While not as serious a carrier of disease as mosquitos, many Tabanids viciously attack both animals and human beings. Most prefer warm seasons and the warmth of the day, but some species are most active at dawn or dusk. While waiting for females, Tabanid males hover in large swarms at "aggregate sites" in relatively open areas. These swarms do not attack, for only females are able to bite.

There are two principal genuses. Tabanus includes the larger black "horse flies", as well as the smaller salt-marsh dwelling "greenheads" and striped horse flies. Equally vicious are the smaller Chrysops or deer flies with multi-colored, cross-banded wings.

Bites are deep and painful, but unless one is allergic the effects will soon pass (if not the memory). Repeated attacks by Tabanids can cause serious blood loss in animals.

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