The Tabanids

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Frontal view. 
Tabanidae is one of the largest of dipteran families, with an estimated 8,000 species and worldwide distribution. The eyes are large, covering most of the head. In life many species display colorful eye banding that all disappears on dried specimens.
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The tabanids or horse flies are stout, medium to large-sized flies. They are recognized because their antennae have three segments with the distal one bearing annulations but no arista. The R4 and R5 veins of their wings diverge and enclose the wing tip. They develop slowly (about one generation per year) but the adults emerge synchronously so they may cause sudden outbreaks. The horse flies are feared by domestic animals, they inflict painful bites that draw abundant blood, and are mechanical vector of a number of infections.
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Dichelacera alcicornis. 
The discal cell is located more or less in the centre of the wing. The large, bean shaped head is much broader than long and the eyes are particularly well developed, as befits predominantly diurnal creatures. The mouthparts of tabanids are particularly well suited to the mechanical transmission of blood-dwelling pathogens from host to host.