16 SEASONAL PEEVALENCE. 



was not in his district, and pointed to a heifer and some goats, 

 which he said he intended to send away before the fly season 

 came on." Our information on this point, however, is as yet 

 very scanty, and to a certain extent conflicting. It was found 

 by Harris [5] that the fly infested the Mural Berge, in the north 

 of the Transvaal, especially during the rainy season ; and Mr. 

 and Mrs. Petherick [37] were informed that at the same period 

 of the year a certain kraal in the country of the Rhol tribe, to 

 the north-west of Gondokoro, was untenable owing to the pre- 

 sence of Tsetse. According to Chapman [30], the Tsetse " often 

 moves about " with the bufialo in the rainy season ; but the same 

 writer subsequently states that " heavy rains are said to kill 

 the fly in the season when they prevail." Kirk [28] tells us that 

 Tsetse are " most numerous and troublesome in the hot sultry 

 weather before rains ;" while Mr. F. J. Jackson [II9], speaking 

 of East Africa, says that, " where it exists," the fly " appears in 

 much greater numbers on a dull or rainy day." It should be 

 noted that in South Africa, at any rate, the rains fall in the 

 summer, the winter being the dry season. It is therefore curious, 

 especially in view of the evidence already adduced, to find that 

 Dr. Bradshaw [77], writing of the fly-belt on the south bank of 

 the Zambesi and Chobe, states that the Tsetse " is much more 

 plentiful during the winter months, namely, from April to end of 

 September, than during the summer " ; while, on the other hand; 

 Selous, referring to the Batonga country between the Zongwe 

 River and the Zambesi in June (mid-winter), says that Tsetse 

 were " pretty numerous, and must be very much so later on 

 during the hot months." Bradshaw, however, is supported by 

 an experience of Dr. Holub, who on the Mo-Njeko River, on 

 August 7th, 1886, found Tsetse more abundant than he had 

 ever seen them before. 



The first of Colonel Bruce's suggestions for future work on 

 f Tsetse-fly disease * is — " That all trustworthy information regard- 

 ing seasonal prevalence [of Nagana] be collected " : it will have 

 been seen from the foregoing statements that " trustworthy 

 information " as to the seasonal prevalence of Tsetse-flies them- 

 selves is ecjually necessary. 



Period of the day at ^he Tsetse, Hke other day-flying insects, does 

 which Tsetse-flies not begin to be active until the sun grows 

 are most active. j^^^ Livingstone [21] states that it is " re- 

 markably alert, avoiding most dexterously all attempts to captui-e 

 * C/. Chapter VII., Appendix A, p. 286. 



