The type of food available as well as the resistance of the various 

 groups in both the adult and immature stages govern the selection 

 of the fauna. The insects which feed on green plants disappear to the 

 northward much more rapidly than those which depend on plant re- 

 mains or on animal food. The separate orders afford a variety of 

 further observations. 



The springtails (Collembola) occur on snow and ice, just as they 

 do in the high mountains. The snow flea of Spitzbergen, Isotoma 

 nivalis, is only half as large as the alpine I. saltans, but occurs in 

 equal numbers, forming black aggregations to the extent of a square 

 foot. A series of cold-resistant forms, including infusorians, rotifers, 

 nematodes, and tardigrades, 6 is associated with Isotoma in this habitat. 

 Eight species of arctic-alpine collembolans are known. 7 



Grasshoppers are represented by only a few forms, which range 

 into the arctic from the south. A few Corrodentia and Dermaptera 

 reach Greenland. Hemiptera are represented by a few species of aphids 

 and a few bugs, such as the shore bug Acanthia and the resistant 

 lygaeid genus Nysius, which also reaches the snow zone in the Alps. 8 

 Beetles are notably few in species in the Arctic. A few arctic-alpine 

 forms occur such as the dung beetles among which 10 of the 12 species 

 in arctic Norway recur in the Alps. 9 



The relation between montane and arctic butterflies is especially 

 noteworthy. Many genera* are represented in the Arctic and in high 

 mountains as well. Hawk moths and bombycids are infrequent in both, 

 while noctuids and geometrids have numerous common species and 

 genera. The same is true of microlepidoptera. This similarity applies 

 to the mountains of Eurasia and North America, and extends even 

 to the southern hemisphere in the Andes. 10 In general, small species are 

 characteristic of the polar region. Species with omnivorous larvae, 

 which will feed even on the resistant grasses and shrubs which survive 

 the arctic conditions, are favored. Their period of growth often extends 

 over two years, as in high mountains. The small arctic form of the 

 widespread Vanessa urticae can be produced experimentally by sub- 



* Pieris, Colias, Polyommatus, Lycaena, Maniola, Oeneis, Vanessa, Argynnis, 

 Melitaea, and Syrichthys. 



