86 HOUSEHOLD INSECTS 



on account of the deleterious effect that may result to 

 the plants growing in the water. 



Much of the drinking water for stock in many of the states 

 in this country is caught and stored in surface pools. The 

 stock is allowed access to these pools at any and all times. 

 These drinking pools often become breeding places for 

 mosquitoes. The water cannot be drained away because 

 it is absolutely essential for the stock. Neither is it 

 desirable to pour oil on the surface because the water is 

 thereby rendered unpalatable and obnoxious to the animals. 

 In such cases, the best way of controlling the mosquitoes 

 is the introduction of certain kinds of fishes into the pools. 



In order for a species of fish to be effective in the control 

 of mosquitoes it must possess certain characteristics. In 

 general, it should be a small fish so that it can reach the 

 shallower parts of the pool. It should also be a top- 

 feeder, a voracious feeder on mosquito larvae, and a pro- 

 lific breeder. Finally, it should have a wide geographical 

 range in order to make it available for as many localities 

 as possible. It is evident that but few species of fishes 

 possess the foregoing combination of qualities. 



It would appear from a knowledge of the habits of the 

 larvae of Anopheles that they are much less easily held 

 in check or destroyed than the larvae of Culex. The 

 larvae of Anopheles are found especially in quiet waters, 

 and in ornamental pools among the lily pads, duckweed, 

 and other plants. They simulate remarkably well their 

 surroundings and are thus screened from observation. 

 Moreover, they live upon the surface, lying and mov- 

 ing in a horizontal plane. It is evident that only 

 those fishes that are small and can penetrate to the 

 spaces of water among the lily leaves and duckweed will 



