eed only mention the canker worm and American tent
caterpillar, and the various kinds of cut worms, as instances.

[Illustration: 43. Parasite of the American Silk Worm.]

We must not, however, forget the good done by insects. They undoubtedly
tend by their attacks to prevent an undue growth of vegetation. The
pruning done to a tree or herb by certain insects undoubtedly causes a
more healthy growth of the branches and leaves, and ultimately a greater
production fruit. Again, as pollen-bearers, insects are a most powerful
agency in nature. It is undoubtedly the fact that the presence, of bees
in orchards increases the fruit crop, and thus the thousands of moths
(though injurious as caterpillars), wild bees and other insects, that
seem to live without purpose, are really, though few realize it, among
the best friends and allies of man.

Moreover, insects are of great use as scavengers; such are the young or
maggots of the house fly, the mosquitoes, and numerous other forms, that
seem created only to vex us when in the winged state. Still a larger
proportion of insects are directly beneficial from their habit of
attacking injurious species, such as the ichneumons (Fig. 43, the
ichneumon of the American silk worm) and certain flies (Fig. 44,
Tachina); also many carnivorous species of wasps beetles and flies,
dragon flies and Aphis lions (Fig. 45, the lace-winged fly; adult, larva
and eggs).

[Illustration: 44. Tachina, parasite of Colorado Potato Beetle.]

[Illustration: 45. The Lace-winged Fly, Its Larva and Eggs.]

But few, however, suspect how enormous are the losses to crops in this
country entailed by the attacks of the injurious species. In Europe, the
subject of applied entomology has always attracted a great deal of
attention. Most sumptuous works, elegant quartos prepared by naturalists
known the world over, and published at government expense, together with
smaller treatises, have frequently appeared; while the subject is taught
in the numerous agricultural colleges and schools, especially of
Germany.

In the densely populated countries of Europe, the losses occasioned by
injurious insects are most severely felt, though from many causes, such
as the greater abundance of their insect parasites, and the far greater
care taken by the people to exterminate their insect enemies, they have
not proved so destructive as in our own land.

In this connection I may quote from one of Dr. Asa Fitch's reports on
the n