144 MOSQUITOES OF NORTH AMERICA 



All the mosquitoes we have so far considered, with the exception of Bancroftia, 

 lay their eggs upon the w^ater, or, in the case of Culex jenningsi, 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 larvas. These are the species of the genera A'edes and Psoro- 

 pJiora. In these fonns 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, wiiere for a long 

 time there has been no water, the larvae 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 A'edes 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 larvae 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 Eochaz 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 A'edes, for example A'edes fvscus and A. canadensis, larvae appear in 

 small numbers at intervals during the summer, after heavy rains. These larvae 

 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 tv/o ways in which such subsequent appearance of larvae 

 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 A'edes 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 {A'edes sollicitans) that upon immersing a piece 

 of sod which contained eggs the young larvae 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 



