While the dragon-fly pupa is under water, the case 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.