384 MEDICAL ENTOMOLOGY 



Roubaud makes a useful distinction between those haunts of the 

 fly (termed by him gites) which are permanent and those which are 

 temporary, and divides these again into those in which the flies subsist 

 mainly on human blood, and those in which the food is derived from 

 other vertebrates, chiefly large game. In the permanent gites the 

 necessary conditions for palpalis are present the whole year round, 

 and in such places, although the cold weather retards the life processes 

 a little and renders the flies less inclined to feed, and therefore less 

 evident, they are met with uninterruptedly throughout the year. The 

 necessary conditions are to be found along the shores of the large 

 lakes, and along water courses which do not dry up in the dry season. 

 Temporary gites, as already indicated, include the large tracts of country 

 which are intersected with a network of small rivers and streams during 

 and after the rainy season. It has been shown that the flies migrate 

 from the permanent gites, which thus act as reservoirs, to the temporary 

 ones, as soon as these latter become suitable, and again return as 

 the water evaporates and the air becomes drier. Palpalis is never found 

 far from rivers and streams, as it is only in their neighbourhood that the 

 necessary degree of humidity is attained. 



The localities described by Roubaud as human gites are of special 

 interest on account of the close association which is shown between the 

 fly and its host. Such haunts usually consist of comparatively small and 

 sharply circumscribed areas, in which, in suitable weather, the flies are 

 always to be found. In the case, for instance, of a permanent river 

 flowing through forest country, the conditions are apparently favourable 

 to the fly at all points, but it is found that the great majority of the 

 individuals are collected together in those places where they are certain 

 to meet with their human hosts at regular intervals, and are thus assured 

 of a food supply. They are often, in fact, limited to the neighbourhood 

 of fords, places where water is drawn by the inhabitants, or washing and 

 bathing places, where they rest concealed in the foliage while digestion 

 is taking place, to reappear when a fresh meal is required. 



Notwithstanding that deep shade is an essential condition of their 

 existence, the flies are most active and bite most freely in sunny 



weather. On dull days they prefer to rest among the 

 Habits , . . , , . 



trees, and tew or none may be seen in places which 



they are known to frequent. This is a point of some importance, 

 as one might be tempted to assume that they are absent in any locality 

 in which they were looked for under these unfavourable conditions, 

 The behaviour of the different individuals at the human gites referred to 



