Horse Fly, common name for any of more than 2000 species of robust, fast-flying, biting flies with short antennae. They are worldwide in distribution. Many horse flies, which are also called gadflies, are large, with broad heads, flattened bodies, and brilliantly colored compound eyes. The females have short piercing and sucking mouthparts. They live on the blood of animals, and their bite is usually painful. Male horse flies, which do not bite, feed on the nectar of flowers. Female horse flies place their eggs on water plants in summertime. The larvae drop to the moist ground or into water after hatching and feed on small animal life, including insects. They hibernate during winter and spend the spring in the pupal stage. Adults emerge in June.
Many of the larger horse flies in North America are often called greenheads because of their large, bright-green eyes. Deer flies are small species of a genus related to horse flies. They are sometimes called strawberry flies or ear flies. Some deer flies transmit tularemia, anthrax, and other diseases to mammals, including humans.
Scientific classification: Horse flies and deer flies make up the family Tabanidae, of the order Diptera. The greenheads of North America are classified in the genus Tabanus. Deer flies make up the genus Chrysops.