The Animal World, A Book of Natural History Part 48

INVERTEBRATES

CHAPTER x.x.xII

INSECTS

We now come to the second of the two great divisions of the animal kingdom, namely, the invertebrates, which includes all those creatures which have no bones. This division in its turn consists of a good many cla.s.ses, just as that of the vertebrates does; and among these is that of the insects, the peculiarity of which is that they must pa.s.s through three stages of development before they reach their perfect form, namely: first the egg; then the grub, or caterpillar; and then the chrysalis, or pupa.

You can easily tell an insect when you see it by remembering one or two simple rules.

In the first place, its body is always divided into three princ.i.p.al parts, which are known as the head; the thorax, or chest; and the hind body.

In the second place, it always has six legs. Spiders have eight legs.

Centipedes and millepedes have many legs. But an insect never has more nor less than six. And each of these limbs is made up of a thigh, a lower leg, and a foot; while the foot itself has from two to five little joints, the last of which usually has a pair of tiny claws at the tip.

Besides these, there are several other ways in which insects differ from the rest of the vertebrates. We need only tell you about one of them, however, and that is that in some form or other they always have four wings. Sometimes, it is true, you cannot see these wings. That is because they are not developed and cannot be used for flying. But still they are there, and by means of the microscope it is almost always easy to detect them.

These wings, however, take all sorts of forms. The wings of a b.u.t.terfly, for example, are very different from those of a beetle or a bee; and because of these differences in the wings, insects are divisible into several smaller groups, which we call orders.

BEETLES

First comes the order of the beetles. These are called _Coleoptera_, or sheath-winged insects, because their front wings, instead of being formed for flight, are turned into h.o.r.n.y or leathery sheaths, or elytra, which cover up and protect the lower pair while not in use.

At least 150,000 different kinds of beetles have already been discovered in various parts of the world, of which America possesses tens of thousands; and probably quite as many more remain to be distinguished.

Of these we can only mention a few of the most interesting.

The tiger-beetles are so called because they are such fierce and voracious insects, spending most of their time in chasing and devouring other insects. The commonest of them is about half an inch long, and is bright green above and coppery below. You may often see it darting about in the hot sunshine, and if you try to catch it you will generally find that it flies away as quickly as a bluebottle.

Ground-beetles are common in gardens. One often seen is about an inch long, and is deep black in color, with a narrow band of violet running round the outer edge of its wing-cases. This, too, is a creature of prey. It cannot hurt you; but if you pick it up it will make your fingers smell very nasty. For it can pour out from its mouth a drop or two of a dark-brown liquid which has a horrible odor.

Then there are a good many beetles which live in streams and ponds, and are called water-beetles in consequence. They can swim and dive very well, and are also able to fly. Almost every night they go for long journeys through the air. And when they want to go back into the pond they hover above it for a moment, fold their wings, and drop into the water with a splash. Only sometimes they fly over the roof of a greenhouse, and mistake that for a pond; and then you can imagine the result!

The c.o.c.ktails are beetles with short wing-cases and very long, slender bodies, which they carry turned up at the rear end. Some of them are quite large, like the ugly black "coach-horse," but many are very small.

Indeed, most of the "flies" which get into one's eyes on warm sunny days in England are really tiny c.o.c.ktail beetles, and the reason why they make one's eyes smart so dreadfully is that they pour out a little drop of an evil-smelling liquid from their mouths, just like the purple ground-beetle.

SCAVENGERS

The burying-beetles are so called because they bury dead animals. Have you ever wondered why we so seldom find a dead mouse or a dead bird, although these creatures must die in thousands every day? One reason is that as soon as they are dead a couple of "scavengers" are almost sure to come and bury them. They are big black beetles, sometimes with two broad yellow stripes across their wing-cases, and they dig by means of their heads, scooping out the earth from under the carca.s.s till it has sunk well below the surface of the ground. Then they lay their eggs in it, come up to the surface, shovel back the earth till the dead body is quite covered over, and then fly away. And when the eggs hatch, the little grubs which come out from them feed upon the carca.s.s.

