120 MOSQUITOES OF NORTH AMERICA 



the bark or other protected situations. There they remain quiescent until the 

 return of warm weather, closely hugging the surface upon which they rest. 



Stephens and Christophers state that in India the Anopheles pass the season 

 of hot, dry weather in the houses. They found that while they feed regularly 

 they do not lay eggs even when breeding opportunities are present. The species 

 of Culex must also, in the absence of breeding-places, pass the dry season in 

 the adult state, although no exact data concerning them are available. 



In temperate ISTorth America a few species pass the winter in the larval state. 

 Such is well known to be the case Avith Wyeomyia smithii. Larvge of all sizes are 

 overtaken by cold weather in their habitat, the water in the leaves of the pitcher 

 plant. They become enclosed in the solid ice and when liberated in the spring 

 continue development in the normal manner. This appears to be the only way in 

 which this species passes the winter and the hardiness of these larvae can be un- 

 derstood when one considers that the species occurs as far north as Minnesota 

 and Ontario. Culex melanurus hibernates in the larval state. The larvas live in 

 spring-holes in marshes and remain at the bottom during cold weather. The 

 larva of Megarhinus scptentrionalis, which normally lives in water in hollow 

 trees, hibernates, although, apparently, it will not survive freezing. It goes to 

 the bottom in cold weather and remains submerged. The larva of Bancroftia 

 signifer, which usually is found associated with Megarhinus, also hibernates. 



In England and in the more southerly part of Europe, where the winters are 

 much less severe than in North America, one species of Anopheles (A. bifur- 

 catus) regularly hibernates as larva. The larva in various stages of develop- 

 ment have been found in the winter, living beneath the ice, by a number of ob- 

 servers, and these larvas later produced images. In Switzerland, Galli-Vallerio 

 and his collaborators have made observations through about ten consecutive 

 winters that show that Anopheles hifurcatus and Culiseta annulatus regularly 

 hibernate there as larvae. 



The majority of the mosquitoes in temperate climates hibernate in the egg- 

 state and in far northern regions this is the only mode of hibernation. These 

 hibernating eggs hatch in the spring, in the water from the melting snow; 

 consequently these larvse appear very early. Galli-Yallerio and Rochaz de 

 Jongh found that in Switzerland the hibernating eggs hatch during the winter 

 if pools are formed by rains or by a thaw. The larvre survived under the sub- 

 sequently formed covering of ice and later produced imagos. 



MATING-HABITS. 



The mating-habits of a very limited number of species of mosquitoes are 

 known. From the observations at hand it is evident that there is considerable 

 diversity and it must be pointed out that for one large group, the Sabethini, we 

 have no records whatever. With many species the males " swarm," that is, they 

 gather and hover in the form of a cloud, to which, it seems, the females are 

 attracted. In some cases there are two swarms or clouds, one of males the other 

 of females. There are species, it seems, that do not swarm and others have the 

 habit but weakly developed. 



