490 OTHER BLOOD-SUCKING FLIES 



performed in a pool with a surface of a little over a square yard, 

 he caught in five days 1260 male and 258 female Tabanus, and 

 416 male and 33 female Chrysops. This " pool of death " was 

 literally studded with " floating islands of dead tabanids." 

 The flies are said to visit the pools even after sucking blood. 

 Portchinsky suggests the construction of traps of this nature in 

 pastures where tabanids are troublesome, fencing them in, of 

 course, to prevent the stock from getting access to them. 



From the solitary nature of the flies, and the great variety of 

 breeding places which may be selected, it is obviously impossible, 

 in most cases, to exterminate tabanids during their early stages. 

 Natural enemies probably do much to limit their numbers; 

 fishes and large carnivorous aquatic insects prey upon the larvae, 

 and birds and hornets on the adults. Hine describes seeing 

 bald-faced hornets, Vespa maculata, capture and cut to pieces 

 horseflies which were too large for them to carry. 



Tsetse Flies 



Next to the mosquitoes the tsetse flies are the most important 

 of the biting flies. The history and destiny of the African con- 

 tinent has been and will be very largely controlled by these 

 insects. As far as their own biting power is concerned, tsetse 

 flies are of little importance; their bites are less painful than are 

 those of many other biting flies of similar size. It is in the role of 

 carriers of trypanosome diseases that they gain their importance. 

 Not only the two or possibly three forms of human sleeping sick- 

 ness, but also a large number of deadly trypanosome diseases of 

 animals are transmitted by these insects. The native wild ani- 

 mals of Africa are largely immune to these diseases and serve as 

 a reservoir for them, but domestic animals and man succumb in 

 large numbers, in fact to such an extent that some parts of Africa 

 are uninhabitable, and in other parts it is impossible to keep 

 domestic animals of any kind. The abundant and varied wild 

 game of Africa, particularly the numerous species of antelopes, 

 are the chief natural source of food for tsetse flies, .and since the 

 flies serve as intermediate hosts for the trypanosomes harbored 

 by the wild game, it is obvious that when man or domestic ani- 

 mals are bitten by these flies they are in great danger of being 

 inoculated with one or more species of trypanosomes. 



