128 ON THE NATURAL HISTORY OF BEETLES 



the percolation of rain and other ungenial weather, which causes 

 the bark to peel off, causing permanent injury to the tree. These 

 bark-burrowers belong principally to the family of Scolytidce, includ- 

 ing the genera Scolytus, Hylesinus, Hylurgus, Tomicus {Bostrichus), 

 &c. They may be distinguished into two classes, viz., those that 

 bore into the heart and body of the trunk of the wood, and those 

 that confine their inroads to the inner bark with its adjacant sap- 

 wood or alburnum. Probably in the case of coniferous trees, the 

 operations of these internal wood-borers are chiefly of the latter 

 description ; while there are many insects which attack hardwood 

 timber, and do not confine their inroads to the inner bark, but 

 chiefly burrow into the heart of the trunk itself, rendering even 

 large willows, poplars, oak, elm, and other timber trees so hollow 

 as to be easily blown down. Of these destructive creatures are the 

 stag-beetle family (Lucanidre) ; and the very widely-branched 

 tribe of Capricorn beetles, including Primus, Gerambyx, Lamia, 

 Stenocorus, Leptura, Rhagiurrt, Gnoma, Saperda, Callidium, and 

 Clytus (Fab.) 



Xor are the ravages of these mischievous creatures apparent and 

 important in the forest and plantation alone, but very frequently 

 the doings of some of them only become known in after years, 

 when trees apparently sound have been felled and converted into 

 timber for construction purposes. This is owing to the length of 

 time sometimes necessary for the full development of the larvse of 

 many of the species. For example, in the order of Hymenoptera, 

 one genus called Sirex is peculiarly destructive to fir timber. In 

 woods in Yorkshire, Stephens reports that whole plantations of firs 

 have been known to be destroyed by the operations of its larvae 

 under the bark. Two of the most conspicuous and destructive 

 members of this genus are Sirex gigas and juvencus, both of 

 which have been known to issue from the wood of joists and floor- 

 ing in houses, after the timber had been wrought up and used for 

 three years. 



The other principal bark-boring beetles which affect Coniferre are 

 Tomicus pinastri, laricis, micographus, typographus (already re- 

 ferred to), and chalcographies, which are happily, however, less known 

 in Great Britain than in the continental forests. We have, however, 

 more common in this country, the well-known Hylurgus piniperda, 

 and the two large weevils, Pissodes notatus and pint* Another 

 secondary ailment, which frecpuently befalls the victim of these bark- 

 * This insect is said to be common in Rannoch. 



