144 MOSQUITOES OF NORTH AMERICA 
All the mosquitoes we have so far considered, with the exception of Bancroftia, 
lay their eggs upon the water, or, in the case of Culex jenningst, into the water. 
In these the development of the larva within goes on uninterruptedly and the 
eggs hatch within a short time. We now come to a group of mosquitoes in which 
the eggs lie dormant for some time to await favorable conditions for the de- 
velopment of the larva. These are the species of the genera Aédes and Psoro- 
phora. In these forms the eggs are laid singly or in small batches, never fastened 
together in the form of a raft, and, in most cases at least, not upon the water. 
That they are not laid upon the water is shown by the fact that, where for a long 
time there has been no water, the larve appear promptly when puddles are 
formed. In these mosquitoes the female does not mature all her ova at one time ; 
therefore they are deposited in several batches, at intervals. To Aédes belong 
the mosquitoes which are so troublesome in the northern regions and we have 
already touched upon their breeding-habits in our discussion of the adults. 
The eggs are laid in the summer and they do not hatch until the following 
spring, when the larve appear in great numbers in the water from the melting 
snows. The females must deposit their eggs upon the ground, at least in most 
cases, for by the time they have developed their ova the breeding-places have 
usually dried out. Galli-Valerio and Rochaz de Jongh, in Switzerland, have 
_ found hibernating single eggs attached to fallen leaves in depressions of the 
) ground. It appears that the hibernating eggs, although they may be repeatedly 
) submerged, will not hatch before they have been subjected to freezing tempera- 
{ tures. Thus these mosquitoes appear in one great annual brood, in spite of the 
' fact that the eggs are not all laid at one time. With a few species of these 
northern Aédes, for example Aédes fuscus and A. canadensis, larvee appear in 
small numbers at intervals during the summer, after heavy rains, These larve 
are undoubtedly from hibernated eggs which failed to hatch in the spring, and 
not from freshly laid ones. Eysell, who observed species with similar habits in 
Germany, suggested two ways in which such subsequent appearance of larve 
might be accounted for. Eggs which were not submerged in the early spring 
might be washed into the pools by heavy rains. Or the water in the pools might 
be raised to a higher level and reach eggs until then unsubmerged. 
A peculiarity of the eggs of the group we are now considering is that not all 
of them hatch at one time; a certain number lie over until later in the season or 
even until another year. To the southward the species of Aédes depend for the 
most part upon the rains for their development. In regions with a well-marked 
dry season the eggs must withstand desiccation for a long period. Here the eggs 
lie upon the ground from one rainy season to another, hatching with great 
promptness when submerged by the rains. Viereck found that in the case of one 
of our salt-marsh mosquitoes (Aédes sollicitans) that upon immersing a piece 
of sod which contained eggs the young larve appeared within three minutes. 
This prompt hatching is of the greatest importance as in hot climates rain- 
puddles dry out very rapidly and the mosquito must reach full development 
before this occurs. As it is, whole broods must often perish through the too 
rapid drying up of their breeding places. Another provision, to insure the 
