, Auburn University

Last full review/revision Aug 2013 | Content last modified Jun 2016

The spider or new forest fly, Hippobosca equina, is widely distributed throughout Europe, Asia, and Africa. These winged keds parasitize horses and rarely cattle throughout the UK. Its bite is characterized as a nuisance and disturbance to large domestic animals. It has a predilection for feeding sites in the perineal region and between the hind legs.

The winged adult is ~10 mm long with a flattened, shriveled body. The life cycle is similar to that of Melophagus ovinus, in that the female produces one larva at a time, and at the time of maturity the larva falls away from the female fly and pupates in the soil.

Treatment is rarely indicated, but many of the repellents used for other blood-feeding periodic parasites may be used.

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