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.