REPORT ON MOSQUITOES. 125 



drained or that are held to be desirable for any reason. Drain- 

 age for swamp areas is always best, wherever possible, but dense 

 woodland swamps or huckleberry swamps or such as are very 

 densely overgrown with tall vegetation require no treatment. 

 The dangerous areas are those that are open, partly filled with 

 grasses, reeds, lilies, arrow heads and other plants of that char- 

 acter and with overgrown shallow^ or grassy edges. Such an 

 area though it may be naturally stocked, is dangerous, because 

 the grasses and other plants are so dense that the fishes cannot 

 move among them.- There are many little spaces, therefore, 

 where the wrigglers are undisturbed, while Anopheles, keeping 

 on the surface over partlv submerged leaves, is beyond the reach 

 of our native fishes. Such a swamp area if not readily drainable 

 should be opened up by taking out the obstructing vegetation or 

 cutting it below the surface, that the wind may have unobstructed 

 swing and surface feeders among the fish may be able to move 

 about freely. The shallow edges should be deepened and the 

 material removed used to limit the swamp areas or fill shallow in- 

 dentations or detached depressions. If only a small amount is 

 available the vegetation at the edges may be burnt with a gasoline 

 blast torch, of which there are several types on the market, one 

 of them especially adapted for this sort of work. With such a 

 torch even green vegetation can be scorched and destroyed to the 

 water surface, forming a clearing sufiicient to expose the larvae 

 to their natural enemies. Oil or other larvicide applications are 

 unsatisfactory in such areas. The preparations that are sup- 

 posed to mix with the water are cut out because of the amount of 

 water to be affected and the surface oils are difficult to get among 

 the grasses and overgrown edges so as to really cover the surface. 

 Conditions demanding treatment will vary; but the underlying 

 principles are, drainage where possible; open water stocked with 

 fish where drainage is impossible. The conditions favoring the 

 development of mosquitoes have been described at length in gen- 

 eral and in detail for each species. The task is to remove these 

 favoring conditions. Any practical engineer should be able to 

 deal with local problems once the source of danger is fixed. 



Running streams are rarelv sources of trouble; but where 

 they are sluggish or form shallow overgrown pools, or are ob- 

 structed in any way, some Anopheles may and often do develop. 

 In such cases the bed of the stream should be cleaned or the 

 channel should be deepened, using the material removed to fill 

 the shallow edges and narrow the bed. Under the conditions 

 usuallv found in streams, breeding is so very restricted that it 



