THE ROMANCE OFTHE ANIMAL WORLDCHAPTER IA MICROSCOPIC COMBAT—A SNAIL’S FRIENDSHIP—HERMIT-CRAB AND SEA-ANEMONE IN PARTNERSHIP—A CRAB IN AMBUSH—CRABS THAT EAT COCOANUTS.
A MICROSCOPIC COMBAT—A SNAIL’S FRIENDSHIP—HERMIT-CRAB AND SEA-ANEMONE IN PARTNERSHIP—A CRAB IN AMBUSH—CRABS THAT EAT COCOANUTS.
Before there can be any romance—as I understand the word—in animal life, there must be some degree of intelligence in the romance-making animals. The question, therefore, is, at what stage in the ascending scale any conscious exertion of brain-power—any evidence of what we call a mind—begins to show itself. I say this because I have to begin somewhere, and in my selection of subject-matter to illustrate the title of this book, I had intended to pursue a plan similar in principle to that resolved on by Koko, in Mr. Gilbert’sMikado, who, with a view to becoming perfect as an executioner, was going “to begin with a guinea-pig and work his way through the animal kingdom, till he came to a second trombone.” Of courseImust begin much lower down than a guinea-pig, and the nearest approach I can hope to make to a secondtrombone will be a gorilla—but the principle is the same. However, on further consideration, I think that this scheme, if rigidly followed, may prove too exacting, and also give an appearance of scientific pretension to this humble little work, which it is entirely guiltless of. I have decided, therefore, to soften and modify it by the employment, when occasion offers, of another and somewhat opposed principle, that, namely, of letting one thing link itself to another as it does in ordinary conversation, either through suggestion or association, quite irrespective of whether there is any or no natural—that is to say, systematic—connection between the two. For instance, should alligators be the theme, and should they, after lying like logs on the water, and so forth, proceed, in the dramatic development of their character, to seize and devour some unsuspecting mammal, I shall use the incident as a convenient opportunity for treating of that mammal—should there be anything to say about it—without waiting for its proper turn to be treated of to arrive, as upon the first-stated principle I should have to do. But where opportunities of this sort do not present themselves—if birds have only to do with birds, insects with insects, and so forth—then I shall be systematic, and so go on, letting the one method balance the other. A third principle—that, namely, of paying no attention to either of the other two—will also occasionally be acted upon, and if, as a result of the three, no principle at all should be discernible by the reader, I would ask him to look upon that as a merit, since “Summa ars est celare artem.” And now, having explainedmy system, which I think is an easy and flexible one, I will proceed to put it into practice in the best way I can.
The lowest of all animals are theprotozoa, yet even here, as it appears to me, we begin to see the dawnings of that intelligence, without which that kind of interest which the life and acts of any creature should possess, in order to make it the subject for a work like this, can hardly be said to exist. Theinfusoriastand at the very bottom even of the protozoa. Most of them are so small as to be invisible, except through the microscope, and they are not supposed ever to think. Yet a creature belonging to this humble group, having a cup-shaped body, with a grasping arm or tail to it, has been seen to attach itself, with this, to the cup of another individual of the same species, considerably larger than itself, and cling there with a pertinacity very suggestive of a firm intent. Upon this the larger one became, to all appearance, very excited, and, moving about in the water—for these creatures are aquatic—till it came to some weed, fastened with its one limb on a piece of this, and proceeded to jerk itself backwards and forwards, with great suddenness and vigour, and with the evident design, as it seemed, of ridding itself of the intruder. The latter, however, held on like grim death, and this hard-pitched battle, which had all the appearance of being intelligently directed, went on between these two microscopic and simply formed creatures, for quite a long time. At length the smaller of the two was jerked off, upon which it made a second attempt to establish itselfas before, but was defeated by the efforts of its more powerful adversary. The witness of this interesting scene tells us it was very difficult to believe that the two lowly organisms engaged in it, though consisting but of a single cell, without a head and with no trace of a nervous system, properly so called, were not sentient beings, conscious of what they were doing, and of why they were doing it.
