494 



OTHER HLUUD-SUCKIXC; I'LIES 



companied by natives. Black or dark clothes are preferred to 

 light ones; khaki color, however, appears to be particularly 

 attractive to them. Moving objects seem to attract the files, 

 and they are said to follow launches when moving, though they 

 leave them alone when quiet. 



When biting, these flies spread apart their front legs, lower the 

 proboscis into the skin and begin to gorge. The abdomen of 



an unfed tsetse is very 

 flat (Fig. 232A) but after 

 30 or 40 seconds of feed- 

 ing it becomes distended 

 like a balloon, some- 

 times containing over 

 twice the weight of the 

 fly in blood (Fig. 232B). 

 The flies do not feed ex- 

 clusively on blood, but 

 also suck plant juices 

 and .show definite, selec- 

 tive taste for various 

 fluids presented to them 

 under a membrane, according to experiments by Yorke and 

 Blacklock. Both warm- and cold-blooded animals are sucked, 

 Ijut flies fed only on a cold-bloodetl animal (crocodile) never 

 produce offspring. It has been thought that perhaps water 

 fowl constitute an important article of diet for tsetses, but in 

 the case of Glo.ssina morsitans, at least, ])irds' blood proved 

 rather indigestible for them, and often produced a clot in the 

 digestive tract, resulting in abortion in female flies. In the case 

 of such species as G. palpalis, however, bird blood may i)e more 

 easily digested, and the diurnal habits and clo.'^e adherence to 

 the vicinit}' of water would argue in favor of subsistence on 

 water animals, in part at least. On the other hand, the habit of 

 many species of fretiuenting places where game animals come to 

 drink or browse and of feeding early in the morning and at even- 

 ing is apparently an adaptation to the hal)its of such hosts as 

 wild game animals. Examination of the stomach contents of 

 wihi flies usually shows a iireponderaiice of mammal blood, but 

 Carpenter, studying T/. palpalis in Uganda, often found tli;it a, 

 large proportion of sf)nic collections of flies had fed on rej)tiles. 



Fi(i. 2.32. Glossina morsitans before (.1) ami 

 after (B) feeding. X 4. (After Austen. j 



