280 THE RELATIONS OF ANIMALS TO DISEASE 



and legs when at rest. Culex lays eggs in tiny rafts of one hundred 

 or more in standing water ; thus the eggs are distinguished from 

 those of anopheles, which are not in rafts. Rain barrels, gut- 

 ters, and old cans may breed in a short time enough mosquitoes 

 to stock a neighborhood. The larvae are known as wigglers. 

 They appear to hang on the surface of the water, head down, in 

 order to breathe through a tube at the posterior end of the body. 



In this stage they may be rec- 

 ognized by their peculiar move- 

 ment when on their way to the 

 surface to breathe. The pupa, 

 distinguished by a large head 

 and thoracic region, breathes 

 through a pair of tubes on the 

 thorax. The fact that both 

 larvae and pupae take air from 

 the surface of the water makes 

 it possible to kill the mosquito 

 during these stages by pouring 

 oil on the surface of the water 

 where they breed. The intro- 

 duction of minnows, gold fish, 

 or other small fish which feed 

 upon the larvae in the water 

 where the mosquitoes breed 

 will do much in freeing a neigh- 

 borhood from this pest. Drain- 

 ing swamps or low land which 

 holds water after a rain is an- 

 other method of extermination. Some of the mosquito-infested 

 districts around the city of New York have been almost freed 

 from mosquitoes by draining the salt marshes. Long shallow 

 trenches are so built as to tap and drain off any standing water 

 in which the eggs might be laid. In this way the mosquito has 

 been almost exterminated along some parts of our New England 

 coast. 



Since the beginning of historical times, malaria has been preva- 

 lent in regions infested by mosquitoes. The ancient city of Rome 



Life history of two mosquitoes — at 

 the left, culex ; at the right, anopheles, the 

 malarial mosquito. Note the four stages 

 of each — eggs, larva, pupa, adult. 



