HABITS OF THE LARV/E. 



So far as known the larvge 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 larvae 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 larvae 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 

 Aedes 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 larvae 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 larvae in such regions is astounding, but it is conditioned by 

 the rapid evaporation of the rain puddles in such a climate. The eggs which had 

 lain upon the ground for a year, and perhaps two years, upon being submerged 

 hatch at once ; the larvae 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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