Coming to the earthworms, which stand higher than the protozoa, though still very lowly, there seems little doubt that they are capable of forming and carrying out an intelligent purpose, since, when they pull leaves into their holes, they always catch hold of them by the proper part, so that they go down easily, and this they do even with the leaves of foreign trees, of which they can have had no previous experience. And if worms have experience, snails have both that and something better, or, at any rate, still more interesting to discover in a creature of this kind. “They appear,” says Darwin, “susceptible of some degree of permanent attachment. An accurate observer—Mr. Lonsdale—informs me that he placed a pair of land-snails, one of which was weakly, in a small and ill-provided garden. After a short time the strong and healthy individual disappeared, and was traced, by its track of slime, over a wall and into an adjoining well-stocked garden. Mr. Lonsdale concluded that it had deserted its sickly mate; but after an absence of twenty-four hours it returned, and, apparently, communicated the result of its successful exploration, for both then started along the same track, and disappeared over the wall.”
Both snails and worms, however, stand higher in the scale than do the sea-anemones, amongst which latter creatures—those flowers of ocean, rivalling with their pillared stalks and many-coloured living petals the proudest ones on earth—we yet find an instance of what is called commensalism—the living together, that is to say, in friendly community of two separate and often widely sundered species, each thereby obtaining some benefit for itself. The other party to the arrangement is in this instance a crab—the hermit-crab—that curious anchorite which by living and moving about in the disused shell of another creature escapes the many dangers which would otherwise threaten its soft and palatable body. Indeed, the association may almost be said to be between three, rather than two, different species, each of them belonging to a separate and well-marked division of the animal kingdom—viz. to the mollusca, the crustacea, and the cœlentera respectively. As, however, the mollusc is represented by its house only, and not by itself—though, indeed, its house is structurally a part of it—it will be safest to consider the alliance as a dual rather than as a triple one. That the anemone establishes itself on the shell, not by mere chance, as might sometimes happen, did the crab allow of it, may be demonstrated in a very delightful way; for if, when it is attached to a stone, a hermit-crab should be placed in its vicinity, it will, after a time, abandon its post, and gliding, like a snail, to the hospitable portals of its friend’s domain, proceed to attach itself there, much to the satisfaction of the latter. For that the crab’s participation is of anactive kind, that he does not merely not mind the anemone, and that the latter has more than his sanction, is, likewise, a thing that can be proved. This discovery was first made in 1859 by Mr. Gosse, the naturalist, for up to that time it had always been imagined that the crab, at any rate, was indifferent. Mr. Gosse, however, by the simple expedient of detaching the anemone from the shell, demonstrated that this was not the case, for on each occasion that he did so the hermit-crab picked it up again in its two claws, and pressing it against its shell, held it there for about ten minutes, at the end of which time it was sticking fast, as before. The crab, therefore, must derive some advantage from the presence of the anemone in return for the protection which he perhaps affords the latter against certain enemies. Or possibly the constant change of locality, with its increased chances of procuring food, is the real or the principal benefit conferred. But how does the crab benefit? This, at first sight, is not quite so easy to see. The explanation usually given is that it is “masked” or concealed by the sea-anemone, which is by no means small in comparison with the size of the shell, but often almost and completely covers it, forming a sort of cloak round it at its base, and towering like a pillar above it, so that of the two it is by far the more conspicuous object, especially when the crab is withdrawn, or partly withdrawn, into its shell. Nor is it always one anemone only that is affixed to the shell; there may be as many as two or three, or even more, and in some cases not only the shell, but the crab’s own claws may be thus utilised. Certainly, therefore, if concealment is a gain tothe crab, it obtains this advantage by the arrangement. If, too, it has any special enemies of its own—as it is very probable that it has—the stinging cells of its allies would be likely either to incapacitate them or keep them at a distance. Of one thing, at least, we may be certain, that some advantage is obtained—and, no doubt, it is a substantial one—by each of the individuals in this strange copartnership—for throughout nature, in associations of the kind, the principle expressed by the homely Scotch saying of “giff, gaff”—Anglicè, “nothing for nothing”—obtains. Apparent instances may indeed be found of one species doing something for the benefit of another, since the very nature of these arrangements is such as often to give them this appearance. But such instances are apparent only. Whatever it looks like, and whatever either or any of the parties concerned may do, they always do it for their own, and not for one another’s benefit.