Among the largest beetles are those called stag-beetles because the jaws of the male look very much like the horns of a stag. Those of the female are much smaller, but are so sharp and strong that they can really give a rather severe bite. These occur in various parts of the world, and are fond of flying slowly about on a warm summer evening, generally about twenty or thirty feet from the ground.

The c.o.c.kchafer is common everywhere in spring, and if you shake a young birch-tree, or a hazel-bush, three or four of the great clumsy insects will very likely come tumbling down. They are rather more than an inch long, very stoutly and heavily built, and are chestnut brown in color, while their bodies are drawn out into a kind of point behind. The grubs of these beetles live underground, and do a great deal of mischief in fields and gardens, for they feed upon the roots of the plants, and very soon kill them.

Dor-beetles, too, are very common everywhere. You may often see them flying round and round in great circles on warm summer evenings, making a loud humming noise as they do so. They often blunder in at open windows, attracted by the lamplight, and children are afraid of them, but they can do no harm. If you catch one you will find that it is nearly black. You will also see that its front legs are broad and strong, and that they are set with a row of stout h.o.r.n.y teeth. With these legs the beetle digs, using them with such address that in the course of an hour or two it will sink a hole in the ground ten or twelve inches deep, in order to lay its eggs at the bottom.

The famous Scarabaeus of Egypt, which in days of old some of the people of that country used to revere, because they thought it a symbol of immortality, is really a kind of dor-beetle.

SKIPJACKS AND GLOWWORMS

Skipjacks, too, are beetles. You may know them by their long, narrow, glossy bodies, and by the fact that the head is hidden under the thorax, so that you can hardly see it from above. One very odd thing about them is that they are constantly losing their footing and rolling over on their backs; and their bodies are so shiny, and their legs are so short, that when they do so they cannot get up again in the ordinary manner.

But after lying still for a moment they arch themselves into the form of a bow, resting only upon their heads and the very tips of their tails, and suddenly spring into the air, making an odd clicking noise as they do so. And as they fall they turn half round, and so alight upon their feet. For this reason they are often known as click-beetles.

These insects are the parents of the well-known wireworms, which often do such mischief in our fields and gardens, living underground for three or even four years, and feeding upon the roots of the crops, and of such bushes as the currant.

Then the glowworm is a beetle. Perhaps you may have seen its little pale green lamp shining in the gra.s.s on a summer evening. The light comes from a liquid inside the hind part of the body, the skin of which is transparent, and forms a kind of window, so that it can shine through; and the insect has the power of turning on its light and shutting it off at will. The lamp of the female beetle is very much brighter than that of the male, and while the male has both wing-cases and wings, and can fly very well indeed, those of the female are so small that one can hardly see them. Indeed, she looks much more like a grub than a beetle.

DEATHWATCHES AND OIL-BEETLES

Deathwatches are small brown beetles which burrow into dead wood and call to one another by tapping with their h.o.r.n.y heads. You may often hear them if you happen to be lying awake at night in a room in which there is old woodwork; and in former days people were silly enough to think that when this sound was heard it was a sign that somebody in the house was going to die! That is why these beetles are called deathwatches. They are quite small, and are brown in color, with rather long feelers and legs.

Crawling on gra.s.sy banks in the warm sunshine on bright spring days, you may often see a number of oil-beetles. These are large bluish-black insects which have an odd habit, if you pick them up, of squeezing out little drops of a yellow oily liquid from the joints of their legs! This oil has a pungent smell, and no doubt prevents birds, etc., from eating them. You will notice that the female beetles have enormous hind bodies, which they can hardly drag along over the ground. This is because they contain such a very large number of eggs, thirty thousand often being laid by a single beetle. She places them in batches in holes in the ground, and very soon afterward they hatch, and odd-looking little grubs with six long legs come out of them. No sooner have they left the egg-sh.e.l.ls than these tiny creatures hunt about for a flower with sweet juices, which is likely to be visited by a wild bee. When they find one, they climb up the stem and hide among the petals. Then, when the bee comes, they spring upon it and cling to its hairy body, and so are carried back to its nest, where they feed upon the food which the bee had stored up for its little ones.

