87 



cent. It is stated that a similar investigation during the wet season 

 months of February and March yielded only 1 per cent, of flies con- 

 taining non-mammalian blood, but the actual numbers are not given. 

 As a possible explanation of this difference, it is suggested that the 

 flies are probably much more voracious during May than in the wet 

 season, as it is believed that the greatest number of larvae are deposited 

 in May. It is clear, however, that a seasonal change in the available 

 food supply is probably also an important factor." 



Finally we may note a few of the data furnished by Dr. G. D. Hale 

 Carpenter, in his " Second Report on Bionomics of Glossina fuscipes 

 (palpalis) of Uganda" (25). With reference to the percentages of 

 flies in which mammalian (M.) or non-mammalian (N.) blood was found 

 at three different localities, Dr. Carpenter gives the following figures : 

 Jinja (shore of Lake Victoria), M. 31-5 per cent., N. 68-5 per cent. ; 

 Damba Isle, M. 15-2 per cent., N. 84-8 per cent. ; Bugalla Isle, M. 

 68-7 per cent., N. 31-3 per cent. "If one examines flies daily," 

 writes Dr. Carpenter, " and notes the proportions of M. and N., one 

 is at once struck by the fact that from day to day the proportions are 

 very different. If, for instance, there are fresh tracks of Varanus (the 

 large monitor lizard known in Uganda as ' Nswa-swa ') on the sand when 

 flies were caught, the proportion of N. to M. of that day is much greater 

 than the average. This shows with what eagerness the flies avail 

 themselves of any source of food which presents itself ; and also, that 

 it is quite impossible to gauge correctly the proportions of M. to N. from 

 one or two casual examinations in any particular locality. 



" The proportions of M. to N. were found to vary considerably from 

 one month to another, but when the results were plotted out in a curve, 

 and compared with the curves of temperature, humidity, number of 

 flies, etc., no correlation whatever could be seen, and the variations 

 appeared purely fortuitous." 



As regards the origin of the non-mammalian blood, it was found 

 from examination of a large number of flies that this works out as 

 follows: Avian, 4-3 per cent. ; reptilian, 95-7 per cent., the chief 

 source of the reptilian blood being undoubtedly Varanus. " Amphibian 

 or ophidian blood," says Dr. Carpenter, " has never been found." 



Dr. Carpenter adduces facts showing that, in spite of the difficulty 

 in deciding whether G. palpalis imbibes vegetable juices in addition to 

 its normal diet of blood, " strong evidence has been obtained," by 

 microscopic examination of the gut contents of no fewer than 1,239 

 flies, " that it feeds from plant tissues." In a similar manner " definite 

 microscopical evidence " has been secured that, " on occasion," the 

 fly sucks up water. 



THE DRINKING OF WATER BY TSETSE-FLIES. On this subject, 

 besides the statement by Carpenter to which reference has just been 

 made, and Lloyd's remarks quoted on p. 84, additional information 

 has been furnished both by Lamborn and Swynnerton. The former, 

 writing with reference to G. morsitans and G. brevipalpis in Nyasaland 

 (83), observes .: " I have repeatedly seen flies settled on wet sand, for 

 the purpose, I imagine, of drinking, though as the fine proboscis only 

 is lowered, while the palps remain in the usual position in front of the 

 head while the insect is feeding, and as it does not permit one to 

 approach very near, it has been impossible to settle the point. I have 

 endeavoured to study the matter further by starving flies in captivity, 

 providing them only with wet sand, but even though they survived 

 longer than a similar number kept entirely without water, I was not 



