THE WINGS
Bees belong to a class of insects known as _Hymenoptera_, which means
with membranous wings; the wings of the bee are found to be composed
of beautifully fine membranes. They are four in number, and, like the
legs, are joined to the thorax. The front ones are called the anterior
wings, and the back ones, which you will notice are smaller, are called
the posterior wings, because they are behind the others. The membranes
are strengthened by a kind of framework, just as a kite is strengthened
by a framework of light sticks. The ribs of the framework are called
“nervures,” and, as you will see from (_a_) Plate XI., there are
divisions of transparent membrane in between; these are called cells.
The nervures are hollow, and like our veins, they contain blood.
We have seen that the bee possesses two pairs of wings, and we may
wonder why this should be so, when we know that one large pair is much
more powerful for flying purposes than two small pairs. You have no
doubt noticed that when a bee is at rest on a flower the wings are
neatly folded over the back. Now if the bee had only one pair of large
wings it would not be able to fold them so compactly--the wings would,
in fact, stand out on each side of the body. We shall presently see
that the bees, in the course of their duties, have to clean out the
cells of the comb, and in order that they may do this it is necessary
for them to be able to crawl right into the cell itself. The cells in
which the young worker bees are raised are only 1/5th inch in diameter,
and if the wings projected when in the folded position, the bee would
not be able to enter the cell. The wings therefore have been divided,
so that when folded they may lie one over the other on the bee’s back,
and we find that the wings, when folded, take up only 1/6th inch of
room. This leaves just sufficient space for their owner to enter a
cell. You will notice that a blue-bottle fly has only one pair of large
wings, for it does not need to fold them closely over its back, as it
has no cells to clean.
Remembering what I have told you about the greater flying power of one
pair of large wings, you might imagine that the division into two pairs
which we have seen to be necessary would handicap the bee in flying.
The difficulty is overcome by a most ingenious device, by which the
bee, when flying, is able to fasten together the wings on each side, so
as to form one pair of broad wings.
Let us now turn to (_a_) Plate XII., which shows part of the wings on
one side of a bee’s body. Along the top edge of the lower wing there
is a row of tiny hooks, and the lower edge of the upper wing is curled
over, thus forming a kind of ridge. When the bee takes to flight the
front wing is stretched out from over the back, and during this action
it passes over the upper surface of the back wing. When the ridge
reaches the hooks it catches upon them and is held fast. In this manner
the two wings are locked together. (_b_) Plate XII. shows the wings
hooked together ready for flying. When the bee comes to rest she folds
her wings, and in doing this they are automatically separated, for the
ridge slips away from the hooks that hold it.
[Illustration: PLATE XII
(_a_)
From a photo-micrograph by] [E. Hawks
Wing unhooked, showing Hooklets and Ridge
(_b_)
From a photo-micrograph by] [E. Hawks
Wing hooked, as in Flying]
The number of hooks varies, and there are sometimes more on one side of
the body than on the other. As a general rule it is found that a worker
bee has from eighteen to twenty-three of them, the one shown in (_a_)
Plate XII. having nineteen, as you will be able to count. The queen
does very little flying, and so her wings are not large, in proportion
to her size. Therefore she has not usually so many hooks, and sometimes
they are found to number as few as thirteen. The drone has large and
powerful wings, and his hooks vary between twenty-one and twenty-six in
number.
Bees are able to move their wings very quickly, and you will agree with
me in this when I tell you that it has been shown that the vibrations
number at least 190 per second! The flight of the bee is greatly
assisted by a number of air-sacs called _tracheæ_, contained in the
thorax. These fill with air and make the body more buoyant, just as a
lifeboat is made more buoyant by its air-chambers. When a bee has been
at rest for a little time it cannot begin to fly straight away, for the
air-sacs are empty. It therefore runs along the ground to get a start,
as an aeroplane does, and by vibrating its wings fills the tracheæ.