Tabanids are large biting flies generally called horse-flies, although other vernacular names include greenheads (some species of Tabanus), clegs and stouts (Haematopota) and deer-flies (Chrysops). All belong to the family Tabanidae, which comprises some 4300 species and subspecies in 133 genera. Medically the most important are species of Tabanus, Chrysops and Haematopota. Tabanids have been incriminated in the spread of anthrax and tularaemia and might be involved in the transmission of Lyme disease (usually transmitted by hard ticks). But their main medical importance is that species of Chrysops, mainly C. silaceus and C. dimidiatus, are vectors in West and Central Africa of the filarial worm Loa loa.

The Tabanidae have a worldwide distribution. Species of Tabanus and Chrysops are found in temperate and tropical areas, but Haematopota is absent from South America and Australasia and is uncommon in North America.

External morphology

A generalized description is presented of the Tabanidae, with special reference to the genera Chrysops, Tabanus and Haematopota.

Tabanids are medium to very large flies (6–30 mm long). Many, especially Tabanus species, are robust and heavily built, and this genus contains the largest biting flies, some with a wingspan of 65 mm. The colouration of tabanids varies from very dark brown or black to lighter reddish brown, yellow or greenish; frequently the abdomen and thorax have stripes or patches of contrasting colours (Fig. 7.1). The head is large and, viewed from above, is more or less semicircular (Fig. 7.2); it is often described as semilunar.