Horsefly, or Gadfly, a large fly that irritates domestic animals, primarily horses, cattle, and hogs. It is a carrier of anthrax and tularemia (rabbit fever).
The black horsefly is about one inch (2.5 cm) long. It has a broad head, brownish-black wings, and a beaklike mouth. The mouth is adapted to feeding on liquid—the female feeds on blood, the male on nectar. To draw blood from a victim, the female pierces the skin with her mouth, often inflicting a painful wound.
Horseflies belong to the family Tabanidae of the order Diptera. The black horsefly is Tabanus atratus.The horsefly female feeds on blood, the male on nectar.