320 SLEEPING SICKNESS [CH. 



large scale, whole tracts of country have been deforested, and 

 in consequence, the streams have dried up and the tsetse-flies 

 have disappeared. 



The destruction of animals on which the flies feed is a 

 proposal that needs very careful examination. Koch advocated 

 the destruction of the crocodile, but as mentioned above 

 (p. 264) it is very doubtful whether this scheme would be of 

 much use, and the available evidence is decidedly against it. 

 The destruction of the big game is not likely to affect the 

 numbers of G. palp alls, for it rarely feeds on these animals, as 

 they mostly come to the water at early morning or late evening, 

 when the flies are not about. The main food supply of this 

 insect has not yet been satisfactorily decided. 



Minchin has suggested the introduction of jungle-fowl, 

 which might scratch up the pupae and devour them, but it is 

 possible that the birds might find plenty of other food. In 

 any case the experiment might be tried, for at present we know 

 very few enemies of this redoubtable insect. A knowledge of 

 the insectivorous birds that prey upon the tsetse-fly is much 

 to be desired, for we are almost in complete ignorance of this 

 subject. 



With regard to the collection or destruction of the pupae or 

 of the flies themselves, there is little hope of any considerable 

 reduction in numbers being effected by these means. Dr Bal- 

 four is of the opinion that fly-traps might be of some use and 

 mentions an incident in support of this view. In the Sudan 

 occurs a limited fly -belt, about twenty miles long and three or 

 four miles in breadth. The fly is G. morsitans which in this 

 locality haunts the neighbourhood of wells. ' This limited and 

 peculiar distribution is said by the natives to be due to the fact 

 that the fly was intentionally brought here from the river for 

 purposes of revenge ! This may or may not be true, . . . but 

 certain it is that at the present time the natives trap the fly in 

 gourds containing blood as a bait, and then liberate them in 

 spots where the cattle or horses of their enemies are grazing or 

 are collected together. The trap is a spherical gourd with a 

 hole cut in the top. It is half-filled with blood, and carefully 

 watched. As soon as a number of flies have entered it in quest 



