Gadfly, a dipterous insect, belonging to the genus tabanus (Linn.), with three-jointed antennae and wide-spreading wings. The gadflies attack not only man, but cattle, horses, camels, and various ruminating animals. The most common species in the United States is the T. atratus (Fabr.), of a black color, with a whitish bloom on the back, like that of a plum; the eyes are very large, almost meeting at the top of the head, and of a shining purplish or bronze black color, with a jet-black band across the middle; it is about an inch long, with an expanse of wings of nearly two inches. The orange-belted gadfly (T. cinctus, Fabr.) is smaller and less common, black, with the first three abdominal rings orange-colored. A smaller and very common species is the T. lineola (Fabr.), which has a whitish line along the top of the hind body. There are many other American species, described and undescribed.

There are about 40 European species, for a knowledge of whose habits and metamorphoses we are principally indebted to De Geer. The species which so.torments cattle is the T. bo-tinus (Linn.), about an inch long; the thorax and abdomen are dark brown, the former with yellowish hair, and the latter with a reddish yellow cross band on the hinder edge of the segments, and bright yellow triangular spots; abdomen yellowish gray, with black triangular spots; thighs dark brown, and tibiae bright yellow. These insects appear about the end of June, and continue their attacks through summer; the proboscis, though not very long, is armed with six very sharp needles, by which they can pierce the thickest hide. In the allied genus chrysops (Meigen), or golden-eyed gadflies, may be mentioned the C. coecu-tiens (Meig.), about one third of an inch long, common in Europe in meadows and pasture lands, stinging both men and horses very severely; the yellowish brown thorax is marked with three long black stripes; wings white with blackish brown spots; abdomen yellowish.

American species are C. ferrugatus (Fabr.), black, and C. vittatus (Wied.), striped black and yellow; they are found in woods and thickets in July and August. The genus hoema-topota (Meig.) contains the troublesome gadfly called cleg in Scotland; this, the H. pluvialis (Meig.), is about the size of the common house, fly; the large eyes are greenish, with four undulating brown bands running through each of them; the body is gray, with brownish cross stripes; the wings gray, spotted with brown. It attacks man, cattle, and especially horses, in sultry weather just before rain; the wounds are painful at the time, but are not followed by any lasting burning or itching.-The name of gadfly is also given to several species of oestrus, especially to that which deposits its eggs about the knees and sides of the horse, and which, conveyed into the stomach, constitute the disease known as bots. (See Bots.)