50 THE TAIGA, OR CONIFEROUS 



arborea) of Europe just reaches the south of the taiga, 

 but the tree-frogs of North America have a more 

 northerly extension. 



In insects the northern forests are rich, for the 

 perennial vegetation feeds many herbivirous forms, 

 and many carnivorous or parasitic forms prey upon 

 these. Many of the beetles especially are important 

 pests from the point of view of the forester. 



As examples of wood-eating forms we may mention 

 the wood-wasps (Sirex), of which a large species (8. 

 gigas) often appears in summer-houses or other wooden 

 erections in Britain, where it has been introduced with 

 pinewood. The adult female has a boring apparatus, 

 by means of which she bores a hole in trunks of pine 

 trees in order to lay her egg at the bottom of the 

 excavation. The wood-wasps are preyed upon by 

 ichneumon flies, whose delicate senses enable them to 

 find the burrows of the wasps, when they insert their 

 long ovipositors and lay their eggs close to the wasp's 

 egg, so that the resultant larvae may prey upon the 

 wasp larva. There is here a singularly delicate adjust- 

 ment between host and parasite, comparable to the 

 relation which exists between the length of the pro- 

 boscis of certain butterflies and the length of the tubes 

 of the flowers which they visit. 



Another form which feeds in the pine woods is the 

 pine saw-fly (Lophyrus pini), whose larvae feed upon 

 the needles, sometimes in countless numbers. 



Wild bees also occur in the woods, the forms which 

 store up honey extending much further north in the 

 Old World than in the New. In Asia wild honey bees 

 reach the Arctic circle, while in North America, accord- 

 ing to Marshall, they scarcely pass latitude 50° N. The 

 honey is greatly prized by bears, who rob the nests 



