Gadfly, a name applied to large flies which goad or sting domestic animals, more commonly called horseflies in this country. The term is improperly applied to many botflies. Gadflies have wonderful powers of flight, being able to keep up with the swiftest quadruped without apparent effort. The sting frequently draws large drops of blood, and is exceedingly painful. Naturalists inform us that the male gadfly is satisfied with such nourishment as he can sip from weeds and flowers, but that the female is savagely eager to feast on blood. Gadflies proper are closely related to the smaller yellow-barred pest of the woods known as the deer-fly. See FLY.