180 INDIKECT INJURIES CAUSED BY INSECTS. 



most formidable wood-borers with us is the larva of the great 

 goat-moth ( Cossus Ugniperda ^ ), which attacks willows, pop- 

 lars, and occasionally even elms and oaks ; and from its 

 large size, and living above two years in the larva state, the 

 holes which it makes are a great deduction from the value of 

 the tree, even if it be not entirely destroyed. The larvae of 

 Zeuzera cesculi, though much smaller, has similar habits, and 

 is injurious by boring into apple, pear, and walnut trees. 



The insects which attack the bark of trees mostly belong 

 to the family of Scolytidce Westwood (including the genera 

 Scolytus, Hylesinus, Hylurgus, Tomicus, &c.); a numerous tribe 

 of beetles, the larvae of which, after being hatched from the 

 eggs deposited by the parent beetle, excavate in the substance 

 of the inner bark, and partly also in the adjoining alburnum 

 or sap-wood, lateral parallel channels more or less sinuous, 

 proceeding on each side from a central one (that in which the 

 eggs were placed), and thus giving to the under side of the 

 detached bark and exposed alburnum that pinnated laby- 

 rinthine appearance, and fancied resemblance to letters, which 

 made Linne affix to one of these insects, to be presently al- 

 luded to, the trivial name of Typographus. When in small 

 numbers these larvae may do no great injury"; but where they 

 abound, as they often do, by interrupting the course of the 

 latex, or descending sap, and admitting wet between the bark 

 and wood, decay speedily ensues, and the tree perishes. Al- 

 most every kind of tree is liable to the assaults of one or more 

 species of this tribe of insects. Even fruit-trees, as the apple, 

 plum, &c., have each their Scolytus; and at Rouen I found a 

 species, I believe undescribed, which feeds on the mountain 

 ash. It is to our large forest trees, however, that they are 

 most injurious. Thus the common ash is assailed by Hylesinus 

 fraxini, the pinnated labyrinths of whose larvse you can 

 hardly fail to observe on the first piece of loose bark you de- 

 tach from the rough-split posts and rails made of this wood ; 

 while the bark-borer of the oak is a small beetle of an allied 

 genus, Scolytus pygmceus, which with us does no great harm, 

 but so abounded of late years in the Bois de Yincennes, near 



I Curtis, Brit. Ent. t. 60. 



