The plate has fine teeth upon its edge. When the prey comes by, the larva snaps out its rod, with the plate, as if they both were on a spring, and so catches the things that are swimming along a little way off. They do not see their foe, and do not know that he can reach so far with his sweep net.
The teeth on the edge of the plate shut up, and then the rod folds back, and puts the food into the hungry larva’s throat. I suppose the little creatures that swim along feel quite happy and safe, and then, all at once, out springs this weapon, and they are gone.
But this little plague of the pond is not quite safe himself. There are some other creatures down under the water that eat him. All nature is a kind of game of “tit for tat,” you see.
The larva of the dragon-fly breathes air. He has no lungs as you have, but gills as a fish has. How does he get air?
Through his body goes a long tube. The tube ends in a horny point at the tail. This point is made of five very fine spikes. These spikes and this tube are able to take from the water some of the air that is in it. Thus he gets air much as a fish does.[21]
This spike on the tail of the larva has a very strange use. It shoots out the water which it has taken in, as you would shoot water from a squirt-gun. It shoots the water out with such power that it drives the larva along in the water.
Did you ever see a steamboat driven through the water by a screw or wheel at the stern, or hind part? What do you think that the man who first made such a boat said? He said that he took his idea of how it should be made by seeing this queer larva move in the water.
When this creature seizes food, he likes to strike it from below. He rises under it in the stroke, as the shark does. Dragon-fly larvæ are very bold. They can eat large and hard insects.
When the larva changes to a pupa, it becomes more lively, fierce, and hungry than ever. It does not change its form at this time as much as most insects do.
The dragon-fly pupa has six legs, and each foot has strong hooks on it. Its color is pale brown, clear and shining, and its case is horny. Some rings of the body have horny spikes upon them. Upon the case of the chest is a pattern like wings.