THE TSETSE PROBLEM IN NORTH MOSSURISE. 341 



but buffalos absent, we saw a good deal of fly and were often attacked by '" feeders " 

 (as distinguished from " followers "). In the Masando vleis in 1900 with game 

 temporarily very scarce and buffalos absent I was very greatly pestered. This 

 time, in the same Masando vleis, with buffalos present, I found few flies, and at a 

 series of vleis a few miles further east which the buffalos had just reached in numbers 

 I found none, though the natives stated that they had been there in great quantities 

 up till then. At first at these places I had not the cattle, and it was legitimate to 

 suppose, as the natives did, and it was doubtless true of the males, that the tsetses 

 were " away following the game." But the female fly is a feeder, and apparently 

 follows little, and the cattle quickly showed that flies were present, but that they 

 were being kept too well fed to show themselves to less acceptable man. 



It is easy, understanding the working of the fly's preferences,, to see that a failure 

 to find non-mammalian blood in an examination of its blood-contents is quite 

 compatible with the possibility that it might live on birds and reptiles were mam- 

 mals removed. 



It folloAvs also from my observations on this expedition that the old idea that 

 tsetses possess a preference for the buffalo may be perfectly correct, though it will 

 show itself strongly only where, and while, buffalos are so abundant as to make 

 the fly comparatively independent of less favoured food. The special enthusiasm 

 I saw shown for an actual congener of the buffalo seems to be highly significant 

 in this connection. 



Unfortunately there would seem to be no very practical method of utilizing the 

 flies' preferences except by using cattle to draw them out. With its favourit-es 

 destroyed it will live well on the next best and so on. Arsenic-tolerant cattle, 

 sufficiently saturated, might be worth experimenting with as bait. 



Drinking of Water by Tsetses. 



My flies frequently applied their proboscides to grass-stems put into the tube 

 wet (to simulate the effect of dew), never to those inserted dry. My native 

 informants on the Umvuazi agreed in asserting that they frequently saw tsetses in 

 numbers " drinking " on the wet sand of the river in very hot weather. I have 

 ^vatched Tabanus on the wet mud of pig wallows at the Amanzimhlope head- waters 

 with its proboscis in definite contact with the moisture, as were those of non-biting 

 Muscid flies of several species that were also present, and this habit of drinking 

 is a common one in hot weather on the part of both Diptera and butterflies. King- 

 horn and Lloyd have both noticed tsetses at the edges of puddles ; Moiser obtained 

 records of it from his natives, and saw his captive flies insert their proboscides into 

 the wet soil of thfeir bottles ; and Lloyd obtained the same result from moistened 

 sponge and moistened blotting paper that I obtained from wet grass. Carpenter 

 has gone further, for he has traced the presence of the liquid inside the fly. The 

 point is not merely of importance in relation to the hot- weather needs of the fly ; 

 it may also be important, it seems to me, in relation to the possibility of poisoning 

 the highly localised male swarms of G. morsitans by spraying the grass they rest on. 



Lloyd's positive results from slices of water-melon go to confirm Maugham's obser- 

 vations (under natural conditions) as to the sucking of vegetable juices. It is probably 

 moisture rather than real nourishment that would thus be sought and obtained. 



