IX 'FLY' BELTS 167 



and, speaking generally, full of tse-tse flies as well, 

 all open pieces of grass country, where there are 

 neither trees nor bushes, and all reed beds of any 

 size, will be found to be free from these insects. 

 When buffaloes feed out into such places from 

 the surrounding forests, the " flies " soon leave 

 them and return to the shelter of the trees. 

 Similarly, if one side of a river be covered with 

 bush and forest down to the water's edge, and if, 

 along this forest-covered bank, tse-tse flies swarm, 

 these insects will never cross even a narrow channel 

 to open reed beds or grass land on the other side. 

 Dr. Livingstone has mentioned how, though he 

 found tse-tse flies swarming along the southern bank 

 of the Chobi river in 1853, his oxen were perfectly 

 safe from these insects in the open grass lands 

 on the other side of the river ; and in my own 

 experience, although I have often crossed this 

 same part of the Chobi by canoe, and seen 

 numbers of '' flies " on meat, or on the natives or 

 myself, as we left the southern bank, I never knew 

 one of them to cross the river with us. As soon 

 as we got to a short distance from the southern 

 bank, they all left us and flew back to the shelter 

 of the trees and bushes. But the most extra- ] 

 ordinary thing about the tse-tse fly is, that in certain | 

 low-lying countries away from the wooded banks | 

 of the larger rivers, these insects were not found 

 everywhere, but only in certain forest areas, known 

 to the early South African pioneers as "fly" belts. 

 I am speaking now, of course, of the time when 

 natural conditions and the balance of nature had 

 not been upset by North Europeans ; for no 

 charge of this kind can be made against the 

 Portuguese, who were always poor hunters. 



No one, I think, has ever been able to explain 

 why the tse-tse flies never spread from the *' fly '* 

 belt which was crossed by the old waggon road 



