28 THE TUNDRA AND ITS FAUNA 



curious that they should be abundant in this cold 

 region, but the cause is to be looked for in the un- 

 developed condition of the drainage system, already 

 mentioned. The absence of any run-off in winter gives 

 the tundra, as we have noted, the characters of a semi- 

 arid region, with the result that the water formed in 

 summer by the melting of the snow tends to accumu- 

 late in innumerable lakes and pools. In these the 

 mosquito larvae swarm, and the natural checks, e. g. in 

 the shape of small fish who feed on the larvae, must be 

 insignificant. From the pupal stage the adults emerge 

 towards the middle of June, and they are then extra- 

 ordinarily abundant till the middle of August, when 

 they disappear, after having laid their eggs in the pools. 

 These pools freeze or dry up with the onset of winter, 

 but the eggs or larvae remain uninjured, to hatch or 

 recommence active life with the coming of water in the 

 spring. It is possible that the life-history is lengthened 

 by the cold, but the rapidity of reproduction is certainly 

 not checked, except in the coldest regions. In addition to 

 mosquitoes a considerable number of other flies occur, 

 especially about the houses of the Eskimo, &c., breeding 

 in the refuse thrown out. Indeed, fiies predominate 

 among northern insects, the percentage increasing as 

 we pass northwards. The reason lies apparently in 

 the fact that the larval stage is usually short, and 

 can be run through in the brief period of warmth. 



With the exception of the curious parasites known as 

 Strepsiptera, all the other orders of insects are repre- 

 sented, the bees and butterflies fulfllhng here their 

 usual role as fertilizers of flowers. The very short 

 active period of vegetation has a curious effect upon 

 the development of plant-eating insects. As is well 

 known, in more temperate countries butterflies usually 



