ANIMALS FED UPON 39 



On Ngamba Isle I was able to see two flies upon a large 

 crocodile that was resting among the bushes and had 

 not run away at my approach ; one of them had certainly 

 fed. 



In a single case out of the forty-four in which the 

 blood in wild flies was recognizable the corpuscles agreed 

 well with those of a tortoise. Glossina seems to recog- 

 nize even this as a source of food, for I saw a tortoise 

 one day with a fly on its back making vigorous attempts 

 to find a way for its proboscis through the shell. But 

 though a crocodile's plates are not insuperable, I fancy 

 that the carapace of a tortoise is proof, and the fly would 

 have to penetrate a leg or the neck. 



No example of blood that could be attributed to snakes 

 was found among the forty-four cases, but the python 

 certainly must be counted as a source of food. On 

 Kimmi in 1914 I came upon a small specimen lying among 

 marshy grass close to the water, and two flies were on 

 it, one of which had the swollen red body indicative of 

 a good feed. Other snakes also seem to be attractive, 

 for on Ngamba in 1914 I saw a black species lying on 

 rocks about to shed its skin and in the usual lethargic 

 condition. Two male flies were upon it and were 

 obviously attracted by it, though they did not seem 

 desirous of feeding. 



Lastly, the lung fish, Protopterus (the " Mamba "), 

 has been suggested as a source of food, though I do not 

 understand how it could serve as such, seeing that it only 

 appears at the surface of the water for a brief interval 

 to obtain a supply of air. Examination of its blood showed 

 that it is a physical impossibility for the fly to feed upon 

 it, for the corpuscles are so enormous that only one at 

 a time could pass up the proboscis, which would require 

 a very great effort of suction on the part of the fly ! 



The figures that have been given represent the result 

 of examination of many thousands of wild flies. For 



