50 



or less everywhere with that of the wide expanse of Katanga " orchard 

 bush/' Bush fires, however, modify for the time being the limits of 

 the G. morsitans area, by causing a true temporary migration of the 

 insect. Thus, after the bush to the east of Katompe is burnt in the 

 middle of the dry season, the fly invades the station in fairly large 

 numbers, and may even be seen from two to five kilometres to the 

 west of it, although its ordinary boundary lies a few kilometres to the 

 east of the settlement. 



Some recently published observations by Dr. Roubaud (I23a) on the 

 habitats of G. morsitans in French West Africa are of sufficient 

 importance to be worth quoting in extenso. "In G. morsitans," writes 

 the distinguished French authority, " we have a true savannah fly, 

 which is most often to be found among tall grass or bush far from 

 sheets of water. It is a species that loves dry places (espece xerophile)i 

 and is met with in the sparsely covered savannah-park, sometimes even 

 amidst the thorn-scrub of the zone bordering on the Sahara (zone 

 sahelienne). The presence of watercourses, at least in the period 

 following the winter season, appears to be a matter of indifference to 

 it, and it may frequently be observed resting on the ground or on 

 herbage a long distance from water of any kind. When, however, the 

 drought becomes excessive, the fly returns to the vicinity of streams, 

 which it henceforth does not leave to any great extent. 



" Of all species of Tsetse-flies, G. morsitans is the one most readily 

 noticed on entering a zone frequented by it. Here it is generally in 

 great abundance, and, flying openly along the tracks and paths, it 

 assails the traveller in dense swarms, which accompany him as he 

 proceeds. It is more especially this habit of collecting together in 

 large numbers, which is so entirely characteristic of the species, that 

 gave rise to the, nowadays classic, English term fly-belts. 



" The study of the physiological peculiarities of this Tsetse-fly serves 

 to explain very clearly the peculiarities of its habitat. A high degree 

 of atmospheric humidity is inimical to it ; when subjected to the action 

 of air completely saturated with moisture it speedily succumbs, 

 whereas G. palpalis and G. tachinoides are capable of resisting similar 

 hygrometric conditions for a long time, even in a confined space. 

 Conversely, G. morsitans can be kept for a long period in a medium 

 of which the hygrometric index is below 35 per cent., although such a 

 medium is rapidly fatal to the two moisture-loving species referred to. 

 Lastly, though the absolute capacity for resistance to heat displayed by 

 G. morsitans is perhaps not quite so great as that of G. tachinoides, 

 the former is able to support a daily mean temperature exceeding 

 32 C. [89-6 F.] ; and, as has been observed in the scantily covered 

 savannahs frequented by this species, it resists thermic variations 

 which may reach 40 C. [104 F.] at extreme temperatures. 



" More even than G. tachinoides and G. longipalpis, which are 

 ' wild ' species having no habitual connection with man, G. morsitans 

 is, par excellence, the big game fly. All the savannahs in which it is 

 met with are sparsely populated but remarkably rich in game : e.g., 

 the contiguous plains of Upper Gambia and Guinea, the Niom region 

 in Saloum, the north of Dahomey in the vicinity of Western Nigeria, 

 etc. The presence of the large wild mammals in abundance seems 

 indeed to be the principal factor upon which the occurrence of this fly 

 in a given region depends. 1 Many tracts of savannah in the Guinea 



1 Cf. G. Bouet and E. Roubaud, " Trypanosomiases et Glossines de la Haute- 

 Gambie et de la Casamance." Bull. Soc. Path. Exot., Paris, t. v. (1912). 



