ANOPHELINE OR MALARIA MOSQUITOES 45 



Life History. — As in all other mosquitoes and in- 

 sects in general, the life history (Fig. 20) depends greatly 

 upon temperature and moisture. In early spring and 

 late autumn the development is retarded, owing to the 

 lower average temperature. Again, if not sufficient 

 moisture is present, the eggs will not hatch readily. 



In midsummer the egg stage is rarely longer than 



Fig. 20. Showing the life history of the malaria mosquito (Anopheles), (a) egg (after 

 Howard) ; (b) larva or wriggler ; (c) pupa or tumbler ; (d) adult mosquito. Time required 

 from egg to the adult is about twelve days in midsummer. 



twenty-four hours' and often nearer twelve hours' 

 duration. The larva emerges by pushing the cap 

 from the egg, and begins its existence in the water, 

 usually clinging close to debris or scum. The larval 

 stage is most easily affected by temperature changes, 

 but lasts usually from twelve to fifteen days, during 

 which period the skin is shed several times. The change 

 into the nymphal or pupal stage is undergone very 

 rapidly and usually occurs overnight ; often great 

 numbers undergo this change in the early part of the 



