﻿58 DR. ROBERT E. MCCONNELL — NOTES ON THE OCCURRENCE 



On the Nile itself there seems to be do marked diminution of their numbers in 

 the dry season. It would appear that a dense belt of reeds or papyrus in the 

 course of a stream — even if only about one hundred yards wide — would prove a 

 complete obstacle to their upward advance, unless a game or human track bridged 

 the interval. Advantage might be taken of this by completely clearing the banks 

 of the higher reaches of streams in the dry weather, then putting in a small dam 

 at the boundary of this fly-free area, backing it up with soil and putting in 

 papyrus. In a region like this Province, where almost every source of supply of 

 household water harbours these flies, it would be of interest to undertake an 

 experiment of this nature. 



I had become impressed with the apparent marked numerical superiority of the 

 males along the large rivers and of the females on the smaller streams. In roughly 

 testing this, 40 flies taken on the Nile in October were found to comprise 35 

 males and 5 females ; and 77 taken in July comprised 67 males and 10 females. 

 Of 56 flies captured in September near the mouths of small tributaries of the 

 Nile between Nimule and Wadelai, 24 were males and 32 females. I feel sure 

 that if in the latter enumeration the flies had been taken from some 20 miles up- 

 stream the females would have been shown to outnumber the males to a much 

 greater extent. These figures are too small to attach any importance to them, 

 but they seem to be borne out by the results obtained by others. Although he 

 did not contrast the sites of capture in this light, Kleine (quoted S.S. Bulletin 

 No. 11, 1909) found that of two batches of flies from islands in Lake Victoria, 

 23 per cent, and 13 per cent, respectively were females while of a large number 

 taken on the banks of the Mori River 68 per cent, were females. Of a large 

 capture on an uninhabited island in Tanganyika, Kinghorn and Montgomery 

 found only 9 per cent, to be females, while Degen in Lake Victoria of a still 

 larger number found the females to form 22'19 per cent. Bagshawe took 1,176 

 males and 1,662 females in Lakes George and Edward and tributary streams : it 

 would have been interesting if he had kept the river returns separate. 



In this Province the population is small and the villages widely scattered. 

 Game over wide areas has succumbed to the ruthless methods of hunting adopted 

 by the inhabitants, therefore on many smaller streams the opportunities of 

 feeding on blood of the larger mammals would be rare. On the Nile itself hippo- 

 potami and crocodiles exist in large numbers but only rarely in the tributaries. 



I have frequently taken pet monkeys to fly-infested places but owing to their 

 alertness have never observed one to be bitten. Indeed they try to capture the 

 insects if they alight, and, if successful, greedily eat them. 



I have been unfortunate in not finding any pupae or pupa- cases in the Province. 

 It would seem that the marked contrast between the sites in which the pupae are 

 found on the Guinea Coast and in Uganda might have given a hint of a specific 

 difference in the flies. 



At one time I made up my mind that these flies on settling did not move 

 about on the host, but latterly I have observed two instances which proved that 

 that opinion was inaccurate. These flies moved about two inches ; in one case there 

 was no obvious cause for the movement, while in the other a passing twig 

 disturbed it. 



