TSETSE FLIES 351 



spoor. Soon after we had passed the fly countrv', 

 however, we encountered game, not very plenti- 

 fully it is true, but sufi&eient to enable us to 

 provide our hard-worked carriers and servants 

 with a welcome change of diet. I could, if it 

 were necessary, cite other instances of fly- 

 infested, gameless areas. 



In the light of these indisputable facts one 

 asks oneself in vain by what means these cotmtless 

 thousands of insects feed themselves. It cannot 

 be upon human beings, because villages do not 

 occur far from the waters of the two rivers I have 

 mentioned ; it cannot be upon game, for to aU 

 intents and purposes there is none ; and it cannot 

 be upon the small mammals, because these are 

 almost aU nocturnal, and do not leave their day- 

 light refuges until after the tsetse fly's period of 

 activity. Putting these aside, it seems highly 

 improbable, when we come to consider the average 

 duration of this insect's life, that it can maintain 

 itself exclusively during the whole of that period 

 upon the blood of reptUes, yet here we are con- 

 fronted with an immense, fly -infested area, which 

 is known to have been the haunt of the tsetse for 

 many years, and in which it is impossible to 

 discover, in the blood of any li\'ing creature, 

 sufficient nutrition to account for their long- 

 continued presence. In these circumstances it is 

 difficult indeed to imagine what useful purpose 

 can be ser%-ed by advancing the contention that 

 the extirpation of the large, four-footed mammals 

 would infallibly be followed by the disappearance 

 of the fly. 



