LESSON XLII.
UNDER THE WATER.
Now let us hear the story of the dragon-fly from its beginning. While it is an egg, a larva, and a pupa, it lives under the water. Only when about to burst from the pupa-case, and at last get its wings, does it leave the water and seek the upper air.
In all its early stages the dragon-fly lives in cool, still shallows, among green and graceful water-plants. There the sunshine glows all about it, as it darts over the bottom of the pond, hunting for food.
The mother dragon-fly, as she flits over the water, drops her eggs upon it. They sink to the bottom. She may put them into plant stems.Their cases are waterproof. If the eggs are not eaten up by beetles and other fellow-citizens under water, they are quite safe, and soon the larvæ hatch out.
Home of the Dragon-fly.
Home of the Dragon-fly.
Most insects move quickly in the larva state, and are dull or quite asleep in the pupa-case. This is not the way with the dragon-fly. He is busy and strong all his life. The egg settled upon the pond bottom is quiet; the larva moves about, but is rather slow and lazy. The pupa dashes here and there, and frightens all the little animals in the pond. At last the perfect insect rises on the wing. It darts about with almost the swiftness of light.
The larva of the dragon-fly is gray. It has six legs. It is always hungry, and feeds on small water-animals, as beetles, grubs, shrimps, leeches, and their young.
This larva does not run after its food, but lies waiting for it. On the bottom of the pond, hidden in the shadow of a leaf, root, or stone, or seated on stems or leaves that are under water, the larva waits patiently for its prey to come by.
Did you ever see a person with a net for catching insects? This net is a fine bag set on a little hoop. The hoop is fastened upon a long handle. Sometimes the handle has joints, and will fold up. As insects dart by, the person with the net brings it down over them with a quick motion.
The dragon-fly larva has something much like this with which to catch its food. The lower jaw is fastened by a hinge to a little jointed rod. The rod, and the jaw-plate upon the end of it, when not in use, are folded down upon the head of the insect.
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, andthen 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 firstmade 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.
These pupæ dash about the bottom of the pond, swimming or running, and eat almost everything that lives there. The body and head of the pupa are thicker than those of the grown-up dragon-fly. They are made for seizing and killing prey.
When it is nearly time for the pupa to come out as a dragon-fly, the case grows clearer, like glass. The large, beautiful eyes grow brighter and brighter, and the pupa leaves the deeper part and gets near the edge of the pond.
FOOTNOTES:[21]See Seaside and Wayside, No. 3. Lessons on Fish.
[21]See Seaside and Wayside, No. 3. Lessons on Fish.
[21]See Seaside and Wayside, No. 3. Lessons on Fish.