132 INJUBY TO THE FOREST BY INSECTS. 
Injury to the Forest by Insects. 
The action of the insect on vegetation, as we have thus far 
described it, is principally exerted on smaller and less con- 
spicuous plants, and it is therefore matter rather of agricul- 
tural than of geographical interest. But in the economy of 
the forest European writers ascribe to insect life an importance 
which it has not reached in America, where the spontaneous 
woods are protected by safeguards of nature’s own devising. 
The insects which damage primitive forests by feeding upon 
products of trees essential to their growth, are not numerous, 
nor is their appearance, in destructive numbers, frequent, and 
those which perforate the stems and branches, to deposit and 
hatch their eggs, more commonly select dead trees for that pur- 
pose, though, unhappily, there are important exceptions to this 
latter remark.* I do not know that we have any evidence 
* The locust insect, Clitus pictus, which deposits its eggsin the American 
locust, Robinia pseudacacia, is one of these, and its ravages have been and 
still are more destructive to that very valuable tree, so remarkable for combin- 
ing rapidity of growth with strength and durability of wocd. This insect, I 
believe, has not yet appeared in Europe, where, since the so general employ- 
ment of the Robinia to clothe and protect embankments and the scarps of 
deep cuts on railroads, it would do incalculable mischief. As a traveller, 
however, I should find some compensation for this evil in the destruction of 
these acacia hedges, which as completely obstruct the view on hundreds of 
miles of French and Italian railways, as do the garden walls of the same 
countries on the ordinary roads. 
The lignivorous insects that attack living trees almost uniformly confine 
their ravages to trees already unsound or diseased in growth from the depre- 
dations of leaf-eaters, such as caterpillars and the like, or from other causes. 
The decay of the tree, therefore, is the cause not the consequence of the in- 
vasions of the borer. This subject has been discussed by Perris in the 
Annales dela Société Entomologique dela France for 1852, and his conclusions 
are confirmed by the observations of Samanos, who quotes, at some length, 
the views of Perris. ‘‘ Having, for fifteen years,” says the latter author, 
‘‘incessantly studied the habits of lignivorous insects in one of the best 
wooded regions of France, I have observed facts enough to feel myself war- 
ranted in expressing my concluzions, which are: that insects in general-—I am 
not speaking of those which confine their voracity to the leaf—do not attack 
