498 LAND ANIMALS 



are present in considerable numbers. At high altitudes insects are 

 dependent on the heat of the sun-warmed earth, for they require a cer- 

 tain minimum temperature to function, 12° to 15° in butterflies, which 

 is higher than the air temperature at high altitudes in the alpine zone. 

 Since both ground and air temperature fall below this limit at night, 

 nocturnal insects are ruled out, and such noctuid and geometrid moths 

 as occur are forced to adapt themselves to diurnal life. 32 Once in flight, 

 the muscular motion generates enough heat to make some insects less 

 dependent on that of the environment. As a means of conserving this 

 internal heat, many alpine insects have a dense hairy covering, es- 

 pecially notable in the bumblebees, but also found in many flies, and 

 in the Apollo butterfly. In accordance with the adverse effects of the 

 strong winds above mentioned, many wingless or flightless insects are 

 found in the alpine zone, especially among grasshoppers and ground 

 beetles. 



Collembola range into the snow zone itself. The best-known form, 

 the glacier flea, Isotoma saltans, ranges up to 3800 m. in the Alps. 

 Thirty-two of the 95 species of Collembola known from Switzerland 

 occur in the snow zone. Many species are ubiquitous widespread forms 

 such as Entomobrya nivalis and Isotomurus palustris. Others, like 

 Isotoma saltans and I. westerlundi, are stenozonal, and confined to 

 snow and ice. The latter are black or dark blue, and are consequently 

 quickly warmed by the sun's rays. At night they are frozen rigid and 

 freeze fast to snow and neve. 33 They feed on the pollen of conifers, 

 which blows into the alpine and snow zones. Their numbers may be 

 countless, so that snow and ice are blackened by them. A few other 

 extremely resistant organisms occur with the Collembola. The "red 

 snow" of the Aar glacier (colored by algae) contains also a tardigrade 

 and the rotifer Philodina roseola?* 



Just as the reindeer is attended by the wolf, and the baboon by 

 the leopard, so we find minute predators feeding on the snow-zone 

 Collembola, mostly mites of the families Bdellidae, Trombididae, and 

 Gamasidae. 33 



Grasshoppers are the only Orthoptera of the alpine zone, and they 

 are found principally in the lower portion where a more abundant 

 vegetation and longer season enable them to develop. Hingston found 

 grasshoppers as high as 5490 m. on Mount Everest. 35 Only a few of 

 the alpine species are confined to this zone. Podisma frigida in the 

 Alps represents these truly alpine forms, which usually have stocky 

 bodies, are densely haired, and have thick and somewhat bent legs. 36 

 A large proportion of the alpine Orthoptera are flightless, in both Old 

 World and North American mountains. 37, 38 Fifty-four per cent of the 



