Thick in yon stream of light, a thousand ways,
Upward, and downward, thwarting, and convolved,
The quivering nations sport; till tempest winged,
Fierce Winter sweeps them from the face of day.
E'en so luxurious men unheeding pass
An idle summer life in fortune's shine,
A season's glitter! Thus they flutter on
From toy to toy, from vanity to vice;
Till blown away by death, oblivion comes
Behind, and strikes them from the book of life.
The neuroptera, or _nerve-winged_ insects, have four wings, which
are membranaceous, naked, and so interspersed with delicate veins,
that they have the appearance of beautiful network. Their tail
has no sting; but that of the male is frequently furnished with
a kind of forceps or pincers. The genera are:--1. _Libellula_,
dragon-fly.--2. _Ephemera_, May-fly, or trout-fly, &c.
The _libellula_, or dragon-fly, is an insect of very splendid and
variegated colours. It is a large and well known fly, and frequents
rivers, lakes, pools, and stagnating waters, in which the females
deposit their eggs. The egg, when deposited by the parent in the
water, sinks to the bottom, and remains there till the young insect
has acquired sufficient maturity and strength to burst from its
confinement. The larva, at first small increases to nearly half the
size of the perfect fly, by changing its skin at different intervals
like the caterpillars of moths and butterflies. The appearance of
the little cases containing the rudiments of the wings, at the lower
margin of the thorax, denotes its change to the state of pupa. The
head of this larva is exceedingly singular, being covered with a
mask extending over the whole of the fore part of the head, with
cavities in the anterior surface to suit the different prominences
of the face to which it is fitted with perfect neatness. Its form is
triangular, growing smaller towards the bottom: in the latter part
there is a knuckle which fits a cavity near the neck, and on this
part it turns as on a pivot. The upper part of this mask is divided
into two pieces, which the insect can open or close at pleasure,
and it can also let down the whole mask, should occasion require.
The inner edges of these two pieces are toothed like a saw, and
serve the animal as a pair of forceps to seize and retain its prey.
This is the general principle on which these projecting forceps are
constructed in the larva of the libellulæ; they differ in shape in
the several species, but uniformly act in a similar manner.
These animals generally live and feed at the bottom of water,
swimming only occasionally. Their motion in the water can scarcely
be called swimming; it is accomplished by sudden jerks repeated
at intervals. This motion is not occasioned by their legs, which
at this time are kept immoveable and close to the body: it is
by forcing out a stream of water from the tail that the body is
carried forward, as may be easily perceived by placing them in a
flat vessel, in which there is only just water enough to cover
the bottom. Here the action of the water squirted from their tail
will be very visible; it will occasion a small current, and give
sensible motion to any light bodies that are lying on the surface.
This action can only be effected at intervals, because after each
ejaculation the insect is obliged to take a fresh supply of water.
The larva will sometimes turn its tail above the surface of the
water, and force out a small stream, as from a little fountain, and
with considerable force.
Under the same order is comprehended the _phryganea_, or spring-fly:
the caterpillars of this genus live in the water, and are covered
with a silken tube. They have a very singular aspect; for, by means
of a gluten, they attach to the tubes in which they are enclosed
small pieces of wood, sand, gravel, leaves of plants, and not
unfrequently live on testaceous animals, all of which they drag
along with them. They are very commonly found on the leaves of the
water-cress; and, as they are often entirely covered with them, they
have the appearance of animated plants. They are in great request
among fishermen, by whom they are distinguished by the name of stone
or cod-bait. The fly, or perfect insect, frequents running water, in
which the females deposit their eggs.