There are 31 species and subspecies of tsetse flies, but the actual numberdepends on how many forms are recognized as subspecies. All tsetse flies belongto the genus Glossina, the only genus in the familyGlossinidae. Apart from two species found in southwest Arabia, tsetse flies arerestricted to sub-Saharan Africa from approximately latitude 10° north to20° south, but extending to 30° south along the eastern coastalarea. Some species, such as Glossina morsitans, are foundacross West Africa to Central and East Africa, whereas others are morerestricted in their distribution. For example, G. palpalisoccurs only in the West African subregion.

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

External morphology

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