340 C. F. M. SWYNNERTON. 



It is doubtful whether brevipalpis, a relatively easily detected and easily caught 

 fly, would readily adapt itself to man. With regard to morsitans it may be said 

 that the conditions favouring its dry season centres would have to be present as 

 well as the villages. I only saw one such apparent coincidence here, but there is 

 no reason why it should not be common. The size of the human population and 

 its effect on the bush when really large are further factors to be considered. 



Of our fly areas here the " Oblong " is uninhabited and the higher Mafusi and 

 worsitans areas are not thickly inhabited. I believe it is very different on the actual 

 Lusitu, but there brevipalpis would be the fly permanently present. 



I was mysslf bitten by morsitans far less than my natives, but this was presumably 

 a matter of skin-colour and clothes ; Mabuzana, living near the Mtshanedzi south 

 of Gogoyo's, volunteered the information that tsetses were specially attracted by 

 a black coat. I said " How do you know that ? " " Because I have one ! " 



Perhaps more surprising than the preferences shown in relation to man are those 

 shown with regard to his domestic animals. I had three female native goats with 

 me throughout the trip and in about the fifth week added a male ; and until I 

 obtained cattle, about a week later still, I used these goats connnuously for bait. 

 They proved most unsatisfactory, and although they were occasionally bitten, 

 I have little hesitation in saying that even man was much preferred to them both 

 by morsitans and pallidipes and was not liked worse than they were by brevipalpis. 

 Put ahead of the cattle they failed to draw fly where the cattle would draw many, 

 A dog that was wi^b me throughout the trip and still remains healthy was relatively 

 little bitten. Healthy-looking native dogs and goats were present throughout 

 the fly-areas and were stated to be much bitten in the rains. I reguKrly fed my 

 flies on the goats and once they bit they fed fully, but a relative reluctance to bite 

 was distinctly seen, and this reluctance extended to a sheep on which I fed the flies 

 that I finally brought home with me. The relative reluctance shown by Dr. J. W. S. 

 Macfie's flies to feed on guinea-pigs, dogs and cats is worth recalling, also the 

 preference of Lloyd's flies for monkeys as against goats. 



Experiments that I carried out on Asilidae showed that those flies possess 

 graded preferences along the same lines as carnivorous vertebrate animals 

 experimented on, so that there would be nothing extraordinary in the tsetses doing 

 the same. Experiments on carnivorous animals, including lions, showed the 

 following order of preference : — (1) Pig, wild and domestic ; (2) beef (nearly equal 

 to pig) ; bushbuck and sable antelope were liked very nearly as much ; (3) goat, 

 sheep, dog, man, blue duiker. These last were liked far less than (2). It seems 

 probable from the evidence I obtained on this trip that the preferences of the 

 tsetses I had to do with would follow much the same general lines. 



Asilidae often attack the highly nauseous Acraeine butterflies and tsetses attack 

 man, but their preferences are very real nevertheless, in view of the fact that after 

 a feed they do not wait till hungry enough for Acraea or man before feeding again 

 should anything better turn up. Lloyd and others have shown, and my own 

 observations confirm them, that when there is nothing better to turn up, the fly 

 will at last " occur in such quantities " — ^that is to man — "as to be a source of 

 the greatest annoyance " (Maugham). At Kanyezi's vleis, with some game about 



