Gadfly is a name given in the United States to the large black or blue-black, blood-sucking "horseflies" of the family Tabanidae, called in Great Britain clegs or breeze flies. They are powerful in flight, and the females are furnished with a lancet-like proboscis which can pierce the thickest skin. They are present and dreaded by animals in nearly all parts of the world, and in Brazil are an even dangerous annoyance to man as well.
In Great Britain this name is usually applied to tbe botflies of the family Oestridae. An example is Bypoderma bovis, of which the larvae form bots or warbles. The adult fly deposits its eggs on the skin of cattle, where they hatch into maggots. The maggots bore through the skin and form tumors ("warbles") beneath it. When full fed they quit their host, fall to the ground, bury themselves, and after pupation emerge as flies. These, settling on cattle, cause them to gallop about in a frenzy in summer time. Other examples of the same family are the botfly of the horse (Gastraphilus equi). In the sheep botfly (Oestrus ovis), which has a similar life-history, the maggots enter the nostrils, and live in the frontal sinuses.
