356 C. F. M. SWYNNERTON. ^ 



for a considerable distance. As one walks each, male moves on in front of one for 

 at most a few feet, evidently scanning the walker for any females that may be with 

 him, then falls behind. At one time when a domestic matter called me home from 

 the Buzi, my police boy, left in charge of the work, captured no less than 88 of these 

 flies, every one a male, on three successive evenings without the aid of cattle along 

 the same stretch of path. The path, here passed alternately through bush suitable 

 to brevipalpis and more open spaces. On emerging into the latter one ceased to 

 see flies ; on entering bush further on one found them in the path. This was a little 

 curious seeing that it was after sunset and rather suggested that they had not come 

 far. 



The males of G. morsitans, though occasionally seen like this on game paths, 

 were found mostly crowded together in the short grass beside the path — some of 

 them on the path— and were also (as events each time fully proved) watching for 

 females or carriers to take them to the females. G. morsitans usually waited in 

 a crowd, brevipalpis always in a queue. 



Travelling Habits. 



G. morsitans utilises man as a carrier far more freely than the big fly does, and 

 as these followers occasionally bite, they would give an unobservant person the 

 impression of persistent attacks by large numbers of tsefcse. Ifc is, actually, nothing 

 of the kind, but, in essence, a ride in search of females. This is mosfc clearly seen 

 when the flies are few and on the back of the person in fronb. I have watched 

 male flies, each with its station on a particular spot on the back of my guide, travel 

 thus for miles. They would keep taking short flights off all the time and at once 

 return to their previous station. Whenever I saw the object of the flight it was 

 another fly, and the fact that the flights were in search of females was sometimes 

 proved by a witnessed pairing. 



That these rides on man would be useful even where the females were nob feeding 

 on man was supported by the many instances I saw in which flies came out to us 

 and turned back, evidentally rejecting us. (These observations were on brevipalpis.) 



Where I have walked slowly the tsetses {jnorsitans) have some times contented 

 themselves with moving along in the grass beside me. More often they — or some 

 of them — attached themselves to me when I was moving and each time I stopped 

 dropped to the grass again till a movement showed it was time to start. There 

 can be little doubt that when on the grass they watched for females coming to me, 

 for such females were at once assailed. The low position adopted by the tsetses 

 during these waits was doubtless of considerable use in showing them the females 

 against the sky, and in helping them to detect and keep in touch with moving 

 objects generally. Flies that had flown ofl: a man's back to accost another fly 

 always returned flying very low and rose to his back. The principle is that of 

 the nightjar or of the man who stoops to watch crepuscular insects or birds. These 

 clusters of male flies varied greatly from day to day in numbers and position, 

 reductions definitely resulting both from the depredations of birds and from the 

 flies attaching themselves to passers by. With buftalos present the clusters 

 practically became non-existent. They always tended to form again later, but 

 were not always composed of the same individuals, for experiments with marked 



