﻿INSECTS OF EASTERN TROPICAL AFRICA. 301 



On the vexed question of the relations of G. morsitans with game, there is, as 

 might be expected, much conflict of evidence, more particularly as on this subject 

 opinions are very apt to be somewhat biassed. Six gentlemen are of the opinion 

 that this species is entirely dependent upon the presence of big game. The. view 

 of eight others however is precisely the opposite, whilst three are of opinion that 

 the fly is only partially dependent upon the larger mammals. It must be 

 admitted that the majority of the more experienced observers group themselves 

 amongst those who believe that G. morsitans can, and indeed does, exist in the 

 absence of the larger mammalia. The importance of this point is increased by 

 the fact that it agrees with the recently published views of men of such great 

 practical experience as Major J. Stevenson Hamilton and Mr. R. B. Woosnam. 



There is however a remarkable unanimity of opinion in the answers as to the 

 spread of G. morsitans in recent years in Northern Rhodesia and Nyasaland, 

 practically all observers, with the important exception of Sir Alfred Sharpe, 

 agreeing that this has been the case. Some gentlemen associate this spread with 

 the increase and scattering of big game ; others, Messrs. Fraser, Manning and 

 van Schalkwijk, with the movements of natives. Mr. Thornicroft notes a special 

 increase along main roads. Amongst the few people who were in the country 

 when the rinderpest swept through it, there is an agreement that the fly 

 disappeared to a large extent about this time. This is an important point in 

 respect of the above-mentioned spread of the insect, since only one observer, 

 Dr. Prentice, even suggests that the fly has now spread to an area where it did 

 not occur previous to the rinderpest. Five gentlemen, Messrs. Brown, Edwards, 

 Barrington, Manning and Young, refer to the disappearance or reduction in 

 numbers of the insect with the advent of natives and the consequent clearings in 

 the neighbourhood of villages. 



In respect of my own personal experience and observations of Glossina morsitans^ 

 I am of opinion that among the essential factors which determine the distribution 

 of this species, are a combination of the presence of such vegetation as will pro- 

 vide moderate but not excessive cover, coupled with a hot and moderately or even 

 very dry climate. This, it is true, does not explain the sometimes marked 

 definition of a fly-area without apparent change in the conditions, a point on 

 which we still appear to be as much in the dark as ever. It does however explain 

 to some extent the difficulty of defining the character of the country in which the 

 fly occurs, when extensive regions are considered, since a considerable variation 

 in the two factors of vegetation and climate might produce the required medium. 

 In many parts of Southern Africa the actual amount of cover required is not 

 excessive, though probably a limited amount of trees, bush or at least thin scrub 

 is necessary. Personally, I am of opinion that, at least for the adult fly, long- 

 grass itself would provide sufficient cover, but for the fact that this type of 

 country is burnt clear during the dry season practically every year. That 

 G. morsitans inhabits open grass country has been denied by many observers, but 

 it must be remembered that the great majority of Europeans do most of their 

 travelling in the bush during the dry season when the grass is burnt. I have on 

 several occasions, particularly in Northern lihodesia, noted that when the grass 

 is long (not less than four feet) G. morsitans is inclined to be more numerous in 

 grassy areas of limited size than in the woodland or bush-covered country 



