There are 31 species and subspecies of tsetse flies, but the actual number depends on how many forms are recognized as subspecies. All tsetse flies belong to the genus Glossina, the only genus in the family Glossinidae. Apart from two species found in southwest Arabia, tsetse flies are restricted to sub-Saharan Africa from approximately latitude 10° north to 20° south, but extending to 30° south along the eastern coastal area. Some species, such as Glossina morsitans, are found across West Africa to Central and East Africa, whereas others are more restricted in their distribution. For example, G. palpalis occurs only in the West African subregion.

Tsetse flies are vectors of both human and animal African trypanosomiasis, the disease in humans being called sleeping sickness. The most important vectors are G. palpalis, G. tachinoides, G. fuscipes, G. pallidipes and G. morsitans.

External morphology

A general description of tsetse flies, without special reference to any particular species, is as follows. Adults are yellowish or brown-black robust flies that are rather larger (6–14mm) than house flies. Some species have the abdominal segments uniformly coloured, whereas others may have lightercoloured transverse stripes and a median longitudinal one. Tsetse flies are distinguished from other flies by the combination of (1) a rigid forward-projecting proboscis and (2) a closed cell between wing veins 4 and 5 which, with a little imagination, looks like an upside-down hatchet (i.e. axe, cleaver or chopper) and consequently is often termed the hatchet cell (Figs. 8.1b, 8.2a, Plate 10). The hatchet cell serves to conclusively identify a tsetse fly. At rest tsetse flies also differ from most flies in having the wings placed over the abdomen like the closed blades of a pair of scissors (Fig. 8.1a).