The Animal World, A Book of Natural History Part 53

If you ever catch one of these spiders, and keep it for awhile in a jar of water with a little piece of water-weed, you may see it spinning its wonderful nest, and filling it with air, perhaps half a dozen times a day.

GOSSAMERS

Before we leave the spiders altogether, we must tell you something about the wonderful little creatures called gossamers. These are really the young of a good many different kinds of spiders. It often happens, of course, that several families, with perhaps five or six hundred little ones in each, are all living quite close to one another. The result is that there is not sufficient food for them all. So they make up their minds to go out into the world and seek their fortunes; and this is how they do it.

Choosing a warm, sunny morning in the early part of the autumn, all the little spiders climb the nearest bush, and each one makes its way to the very tip of a leaf. Then, clinging firmly to its hold, it begins to pour out a very slender thread of silk from one of its spinnerets. You know that on warm, sunny days the air near the ground soon becomes heated and rises, as hot air always does; and in rising it carries up these delicate gossamer-threads, as they are called, with it. Still the little spiders hold on, and pour out their lines, till at last each has several feet of thread rising straight up into the air above it. Then suddenly they all let go, and are carried up into the air at the ends of their own threads. So they go on, up and up and up, till at last they meet a gentle breeze, which carries them along with it. So, perhaps, they travel for thirty, forty, or fifty miles, or even farther still. And when at last they make up their minds to descend, all that they have to do is to roll up the threads which have been supporting them, and down they come floating gently back to earth. One good name for them is ballooning spiders.

Haven't you sometimes found on a warm autumn morning that all the trees and bushes, and even the gra.s.s and low plants, are quite covered with threads of silk? The next time you see such a sight look carefully, and you will find that on every thread a little baby spider is sitting.

Then you may be quite sure that all these little spiders set out early in the morning to seek their fortunes, and that, borne up by their slender threads, they have traveled for many long miles through the air.

SCORPIONS

These formidable creatures are closely related to the spiders. They are found in all warm countries, with the exception of New Zealand, and may easily be known by two facts. In the first place, in front of the legs they have a pair of great, strong claws, which look very much like those of a crab. And in the second place, the last five joints of the body are narrowed into a long, slender tail, at the end of which is a claw-like sting. When they attack an enemy, or seize a victim, they grasp it with the claws, turn the tail over the back, and force the sting into its body. And the poison which is introduced into the wound is so powerful that the sting of a large scorpion is almost as severe as the bite of an adder.

During the daytime scorpions hide away under stones and logs, or in crevices in the ground, or perhaps under the loose bark of dead trees.

But very soon after sunset they come out from their retreats and prowl about all night long in search of insects; and it is at such times that they invade camps and houses, get into shoes, etc., and persons get stung unless they are very careful.

CENTIPEDES AND MILLEPEDES

One can easily recognize centipedes by the great number of their feet.

The name centipede, indeed, means hundred-footed. None of these creatures, however, have exactly a hundred limbs. Some only have fifteen pairs of legs; some have as many as one hundred and twenty-one pairs.

But whether they be many or few, the number of pairs is always odd.

Another very curious fact about centipedes is that they have no less than four pairs of jaws. But the fourth pair take the form of fangs, which are very stout and strong, and very much curved, while at their base, just inside the head, is a little bag of poison. In the northern centipedes, which are quite small, the fangs are not large enough, nor the poison sufficiently strong, to cause a serious wound.

But some of the tropical species, which grow to the length of nearly a foot, are quite as venomous as the largest scorpions.

The food of these creatures consists chiefly of worms and insects. But the larger ones will kill lizards, and even mice, and have been known to prey upon victims actually larger than themselves.

The eggs of centipedes are laid in little cl.u.s.ters on the ground in some dark, damp nook, and when they have all been deposited the mother centipede coils herself round them, and there remains guarding them until they hatch.

Millepedes, in some ways, are very much like centipedes; but they only have two pairs of jaws instead of four, and they are nearly all vegetable-feeders. The long, smooth, and slender _Julus_ millepedes are plentiful in every garden. And in tropical countries they sometimes grow to a length of six inches. Even the largest, however, are perfectly harmless, for they have no poison-fangs as the centipedes have, and the only way in which they ever attempt to defend themselves is by pouring out a small drop or two of a fluid which smells rather nasty, and no doubt protects them from the attacks of birds.

