IN all the wealth of Ocean-life, perhaps no creature flourishes more abundantly than do Crabs and their relatives.

We still talk of Jelly-fishes, Starfishes, Craw-fishes, Cuttlefishes, but no longer of Crab-fishes.

Once upon a time that name was equally common. Everything that had its home in the sea was popularly supposed to be a fish. We know now that not one of the above belongs to any Fish tribe; yet in Conservative style we keep the old titles going.

Crabs and Lobsters, Shrimps and Prawns, are members of the vast Crustacean division or family. They are so called on account of the hard protecting crust, or armour, by which their soft bodies are guarded. Chief and foremost among the numberless kinds included under this head is the busy vigorous sidling Crab.

And very important animals are crabs, in the economy of the Ocean. Not only from their enormous numbers; not only from the wide extents of land and sea which own to their presence; not only from the fact that they form a principal item of food to fishes and even to whales; but also because at least one species is reckoned excellent eating for man.

There are land-crabs as well as sea-crabs. There are deep-sea crabs, as well as shallow-water and shore crabs.

There are crabs much less than half-an-inch across; and there are giant Japanese crabs, carrying heavy back-armour or “carapace,” about a foot in length and breadth, while the sprawling limbs extend to a yard and a half or more on either side.

Those of ordinary sizes are found everywhere; in numbers beyond reckoning. Not only in tropic waters, but in moderate climes, and in frigid zones; alike near the poles and under the equator. Different species, of course, in different parts, but all connected.

Moreover, they are quite as much at home in the depths of the sea, with miles of water piled over their heads, as on shelving beaches near to land.

During the Challenger Expedition crabs were fished up from all depths—from one mile, two miles, three miles, even between three and four miles. In those dark and icy regions the cold must be great, the pressure tremendous; still crabs innumerable are there.

Some sub-ocean kinds have displayed what may be looked upon as an inquiring disposition.

A ship passing near the Azores brought up in a trap many large ones, belonging to a then new species. And the curious part of the matter was that not all of them need have come. Some were entrapped, and could not get away; but others rose to the surface of their own free will, clinging to the outside of the trap, and not attempting to escape, even when drawn out of the water, and on deck.

Perhaps they were dazzled by the unaccustomed brightness of light, after the few and feeble glimmers below. But the puzzle remains—why, in the beginning, they should have chosen to leave their home, and to journey upward into unknown regions? Were they of an aspiring character? Had they friends caught in the net, from whom they would not be parted? Or was the attraction merely that of the appetising food which those friends were enjoying?

An interesting haul was one day made by the Challenger while crossing the Bay of Biscay; not indeed from a great depth, since the Bay is in no part very profound, but from the sea-bed. More than five thousand small sharp-clawed crabs came up in company; and they took quite kindly to the new conditions of life on board. They cheerfully explored the whole vessel, turning up in every direction, during the next few days.

Something in the nature of a love for home has been shown by crabs, at least in one instance. Many years ago a singular story to this effect was told in a scientific paper.[8]

The fishermen of Falmouth, capturing crabs off the rocks at Lizard Point, brought them by boat to Falmouth Harbour, and kept them there till needed, in a box sunk under water, some four miles out. Each crab had been branded on the back with its owner’s mark.

By accident one of these boxes was broken; and all the prisoners made good their escape. Naturally, no one expected to see them again.

But only two or three days later those very same crabs—with branded carapaces—were caught anew by the fishermen; not near Falmouth, but as before, off the Lizard. How they had managed to get there, how they had first found their way to Falmouth Harbour, a distance of four miles, and then for miles more along the coast, are questions more easily put than answered. The word “instinct” fails to meet the difficulty.

One thing only is clear, that they preferred the neighbourhood to which they were accustomed.

Very fearless creatures are small crabs, generally; brave, no doubt, partly because of their numbers.

In nets and trawls, where animals of many kinds are together for long hours of captivity, the weak are often destroyed by the strong, before they can be drawn up.

But sometimes the weak combine together, and prove too much for the strong. Notably this was the case, when a dog-fish, brought up from a depth of over fourteen hundred fathoms, was entirely disposed of in twenty hours by crowds of hungry little crustaceans.

