IX 'FLY '-INFESTED AREAS 169 



The tse-tse flies, however, used always to come 

 with the buffaloes for several miles beyond their 

 usual boundary, but gradually left them, and in 

 my own experience I never knew them to quite 

 reach the waggon road. 



It will thus be seen that although " fly "-infested 

 areas are, as a rule, well defined and well known 

 to the natives, the movements of large herds of 

 buffaloes may carry these insects — sometimes in 

 great numbers — for a short period of time, for a 

 few miles beyond their usual limits. Within a 

 large area of country throughout which tse - tse 

 flies exist, such as the level forest country in the 

 valley of the Zambesi intersected by the lower 

 courses of the Sanyati and Panyami rivers, or the 

 country near the east coast, in the neighbourhood 

 of the Pungwe river, tse-tse flies used to move 

 about, so that in a place where they were found 

 in great numbers on a certain date, hardly any 

 would sometimes be met with in the same place 

 a month later. In my experience, in such cases 

 the tse-tse flies always moved about with the 

 buffaloes, within these areas, where all other con- 

 ditions were suitable to their existence. 



In ''fly "-infested areas where these insects are not 

 very numerous, comparatively few or possibly none 

 at all will be seen during the months of May, June, 

 and July, when the days are short and not ex- 

 cessively hot and the nights are bitterly cold. In 

 fact, it is quite possible to pass through a good deal 

 of '' fly " country during these months without ever 

 becoming aware of the existence of these insects. 

 But as the days get longer and hotter, and the 

 nights less cold, if there are any tse-tse flies in a 

 district at all they will be found to increase very 

 rapidly in numbers. They become most numerous 

 and most troublesome, I think, in October and 

 November, just before the commencement of the 



