HABITS OF THE LARV£E. 
So far as known the larva of all mosquitoes are aquatic. The larval forms of 
so many of the genera are now known that it can be considered safe to assume 
that there will be no exceptions found. It has already become apparent from 
the egg-laying habits that mosquito larve occur in a great variety of situations. 
What has not been sufficiently understood until recently is that each species, or 
group of species, has its own very definite habitat—a fact of the greatest eco- 
nomic importance. By far the most of the mosquito larve occur in small de- 
posits of water. While certain species do occur in large bodies of water, such as 
ponds and streams, this is under unusually favorable circumstances, and even 
then they are present only in small numbers. In the larger bodies of water fish 
and other life act as a check upon mosquitoes, if, indeed, their eggs are deposited 
there at all, which there is reason to doubt. 
Those species of mosquitoes which appear in the greatest abundance develop 
in transient deposits of water. This is the case with the mosquitoes of the genus 
Aédes which are so troublesome in our northern woods and in the arctic regions 
in early summer. The eggs of these mosquitoes are deposited upon the ground 
during the summer. There the eggs lie until the following spring; although 
they are repeatedly wetted or even immersed in water they will not hatch until 
the following spring. Then, with the melting of the snows, the eggs promptly 
hatch and the larve appear in the pools of snow-water in immense numbers. 
The previous freezing appears to be a necessary stimulus to their development. 
In the course of a few short weeks the entire mosquito crop of those regions is 
produced. 
It has often been noted that upon the plains of the arid and semi-arid west 
mosquitoes occur at times in immense numbers and their presence, in the 
absence of all water, has seemed inexplicable. Yet these too pass their larval 
life in the water. On the northern plains these mosquitoes develop in the very 
transient snow-water, in the manner described above; south of the regions of 
heavy snow-fall they depend upon temporary deposits of water resulting from 
heavy rains. Similarly, in semi-arid tropical regions the appearance of mos- 
quitoes depends upon the heavy rains of the summer months. The rapidity of 
development of the larve in such regions is astounding, but it is conditioned by 
the rapid evaporation of the rain puddles in such acclimate. The eggs which had 
lain upon the ground for a year, and perhaps two years, upon being submerged 
hatch at once; the larve reach their full growth within one or two days and the 
pupal period is a matter of hours. Even so a whole brood may perish from the 
too rapid drying of the pools. There is a remarkable provision to prevent the 
extermination of the species through such circumstances, in the fact, above 
mentioned, that not all the eggs hatch at one time. Part of them lie over 
until a succeeding rain, and some of them even until another year. Thus the 
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