Tsetse can be distinguished from other large flies by two easily observed features. 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.
Fossilized tsetse have been recovered from the Florissant Fossil Beds in Colorado, laid down some 34 million years ago. Twenty-three extant species of tsetse flies are known from Africa.
Tsetse were absent from much of southern and eastern Africa until colonial times. The accidental introduction of rinderpest in 1887 killed most of the cattle in these areas, and the resulting famine removed much of the human population. Thorny bush ideal for tsetse quickly grew up, and was populated by wild mammals. Tsetse and sleeping sickness soon colonised the whole region, effectively excluding farming and animal husbandry. Hunters and conservationists supposed that the empty, game-rich land was typical of primeval Africa. Large areas were turned over to reserves, first for game hunting and later for conservation. Sleeping sickness was described by conservationists as "the best game warden in Africa".