Most of the crabs and lobsters, shrimps and prawns, which live on or near the bottom, send their young ones up into higher levels for education. There for a while the juveniles swim and develop, till old enough in their turn to take to the ocean-bed. Great numbers have meanwhile been preyed upon by multitudes of fishes in those upper levels.

Crabs undergo curious changes in the course of their growth from infancy to adult age. At certain stages they are so utterly unlike in appearance to what they become later, that for a long while they were classed by naturalists under separate names, being actually reckoned as different creatures.

Since the protecting armour of a crab is far too rigid to admit of its stretching, it becomes from time to time too tight for the growing body within. When it can no longer be endured, it has to be cast off, and a new suit, larger in size, has to form in its place.

This armour, like the shells of foraminifers, and the skeletons of coral-polyps, is unconsciously secreted by the crab; and during the formation of a new suit of armour the crab has a time of weakness, of delicate health, and also of dangerous exposure to the attacks of enemies.

Some kinds of crabs have sunk to the miserable level of parasites, living on the exertions of others, and refusing to exert themselves. One prefers to think of the active and independent and intelligent kinds; and really, crabs have a good deal of intelligence. Quite as much as an average insect; though perhaps few of them could compete in an examination with ants or bees.

If any might do so successfully, it would be in all probability some member of the Spider-crab family.

To this slender-limbed untidy class belongs the unwieldy Giant-crab of Japan. But it is his smaller relatives who excel in sense. The spider-crab has a slovenly appearance, because he attaches to himself stray bits of sea-weed and scraps of sponge or other growths, with the plain intention of becoming less easily seen.

He keeps to no regular or permanent style of adornment. The nature of his trimmings depends entirely on the character of his surroundings.

Many years ago my father had been for a short dredging excursion, near Worthing; and he brought home with him one of these small creatures, elaborately ornamented with slim strips of bright-red sea-weed.

He placed the crab in a basin of water, which contained a supply of green sea-weed. And next morning a change was seen. The crab had cast aside his red ribbons, and had decked himself out with a smart array of green ribbons instead. Such conduct may, if we choose, be accounted for by the magic word “instinct;” but it certainly wears the aspect of deliberate intention, and even of some dim consciousness of cause and effect, not to speak of a knowledge of colour.

This habit of the spider-crab is now well known and recognised; and he has been closely watched during the “dressing” process.

It has been noted that he always puts each slip of sea-weed or scrap of sponge, or aught else that he uses for the purpose, to his mouth, before fastening it to his body or limbs. A suggestion has been made that his object in so doing is to lick it and render it sticky.

Perhaps in some cases it could not otherwise be attached; but many of the spider-crabs have hooked hairs, exactly adapted for holding fast such objects as they love to adorn themselves with.

Nor are the adornments always merely stuck on. Both sea-weeds and sponges frequently take root, and flourish as healthy growths upon the crab’s back. It is an extraordinary fact that the crabs seem to know perfectly well from which kinds of sea-weed or zoophyte they may snip off little bits, with a prospect of not killing them.

So unerring, indeed, is their knowledge in this respect, that, as an authority on the subject has stated, “the keepers of Aquaria have only to consult the crabs to learn what kinds of sea-animals will bear being thus transplanted piecemeal.”[9]

Is this too merely “instinct”?

Many a time baits were lowered in the nets of the Challenger to attract victims. Oddly enough, it was found that no more effective bait could be used for crabs and their kindred than—pieces of looking-glass! May one imagine that some friendly Medusa lent her little glimmer, far below, to enable the Hermit-crabs, when putting on fresh ribbons, to see their reflections, and judge of the effect? It reads rather like a page of Alice in Wonderland.

Hermit-crabs or Soldier-crabs, having an insufficient protective armour of their own, are in the habit of using empty Mollusc shells to shelter that part of their bodies which is not guarded. One of these crabs, when young, chooses a shell, fitted to its size; and when grown too large for it, that shell is discarded in favour of a new one.

But whether the said crab commonly contents himself with an empty habitation, the occupant of which has died earlier, or whether he first kills and eats the live Mollusc, and then “commandeers” the shell, does not seem to be known with certainty.