IN THE ILORIN PHOVINCE OE NORTHERN NIGERIA. 11 



regions at all times. Now many of those areas, thus permanently or inter- 

 mittently avoided, appear, to the cursory observer, ideal cattle countries ; but 

 their long experience has taught those people that, if they do not act as 

 described, their cattle will die. They believe that in the regions avoided the 

 water is either permanently or intermittently poisonous. . . . Investigation 

 invariably shows that the water itself is not poisonous, but is haunted by tsetse- 

 fiies." The eastern division of Ilorin province is one of the areas shunned at all 

 times, although the country appears to afford excellent grazing grounds ; and 

 this is doubtless due, as Dr. Blair points out, to the presence of tsetses. But I 

 have already stated that tsetses haunt practically every stream in the western 

 division, and that nevertheless cattle are abundant. There is, however, one 

 great difference between the two districts : whereas G. submorsitans occurs all 

 over the eastern division, it is apparently completely absent from the western ; 

 and this being so, I think the assumption is reasonable that it is this species that 

 is inimical to live-stock. If further proof be necessary, it is furnished by the 

 fact that the one district in the eastern division in which cattle are kept is the 

 only one in which G. submorsitans has not been found. 



The Southern Division. 



The southern or Offa division of the province has been less thoroughly surveyed 

 for tsetse-flies than either of the other two, and the tour on which most of the 

 entries on the map are based was made in September, a very wet month, when 

 circumstances were unfavourable for collecting. Nevertheless the 79 collections 

 were obtained from localities fairly evenly distributed over the whole division, 

 and are probably representative. The only tsetses taken were G. palpalis and 

 G. tachinoides. G. palpalis appears to be distributed over the whole division, 

 and G. tachinoides, although caught at only a few places, may be more widely 

 distributed, at any rate in the western districts, than is indicated on the map. 

 The vegetation in this division, however, is less open than in the western division, 

 and resembles the typical habitat of G. palpalis more closely than that of G. tachi- 

 noides. It has been pointed out by Roubaud* that, in West Africa, G. palpalis 

 is gradually replaced by G. tachinoides as an advance is made inland beyond the 

 forest belts. In this respect the province of Ilorin would seem to cover the 

 intermediate zone, G. palpalis predominating in the southern division, but 

 occurring in approximately equal proportions with G. tachinoides a little further 

 north, in the western and eastern divisions. 



The most remarkable feature of the survey is the apparent absence of G. sub- 

 morsitans, a species which occurs in large numbers in the southern part of the 

 eastern division. It is possible, of course, that the fly may have been overlooked ; 

 but it is improbable that no single specimen should have been taken if the species 

 is at all common. From the fact that Fulani cattle are not taken to graze in the 

 southern and eastern parts of the division it was anticipated that G. submorsitans 

 would have been found ; and, if it is really absent, some other explanation than 

 the presence of this fly must be given to account for the fact that the greater 

 part of the region is shunned by herdsmen. 



# Comptes Rendus de l'Academie des Sciences, 2nd Oct. 1911. 



