The Bees and the other stinging groups have four wings like all the
_Hymenoptera_. These wings are almost always clear and transparent, at any
rate amongst the British species, there being only one exception which I
can call to mind in the female of the cuckoo of our large red-tailed
humble-bee, which has the wings blackish; also they are never spotted, as
in some flies. The hind or lower wings unite with the upper by a series of
very beautiful hooks which extend along their upper margin and fix on to
the posterior edge of the front wing, which is folded back on itself so as
to receive them; in flight the two wings are united, but when at rest they
separate; these hooks are beautiful objects under a microscope; their
numbers vary; and in some cases this variation is useful in distinguishing
closely allied species from one another. The hum of a bee is caused, to a
great extent, by {111} the vibration of the wings, but it has been shown
that a loud buzzing noise can be emitted by bees which have lost their
wings; this proceeds from the spiracles or holes in the outer covering of
the creature through which it breathes. It is therefore not always easy to
say how much of the hum is caused by wing vibration and how much by the
action of the spiracles. Some, in fact most, of our solitary bees are
almost silent in flight, and their note can be heard only when large
numbers are flying together; others have a very peculiar shrill hum, by
which even the species can almost be recognized. In bright, hot, sunny
weather their flight is more rapid and their note attains a higher pitch.
The bees with the highest pitched hum with which I am acquainted are the
two smaller species of _Anthophora_ and _Saropoda bimaculata_.
In early spring, when it is hot in the sunshine and cold when a cloud
covers the sun, it is no unusual thing to see a bee drop to the ground. The
cold seems to paralyze altogether their powers of flight. When at rest a
bee folds its wings along the sides of its back, but only in the wasp tribe
is there the arrangement for them to be {112} folded longitudinally. The
shape of the wings varies very little, but the arrangement and number of
their cells vary considerably. There are some very interesting genera in
which the neuration of some of the cells is so slightly indicated that they
are hardly visible, and can be seen only when the wing is held in certain
lights; these faintly indicated cells are nearly always those towards the
apex of the wing, the neuration of the basal part of the wing being as
strong as in the other genera. There are a few moths in this country which
very much resemble, both in the colour of their bodies and their clear
wings, the wasp tribe, but they may be known by the brown band of scales at
the apex of the wings and also by the absence of the narrow waist, which
exists in all the stinging tribes. The only wingless forms which we know
are to be found amongst the ants and the fossors, and as a rule are
females, but in a few cases in the ants, and in some foreign species of the
genus _Mutilla_, the male is apterous also.
* * * * *
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