REPORT ON MOSQUITOES. 45 



known to us at present can breed except in water. It need not 

 be clean water and there need not be much of it ; but water there 

 must be in which the wrigglers or larv^ can feed and grow, 

 They are built for an aquatic life and for eating the micro-organ- 

 isms that live in water. On land they are absolutely helpless, 

 without power of motion and without the ability to take food. 



Without water, therefore, there can be no development of 

 mosquito larvae, and it is matter of the utmost importance to 

 determine under just what circumstances a body of water becomes 

 dangerous as a mosquito breeder and what waters are safe. 



In the first place, large ponds or open permanent pools are 

 safe except at the edges, because mosquito larv?e will not breed 

 where the water is disturbed by the wind, forming waves or 

 ripples. If the pond or pool is inhabited by fish other than those 

 that live on the bottom or in the mud, no larvae can maintain 

 themselves except in shallow, grassy borders where fish cannot 

 penetrate. Any permanent pond or pool can be made mosquito 

 safe by cleaning up the edges and stocking with fish. As to the 

 kinds of fish, that is discussed under another heading. Every 

 fountain or artificial water basin, no matter how small, should 

 be stocked, if only with gold fish, and it goes without saying that 

 this applies to larger bodies as well. Any area of shallow, stag- 

 nant water sheltered from the wind and without fish may become 

 dangerous from the mosquito breeding standpoint, whether large 

 or small. Along the grassy edges of ponds not otherwise dan- 

 gerous. Anopheles find convenient places for developing. 



Running streams are usually safe except in the quiet eddies, 

 where Anopheles loves to hide close to the banks. There are also 

 a few territans bred in such places ; but not many. Almost any 

 of the minnows or sunfish that usually inhabit such streams will 

 serve to keep them clean, except where the edges are shallow and 

 grassy ; but here other larvae and aquatic insects generally tend 

 to keep them down. As a rule, larger streams in rocky or gravelly 

 bottoms are entirely safe. Sluggish streams in open meadow 

 land over a mud bottom are likely to be more or less trouble- 

 some. 



Pools covered with duckweed are not mosquito breeders when- 

 ever the weed covers most or all of the surface. The plant forms 

 so complete a cover that the mosquito larvae cannot reach the 

 surface, hence choke to death. Such pools also are the favorite 

 habitation of many aquatic insects. So pools that are filled with 

 the green, slimy and stringy Spirogyra contain no wrigglers, 

 because the latter become entangled in the vegetable threads and 

 die. In fact, the mere presence of a small quantity in a breeding 

 jar seems to act almost as a poison to the larvae. 



