Tsetse Fly, any one of a genus of two-winged flies found in Africa. These flies are slightly larger than houseflies and are light brown to near black in color. Unlike most other flies, tsetse flies do not lay eggs. A single egg hatches in the female's uterus and emerges as a fully developed larva. The larva becomes a pupa enclosed in a hard pupa case, and in three to four weeks an adult tsetse fly emerges.

There are about 20 species of tsetse flies, many of them responsible for transmitting diseases to animals, including humans. The flies themselves do not cause the disease, but when the flies bite humans and other animals they introduce tiny parasites into the bloodstream. The parasites, called trypanosomes, are protozoans that cause such diseases as African sleeping sickness in humans and nagana in cattle and other animals. The flies can be controlled by such means as cutting down the vegetation in which they live or by spraying with insecticides.

Tsetse flies are of the genus Glossina of the family Muscidae, of the order Diptera.

Tsetse flyTsetse fly are two-winged bloodsuckers much larger than house flies.