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L OOK at a worm crawling about on the earth. Then look at a fly with blue or green body and thin wings. See how it whirls in the air! You will say, "These two are not at all alike."
Yet there is one time in a fly's life when it is very like a worm.
For this reason many wise people set flies and worms next to each other when they study them.
You know, as soon as you look at a fly, that it is an insect.
You have learned that an insect has wings, six legs, a body in three parts, and a pair of feelers like horns.
Insects breathe through all the body, and not by lungs as you do. They have a row of holes in each side to breathe through.
The life of an insect passes through three states. These are the egg, the grub or worm, and the pupa. When it is in the pupa it gets legs and wings. The word "pupa" means baby or doll.
There are some kinds of insects that vary in some of these points. The fly is one that varies from this rule.
If you look at a fly, you will see that it has two wings, not four. It is not one of the hook-wings.
Many insects can fold their wings. The fly cannot fold its wings; it lays them back over its body.
Let us first look at a fly when it is most like an earth-worm. The fly comes, in the first place, from a tiny egg laid by the mother fly.
When the egg opens, the baby fly is not like a fly, but like a little earth-worm, both in its looks and in the way in which it is made. It is a small white worm with rings, and on the rings are hooks.
If you wish to watch this change, lay a bit of meat in the sun on a hot day. Soon flies will lay eggs on it.
The next day these eggs will be turned to grubs, which grow very fast. The fly's eggs are small and white, and are put upon the meat as if they had been planted on one end.
The worm of the fly has a pair of jaws like hooks. It has two little dots which will become eyes when it has grown to a fly. In the hooked jaws and these eye-points it is not like an earth-worm.
The fly grub eats and grows. Then its skin gets tough and hard, and forms a little case like a barrel. This shuts the worm in it, as in a coffin. Now the baby fly seems to be dead.
But it is not dead. It is turning into a creature that has wings and legs, and can fly and walk.
As the fly lies in its case, first the legs and then the wings grow. It gets a head with mouth, eyes, and a trunk or tube, and from a poor worm it turns to a wonder, as you will see.
But in its little coffin it is shut close, and its legs and wings are all bent up. In a few days the change is made. Now it is ready to come out.
It moves, and pulls, and gets free from the hard case. Then it strikes the end of the case with its head time after time. At last it breaks the case open, and out comes the fly!
Then it stands in the air, and in the sun if it can, and shakes itself. It is cold and weak; but the air dries its wings and blows out the wrinkles.
In a very few minutes the fly is strong and gay.
Then it spreads its wings and sails off to enjoy its life, and to look for something good to eat.