Tsetse, sometimes spelled tzetze and also known as tik-tik flies, are large biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus Glossina, which are placed in their own family, Glossinidae. The tsetse are obligate parasites that live by feeding on the blood of vertebrate animals.

Tsetse are similar to other large flies, such as the housefly, but can be distinguished by various characteristics of their anatomy, two of which are easy to observe. Tsetse fold their wings completely when they are resting so that one wing rests directly on top of the other over their abdomens. Tsetse also have a long proboscis, which extends directly forward and is attached by a distinct bulb to the bottom of their heads.

Tsetse have an unusual lifecycle which may be due to the richness of their food source. A female fertilizes only one egg at a time and retains each egg within her uterus to have the offspring develop internally during the first three larval stages, a method called adenotrophic viviparity. During this time, the female feeds the developing offspring with a milky substance secreted by a modified gland in the uterus. In the third larval stage, the tsetse larva leaves the uterus and begins its independent life. The newly independent tsetse larva crawls into the ground, and develops a hard outer shell called the puparial case, in which it completes its morphological transformation into an adult fly.

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