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 North America a few species pass the winter in the larval state. 
Such is well known to be the case with Wyeomyia smithii. Larve 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 larvee 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 larve live in 
spring-holes in marshes and remain at the bottom during cold weather. The 
larva of Megarhinus septentrionalis, 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 larve in various stages of develop- 
ment have been found in the winter, living beneath the ice, by a number of ob- 
servers, and these larve later produced imagos. In Switzerland, Galli-Vallerio 
and his collaborators have made observations through about ten consecutive 
winters that show that Anopheles bifurcatus and Culiseta annulatus regularly 
hibernate there as larve. 
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 larve appear very early. Galli-Vallerio 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 larvee 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. 
