462 MOSQUITOES 



Other efficient enemies are whirligig beetles (Gyrinidse), pre- 

 daceous diving beetles and various aquatic predaceous larvae, in- 

 cluding some species of mosquito larvse. Among birds, ducks 

 have been quoted as efficient destroyers of mosquitoes and Dixon 

 of Pennsylvania recently demonstrated their ability to keep ponds 

 free of larvae; he believes the mallard duck surpasses any other 

 creature in the number of mosquito larvse and pupae which it can 

 destroy. As destroyers of adults the value of such birds as 

 swifts, nighthawks, swallows, etc., is well known. Bats, also, 

 have been exploited as mosquito destroyers. The erection of 

 " bat roosts " for propagation of these animals has been tried in 

 Texas, and was found to reduce markedly the numbers of mos- 

 quitoes, and was financially profitable on account of the guano 

 which could be collected. 



