492 



OTHER BLOOD-SUCKING FLIES 



FIG. 230. 

 pygium o f 

 tsetse fly. 

 Alcock.) 



Hypo- 

 male 



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 antenna? 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), 

 (After 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 by 

 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 limita- 

 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 Nigerian sleeping sickness, is 

 seldom found more than 30 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 



FIG. 231. 

 flies. 



\\\ 



Approximate ranges of tsetse 

 (Compiled from Austen.) 



range of entire genus glossina 

 range of g. morsitans 

 range of g. palpalis 



