MOSQUITOES AND FLIES 



more northern one common about Washington, D. C, 

 where it breeds in rock pools along the Potomac River. 



The larva of Aedes (Fig. 178 A) resembles a Culex larva, 

 but it feeds more habitually at the bottom of the water 

 and may spend long periods below without coming to the 



Fig. 179. Mosquito pupae in natural position resting against the under 



surface of the water 



A, Aedes atropalpus. B, Anopheles punclipennis 



surface for air. In its search for food it noses about in the 

 refuse at the bottom of the water and voraciously con- 

 sumes dead insects and small crustaceans. The pupa like- 

 wise (Fig. 179 A) does not differ materially from a Culex 

 pupa. When quiet it floats at the surface of the water 

 with the entire back of its thorax against the surface film 

 and the tips of its breathing tubes above the surface. 

 Probably no mosquito pupa hangs suspended from its 

 respiratory tubes in the manner in which the pupae of 

 various species are often figured. 



Aedes aegypti is the only known natural carrier of the 

 virus of yellow fever from one person to another. The 

 disease can be taken only from the bite of a mosquito of 

 this species that has become infected by previous feeding 

 on the blood of a yellow-fever patient. The organism 

 that produces yellow fever is perhaps not yet definitely 

 known, though strong evidence has been adduced to show 



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