VORACITY OF INSECTS. 147 



were almost entirely destroyed by the larvse of an insect 

 called the " turnip-fly." The parent insects were seen buzzing 

 over the fields, and depositing their eggs in the plants, \vhicli 

 they do not themselves employ as food ; and in a few days all 

 the soft portions of the leaves were destroyed, and nothing 

 but the skeletons and stalks were left. Some kinds of timber 

 occasionally suffer to no less an extent from the devastations 

 of insects, whose operations are confined to the wood, and do 

 not manifest themselves externally, until the tree is seen to 

 languish and at last to die. The pine-forests of the Hartz 

 mountains in Germany have been several times almost de- 

 stroyed by the ravages of a single species of beetle, less than a 

 quarter of an inch in length. The eggs are deposited beneath 

 the bark; and the larvae, when hatched, devour the sap- 

 wood and inner bark (the parts most concerned in the func- 

 tions of vegetation) in their neighbourhood. It was estimated 

 that, in the year 1783, a million and a half of pines were 

 destroyed by this insect in the Hartz alone ; and other forests 

 in Germany were suffering at the same time. The wonder is 

 increased, when it is stated that as many as 80,000 larvae are 

 sometimes found on a single tree. 



148. But every class in the Animal Kingdom has its car- 

 nivorous tribes, which are adapted to restrain the too rapid 

 increase of the vegetable-feeders (by which a scarcity of their 

 food would soon be created), or to remove from the earth the 

 decomposing bodies that might otherwise be a source of dis- 

 ease or annoyance. The herbivorous races, being for the most 

 part very prolific, would very rapidly increase to such an 

 extent as to produce an absolute famine, if not kept in check 

 by the races appointed to limit their multiplication. Thus, 

 the myriads of Insects which find their subsistence in our 

 forest-trees, if allowed to increase without restraint, would 

 soon destroy the life that supports them, and must then all 

 perish together ; but another tribe (that of the insectivorous 

 Birds, as the woodpecker) is adapted to derive its subsistence 

 from them, and thus to keep their numbers within salutary 

 bounds. Their occasional multiplication to the enormous 

 extent mentioned in the preceding paragraphs, is probably 

 due in general to the absence of the races that should keep 

 them in check. This may occur from accidental causes, or 

 may be produced by the interference of Man. Thus, a set of 



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