CHAPTER x.x.xV

CRUSTACEANS

We now come to a very important cla.s.s of animals, which includes the crabs, the lobsters, the shrimps, and the prawns. These creatures, together with the mollusks, are often called sh.e.l.l-fish, although the "sh.e.l.l" of a crab is not in the least like the sh.e.l.l of an oyster, for example, or like that of a whelk, or a snail. It is only a sort of crust upon the skin, made chiefly of carbonate of lime. That is why these animals are called _crust_aceans; and instead of growing, like true sh.e.l.ls, this coat never increases in size at all.

But crabs and lobsters grow? Yes: but not as other animals do, a little every day. They only grow, as a rule, once a year; and they get a whole twelvemonth's growth into about two days!

When, in warm weather, the proper time approaches, they hide away in some crevice among the rocks, where none of their enemies are likely to find them. This is because they are going to throw off their so-called sh.e.l.ls; and they know that when these are gone they will be deprived of their natural armor, and of their weapons too, and so will be quite at the mercy even of foes much smaller than themselves. Then a very strange thing happens. Part of their flesh actually turns to water! Sometimes, if you happen to take up a crab in a fish-market, and shake it, you will hear water swis.h.i.+ng about inside it. This is a "watery" crab, and is not good to eat; for it was just about to change its "sh.e.l.l" when it was caught. A good deal of its flesh has actually turned to water.

Now this always happens a few days before the "sh.e.l.l" is thrown off; and the animal wriggles and twists about inside it, in order to loosen the attachments which bind it to its body. It also rubs its feelers against its legs, and its legs against one another, in order to loosen their hard coverings in the same way. This goes on, perhaps, for three or four days. Then, suddenly, the "sh.e.l.l" splits across, and the animal, with a tremendous effort, springs right out of it, while the "sh.e.l.l"

closes up again, and looks just as it did before. One might really think that there were two crabs instead of only one.

For some little time the animal now lies perfectly still. It is exhausted by its efforts, and its muscles are so cramped that they feel quite hard to the touch. This cramp soon pa.s.ses off, however; and then at once the animal begins to grow. It grows very fast. Indeed, you can almost _see_ it grow, for a whole year's increase in size has to take place in about forty-eight hours. Then a fresh crust is gradually formed upon the skin, and two or three days later the animal is once more clad in a coat of mail, and is ready to leave its retreat and face its enemies. For a whole twelvemonth after this it grows no bigger. But at the end of that time the process is repeated, and so on, year after year, until at last the animal reaches its full size.

FORMS OF CRUSTACEANS

The bodies of the crustacean animals are made up of a number of rings, or segments, like those of the insects. But there are always twenty of these rings, instead of thirteen; six forming the head, while there are eight in the thorax and six in the hind body.

Then--again like the insects--crustaceans have feelers, or antennae, upon their heads. You can see these very well indeed in a lobster or a shrimp. But instead of having one pair of these organs, as insects have, they always possess two pairs. And it is rather curious to find that at the base of the front pair there are two little organs which seem to be ears, specially formed for hearing in the water, while at the base of the second pair are two other little organs which seem to serve as a nose, specially made for smelling in the water.

And--once more like the insects--crustaceans have to pa.s.s through several different forms before they reach the perfect state. They are hatched in the first place from eggs, which the mother animal carries about with her for some little time firmly fastened to the hairs of the swimmerets, which we find under the hind part of her body. You will often find a shrimp with quite a large bunch of these eggs; and if you look at them carefully with a good strong magnifying-gla.s.s, you will see that they are all glued down to hairs.

Inside each of these eggs an odd little creature is formed, which is called the nauplius. Sometimes it is hatched while still in that state, and swims about through the water. But in almost all the higher crustaceans a change takes place before it leaves the egg, and it appears at last in the form of a zoea.

This is a kind of crustacean caterpillar, and a very odd little creature it is. A great naturalist once described it as an animal "with goggle eyes, a hawk's beak, a scorpion's tail, a rhinoceros' horn, and a body fringed with legs, yet hardly bigger than a grain of sand!" Certainly it does not look in the least like the crab, or lobster, or shrimp into which it is going, by and by, to turn. And it swims in the oddest way possible, by turning endless somersaults in the water!

These zoeas are sometimes found in immense shoals, the surface of the sea being quite thick with them for miles. And they are useful little creatures, for they feed on the tiny sc.r.a.ps of decaying matter which are always floating about in the sea, just as tadpoles and gnat-grubs do in ponds, thus helping to keep the water pure. But a very great number of them are devoured by whales. For when whalebone-whales are hungry, they swim with open mouths through a shoal of these little creatures, and then strain them out of the water by means of the whalebone fringe which hangs down from the upper jaw.

