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Horse-fly is the most widely-used English common name for members of the family Tabanidae. Apart from the common name "horse-flies", broad categories of biting, bloodsucking Tabanidae are variously known as breeze flies, clegs or clags, deer flies, gadflies, or zimbs. In some areas of Canada, they also are known as Bull Dog Flies. In Australia some species are known as "March flies", a name that in other English-speaking countries refers to a very different Dipteran family, the non-bloodsucking Bibionidae.
The Tabanidae are true flies, that is to say, members of the insect order Diptera. Tabanid species that habitually attack humans and livestock are widely regarded as pests because of the bites that females of most species inflict, and the diseases and parasites that some species transmit. The various species of Tabanidae range from medium-sized to very large in size. Some species, such as deer flies and the Australian March flies, are known for being extremely noisy during flight, though clegs, for example, fly quietly and bite with little warning.
In spite of their roles as pests, Tabanidae also are important pollinators of some flowers. In particular, several South African species have spectacularly long proboscides adapted to the extraction of nectar from flowers with long, narrow corolla tubes, such as Lapeirousia and some Pelargoniums. Tabanidae occur worldwide, being absent only at extreme northern and southern latitudes.
Taxonomy and description 
The genus Zophina is of uncertain placement, though it has been classified among the Pangoniinae. Two well-known genera are the common horse flies, genus Tabanus Linnaeus, 1758 and the deer flies, genus Chrysops Meigen, 1802 are also known as banded horse flies because of their coloring. Both genera give their names to subfamilies. The "Blue Tail Fly" in the eponymous song was probably a tabanid common to the southeastern United States.
Adult horse flies feed on nectar and sometimes pollen. Females of most species are anautogenous, meaning they require a blood meal before they are able to reproduce effectively, if at all. Much like male mosquitoes, male Tabanidae are not ectoparasitic and lack the mouth parts (mandibles) that the females use in drawing the blood on which they feed. Most female horse flies feed on mammalian blood, but some species are known to feed on birds or reptiles. Some are said to attack amphibians as well.
Biting behaviour 
Horsefly bites are painful, the bites of large specimens especially so. Most short tongued (short proboscid) species of horse flies use their knife-like mandibles to rip and/or slice flesh apart. Flies with longer proboscides bite more like a mosquito, their stylet-like mouthparts piercing the host's skin like needles.
The horse fly's bite is more immediately painful than that of its mosquito counterparts, although it still aims to escape before its victim responds. Moreover, the pain of a horse fly bite may mean that the victim is more concerned with assessing the wound, and not swatting the interloper. In any case defense is difficult, considering the agile nature of the fly. However, inhabitants of regions where the flies are a pest usually learn to swat immediately at the first hint of the bite. That usually gets the fly, especially if its escape is hampered by its having bitten through clothing. The bites may become itchy, sometimes causing a large swelling afterward if not treated quickly.
Eggs are laid on stones or vegetation usually close to water. On hatching, the larvae fall into water or moist earth, feeding voraciously on invertebrates, such as snails, earthworms and other insects.
Tabanidae are known vectors for some blood-borne diseases of animals and humans. Tabanidae are very good vectors of the equine infectious anaemia virus, as well as some Trypanosoma species. Species in the genus Chrysops are biological vectors of Loa loa, transmitting this parasitic filarial worm between humans. They have also been known to transmit anthrax among cattle and sheep and tularemia between rabbits and humans (and are the most common vector of such transmission in the Western US).
Blood loss is a common problem in some animals, when large flies are abundant. Some animals have been known to lose up to 300 ml of blood in a single day from tabanid bites, which can severely weaken or even kill them.
See also 
- Cirrus Digital Horse Fly Tabanus sulcifrons.
- Webster's Revised Unabridged Dictionary (1913), p. 707.
Data related to Tabanidae at Wikispecies
|Look up horsefly in Wiktionary, the free dictionary.|
- Information about horsefly bites
- Horsefly Tabanus sp. diagnostic photographs
- Virtual Field Guide Tabanidae Images
- Family description and images
- Chrysops, Diachlorus, and Tabanus spp. on the UF / IFAS Featured Creatures Web site
- Diachlorus ferrugatus, yellow fly on the UF / IFAS Featured Creatures Web site