Supposing that concealment is the principal advantage accruing to the hermit-crab from its relations with the sea-anemone, it seems likely that this is more for the sake of securing prey than of avoiding enemies—though, indeed, both objects seem fairly attained by the shell. Another crab—the Hyas of Otaheite—arrives at similar results by means which are somewhat similar, but which, in this case, constitute a ruse which is all the creature’s own. It deliberately loads on to its back a cargo of seaweed mingled with the sand and débris of the coral, amongst which it lives, and having done so, remains motionless, awaiting the advent of anything that may serve as a meal. The tips of the ready claws lie just within the weedythatch, whilst the eyes at the ends of their stalks are raised above it, so as to obtain a full view. They are, however, indiscernible, except in a fatally close proximity. Time passes, the sun shines brightly down through waters clear as the clearest crystal and bluer than the bluest sky. Fishes, rainbow-hued and flashing, sometimes, with the iridescent sparkles of the humming-bird—the jewels of the tropic seas—pass and repass often quite near to the unseen peril, but except by the motion of their own bodies, or the throb of the waves, the weeds which conceal it remain unstirred. Nothing happens: yet the eyes observe, the claws may, perhaps, itch; but their owner moves not. Such beings are not for him. They are beyond his sphere, too bright, too beautiful, above all, too quick. Medusæ, too, of substance translucent as the waters they move in, and washed with the colours of the sea itself, go by, sometimes in flocks, alternately expanding and contracting their smooth, bell-like bodies, whilst threads and filaments of varied form, and delicacy more exquisite than that of the finest lace, stream in beauty behind them. Sea-horses swim vertically like little mermaids, twining their tails together, or around the long fronds of many-tinted seaweeds, whilst strange and varied forms of mollusc and crustacean move upon the shell-strewn sand, or amidst the bright mazes of the coral—but still our crab makes no sign. At length a small creature of the shrimp or prawn kind—a crustacean like itself, and more active it would seem, for it swims, though backwards and in a curious jerky way—approaches the little heap; the crab’s eyes glisten—they would, at least, were they capable ofdoing so. Alternately shooting up and sinking down again, the unsuspecting creature continues to play about in the close neighbourhood of that deadly ambuscade, and at length, in one of the latter movements, comes well within reach. It is almost on the bottom, its tail stirs the weeds and is about to bend again, when with a rush the lurking enemy is upon it, seizes it between its fatal claws, and retiring backwards amidst the shelter which the violence of its sudden movement has partially removed, proceeds to devour it at its leisure. Such is the stratagem, and such the sure, if somewhat slow, result. All sorts of creatures are thus secured by the crab, including, perhaps, on special occasions, a small and less wary fish or so.
What makes the thing still more curious and interesting—from the standpoint of the evolutionary naturalist—is that the back of the clever strategist is covered all over with a crop of stiff, wiry bristles, which, curving inwards, maintain a firm hold of the weeds that lie upon them, and prevent their slipping off. No doubt these bristles have become more and more developed as the crab has become more and more in love with the ruse, to the success of which they now largely contribute: but which came first, the ruse or the bristles, that no one can say. On the one hand, the bristles, whilst yet small and but slightly curved, might sometimes, catching amongst and holding fragments of seaweed, etc., have suggested to the crab the use to which these might be put; but, on the other, as many creatures hide themselves in order to dart out on their prey, and as a good way of doing so in the case of a flat-backed creature would be by placing things onits back, the crab may possibly have thought of this without any structural facility to suggest the idea.