After a time the zoea throws off its skin and appears in quite a different form. It is now called a megalopa, or big-eyed creature, because it has very large eyes, which are usually set on foot-stalks, and project to quite a long distance from the sides of the head. And as the zoea is a kind of crustacean caterpillar, so the megalopa is a kind of crustacean chrysalis. It generally has a long, slender body, made up of several joints. And it swims by flapping this to and fro in the water.

CRABS

First among the crustaceans come the crabs, of which there are a great many different kinds. They are distinguished by having the tail tucked under the body, and firmly soldered, so to speak, to the "sh.e.l.l" on either side.

You can find several kinds of these creatures by hunting among the rocks on the sea-sh.o.r.e when the tide is out. There is the common sh.o.r.e-crab, for example, which is green in color. It is generally to be found hiding under ma.s.ses of growing seaweed. But sometimes you may see it prowling about in search of prey. It is wonderfully active, and will even pounce upon the sandhoppers as they go skipping about, just as a hunting-spider will pounce upon flies, seldom or never missing its aim. It will catch flies, too, leaping upon them when they settle, and shutting them up, as it were, in a kind of cage formed by its legs. Then it pokes one claw carefully into this cage, seizes the prisoners, pulls them to pieces, and pokes the fragments into its mouth.

Swimming about in the pools, too, you may often find a fiddler-crab, which is so called because its movements in the water rather remind one of a man who is playing the violin. You will find that its hind legs are very much flattened, and are fringed with stiff hairs, so that they may be used as oars. In fact, the animal rows itself through the water. Both these crabs, sad to say, are cannibals, and are always ready to attack and devour their own kind.

Then there is the edible crab, or blue crab, which is common on many parts of our coasts. The edible crab of Europe is somewhat different.

You are not likely to meet with the larger examples, which live in deeper water. But even the smaller ones can give a very sharp nip with their great claws, and you will find it as well to be very careful in handling them. The best plan is to seize them with the thumb and finger just behind these claws, then they are perfectly harmless. The larger crabs, which sometimes weigh as much as twelve pounds, are extremely powerful, and in more than one case a man has been killed by them, having been seized by the wrist as he was groping among the rocks, and held in a grip from which he could not break away until he was drowned by the rising tide.

These crabs are captured by means of crab-pots, made of basketwork, which have the entrance so formed that while the crabs can easily enter, they cannot possibly get out again. These pots are baited with pieces of fresh fish, and are then weighted with stones, and lowered to the bottom of the sea among the rocks, at a depth of from three to about twenty fathoms. They are also caught on lines baited with meat. No hook is needed, for the crab clings to the meat till it reaches the surface of the water, when it must be flung into the boat or somehow captured quickly, before it has time to let go and sink.

Some crabs live on dry land, sometimes at a distance of two or three miles from the sea, which they only visit at intervals. Among these are the famous calling-crabs, found in many of the warmer parts of the world. These crabs obtain their name from the fact that one of the great claws of the male is very much larger than the other. So big is it, indeed, that it has to be held aloft over the body when the animal is running, in order to prevent it from losing its balance and toppling over. And as soon as the crab begins to move this huge claw is jerked up and down, just as if the creature were "calling," or beckoning, to its companions. The calling-crabs live in burrows in the sand, which are often placed as close to one another as those in a rabbit-warren.

HERMIT-CRABS

Next we come to those small, curious creatures known as hermit-crabs, which form a kind of connecting link between the crabs and the lobsters, for their tails, instead of being firmly soldered down underneath their bodies, are quite free.

But the odd thing about these animals is that their tails have no sh.e.l.ly covering. The front part of the body is protected by a coat of mail, just as it is in all the other crabs; but the hind part is quite bare and soft. The consequence is that a hermit-crab is always very nervous indeed about his tail. He is dreadfully afraid that one of his many enemies may creep up behind, and bite it when he is not looking. So he always tucks it away in an empty sh.e.l.l like that of a whelk or a sea-snail, which he drags about with him wherever he goes!

You may often find these curious crabs by hunting for them in the pools among the rocks at low water. The crab always sits just inside the entrance of the sh.e.l.l, which he closes and guards with one of his great claws. And if you try to pull him out, you will find that you are quite unable to do so, for he has a pair of strong pincers at the end of his body, by which he holds the sh.e.l.l so firmly that you can tear him in two without forcing him to loose his grip.

Sometimes you will find that a sea-anemone has fastened itself to the edge of a sh.e.l.l in which a hermit-crab is living. This is a great advantage to the crab; for while there are many fishes which would be quite ready to crunch him up, sh.e.l.l and all, no fish will ever meddle with a sea-anemone. So as long as the anemone remains on his sh.e.l.l he is perfectly safe.