ANIMAL LIFE OF POLAR REGIONS 507 



Arctic land life. — The land fauna, independent of marine life, is 

 far from rich in the Arctic. The numbers of species and of individuals 

 decrease to the northward as they do with approach to the snow-cov- 

 ered zone in the mountains. Relatively few species are able to survive 

 the rigid selection by the severe environmental conditions. The com- 

 position of the fauna that survives this selection exhibits a similarity 

 with that of high mountains in the groups represented. The arctic 

 fauna is composed in large part of widely distributed (euryzonal) 

 forms which range northward from more temperate latitudes, with a 

 smaller element of local (stenozonal) species absent to the south. Thus 

 of 565 arctic Hymenoptera, only 86 species are confined to the North 

 Polar Zone. 



Many arctic animals are also found in the alpine zones of high 

 mountains or on the tops of moderate ranges without specific dif- 

 ference, for example on the Brocken in the Hartz and on Mount Wash- 

 ington in the White Mountains of New Hampshire. This is not 

 surprising when the animals are widespread and range through the 

 intervening lowlands, like the collembolan Entomobrya nivalis, the 

 tardigrade Macrobiotics macronyx, or the snail Euconulus fulvus. For 

 migratory birds the lowlands obviously do not constitute a barrier. 

 Butterflies, however, like Lycaena orbitulus, which occur in Labrador 

 and arctic America and in Lapland, and reappear in the Pyrenees, 

 Alps, and in the mountains of central Asia, while wholly absent in the 

 intervening areas; breeding birds, like the arctic ptarmigan, whose 

 nearest ally in Europe is found in the Alps; and the arctic hare {Lepus 

 timidus) , which is also closely allied to the alpine species, are under- 

 standable as glacial relicts. 



Arctic insects. — Not all the orders of insects are represented in 

 the Arctic. The Thysanura are absent, as are the panorpids. Others, 

 like the may flies, forficulids, and Neuroptera (in a wide sense) are, 

 in general, rare. The number of species of insects in arctic Scandinavia 

 in 2596, 437 in Greenland, 326 in Iceland, 208 in Nova Zembla and 

 Waigach, and 94 in Spitzbergen and the Bear Islands. Of Hymenoptera 

 380 species are known from Scandinavia north of 65°, 66 in Greenland 

 north of 60°, 31 in Nova Zembla (71°-76°), and 15 in Spitzbergen 

 (76°-81 ): 5 The proportion of species of the separate orders which 

 occurs in the Arctic is quite different from that of their numbers of 

 species as a whole. As in the high mountains, the Diptera predominate 

 and here during the short summer season mosquitoes are a veritable 

 plague; they are followed in importance by Hymenoptera, Coleoptera, 

 Collembola, and Lepidoptera. The proportions of species for the orders 

 are distributed as follows: 



