This fashion of making believe to be dead does not belong to flies only. Nearly all insects, and many other animals, sham death. It is worth while to watch and see how well they do it. When a fly is killed other flies come to eat up its body. They put their trunks or mouth tubes on the dead fly and begin to suck. Soon the body is sucked dry of all its juice. It is only a dry shell. I will tell you something that you can do with a dead fly. If it has not been dead so long that it has grown too stiff you can make the wings move. Hold it by the body. Gently tip up one wing. As you lift up one wing the other will rise too. They move together. It is as if they were set on a little spring. It is as wrong to be cruel to flies as to larger creatures. If they are to be killed, do it quickly, and give as little pain as possible. If we do cruel acts, we make our hearts hard and bad. LESSON XXI. SOME QUEER FLIES. Although flies are of use, they also do evil to men in many ways. It is well to look at things on all sides. The fly you have been reading about is the common house-fly. That fly, with its noise, dirt, and spoiling of food by laying eggs in it, is bad enough. But yet the house-fly makes the least trouble of any of its kind. There are many kinds of flies. To the family of flies belong gnats, midges, mosquitoes, and the big daddy-long-legs with wings. You know well how some of these things sting, you say “bite,” you. Mr. Daddy-long-legs hurts the grass lands with his grubs, which spoil grass roots and the shoots of plants. There is a fly called a “gall-fly” because it bites trees, and lays eggs in twigs. Then upon the twigs grow over the eggs round balls called “galls,” and these injure the trees. There is also the “bot-fly,” which lays its eggs on the hide of the horse. The egg causes the skin of the horse to itch. He licks the place, and the egg goes into his stomach. The egg of the bot-fly is apt to make the horse sick. The grub eats holes in the stomach of the horse. That makes the horse sick. The farmer will say that his horse is sick with “bots.” In Africa flies kill horses and oxen by biting them. The bite poisons the cattle and causes fever. Farmers will tell you of a very bad fly that spoils wheat and other grain. It is called the “Hessian” fly. Flies, as they flit from place to place, sometimes carry with them the poison of disease, as of sores and ulcers. Thus they spread these troubles among people. But while I tell you of that, I must not fail to say that flies, as they go to flowers for honey, carry the dust of the flowers from one to another. This helps new flowers to grow. There is a large and handsome bright green fly, very fine to look at, which bites horses and worries them. It is called the “horse-fly.” In some lands a small sand-fly causes sore eyes. Flies have been on the earth about as long as men have, or a little longer, and there are some dead flies worth a great deal of money.