154 PROTECTION AGAINST INSECTS. 



which does not occur north of the river Main ; the oak proces- 

 sion moth is commonest in north and east Germany. The 

 character of the insect fauna is, however, generally similar 

 over the whole of the Palaearctic region, which includes 

 Europe, the northern coasts of Africa, and Asia north of the 

 great mountain chains that cross it from east to west. The 

 number of species extending over the whole of this region is 

 comparatively small, and there are no zones in it in which 

 the character of the insect inhabitants is abruptly changed. 

 As compared with continental regions under similar climatic 

 conditions, the insect fauna of the British Isles is poor. 



As regards altitude, the distribution of insects depends on 

 that of the trees and shrubs on which they feed, and also on 

 locality and climate. Most insects prefer the warmer plains 

 and hilly districts, especially with a sandy soil, where beetles 

 thrive. Soils naturally poor and those impoverished by 

 removal of litter, sunny aspects, frost-hollows, and stunted 

 vegetation are natural breeding-grounds for insects, and 

 require the most careful supervision on the part of the 

 forester. The number of species and of individuals alike 

 diminishes with increasing altitude ; this is especially the case 

 with Lepidoptera, which are most dependent on climatic con- 

 ditions, but beetles are found at a considerable elevation in 

 mountains. Certain species of weevils and bark-beetles may 

 be considered as mountain insects, such as Otiorrhynchm 

 niger, Fabr., Tomicus cemlrae, Heer, Hylastes glabratus, Zett. 

 Even species of Chermes are found at elevations of between 

 3,000 and 3,600 feet. 



Insects, especially beetles, can support severe winters. 

 This was proved in 1870-1, 1879-80, the summers that 

 succeeded these hard winters being rich in insects. Their 

 horny elytra or wing-coverings protect them, and instinct 

 impels them to creep under roots and into cracks in the bark 

 of trees, or under moss or dead leaves for protection against 

 the weather, or to burrow underground. Moreover, as their 

 enemies, moles and insectivorous birds, cannot touch them 

 when snow or frost covers the ground, and are themselves killed 

 in very severe winters, such weather is really favourable to 

 insect life. A warm winter, which is usually accompanied with 



