There are many other insects which, when young, live below ground,
and become above-ground flying creatures, when full grown, which have
not the carnivorous tastes of the forms we have just mentioned. Many
of these species live on the roots of plants and others upon the
vegetable mold of rich soils. The large white grubs so often found
in the soil of grass lands belong to both of these classes. They are
the larvæ, or young, of several kinds of the clumsy beetles known as
scarabs. The larvæ of the common brown May-beetles, for example, are
root-feeders, living mainly on grass-roots, and they are sometimes so
abundant and destructive as to destroy valuable lawns. The roots are
sometimes so uniformly eaten off by these white grubs that the sod may
be rolled up like a roll of carpet. The white grubs of the beautiful
large green beetles, known as June-beetles, or fig-eaters, in the
South (they do not occur in the more northern states), although they
look almost precisely like the May-beetle larvæ, are not injurious and
feed only upon the vegetable mold of the soil. The wire-worms, which
are the young of the click-beetles, or "snapping-bugs," feed upon the
roots of plants; there are plant lice which live underground and suck
the sap from plant roots, like the famous grape-vine phylloxera; there
are caterpillars which live almost entirely underground and feed upon
living roots; there are maggots which have the same habit; and there
are even bark lice or scale insects which live attached to rootlets in
the same way that the other species live above ground on the limbs and
twigs of trees.
Other insects living above ground all their lives hide their eggs
underground. Most grasshoppers, for example, do this, and many of the
closely related crickets not only hide their eggs in this way, but live
underground themselves in the day time, and come forth at night to
feed, or to collect grass leaves, which they carry into their burrows
and eat at leisure. Other insects also hide below ground during the
day and feed only at night. The full grown May-beetles do this, and
the cut-worms also. The cut-worms are soft-bodied caterpillars and are
greedily eaten by birds and carnivorous insects, so it is essential to
their safety that they conceal themselves as much as possible. There
is an interesting cut-worm which occasionally becomes so numerous that
it has to migrate in great armies in search of food, and these great
masses of caterpillars hurry on, driven by hunger, by day as well as by
night, followed by flocks of birds and other enemies until the majority
of them are destroyed. This cut-worm is generally called the "army
worm."
Other caterpillars, while living above ground and feeding on the
leaves of plants, instead of spinning cocoons for their protection
when they transform to the helpless chrysalis or pupal condition,
burrow beneath the surface of the ground and there transform without a
cocoon. Hundreds of species do this and sometimes these brown pupæ are
so abundant that they are turned up in numbers with every spadeful of
earth.
We are now able to say that the insects found beneath the surface of
the earth are as follows:
1. Insects which live underground during their whole lives, feeding
(_a_) on roots and rootlets; (_b_) on dead and decaying vegetable
matter; (_c_) on other insects.