282 GLOSSINA MORSITANS [CH. 



of all. The flies will readily bite through one thickness of 

 clothing and if the bottoms of the trousers are open they 

 frequently creep up the legs and bite above the socks. 



The males feed on blood as readily as the females, and the 

 large swarms of tsetse are mainly composed of the former. 

 The females seem to be more hardy than the males, for in certain 

 transmission experiments with G. morsitans, Fischer employed 

 636 males and 766 females ; 70 days later only 135 males 

 had survived, whilst 265 females were still alive. 



In captivity moisture is rapidly fatal to this species ; more- 

 over it is very intolerant of high temperatures, for Roubaud, 

 in Dahomey, observed that specimens exposed to 40 C. died 

 within an hour. The fly, however, occurs in districts, e.g. the 

 Luangwa Valley, where the thermometer frequently registers 

 42 C. in the shade. 



Practically nothing is known about the natural enemies of 

 G. morsitans, but Newstead in Nyasaland has found examples 

 of the fly in the food contents of two species of birds, viz. : the 

 common African Drongo (Dicrurus afer) and a small Bee-eater. 

 It is possible that the fly is susceptible to rinderpest for it is 

 difficult to explain the disappearance of this insect from South 

 Africa and the Transvaal on any other hypothesis. 



The well-known hunter, Mr F. C. Selous, has published 

 some interesting observations relating to this question. It 

 is well known that after the great epidemic of rinderpest in 

 1896, G. morsitans disappeared from practically all the country 

 south of the Zambesi. Throughout this region the buffaloes 

 were exterminated, but although there seems to have been a 

 very close association between these animals and G. morsitans, 

 it is well known that the tsetse-fly can thrive on the blood of 

 other animals, and as zebras, giraffes, antelopes, etc. were all 

 left in considerable numbers it is difficult to understand why 

 the fly also disappeared. 



It is possible, of course, that the tsetse-fly had become so 

 restricted in its feeding habits, that when its usual host, the 

 buffalo, disappeared, it was unable to adapt itself to feeding 

 on other animals and simply died out through lack of food, 

 but it seems more reasonable to suppose that the rinderpest 



