Horse Flies and Deer Flies (Diptera: Tabanidae)

The family Tabanidae is primarily composed of two fairly large groups of biting flies known collectively as horse flies and deer flies. They occur worldwide and are represented by 4,300 species and subspecies from 137 genera. Generally, the wings of deer flies possess a vertical dark band from the mid-line of the wing down to the margin, while wings of horse flies can be entirely dark, mottled, or completely clear. Horse fly wings never possess a vertical band down the mid-line of the wing. Members of this family have large eyes; the females are dioptic (eyes widely separated) and the males are holoptic (eyes contiguous). Adult size range varies tremendously. Some deer flies, Chrysops sp., are as small as 6 mm, while some of the larger horse flies, Tabanus sp., can be up to 25 mm in length (Fig. 46).

Horse Flies and Deer Flies (Diptera: Tabanidae), Figure 45

Adult deer fly, showing the vertical dark band of wing (photo, J. Castner, University of Florida).