beetle only the hinder pair, the pair that in the
fly are only 'vestiges.' The front pair of wings in the beetle form hard
horny cases or shields for the protection of the hinder wings, which lie
beneath them when not in use.

The wings of insects are often brilliantly coloured, and this colour may
be caused in two very different ways. Generally the colours of the wings
are due to the way the surface of the wing is made, for this surface
reflects light. But the colour of the wing of the butterfly is to be
traced to a quite different cause. If the fingers be rubbed over the
surface of a butterfly's wing, they will be found to be covered with a
fine coloured dust, whilst the wing itself will become quite transparent
(as in fig. 1). If this dust be looked at under the microscope, it will
be seen that it is made up of a number of tiny scales, most beautifully
shaped (as in fig. 2). Each scale is fixed to the surface of the wing by
a tiny stalk and in a regular order.

From the shape of the wings in the butterfly or moth we can tell more or
less how the insect flies. Long and narrow wings give a swift and rapid
flight, broad round wings a slow and leisured flight.

The wings of insects are moved by only a few muscles, but with wonderful
rapidity. It has been calculated that the common fly makes with its
wings three hundred strokes per second, the bee one hundred and ninety.
The dragon-fly and the common cabbage-white butterfly of our gardens,
however, have a much slower beat of their wings, the former twenty-eight
strokes per second, the latter only nine. The machinery by which they
move is like that of an oar.

[Illustration:

1. Butterfly's Wing (magnified).
2. Scales from Butterfly's Wing (greatly magnified).
3. Earwig (magnified): one wing folded, the other open.
4. Foot of Fly (greatly magnified).]

Insects' wings are folded in various ways. Those of the butterfly, when
at rest, are raised up over the back, so that the upper surfaces of the
right and left wings come together. In the moth the hinder wings pass
under the fore-wings, which are held flat over the back. But the beetle
and the earwig hide their hind-wings beneath a hard case not used in
flight. The size of the hind-wings, however, is so great that before
they can be covered by the horny case, they have to be folded up, and
this is done in a really wonderful manner, especially by the common
earwig.

Most people probably think of the earwig as flightle