black horse fly

Black horse fly (Tabanus atratus). Photo: Ward Upham, Kansas State University,

Updated: March 1, 2023

About horse flies and deer flies

  • Horse flies are about 3/8 to 1 1/8 inches long, usually gray or blackish in color. The wings usually lack dark areas, but some species have wings that are entirely dark. The eyes often have horizontal stripes.

  • Deer flies are smaller, about 1/4 to 1/2 inch long, black or brownish, usually with dark areas on the wings. Their eyes usually have spots.

  • Females are blood-sucking and inflict a painful bite.

  • Males feed primarily on pollen and nectar and are often found on flowers.

  • Females deposit eggs on plants, rocks, and other objects usually in damp locations.

  • The larvae live in wet areas and eat immature insects and other small animals. Larvae pupate in the mud near the edge of these areas.

  • The life cycle may take from 3 months to 2 years to complete.

  • Most are strong fliers and have a range of up to several miles. They are most active during the warmest parts of the day and often follow moving objects.

deer fly

Deer fly (Chrysops ater). Photo: Whitney Cranshaw, Colorado State University, 


  • The use of pesticides for control is not feasible due to the habits of these flies.

  • Insect repellents and wearing protective clothing may help to prevent bites.