CHAPTER III 



THE NATURAL HISTORY OF GLOSSINA 

 PALPALIS 



This species is pre-eminently a frequenter of the shady 

 forests on the shore of the lake, where it may be found 

 in great abundance. 



The method of estimating its numbers is to set trained 

 natives to catch the flies with small nets from o£E the 

 herbage or rocks on which they alight, or from their 

 own clothing when the flies come to feed. At the end of 

 half an hour the boys are whistled in and the catch 

 counted, but, for reasons which will be given later, 

 only the males are used. An average figure is obtained 

 representing the number caught per boy per hour, 

 commonly alluded to as the " male-boy-hour " figure, 

 by means of which one locality can be compared with 

 another. The highest figure I have yet recorded was 

 obtained in 1919 on the north coast of the west of Kome 

 Isle : four boys working for half an hour obtained the 

 average of 125 male flies per boy per hour. If it be 

 considered that each fly is caught in a net, from which 

 it has to be taken out by hand and put into a bottle, 

 and that besides the males there were at least a quarter 

 as many females caught at the same time, it must be 

 admitted that the fly can be very plentiful ! 



One of the first things to be realized is that the number 

 of flies at a locality has little relation to the frequency 

 with which one is bitten, and therefore an impression 



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