n.; pl. Gadflies [ Gad + fly. ] (Zool.) Any dipterous insect of the genus Oestrus, and allied genera of botflies. [ 1913 Webster ]

☞ The sheep gadfly (Oestrus ovis) deposits its young in the nostrils of sheep, and the larvæ develop in the frontal sinuses. The common species which infests cattle (Hypoderma bovis) deposits its eggs upon or in the skin where the larvæ or bots live and produce sores called wormels. The gadflies of the horse produce the intestinal parasites called bots. See Botfly, and Bots. The true horseflies are often erroneously called gadflies, and the true gadflies are sometimes incorrectly called breeze flies. [ 1913 Webster ]

Gadfly petrel (Zool.), one of several small petrels of the genus Oestrelata. [ 1913 Webster ]