56 NATURAL HISTORY OF GLOSSINA PALPALIS 



breeding ground on a ridge was an area of low-lying sand 

 covered by dense vegetation, the leaves of which lying 

 on the sand were mouldy and kept it damp. My fly 

 boys searched for pupae there unsuccessfully, and in so 

 doing of course cleared away the dead leaves and opened 

 up the vegetation, so that a small area of sand about 

 two feet in diameter was much more freely ventilated, 

 though still shaded. 



On a subsequent visit a week later I found, in that very 

 spot, about two dozen fresh pupae which had been deposited 

 there since my former visit. Incidentally this observa- 

 tion shows a very important point which will be alluded 

 to later, that the female fly searches carefully for the 

 most suitable spot for the pupae. 



The soil itself may be of very diverse kinds : fine 

 pebbles, pebbles mixed with coarse sand, coarse brown 

 sand, coarse white sand, fine white sand, light friable 

 earth, vegetable humus and debris, and the very fine dry 

 dust found in caves and probably mostly derived from 

 disintegrated droppings of bats. Coarse sand with or 

 without pebbles has been found to yield the greatest 

 number of j^upae : the very fine white sand such as com- 

 poses the southern beach of Nsadzi (see Fig.) is not so 

 suitable, because I think it holds moisture too much. 

 The very fine dry dust of caves does not seem very attrac- 

 tive to the flies ; possibly it is in its turn too dry. 



Vegetable humus and debris are most important, for on 

 long stretches of shore they often form the only material 

 suitable for pupae, elsewhere there being only bare rocks. 

 Little pockets of humus and dried-up debris under angles 

 of rocks or at the bases of trees in such areas form the 

 only spots in which the fly can deposit its larvae, and 

 these are what I have termed " loci." Other " loci " 

 are sometimes formed in a'forest by loose sand up against 

 the base of a tree trunk not far from the water, often 

 indicated as suitable for palpalis pupae by the presence 



