VORACITY OF INSECTS. 
147 
were almost entirely destroyed by the larvae of an insect 
called the “ turnip-fly.” The parent insects were seen buzzing 
over the fields, and depositing their eggs in the plants, which 
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 larvse 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 Mam Thus, a set of. 
l 2 
