86 



ECONOMIC ZOOLOGY 



it finally reaches the pupa stage, Fig. 68, when it stops feeding and 

 lies quietly on the surface of the water, breathing through tubes situ- 

 ated on the dorsal side of the thorax, instead of near the end of the ab- 

 domen. The larva is heavier than water and has to wiggle actively to 

 get to the surface to breathe, the pupa is lighter than water and lies 

 without effort at the surface. The pupal stage may last from two to 

 six days or more. When the adult is ready to emerge the pupal skin 

 splits down the back and the mosquito slowly escapes; it may take 



PIG. 65. Resting position on vertical wall of Culex (left) and Anopheles 

 (right). (From Howard, Mosquitoes of the United States, after the British Medical 

 Journal.} Enlarged. 



several minutes for the animal to issue from the old skin and for its 

 wings to dry and harden enough for flight; during this time it stands 

 on the floating pupa skin and is, of course, easily upset and drowned 

 by the least roughness of the surface of the water; this is another reason 

 why mosquitoes do not breed in running water. 



How long the adult mosquito lives is difficult to determine; some of 

 them hibernate all winter, but in confinement they usually die rather 

 soon. 



Some species fly for considerable distances, but, as a rule, they re- 

 main very close to their place of birth, so that it may even be possible 



