58 



ENTOMOLOGICAL SOCIETY OF ONTARIO. 



The pupa (Fig. 36) differs fiom the larva in the great swelling of the thoracic seg- 

 ments, and in this stage the insect is lighter than water. It remains motionhss at the 

 surface and when disturbed does not sink without effort, as does the larva, but is only 

 able to descend by a violent muscular action. It wriggles and swims as actively as the 

 larva, and soon reaches the bottom of the vessel or breeding-place. As soon as it ceases 

 to exert itself, it floats gradually up to the surface of the water again. The air tubes no 

 longer open at the anal end of the body, but through two trumpet-shaped appendages on 

 the thorax, from which it results that the pupa remains upright at the surface, instead of 

 with the head downward. This reversal of position enables the adult insect, which issues 

 from the thorax, to support itself on the floating skin while the wings are expanding. 



Fig. 36.— Full-grown mosquito larva (Culcx pungens) at left ; pupa at 



right above, its anal segment below — all greatly 



enlarged. (After Howard). 



The shortest time observed for the life of the insect from the laying of the egg to 

 the emergence of the winged mosquito was ten days, during hot weather at the end of 

 June ; but the length of time which is required for a generation may be indefinitely pro- 

 longed if the weather should be cool. The extreme shortness of this June generation is 

 significant, as it accounts for the fact that swarms of mosquitoes may develop upon 

 occasion in surface pools ot rain water, which may dry up entirely in the course of two 

 weeks, or in a chance bucket of water left undisturbed for that length of time. 



The insect passes the winter in the adult winged state and frequently resorts to 

 cellars and out-houses for the purpose. The degree of cold seems to make no difference 

 to their successful hibernation, as may be understood from their abundance in the extreme 

 north. 



