104 



small surviving herds of game well-nigh confined themselves to one 

 locality " the Tsanjoka Marsh, some ten miles south of Domira Bay " 

 and during this period this was the only spot where G. morsitans 

 was to be found. 



From about 1904, however, when the animals began again to increase 

 in numbers, the game " commenced to scatter over a wider area of forest, 

 and gradually returned to their old haunts over the greater part of the 

 forest. The fly, which had been strictly limited for six or eight years 

 to the Tsanjoka Marsh, spread concurrently with the game." Dr. 

 Murray adds : " The foregoing account of the diminution and spread 

 of tsetse-fly over a comparatively small section of the lake shore forest 

 serves as an example of the close connection between the movements 

 of game and tsetse-fly over the whole Nyasaland fly area. This, of 

 course, only applies to the low-lying parts of that forest, as beyond an 

 altitude of 3,000 ft. tsetse-fly was rarely found in Nyasaland, even 

 though game was abundant in otherwise suitable country." However, 

 Dr. George Prentice, of Kasunga, N'gara, Nyasaland, in a letter dated 

 7th May 1921 an extract from which is published on p. 139 of the 

 number of the journal containing Dr. Murray's communication reports 

 an outbreak of sleeping sickness in two villages on the Lingadzi River, 

 " at an altitude of just 3,500 ft." Dr. Prentice also states that " with 

 the cessation of free shooting in this area there is a very rapid advance of 

 tsetse, and herds of cattle are going down before it, kraals being cleared." 



The agency of big game in distributing and extending the range of 

 G. morsitans, though affirmed, as we have seen, by writers such as 

 Swynnerton and Murray (see p. 101 and supra), is disputed in a recent 

 paper by Jack (75), who, as the result of experience gained in Southern 

 Rhodesia, expresses himself as extremely sceptical concerning this 

 fly's alleged habit of migrating with game. During ten years' investi- 

 gations, Jack has found no tendency on the part of the fly to migrate 

 under the stimulus of hunger or in company with game. There is, 

 however, always the seasonal scattering during the wet season, and 

 sometimes there are forced movements induced by the destruction of the 

 forest ; in the latter case the fly naturally follows the retreating shade. 



There has been a fairly generally accepted idea that G. morsitans 

 locates game, and follows its movements more or less continuously, at 

 least within the limits of infested country, but Jack attempts to show 

 that this is not its general habit. Indications against the theory are 

 that female flies are apparently not known to follow to any great 

 distance at any time ; that gravid females seek seclusion and are not 

 likely to attempt to follow a moving herd ; that hungry flies tend to 

 feed fully and then abandon their hosts, which are unlikely to remain 

 in the vicinity until the flies recover ; and that the fly is diurnal in 

 habit, while game moves largely at night. It would seem, therefore, 

 that the only individuals capable of following game, even for a few hours, 

 are those that do not desire to feed. According to Jack, the probability 

 is that the fly neither ranges the forest in search of its host, nor follows 

 it when encountered for any length of time, but that it lies in ambush, 

 waiting for the animal to come within range of its perceptive powers. 

 The maximum distance at which a hungry fly readily detects its hosts 

 is a short one, possibly less than 100 yds., and following on the part of 

 females has only been proved up to about 400 yds. ; the maximum 

 following distance in the case of this sex remains to be determined. 

 Jack is not yet convinced that the females seek animals and human 

 beings only for the purpose of feeding, though this appears probable. 



The reader, who has taken the trouble to study carefully the whole 

 cf the statements printed in this chapter with reference to relations 



