78 



In order to catch females, Stuhlmann states that it is necessary to use 

 animals such as cattle and mules as decoys, but even so he observes 

 that they are much more difficult to capture than males. He thinks 

 it probable that ' the gravid females are much more wary and move 

 about less than the males, and are consequently more rarely caught.' ' 



CHAPTER VIII. 



TSETSE-FLIES AND THEIR FOOD. 



The study of Tsetse-flies in relation to feeding includes various 

 matters, which it is as well to examine separately. 



All the observations, investigations and experiments made upon this 

 subject are of great practical interest, since they throw light upon the 

 transmission of trypanosomiases by Glossina. 



TIMES WHEN TSETSE-FLIES ARE MOST ACTIVE. THE SEARCH FOR 

 FOOD. It is well known that Tsetse-flies are much more active and 

 pertinacious when they attack moving objects than when the latter 

 are stationary, and it therefore seems logical to conclude that, in 

 singling out an involuntary host, they trust more to the sense of sight 

 than to any other. In the majority of cases, if one remains absolutely 

 motionless in a haunt of G. palpalis not a single insect is seen, but 

 immediately one moves the flies commence to attack, and the same 

 fact is observed in the case of horses and cattle. 



Similarly, when a river steamer approaches the banks in a fly-area 

 in Belgian Congo, swarms of Tsetse fly on board, but if the boat stops 

 the insects cease their attacks, resuming them so soon as it begins to 

 move again. 1 The fact should be borne in mind when clearing places 

 on shore for the purpose of landing-stages, ferries, etc., where 

 movements of some importance in river traffic take place. 



Dr. W. A. Lamborn (82), writing in 1915 of G. morsitans in Nyasaland, 

 says : " Tsetses are especially attracted by moving objects, and it has 

 been my frequent experience that the faster one moves, the more one 

 is beset, for which reason I now invariably walk rather than cycle in 

 a fly area. If one stands still, such flies as may have been hovering 

 around come to rest on objects near by, frequently on a blade of grass, 

 or they settle on the ground, resuming their attentions immediately 

 one is in motion again ; though, if one remains still long enough, as 

 I have often found during a rest for lunch in the open, the majority 

 gradually fly away." Dr. Lamborn adds that, as has already been 

 mentioned, " several flies will often travel on a person for considerable 

 distances without attempting to bite." 



As is well known, Glossina morsitans feeds with avidity on the blood 

 of almost all large animals with which it meets ; according to certain 

 observers it is more aggressive during the hottest hours of the day, 

 while others state that it attacks human beings not only throughout 

 the day, but also during part of the night, especially in warm weather 

 and when the moon is bright. 



1 In the course of his journey on the Congo from Leopold ville to Stanleyville, 

 Dr. J. Bequaert made some very interesting experiments in connection with 

 the pursuit of fast river steamers by Tsetse-flies, by catching flies which flew on 

 board, marking the insects by snipping off the tarsus of a particular leg (varying 

 according to the day of capture), and then releasing them. In this way it was 

 found that a fly had been carried for a distance of some 87 miles, which was 

 doubled on the downward journey. The steamers may therefore be responsible ^ 

 for the dissemination of G. palpalis and trypanosomiasis. 