WEEVILS AND OTHER BEETLES

A great many beetles have a long beak in front of the head, with the jaws at the very tip. These are called weevils, and many of them are very mischievous. Grain of various kinds, for example, is destroyed in enormous quant.i.ties by the wheat-weevil and the rice-weevil, while the nut-weevil is the cause of those "bad" nuts which no doubt most of you know only too well. The mother beetle bores a hole through the sh.e.l.l of the nut while it is small, and the little grub which hatches out from the egg she leaves inside it feeds upon the kernel, leaving nothing behind but a quant.i.ty of evil-tasting black dust.

One of the handsomest of European insects is the musk-beetle, which you may often find sunning itself on the trunks and leaves of willow-trees in England in July. Often you can smell it long before you find it, for it gives out a strong odor much like that of musk. This beetle is sometimes nearly an inch and a half long, with long legs and still longer waving black feelers. In color it is rich golden green with a tinge of copper. But if you put one of its wing-cases under the microscope, it looks like a piece of green velvet studded all over with diamonds, and rubies, and sapphires, and emeralds, and topazes, which seem to turn into one another with every change of light.

The grub of this beetle lives inside the trunks of dying willow-trees, and feeds upon the solid wood.

Then there are the turnip-fleas, little black beetles with a yellow stripe on each wing-case, which skip about just as fleas do, by means of their hind legs. They are only too common in turnip-fields, and often do most serious mischief, nibbling off the seed-leaves of the young plants as soon as they push their way above the surface of the ground, and so destroying the greater part or even the whole of the crop.

And, lastly, there are the ladybirds, common everywhere. But perhaps you did not know that they are among the most useful of insects. The fact is that both as grubs and as perfect insects they live upon the green blight, or greenfly, an aphis which is terribly mischievous in fields and gardens, and destroy it in thousands of thousands. Indeed, if it were not for ladybirds, and for one or two other insects which help them in their task, we should find it quite impossible to grow certain crops at all.

[Ill.u.s.tration: INSECTS INJURIOUS TO AMERICAN MAPLE TREES.

BORING BEETLE (Plagionotus): 1, place where egg was laid; 2, borer or grub in September from egg laid same season; 3, nearly fully grown borer; 4, adult beetle (black and yellow); 5, hole through which beetle escaped from its chrysalis in the burrow; 6, dust of borings packed in a burrow.

MAPLE-TREE PRUNER (Elaphidium): 7, 7a, grubs or borers in burrows; 8, pupa; 9, beetle (brown).

COTTONY SCALE (Pulvinaria): 10, active young (pink); 11, adult female scales, each concealing many eggs under the woolly ma.s.s; 12, leaf with young scale-insects on its under side.]

EUPLEXOPTERA

Next after the beetles comes the order of the _Euplexoptera_, which means beautifully folded wings. This order contains the earwigs. We do not know much about these insects in the United States; but they are so constantly spoken of in books about England, where they are numerous, that it will be well to describe them.

Perhaps you did not know that earwigs have wings; and certainly one does not often see these beetles flying. But nevertheless they have very large and powerful wings, only, during the daytime, while they are not being used, these organs are folded away in the most beautiful manner under the tiny wing-cases. By night, however, earwigs often fly; and when they settle, they fold up their wings most cleverly by means of the h.o.r.n.y pincers at the tail-end of their bodies, and then pull the wing-cases down over them!

That is the real use of the pincers, although the earwig is able to give quite a smart pinch with them if it is interfered with.