ITS ENEMIES 49 



It is noteworthy also that this explanation, were it 

 possible, would, be opposed by the fact that the 

 number of females caught on Tavu varied very little, 

 unlike the male figure, whereas if the flies had been more 

 attracted to Tavu on days when the crocodiles were 

 numerous, there should have been greater variations in 

 the female catch ; perhaps an inverse relation to the 

 number of crocodiles. 



The explanation, however, may be connected with 

 the pairing of the flies, Male flies flock to the coast from 

 out of the forests when crocodiles are there in numbers 

 in order to meet the females, which go to feed on the 

 crocodiles. When crocodiles are fewer on the coastline 

 the male flies may confine themselves more to the forested 

 centre of the island : the boys caught always on the 

 east and west shore and not in the central forest. It 

 will be remembered that on Bulago and Kimmi the flies 

 seemed to frequent different parts at different times. 



Having considered two influences that affect the num- 

 bers of the fly, viz. food and climate, it will be interesting 

 now to deal with the natural enemies of Glossina 

 palpalis in all its stages. 



Considerable attention was paid to this question, and 

 I have spent very many hours observing, in the haunts 

 of the fly, birds and insects that might be expected to 

 destroy the fly. 



Very many insects suffer great mortality in their im- 

 mature stages of egg, larva and pupa, but it will be 

 obvious from what has been said about the reproduction 

 of Glossina that it is hardly likely that any great destruc- 

 tion can be wrought upon egg or larva while within the 

 body of the adult fly. It seemed possible, however, that 

 the fat grub in the fly might be " stung " by some 

 parasite such as the Hymenopterous " Ichneumon flies," 

 and that after it had been extruded the adult parasites 

 might emerge from the pupa. 



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