GLO.SSINA INVESTIGATIONS IN NYASALAND. 37 



It is frequently said that the fly is to be found in regions where the game 

 is " practically extinct " or absent, but I would point out that such expressions are 

 usually employed from the hunter's point of view and more often than not are to be 

 interpreted as meaning that game is not sufficiently abundant as to make shooting 

 worth while, when so much can readily be obtained elsewhere, or that such game as 

 there is has become excessively wary from continual persecution. In the wet season 

 the height of the grass, which renders all except the main paths impassable, makes 

 it difficult to form any opinion as to the amount of game present, and in the dry 

 season much of the ground gets baked almost as hard as stone, so that the smaller 

 animals leave no spoor. 



The powers of flight of the fly are good, and it is probably able to detect its prey, 

 when it requires food, at a long distance, a faculty that may be an important factor 

 in determining its well being, especially in the female, which tends to seclude itself 

 in the later stages of pregnancy. The elaborate antennae, and the special sense- 

 organ connected with them, which, judging by the habits of the male are not employed 

 for the purpose of discovering the opposite sex, would seem to bear this out. Its 

 food is in concentrated form and of the highest possible energy value, so that it 

 requires a meal every five or six days only. The presence of a large number of game 

 animals is not therefore essential to its existence. 



In all the districts in which the fly has been studied, baboons occur sometimes in 

 very large troops, and the presence of pupae in some numbers among the rocks which 

 these animals frequent may indicate that the fly derives some subsistence from them, 

 especially as they occur in places where other animals are largely absent. 



With regard to the other possible sources of food, it is difficult to believe that any 

 material amount can be derived from birds, for captive flies in wide-mouthed jars 

 when afforded an opportunity of feeding on fowls have the greatest difficulty in 

 obtaining blood through the feathers, so that probably certain birds only, e.g. \ailtures 

 with bare necks, ever afford a meal in nature.* Moreover, in a series of 300 flies 

 containing recognisable blood examined by the Royal Society's Commission avian 

 blood was only found in 1 per cent.f 



The supposition that various cold-blooded animals may supply blood seems to be 

 negatived by their very scarcity. The larger lizards, monitors for example, which I 

 have often studied elsewhere, are here extremely rare, for I have seen four only in 

 the course of the year. Agamid lizards are by no means common in the fly areas, 

 and one can hardly conceive seriously of the active little Laceetidae, which are 

 numerous, as contributing materially to the food supply of the fly. A test with toads 

 and with various tree-frogs proved negative. Other reptiles, which are scanty, 

 need hardlv be taken into consideration. 



♦[Compare the observation by Mr. LI. Lloyd on p. 77. — Ed.] 



tLThe evidence that G. morsiians does not normally feed on non-mammalian blood is 

 not quite so conclusive as might appear from these statements. In Northern Rhodesia, 

 Kuighorn, Yorke and Lloyd record (Ann. Trop. Med. Par. vii. 1913, p. 282) that out of 

 82 flies containing recognisable blood no less than 12, or 146 per cent, contained nucleated 

 red cells. Moreover, the preference of G. palpaUs for reptilian blood, which has been 



clearly proved by observations in the field — quite contrary to the laboratory results 



shows how dangerous it is to make assumptions as to the'natural food of these insects 

 based merely on the behaviour of captive flies under unnatural conditions.— Ed.] 



