154 MOSQUITOES OF NORTH AMERICA 



One of their own kind is as likely to fall a prey as any other species and in fact 

 the confinement of several of these larvge in a narrow compass usually ends in 

 the destruction of all of them but one. 



HIBERNATION OF MOSQUITO LARV/E. 



The continuous breeders, such as Anopheles and certain species of Culex, de- 

 velop while temperature conditions are favorable. Cold weather puts an end 

 to their activities and the larvae are destroyed by the freezing over of the water, 

 or perhaps even before. However the larva of certain species normally hiber- 

 nate. This is the case with the pitcher-plant mosquito, Wyeomyia smithii; 

 the larvas survive the complete freezing up of the water in the leaves of the plant 

 and complete their development the following season. The larvae of a few other 

 species of the eastern United States hibernate regularly although they do not 

 withstand actual freezing ; these larvae remain dormant at the bottom during 

 cold weather. The tree-hole breeders Bancroftia signifer and Megarhinus sep- 

 ientrionalis hibernate as larvae and the same is probably true of Coclodiazesis 

 harheri. Culex melanurus hibernates as mature larva. The larvae live in spring- 

 holes in swamps or in the woods and the last brood appears very late in the 

 season. They remain at the bottom during cold weather, and do not produce the 

 imago until the following April or May. 



All the foregoing species, with the exception of Wyeomyia smithii, may be 

 said to be rare and the larvae are not generally in evidence. The observations of 

 Galli-Valerio and Rochaz de Jongh, in Switzerland, show that in Europe the 

 larvae of certain species of mosquitoes hibernate in great numbers. Thus it 

 appears that the larvae of Anopheles hifurcatus hibernate normally, remaining in 

 hiding among the leaves of water-cress (Nasturtium officinale) and other 

 aquatic plants. In the case of Culiseta annulatus, which was observed in a 

 water-barrel in an open field, even pupae continued to appear throughout the 

 winter at temperatures but little above freezing. These observers found that 

 larvae of Anopheles and Culex ( ?) survived in the thin layer of water between 

 two sheets of ice. These observers also found that the larvas of Aedes nemorosus 

 occur during the winter in great numbers. On December 2, 1906, they found 

 great numbers of these larvae in an ice-covered puddle. This puddle had a depth 

 of five centimeters and an area of six square meters and they calculated that it 

 contained about 3,750,000 larvae. The larvae in these puddles did not increase 

 in size during the winter ; early in April they finally began to grow and trans- 

 formed to pupae towards the end of that month. From another observation by 

 these investigators it appears that such larvae are hatched from eggs in mid- 

 winter. Thus they found on January 15, 1903, great numbers of very small 

 larvae in a puddle thickly covered with ice; this puddle had been dry between 

 December 1 and January 1 and had, as the result of warm weather in early 

 January, afterward filled with snow-water. This last species, then, may be 

 classed with those species of Aedes the larvae of which elsevv^here appear in the 

 snow-water of early spring. 



