492 



OTHER BLOOD-SUCKING FLIES 



Fig. 230. 

 pygium o f 

 tsetse fly. 

 Alcock.) 



Hypo- 

 male 

 (After 



mouthparts when the latter are not in use, and it is thus the palpi 



alone that are seen when the long blunt-tipped proboscis is ob- 

 served." The characteristic form of the antennae is shown in 

 Fig. 229. The thorax is relatively large and 

 quadrangular, with a characteristic pattern 

 which is, however, inconspicuous in some 

 species. The abdomen may be nearly uniform 

 dark brown, or pale brown banded with a 

 dusky color. The male has a large oval swell- 

 ing on the under side of the last segment of 

 the abdomen, the " hypopygium " (Fig. 230), 

 which forms a good distinguishing mark be- 

 tween the sexes. 

 Distribution, Habits, etc. — Tsetse flies, fortunately, are lim- 

 ited in their distribution to the middle portion of the African 



continent from south of the Sahara Desert to the northern borders 



of British South Africa (Fig. 



231, = ). One species occurs 



in the southwestern corner 



of Arabia. Tsetses are bj^ 



no means evenly distributed 



over this great area, but are 



limited locally to "fly-belts," 



chiefly along rivers and at 



the edges of lakes. All the 



factors which cause the 



" patchy " distribution of 



tsetses are not known; there 



are cases where close Umita- 



tion to certain areas cannot 



be explained by any known 



requirements of the flies. 



Different species vary in 



their choice of habitats; 



Glossina palpalis (Fig. 236), 



the carrier of Gambian and 



seldom found more than 30 



Fig. 231. 

 flies. 



\\\ ' ' 

 /// • 



Approximate ranges of tsetse 

 (Compiled from Austen.) 



range of entire genus glossina 

 range of g. moTsitans 

 range of g. palpalis 



Nigerian sleeping sickness, is 

 yards from the edge of water 

 where a sandy bottom and overhanging vegetation is abun- 

 dant, though it follows animals and man for a few hundred 

 yards from such positions. This species is found only in shady 



