THE TSETSE PROBLEM IN NORTH MOSSURISE. 367 



brown grooves and this was at 3-4 feet from the ground. Below this area the bark 

 was uniformly black, above it rather more uniformly pale end uncharred. The 

 females also settled, the colours being right, mainly on the lower side of a branch 

 or log, the males settling as frequently on the upper sides, A raised stone and 

 clods of earth were also used for resting under in the brevipalpis experimint. Leaves 

 and thiu twigs were used by active, not resting flies ; these flies were readily dis- 

 turbed. The majority of the brevipalpis remained quiet during the heat of the 

 day, but began to move freely and to buzz against the gauze at sunset. It was 

 then chiefly that this fly, including its females, settled appreciably on non-protective 

 surfaces — Cleaves and twigs, etc. Those definitely at rest on protective surfaces 

 on the other hand, or in holes, were hard to flush, some (females, and particularly 

 more or less gravid or replete females) even allowing me to tap on the bark beside 

 them. The excellence of their concealment was shown when I finally cleared the 

 net. Both I and two smart natives searched every inch of its contents most tho- 

 roughly, as we thought, until we could not find another fly. I then passed my 

 hand over the various surfaces and in this way flushed four more flies, all fem^ les, 

 from the Diplorhynchus trunk. It would seem that Bagshawe's suggestion — ^that fly 

 does not haunt shady papyrus on account of the contrast in coloration — may well 

 be correct. 



A certain number of flies were generally to be found on the net and restless ; 

 these were always males. When the net was cleared and the flies examined one 

 by one this observation was fully confirmed. The hiding flies were mostly, but 

 by no means entirely, females. From my observations in the field also, it seemed 

 €lear that in Glossina, as in so many other animals, the female trusts mainly to 

 concealment for defence against enemies, the male more largely to activity, and 

 that the difference in the requirements of the sexes and their methods of meeting 

 them is the chief reason for the female's special seclusion, though Lambom's factor 

 (avoidance of males) may be operative also. The smallness of the meals usually 

 taken by the males in the field — commonly mere snacks — ^bore a relation no doubt 

 to their need for activity ; not so much to relation to enemies, for the male flies 

 were quite capable of hiding, if necessary, but in relation to tr? veiling and the cap- 

 ture of females. It seems certain also that the males need for food must be far 

 smaller than that of the female. The results generally suggested the consideration 

 of a contributory method of fighting the fly which I shall refer to below (p. 379). 



Distance of Attack. 



Another point tested was the distance from which brevipalpis and pallidipes 

 will attack passing animals. It was undertaken at the end of my stay and I was 

 unlucky in the matter of wind, light variable airs prevailing during the main 

 experiment. However, rushes to the side of the net next the cattle occurred at 

 6 and 8 yards distance, and once, just before sunrise, at 18 yards, the shrub growth 

 that blocked the view on this occasion showing clearly that it was a matter of 

 scent. When the net was to windward of the cattle no general excitement took 

 place, though a very few flies might fly towards them. The short distance from which 

 attacks by brevipalpis took place in the sunny hours was illustrated in my clearing 



