LESSON XLV.
THE WINGS OF THE DRAGON-FLY.
We can find no better example than the dragon-fly, of the way in which insects behave when they leave the pupa-case.
You know that this case is horny or tough, and always seems smaller than the grown-up insect; so the insect must be very closely packed in.
No person could pack a new insect back into the case it has just left.
While the dragon-fly pupa is under water, thecase is kept tough, and yet soft enough to bend. But when the pupa crawls up the stem of the plant into the air, the case soon dries and becomes brittle.
As the fly struggles within, the dry case will easily split. The little wet coat, which covers the body while it is in the case, makes it more easy to slip out of the shell when it cracks open. You know if you have on your finger a ring which is too tight, you can pull it off if you wet your finger.
The wet coat of the fly in the case keeps the wings from being hurt by their close folding. After they are dry and spread out, they are easy to break. Then it is very easy to hurt or spoil them.
The fly seems to know this, and is careful of its wings. In the act of unfolding, the fly holds its wings from touching any object, even its own body.
When the dragon-fly gets free from the case, it knows just how to spread its lovely wings into perfect shape. It stands quite still, and far enough from stems or leaves to keep its wide wings safe.
It does not move its wings, but lets the air do the work, while it holds its bent body away from the wings. The quiver you see through it, now and then, is a motion of the body; and I will soon tell you what it means.
When the fly first comes from the case, its wings are soft, and will bend as easily as wet paper.After they are dry, they are like thin plates of glass. These wings have very many nerves through them. Their frame is like a fine net-work, and, as it is touched by the air, it spreads slowly to its full size. If, at this drying-time, the wings are hurt, they will never come to their right shape.
If any one should try to help a dragon-fly out of its case its wings would be ruined and never take their right shape. Human hands are too clumsy for such work.
When first the pupa comes from the case, the wings and body are of a dull, faded color. But as it stands in the sun and air, you can see it change from minute to minute.
A Child of an Hour.
A Child of an Hour.
Fold after fold of the wings shakes out; ring after ring of the body stretches to its proper length; the joints of the legs come to their right shape and firmness. From all the body of the insect a mist seems to pass away; and the colors of the fly come out, and red, blue, green, gold, shine in beauty.
Now let us look closely at these fine wide wings. Although they are so thin, like gauze, yet they are double. There is a surface on each side, spread over a very fine frame. The parts of this frame are small as the finest hairs.
And yet, though so tiny, they are all hollow. They are tubes or pipes. They carry through the wing, air and a very thin white fluid, which is the blood of the insect.
Now that you know this, can you clearly see how the wings expand? As soon as the dragon-fly is born from its pupa-case, air and this thin fluid are driven through these fine tubes. As they fill, they stretch out, and the thin surface which covers them spreads with them.
If you notice the fly as it is thus getting its shape, you will see that quiver which I spoke of. That motion is the pumping of air and fluid through its tubes; and, no doubt, by this action the fly spreads out its wings and its body. By such a motion the blow-fly spreads out its big head.
The dragon-fly spends about fifteen minutes in getting into shape. Sometimes half an hour is needed. After that, the fly rests for an hour or two, before it tries its wings in the air. Very likely it wishes to give its wings time to get quite firm and hard.
Butterflies, Lace-Wings, May-Flies, and other insects of the kind have their wings made in this way; so what you learn about one will help you to understand the others. You read of the Lace-Wing in the last lesson, and in the next book you will hear about Butterflies.
The May-Flies are very pretty insects. They are something like dragon-flies, but very much smaller, and not fond of tearing up other insects. You will find them in moist places. The body of the May-Fly is much slimmer even than that of the dragon-fly. The wings are unequal. Their heads are smaller. May-Flies have two fore legs, nearly as long as the body, held almost straight out as they fly. On their tails they have three long stiff hairs, twice as long as the body. These hairs spread out, fan-shape.
These insects are often called May-Flies, because they usually come in May. But they have another name, which means the “child of an hour.” This name is given them because they seldom live longerthan one day, and often only for an hour or two. In the egg, larva, and pupa they live about two years; but, once born with wings, they soon die.
And how do they spend that short life? They do not eat, for they have no mouths. As they are not hungry, they do not hunt. They spend their whole time in flying. Their flight is a sort of dance in the air; they rise and fall, and spin about.
Great numbers of them come out together, spin about, and drop their eggs in the water. But soon they flutter down, dead, among the grasses. That isthe story of the pretty May-Fly. I have been on a large island on a day when May-Flies had come out: the air was full of their shining silver shapes—they lit on people’s clothes, and seemed to cover them with a gauze veil.
Would you not like to seek out in their homes, and then read and study about, the very many strange and wonderful insects that are in the world?