NOTES ON THE BIONOMICS OF GLOSSINA MORSITANS. 115 



trees exist and apparently correspond more or less to the areas termed " foci,'* 

 " primary centres," etc., described later in Central and East Africa. These dry 

 season haunts undoubtedly vary to a considerable extent in their efi&cacy as favour- 

 able habitats for the fly, as is indicated by the fact that some of them are intensely 

 and others little infested. The type of diy season haunt where the fly is generally 

 met with in the greatest numbers consists of a vlei, with the necessary evergreen 

 trees along at least some portion of its margin, in a part of the fly area where vleis 

 are scarce. Surface water may be present, or not, but the underground supply is 

 always much nearer the surface than in the surrounding country, with the result that 

 green grass starts growing with the warm weather long before the rains commence. 

 The green grass in the vlei, especially after the dry grass has been burnt of? and the 

 young grass has begun to grow, is intensely attractive to grass-feeding animals^ 

 which often concentrate in considerable numbers around an isolated spot of this 

 nature and move in regularly during the afternoon to feed, passing perforce through 

 the haunts of the fly in doing so. In this way the flies obtain more or less regular 

 meals and the whole conditions appear to be ideal for rapid increase during the latter 

 part of the dry season, namely, regular food, warm weather and shelter for the 

 larvae and pupae. Such centres might conveniently be termed "first grade foci.'* 

 In other parts of the fly areas rivers and vleis are much more prevalent, and intense 

 concentration of both game and fly does not occur. The dry season haunts of the 

 fly correspond, however, with the best grazing grounds at this time of the year, on 

 account of the fact that the superior underground water supply supports both ever- 

 green trees that shelter the fly and green grass that attracts the game. The term 

 " second grade foci " might be permitted in this connection. 



In other places again, the fly aflects shady forest bordering rivers, streams or dry 

 water-courses, and although not the main grounds, game has a tendency either to Ue 

 up in such situations during the day, or to pass through for the purpose of drinking. 

 In the writer's experience, wart-hog, water-buck, kudu, impala and small buck are 

 very commonly found in this type of forest during the daytime, whereas certain 

 types constitute the permanent home of bushbuck. Such spots are rarely heavily 

 infested and may be termed " third grade foci." 



It must be borne in mind that animals of all sorts seek the shade during the heat 

 of the day in hot weather, and as the fly is also dependent upon shade, fly and game 

 must in general tend to meet at the time of year when shade is restricted more readily 

 than at other times when shade, water and grass are everywhere to be found. 

 Provided, therefore, that the temperature is suitable for breeding to proceed at the 

 maximum rate, the dry season should in a general way be more favourable to the fly, 

 assuming its dependence on the larger mammals for its food supply, than the wet. 



It does not follow, however, that this is necessarily the case in particular instances. 

 Certain tracts of country dry up so thoroughly towards the end of the dry season 

 that they are deserted altogether by most species of game. As has been remarked 

 by several observers, however, wart-hog and duyker are usually to be found even 

 after the grass has been burnt ofl over a wide area. These species, especially wart- 

 hog, may serve to keep the flies from starving, but conditions cannot be said to be 

 favourable to increase. Fly under such conditions is almost invariably very hungry, 

 the proportion of the sexes caught tends to approach equality and pupae are 



