HABITAT OF GLOSSINA PALPALIS 383 



prevalence, disappearing as soon as the degree of humidity falls with the 

 drying up of the water courses, even though the temperature is not in 

 itself unfavourable, and though both shade and food supply are present. 

 The shade necessary for the fly is that of dense forest, in which it 

 is well protected from the direct rays of the sun, rather than that of 

 thick shrubs and undergrowth near the ground ; shade and moisture 

 appear to be more important than a particular temperature, for a fall in 

 the latter, though it delays the life processes, does not inhibit them or 

 cause the fly to seek fresh quarters. An excess of moisture, such as 

 occurs in large swamps, is also unfavourable, especially since in such 

 situations the deep shade of forest trees is not usually available. 



The food supply of palpalis is present almost everywhere, as this 

 species is by no means restricted to any particular host or group of 

 hosts. According to Roubaud palpalis, more than any other of the 

 genus, is addicted to the blood of man, a most important fact in relation 

 to the spread of Sleeping Sickness ; but it will feed readily on almost 

 any mammal, on domestic animals, cattle and pigs, on game of all 

 kinds, and particularly on deer and antelope ; birds, lizards and snakes, 

 are also attacked, as has been definitely established by the presence of the 

 characteristic blood corpuscles in the mid-gut of the fly. The food supply 

 does not, therefore, act to any great extent as a factor in determining 

 the distribution of the fly in the broad sense, though it is of some 

 importance, as will be shown later, in determining the precise localities 

 in which the majority of the individuals in any given habitat are 

 found. It is probable, however, that in some cases the disappearance 

 of the fly from a given area may be connected with the migration 

 of the game. 



It will be readily understood that such closely circumscribed condi- 

 tions, which hold, in a greater or less degree, for all species of Glossina, 

 will not be found uninterruptedly throughout a large area. The presence 

 or absence of the flies is determined by the physical conditions of 

 the country, and it is often the case that one locality is heavily infected, 

 while another, not far distant, is practically free from it. It is this 

 circumstance which gave rise to the term ' fly belt ', applied by the older 

 travellers in Central Africa to regions infested with the ' tsetse fly ', 

 (not necessarily palpalis), and so much dreaded by them on account 

 of the inevitable loss of domestic and transport animals which occurred to 

 those who had to traverse them. Such fly belts are not, of course, 

 constant in position, but vary according to the seasonal nature of 

 the rainfall and the migratory habits of the game. 



