The crabs about which I have been telling you live in the sea, though they often leave it for some little time and run about on the shore. But none of them can swim, and if they are thrown into deep water they just sink to the bottom with their legs sprawling, feeling about for some object to which they can cling. Sometimes, however, if you look into one of the pools which are left among the rocks when the tide goes down, you may see a small crab swimming through the water with some little speed. This is quite sure to be a Fiddler Crab, and if you catch it and examine its hinder legs, you will find that instead of being quite slender, with hooked claws at the tips, as they are in most crabs, they are flattened out into broad, oval plates. And you will also find that these plates have a fringe of rather long hairs growing all round them.
Now these are the paddles with which the crab rows itself through the water, and it is called the “Fiddler Crab” because the movements which it makes with them are rather like those of a man who is playing the violin. You can easily keep it in an aquarium, and a very interesting little pet it makes. But you must remember that it is a very savage little animal, and will certainly do its best to kill any other creatures that you may put into the same vessel. Even if you put two fiddlers together they are almost sure to fight; and the one which wins the battle will kill and eat the one which loses it.
When the Fiddler Crab is alive it is really a very handsome little creature, for its blackish shell is covered all over with soft, short down, looking rather like velvet, while its legs are striped with blue, and its claws are partly blue and partly scarlet.
The broad shelly shield which covers the back of a crab is called the “carapace,” and there are certain markings upon it which are rather like the features of a human face. But there is one crab in which these markings are so deep and strong that it looks just as if it were wearing a mask. So it is always known as the “Masked Crab.” It is found on the southern and western shores of England and Wales, and you may always know it if you meet with it, not only because of the face-like markings upon its back, but also because its carapace is a good deal longer than it is broad, whereas in other crabs it is nearly always broader than it is long. Besides this, the great claws are not really “great” at all, for they are very long indeed and very slender, with quite small nippers at the tips, while the greater feelers are quite as long as the claws. So altogether the masked crab is a very odd-looking crab indeed. But if you want to find it you will have to look for it very carefully, for it has an odd way of burying itself in the sand, and only leaving just its feelers and its eyes above the surface.
This is perhaps the very oddest of all our British crabs.
In the first place, it looks much more like a big spider than a crab; for its body is very small, while its legs are very long and very slender. Indeed, the group of crabs to which it belongs is often called “spider crabs” in consequence. In the second place, its carapace is covered all over with rather long sharp spikes, which project in all directions, so that it strongly reminds one of a tipsy-cake! And, in the third place, the crab nearly always has a number of tufts of sea-weed or sponge growing upon its back.
Perhaps you might think that these come there by accident. But they do not. The crab himself plants them there! If you keep him in an aquarium you may often see him doing so. First of all he turns one of his long claws over his back and scratches away at the carapace, so as to roughen the surface. Then he pulls up a little sprig of sea-weed or sponge and actually plants it on his shell, pressing the rootlets firmly down. And besides the spikes upon the shell there are numbers of tiny hooks, which help to hold it in position. Then the crab plants another piece of weed or sponge in just the same way, and so he goes on planting piece after piece until his back is completely covered.
Now why do you think he takes all this trouble?
Well, the reason is that he does not want to be seen; for he has a great many enemies, and he knows perfectly well that if he were to lie among the sea-weeds or sponges at the bottom of the sea they would be quite sure to notice him as they passed by, and then he would almost certainly be killed and eaten. So he clothes himself with either sea-weeds or sponges, as the case may be, and then feels that he is perfectly safe, and that as long as he keeps quite still even the sharpest eye will fail to notice him. And if you catch one of these crabs which is covered with sea-weeds and put it into an aquarium in which sponges are growing, it will very soon strip the weeds off its back and cover itself with sponges instead; while if you catch one that is covered with sponges, and put it into a tank in which sea-weeds are growing, it will strip off the sponges and cover itself with sea-weeds!