Body length ranges from 5-25mm and the compound eyes are well developed. As with most haematophagous diptera it is only the females that take blood in addition to nectar with the males being solely nectar feeders. The principal mechanism for finding their hosts is sight and so the large eyes serve this function well. There is also evidence that CO 2 acts as an odour source especially in some Chrysops spp. The eyes are coloured and are also used to sex the flies.
Males are holoptic and the females dichoptic.
Eye coloration varies between species with unicolourous or horizontally banded patterns seen in Tabanus , spots in Chrysops , and zigzag bands in Haematopota. The antennae are stiff and project forward. Wing veination is pronounced but not used for species diagnosis. At present there are over 3,000 known species of Tabanids. The three main genera of economic importance are the Chrysops , Tabanus , and Haematopota .