MOSQUITOES 305 



that adults and immature forms pass the winter in moist places 

 or even in ice. In the spring, when the ice melts, the transforma- 

 tion is completed and the females soon lay eggs and die. These 

 eggs are placed either on the surface of small, shallow pools or 

 depressions which hold a little water, or upon moist places where 

 the insect instinctively realizes that water will shortly be present. 

 It is a significant fact that a couple of tablespoonfuls of water 

 overlooked in a tin can or broken pitcher hidden under the side- 



Fia. 313. The yellow fever mosquito, female. (After L. O. Howard.) 



walk or under shrubbery will, if the water remains for eleven or 

 twelve days, be sufficient to give rise to a hundred or more of 

 these troublesome insects. In a general way it may be said that 

 the life cycle from egg to adult is about two weeks (Figs. 314 and 

 315). Probably the normal food of mosquitoes was originally the 

 juices of tender plants, and it is very evident that comparatively 

 few of their numbers ever have a chance to feed on man or warm- 

 blooded animals. 



Three Groups of Mosquitoes. In the case of the yellow fever 

 mosquito (Stegomyia calopus), which is a rather small species, with 

 20 



