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.