49 



according to Sir Alfred Sharpe, G. morsitans is ' seldom found above 

 3,000 ft.' 1 



" The idea, formerly generally entertained, that G. morsitans 

 ' appears to avoid the presence of man, and is rarely found in the vicinity 

 of human habitations, or within the confines of a town or other settle- 

 ment,' is only partially true, since native villages in areas in which this 

 species occurs are often infested by the fly." 2 



Since the publication of Austen's " Handbook " in 1911, a consider- 

 able number of investigations have been made with reference to the 

 areas in which Glossina morsitans is found. It is impossible for us 

 to summarise them all, but we give below a short epitome of the 

 conclusions that may be drawn from two series of important researches 

 carried out respectively in Northern and Southern Rhodesia by Messrs. 

 LI. Lloyd and R. W. Jack. It is clear that these conclusions have 

 special reference to Rhodesia. 



1. In the course of the dry season, water remaining in certain spots 

 (rivers and pools) favours the growth of species of trees different from 

 those in the surrounding bush, and enables others to retain their leaves. 

 G. morsitans, therefore, being especially partial to cover, assembles in 

 winter (the dry season) in these spots, which then form well-defined 

 tracts, or, in other words, "fly-belts." This concentration appears to 

 be in no way due to the attraction of water, since, as we have already 

 seen, it has been found in many localities that the fly shows, if anything, 

 a repugnance to the immediate vicinity of rivers. In Southern 

 Rhodesia, according to Jack (75), the type of haunt where G. morsitans 

 is most numerous in the dry season consists of isolated areas of low 

 lying grassland, with evergreen trees along at least some portion of 

 its margin ; here the grass-feeding animals concentrate in large numbers 

 and provide an ample food -supply. 



2. Before or after the dry season fly-belts are much less sharply 

 defined. During and immediately subsequent to the rains, G. morsitans 

 is much more generally distributed throughout the surrounding bush, 

 the trees in which are then covered with leaves and provide the 

 necessary shade. 



3. G. morsitans is concentrated in certain tracts, and its extension 

 towards fresh districts appears to take place very slowly, and to be 

 due to pressure of numbers Thus it is by no means found in every 

 suitable locality. 



4. Fly-belts do not appear to be characterised by geological forma- 

 tion, a peculiar physical aspect of the soil, or a special type of vegetation. 

 Nevertheless G. morsitans avoids places where the vegetation is either 

 impenetrable or insufficient to ensure the shade that it requires. 



As regards Belgian Congo, according to Dr. Schwetz (132), the 

 north-western boundary of the great G. morsitans zone coincides more 



1 Dr. S. A. Neave (103) writes : " The limit of elevation at which G. morsitans 

 occurs in Nyasaland would appear to be about 3,000 ft. In Northern Rhodesia 

 "I have never met with it myself at over about 4,200 ft., though it is said to have 

 been taken at somewhat greater elevations. This difference may perhaps be 

 accounted for by the fact that Northern Rhodesia has on the whole a somewhat 

 drier climate than Nyasaland." 



2 " With regard to the relations of this species with man, though, as is well 

 known, it bites man readily, I think it is doubtful whether it has any preference for 



him as compared with other mammals I am in complete agreement 



with the views expressed by Sir Alfred Sharpe and others that it is the cleared and 

 cultivated area that usually surrounds native villages which is the deterrent, 

 and not the actual human habitations or their accompaniments " (Dr. S. A. 

 Neave, 103). 



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