342 C. F. M. SWYNNERTON. 



IX — ^Distributors of the Fly. 



Game not only helps (a) to feed the fly, and (6) to provide the trypanosonie, 

 but (c) it helps to distribute the fly, carrying it back each summer into the areas. 

 from which the fall of leaf had driven it. 



That the fly does definitely spread at each rainy season, over the latter type of 

 area is shown by native statements, by nagana outbreaks, and by my finding in the 

 highly deciduous country a mudstained pupa-case of G. brevipalpis, one of our 

 most shade-loving tsetses. That the fly wanders back into these areas partly 

 without the aid of game is possible enough ; but without their aid I doubt if it 

 would have re-occupied much country by the time the leaf fell again. The tsetse 

 is a distinctly sedentary insect, and throughout reminded me much of a tick, 

 excelling it mainly in flying a little distance to its prey instead of waiting to be 

 brushed off by it. This, with the details of some of the outbreaks of trypanosomiasis,, 

 the fact that tsetses actually do follow animals for long distances, and the cogent 

 indirect evidence I shall refer to on page 358, support the view that the game is 

 of the first importance to the redistribution of the fly. 



Accepting the hypothesis, the most important point to note is that the fly's 

 chief distributors will be by no means necessarily identical, in a given area, with 

 its chief food animals. The individuals, pairs or herds of most of our antelopes 

 have definite circumscribed haunts and grazing grounds that they keep to. In 

 the case of bushbucks and duikers these are small, and parties of pigs also for long 

 periods together rootle and depredate from particular lairs or lair-areas. Harte- 

 beests also have relatively small beats, and herds of sable antelope and kudu have 

 their permanent grazing grounds, larger than these others, though the kudu is 

 sometimes a wanderer. Animals with this localised habit may be regarded as 

 the fly's most reliable food-supply in its permanent haunts, even though some 

 other animal may temporarily become more important through sheer numbers. 



Elands, on the contrary, are great w^anderers ; elephants cover much ground ; 

 and the buffalo, if it is on the whole less of a wanderer individually, and in the matter 

 of long purposeful " treks " than the eland, nevertheless covers, with its great 

 herds, very large grazing grounds, is continually wandering back and forth between 

 its various centres inside and out of the permanent fly-areas, and breaks up into 

 parties and individuals that, to judge from the spoor, leave little ground in the 

 general range unvisited in the rainy season. Also, as I shall show elsewhere, the 

 buffalo more than any other animal has been increasing its numbers and range 

 here at a great rate for many years past. 



I believe then that these animals, and the buffalo in particular, are mainly res> 

 ponsible for the annual spread of the fly, and that so far as we are concerned, in 

 and near Mossurise, our main grievance against the game is not so much that it 

 feeds the fly (which would be fed and contaminated in any case by the pigs) but 

 that it carries it far and wide in the rainy season and so brings it into contact with 

 the cattle. 



The effect of the difference in the travelling habits of the male and female flie& 

 must of course be duly taken into account. 



