42 NATURAL HISTORY OF GLOSSINA PALPALIS 



hundreds of flies on Damba and Bugalla Islands, as well 

 as at Jinja on the mainland, has shown various forms 

 of algae and other low vegetable organisms that must 

 have come from water ; and once a very minute ostracod 

 crustacean, only about three times the length of a 

 human red blood corpuscle, was found. Figures of 

 these are given in my first and second reports. 



Experiments were made to see if flies lived longer when 

 able to obtain juice from fruit than when starved, but 

 access to fruit made no difference. The longest time for 

 which a wild fly has been kept without food or with only 

 fruit juices available is nine days ; a freshly hatched 

 fly will live for eleven days. After a single feed of blood 

 a fly lived for fifteen days (the longest period). This 

 is a remarkably short period, and if it is so in natural 

 conditions is rather surprising. Animals such as ticks 

 appear to be able to live for months after a single feed of 

 blood; the fly, however, is a more active creature, and 

 lives at a higher rate. 



What is the natural length of life of palpalis ? This 

 was one of the first things to be settled when I went 

 out in 1910. For it was then not at all clear why the 

 flies on the lake shore continued to be infective several 

 years after the presumed sources oi~Trypanosoma gambiense 

 (i.e. the natives) had been removed from reach of the fly. 

 There were two possibilities — either the fly was acquiring 

 infection from some wild animal, or the same flies were 

 still alive on the shore that had been the cause of the 

 epidemic some years before. It was not until 1911 that 

 Duke showed what the reservoir of gambiense was, and I 

 have showed that the fly probably does not live for more 

 than one year. The drier months of the year cause a large 

 falling off in numbers, so that a fly which has been living 

 for some months probably succumbs when the trying 

 period of diminished humidity comes at the beginning 

 of the year. 



