THE TSETSE PROBLEM IN NORTH MOSSURISE. 357 



flies showed that these reappeared in other clusters than those in which they were 

 marked ; and the immense preponderance of unmarked flies in clusters that I had 

 taken pains to mark pretty fully suggested that they were being kept up not merely 

 by arrivals brought from elsewhere and from males that had probably been resting, 

 but by new emergences in the neighbourhood, such as were actually noted in searching 

 for pu})ae. In each case active breeding centres and clusters were never found 

 otherwise than in more or less close contiguity. 



There was a certain amount of day-to-day movement on the part of some of 

 these clusters as a whole, but it was gradual. The one nearest my Kanyezi camp 

 was very stationary, its movements being mere fluctuations, and after a three 

 weeks absence I was able to find both this and the other clusters almost where I 

 had left them and to retake in them a few of my marked flies. 



Males of brevipalpis waiting on game paths were frequently tempted to attach 

 themselves to the cattle and would then often ride for quite a distance. Sometimes 

 they fell behind them, as they fell behind ourselves, probably because they found 

 that they carried no females. 



I measured one of these rides by five male brevipalpis in dull weather, first marking 

 each of them with a dab of white paint. The flies had come to us just before and 

 were following, not feeding. The greatest distance travelled was 5J miles by the 

 one fly that stayed to the end. All five flies were still present at 4 miles and 700 

 yards. Every kind of country was traversed, hrevijoalpis bush, simple coppice 

 -and open grass. 



The flies deserted us on our getting back into their native bush. Elsewhere 

 where brevipalpis had followed us into the open in the daytime it waited before 

 leaving us until it had reached suitable bush, and an individual that once followed 

 far to a camp in the open stayed about for hours (in the evening) before disappearing. 

 All this was interesting in relation to the explanation of outbreaks of nagana in 

 which it appeared that the fly had crossed much open country to bush — patches 

 in the grazing grounds or near a kraal. 



I tested similarly the d'-:tance to which morsitans will follow man. Twice I 

 obtained rather more than six miles, and many times various less, but still long, 

 distances. On one occasion a journey of over six miles was done in three instalments 

 by a marked fly on three successive days. The riders were almost always inter- 

 rupted by reaching, sooner or later, another clump of male flies into which the male 

 riders then disappeared. Otherwise, and with more time to experiment, the rides 

 might well have been much longer, and Bevan (I think) has recorded an observation 

 of Meikle's in which tsetses were still on his cattle 25 miles outside the fly-belt. 

 A common position was on the load of a native carrier. 



In the foregoing experiments and observations the flies that really travelled 

 were invariably the males (marked with a diflerent colour), and it was these only 

 in the case of 'inorsitans and pallidipes that had up to the time of my departure 

 put in an appearance at villages a few miles outside the breeding centre in which 

 they were both captured and released. Hungry flies, including, so far as I saw, 

 all females, came to feed, not follow, and the longest distance travelled in an 

 experiment in which I released a considerable number of hungry marked brevipalpis 



