THE TSETSE PROBLEM IN NORTH MOSSURISE. 379 



Assistance to Natural Enemies. 



Natives destroy great numbers of birds, in both the adult and nestling stages, 

 but I fear it would be impossible to make protection effective. It perhaps matters 

 less here, as the native population is in parts not great and in the " Oblong " it 

 is almost non-existent. The same difficulty applies to elephant-shrews which 

 are greatly trapped. It is a pity that these useful animals cannot be protected, 

 the more so as they are put to death in a peculiarly cruel manner. 



Rewards for the skulls of small carnivora brought in might be useful in better 

 populated fly areas, probably not here. There would in any case be a doubt whether 

 the natives, who trap freely for these animals already as articles of food, could be 

 stimulated very much more by a prospective reward. The greatest enemies of 

 nestling birds here are the tree-snakes (Dispholidus) and probably the only effective 

 remedy against these lies in severer fires. 



Indirect assistance to birds would take the form of destroying trees, etc., the bark 

 of which is specially protective to the tsetses. This method is inapplicable to 

 morsitans and pallidipes because so large a proportion of the trees in Brachystegia 

 bush have suitable bark, grey and somewhat charred, that wholesale clearing would 

 be necessary. In a brevipalpis area the destruction of Diplorhynchus mossmrdyicensis 

 and all rough barked lianas would probably be distinctly useful and should form an 

 essential part of any band-clearing scheme ; not but what other species I could 

 specify are of probable use to this fly in varying but usually less degree. 



Protection of Stocic and Riding Animals passing through Fly. 



I have already described my clearing in this connection (p. 374). In addition I 

 found that very frequently the. animals were not attacked if the carriers 

 were walking immediately ahead of them, without an interval. I sometimes 

 walked at the head of the carriers myself and then noted flies (brevipalpis) coming 

 out to me and turning back — ^rejection, evidently, after inspection. 



Again, when I divided the cattle into two lots (two in front, one after an interval 

 behind — I never had more than three) I found that the first lot drew off all the fly, the 

 last animal commonly getting none. 



In the following experiment both these principles were called in. I wished to 

 protect a donkey in passing through the heavily infested three mile strip foUowing 

 the Inyamarimu. I placed two oxen in front ; the four goats followed them at from 

 forty to eighty yards behind ; then (just behind) came myself and a native, then the 

 donkey with its rider, a native walking in each side of it and one behind ; next, at 

 some distance, came a cow. The oxen both carried fly all the way and were some- 

 times assailed by many ; the goats' driver captured a brevipalpis on himself, but the 

 goats escaped entirely ; one only came to the cow. On emerging from the dangerous 

 bush, the oxen were turned sharply into the grass and took their flies with them, the 

 other animals, which now passed ahead, getting none. The control experiment, 

 if such were needed, had been provided two days before when, on the same path, the 

 donkey was sent on a detour to avoid a bad bit of forest. It ran into a thicket and 

 sustained quite an attack and had to be brought back behind the cattle. 



This suggests that a mob of cattle might be protected in travelling by placing the 

 less valuable animals a little ahead. NaturaUy a mob of cattle is a bigger mark 

 (737) K 



