H OW often people cry out, "Oh, I wish there were no flies! What is the use of a fly?"
But all things that God has made have their uses. And all God's works are worthy of study.
You have learned that worms are of great use. Let us see if Mrs. Fly does any good in the world.
Mrs. Fly is of great use to man. She helps keep him in health. Do you think that very strange?
People say, "Oh, these dirty flies!" And yet these "dirty flies" help to keep the world clean!
Now you know that over all the world, great numbers of animals die each minute, and many of their bodies lie on the ground and decay.
Such bodies in decay cause disease and death to men. In winter, and in cold places, such things do not decay so fast, and so do not make these bad odors.
But in hot days, if such dead things lie about, they will poison the air. Soon we should all be ill.
The work of Mrs. Fly is to lay many eggs in these dead bodies. In a few hours these eggs turn to grubs, and these grubs to little live worms, which begin to eat as fast as they can.
Soon they leave only dry bones, which can do no harm. They change the dead stuff into their own fat, live bodies.
You know that the crabs are among the street-cleaners of the sea. So the flies are among the street-cleaners of the air and land.
Did you ever watch flies dart about, here and there, with a flight like hawks? They are eating up small, evil things, too small for us to see. But these are yet big enough to hurt us if we should get them into our lungs.
Ask your teacher to tell you a little about your lungs.
In and about our homes many bits of things drop, and might decay and mould. This would make the air foul. But the busy and greedy fly drinks up all the soft part of these things.
So we see that what we call the dirty flies help to clean away much dirt. It is true too, that flies carry poison on their feet and trunks from place to place. In this way they do great harm.
The fly serves for food for many birds, and fish and frogs, and some insects. Some of these things we use for our food. Others are full of beauty, or are of use to us, each in its own way.
Thus, though the fly is often a trouble to us, we find it is not without its uses. Look at one of these little creatures through a glass that will magnify it. You will see that the poor insect has really much beauty.
From what you have read in this lesson you must not think that all foul smells kill, nor that things that have no bad smell are always safe. There are some gases that have no odor at all, which yet are very deadly.