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]