ANIMAL LIFE OF POLAR REGIONS 509 



jecting to cold pupae of the same species from temperate latitudes. 

 Endemic forms, confined to the arctic zone, are few. 



Among Hymenoptera, the Tenthredinidae and Ichneumonidae (in 

 the Linnaean sense) are the best-represented families. Ants are few, 

 with only a few species of the genus Lasius. Among bees, the bumble- 

 bees predominate, especially in the extreme north. In the bumblebees 

 the plump body with its small surface relative to size, and its dense 

 hairy covering, conserves the heat generated by the rapid vibration of 

 the wings. Bumblebees may accordingly be active in cool weather 

 when other insects are unable to fly. They become larger and more 

 rough-haired to the northward, as they do with increasing altitudes 

 in mountains. Bombus consobrinus of arctic Norway is larger than the 

 largest forms of the lowlands {B. terrestris and B. hortorum) , though 

 shorter haired; B. kirbyellus, which reaches 77^5° N. latitude in west 

 Greenland, is still larger and broader, and more hairy; B. hyperboreus, 

 which occurs everywhere in the Arctic, is the largest and hairiest species 

 of all. The larger species emerge from hibernation as early as the first 

 of June; the smaller do not appear until the middle of July. 11 As these 

 creatures continue their work during the bright summer nights, they 

 accumulate a food supply sufficient to ensure the development of their 

 larvae in a single season. 



Other poikilotherms. — The number of species of spiders dimin- 

 ishes greatly to the northward. There are 219 species in Lapland, 46 

 in Greenland, and only 29 in the arctic islands. 



The land and fresh-water snails of the Arctic are all very small. 

 They occur principally at the borders of springs. In Norway, favored 

 by the Gulf Stream, 50 species range beyond the tree limit. Twenty- 

 four species have been found in Iceland, and 9 in Greenland. These 

 northern forms are principally widespread species.* Helix (Acan- 

 thinula) harpa, which occurs in northern Scandinavia, Kamchatka, 

 and Canada, is known from a single locality in the Alps, at 2000 m. 

 altitude. 



As in high mountains, reptiles and amphibians are few in the 

 Arctic. Two reptiles and 6 amphibians range beyond the Arctic Circle. 

 In Europe the arctic species are the two frogs, Rana temporaria and 

 Rana arvalis, the viviparous lizard, Lacerta vivipara, and the common 

 viper, Vipera berus. Rana latiremis is the most northern frog of arctic 

 America. None of these species occurs on the arctic islands. Iceland 

 appears to have had frogs (presumably introduced) until the severe 

 winter of 1829-1830 exterminated them. 12 



* Euconulus fulvus, Cionella lubrica, Vitrina diaphana, and a few Pupidae. 



