A true fly (order Diptera) of the family Tabanidae, with very large, iridescent eyes. Many horseflies are large, and swift fliers. Larvae are carnivorous and adults feed on plant material, with only the females biting mammals to obtain the protein they need to produce eggs. The flies are especially troublesome to horses and cattle and their bites transfer several diseases. There are at least 2000 species, found worldwide except in polar regions.