These tiny, furry flies resemble small moths, and like their namesakes they are mainly active at night. They are not robust fliers. The antennae are longer than the head, “and sometimes longer than the body” (Scudder and Cannings, 2006). The antennae have have 12 to 16 segments, and have cup-shaped whorls of setae.
Adults are most common in dark, damp areas, including for example mossy seeps. One genus, called Sand Flies, bite humans and can transmit disease. Fortunately the Sand Flies do not venture as far north as West Virginia.
Moth flies are easy to identify to family, but may be challenging to identify to species.
West Virginia Horse Flies and Deer Flies
Tabanid Flies are medium-sized to large flies usually robust in body shape. The eyes are large and in males the eyes touch. In females the eyes are separated by the frons. The female’s blood-sucking mouthparts are prominent. Some Deer Flies and Horse Flies are pilose but not bristly. The calypters are large. Wings are often darkened, with the dark areas sometimes forming a pattern (Pechuman and Teskey, in McAlpine, 1981).
Females are more often encountered, as they search actively for mammals to bite. Males do not bite. In a few groups within this family females do not feed on blood, and in still other species the females fed on cold-blooded rather than warm-blooded creatures. Males, as well as the females that are not blood feeders, feed on flowers instead.
Tabanids are on humankind’s “bad list” for a number of reasons. One is that some bite humans. Another is that some Tabanids annoy livestock. Still another reason is that Tabanids can be vectors of diseases of both humans and livestock. These diseases include tularemia, anthrax, filariasis, and anaplasmosis.
Larvae of many Horse Fly species feed on tiny invertebrates. Very little is known about the larval diet of Deer Flies in the genus Chrysops.
Larvae in some species of Tabanids go through an unusually long series of instars, as many as nine. Some (especially in northern states and provinces) require two years or even longer to complete their development. Other species take only one year, and some have two broods in a single year.