Horseflies are moderately sized, heavy bodied insects, 6-20 mm long with cloudy wings and large banded eyes. Females have strong, blade-like, piercing and sucking mouthparts for sucking blood of animals but males do not feed on blood but feed on vegetable material or nectar. Thorax is pubescent, yellowish. Larvae have girdle like transverse bands on the body and are found in moist soil, mud, rotting vegetation or in aquatic situations. Pupae are elongated and cylindrical and are found in dry places, generally 1-2 inches below the surface. Pupal period may be as long as three weeks.
They transmit horse disease called, SURRA that is caused by the protozoan, Trypanosoma evansi and T. theileri. They also transmit Anthrax among cattle. The flies are active in warm and sunny days and fly very fast.