FLIES 817 



margin of the forest where it abuts on open grass land ; 

 others in the forest, and others on the grass land. Robber 

 flies seems a poor name for these powerful, hairy, pre- 

 daceous flies, with long narrow bodies and strong legs. 

 Hawk flies would be a better name, seeing how they 

 pounce upon their prey ; in some six years of work in 

 the field I can only once remember seeing an Asilid 

 pounce on its prey sitting. 



Emphasis has already been laid upon the importance 

 to the theory of mimicry of noting the prey of Asilidae. 

 It is, I think, quite certain that the fly injects poison 

 into the victim the moment it has been captured and 

 the proboscis has been plunged into it. The prey seems 

 to succumb at once before it can have been sucked dry, 

 and if one actually witnesses the capture and at once 

 catches both insects the prey is almost always found 

 to be dead, or feebly moving its legs only. Only once 

 have I met with an exception to this. An Asilid was 

 seen to catch a bug, and I struck at it with the net. The 

 fly escaped, but dropped the bug, which was found to be 

 apparently unharmed. 



Another family of Diptera, Chironomidae or " gnats," is 

 worth mentioning here, owing to the abundance in which 

 they appear over the lake during and shortly before the 

 rainy season, resembling clouds of smoke from distant 

 steamers. I have seen, on a calm day, a large area of 

 water covered by the pupal skins of these flies, the pupae 

 having come up irom quite deep water, and the flies 

 rising in a cloud from the surface, which was of a brown 

 tint from the myriads of empty skins. When these flies, 

 called "E'sami" by the natives, and looking more or less 

 like mosquitoes without the sucking proboscis, have 

 drifted in a cloud on to some land they find shelter from 

 the wind on the lee side of trees and bushes, where they 

 may be seen hovering in a cluster, the end of which, 

 furthest from the tree, is strung out and torn by the wind. 