Both these crabs that we have been considering exhibit their intelligence and live their lives in the sea, and it is with salt water and the rocky pools of the sea-shore that crabs, generally, are inseparably associated in our minds. Nevertheless there are land crabs, and even crabs that eat cocoanuts. Whether these latter are also in the habit of climbing the lofty palms on which the cocoanuts grow, throwing them down and then ascending again with them, in order to break them by repeating the process, having previously freed them from their huge husky envelope, does not seem to be quite certain, but such is the account explicitly given by the natives of the Samoan Islands. “I inquired of them,” says Mr. T. H. Hood, in hisNotes of a Cruise in H.M.S. “Fawn” in the Western Pacific, “about the habits of the Ou-ou, or great cocoanut-eating crab, common here, and found the reports previously received from the natives corroborated. It ascends the cocoa trees, and, having thrown the nuts down, husks them on the ground; this operation performed, it again ascends with the nuts, which it throws down, generally breaking them at the first attempt, but, if not successful, repeating it till the object is attained.” This account, Mr. Hood goes on to say, was confirmed by every native subsequently spoken to on the subject. It is difficult to see how the natives should have been mistaken in regard to such a noticeable and very remarkable habit, and on the other hand, if they were inventing, why should they have allinvented in one and the same way? In the new edition of Wood’sHomes without Handsthis account of Mr. Hood is still quoted without any qualifying statement in the form of a footnote. On the other hand, Darwin, when he visited the Keeling Islands, was told by Mr. Liesk, an English resident on one of them, that the crabs fed upon such nuts only as happened to fall from the trees. The Keeling and Samoan Islands are, however, some 5,000 miles apart, and it is at least possible that the crabs of each, though of the same species, may have learnt a different way of getting at the inside of the cocoanut, especially as elsewhere they seem to practise yet a third method.
To begin with Darwin’s account. Mr. Liesk, speaking as an eye-witness, told him that the crab first shredded off the husk, fibre by fibre, beginning always at that part under which the three eyeholes of the nut lay. It then, he said, hammered with its claws, which are heavy and powerful, on one of the eyeholes and, having made an opening, turned round and inserted its thin posterior legs, which are also armed with small pincers, into it, and thus extracted the kernel. This is a plain statement, and in it we see the philosophy of the small and weak pair of claws which are as useful in the last and most satisfactory part of the process as are the larger ones in the pioneer work preceding it. Just as plain, however, is the following statement, which was made by two South Sea missionaries (Mr. Tyerman and Mr. Bennett) at about the same time. They say: “These animals live under the cocoanut trees, and subsist upon the fruit which they find on the ground.With their powerful front claws they tear off the fibrous husk; afterwards inserting one of the sharp points of the same into a hole at the end of the nut, they beat it with violence against a stone until it cracks; the shell is then easily pulled to pieces, and the precious food within devoured at leisure.” Here, then, is quite a different way of getting at the contents of the cocoanut, but the same informants go on to say that “sometimes by widening the hole with one of their round gimlet claws, or enlarging the breach with their forceps, they effect sufficient entrance to enable them to scoop out the kernel without the trouble of breaking the unwieldy nut.” This, perhaps, may mean the same as what Mr. Liesk tells us, but nothing is said about the crab’s turning round. It is not very clear from the account of the two missionaries whether they speak as eye-witnesses or not. Mr. Liesk does, but I should not myself think that his observations had been very exhaustive, and as theVoyage of the Beagle, in which they are referred to, was published nearly sixty years ago, it seems to me a pity if the habits of the cocoanut-eating crab have not been more carefully studied since then. I think myself that a crab which lives on cocoanuts, and may possibly climb the trees on which they grow, is worth taking some trouble about. This, however, is not all that theBirgus latro—for that is his scientific name—does. Not only does he live upon land, but he makes a deep burrow in the ground to dwell in, and with the shredded fibres of the cocoanut husk, which he has torn up, he makes a thick soft bed at the bottom of it to lie on. One would think with all this that hehad said good-bye to the sea for good and all, and would never want to go back to it. But this is not the case. Like other crabs, these strange ones breathe through branchiæ or gills, as a fish does, and in order for them to do so these must be kept moist. The peculiarity of all land-crabs is that their gills remain moist for a long time, but at the end of this time, when they are beginning to get dry, they have to moisten them again. Every night, therefore, the cocoanut crab pays a visit to the sea, and has a cool, refreshing bathe in it. For a little while he is a marine creature again, as his ancestors were before him, but when he has moistened his gills, he goes back to his palm-trees and cocoanuts.
This great strange crab grows to two feet in length, is stout in proportion, and has a fantastic appearance, which it is difficult to describe. It walks very high on two long stout pairs of legs, whilst a pair or two of little ones behind them are too short to touch the ground, and so dangle in the air. Its claws are enormous, its thorax very peculiar, its antennæ are like those of a lobster, and its body behind more like a hornet’s than a crab’s—at least in a picture. What it really resembles is a hermit-crab, to which it is closely related; only to see the resemblance one must take the hermit-crab out of its borrowed shell.