Once a Week (magazine)/Series 1/Volume 7/The green crab
THE GREEN CRAB.
Of all the animated denizens of our sea-shores, there is perhaps none more generally familiar than the common green crab, or the shore-crab, as it is also popularly termed—the Carcinus Mænas of naturalists. Whether at high or low water, at ebb or flow, hiding under overshadowing weeds, or craftily sunk beneath the sand, this quaint, waddling, green-backed crustacean is to be found, equally active, and equally pugnacious. With the exception of children, who are always delighted with the odd manœuvres of the creature, people mostly look upon it with contempt, partly because it is too small to hurt them much, and partly because it is not good to eat, having hardly anything inside its olive-green shell, and the little that there is not being well-flavoured. Yet, beneath that unprepossessing exterior is concealed a vast fund of interest, and the visitor to the sea-side will find himself well repaid by watching the habits of our olive-coloured friend.
The best time and place for observing the green crab in the fulness of its energies is just before high tide. And at the edge of the advancing waters crabs rise out of the sand in all directions, like the warriors sprung from the dragon’s teeth, and as if to complete the analogy, each is supplied with defensive and offensive armour, and each is at mortal enmity with its companion.
As the waters roll towards the shore, the crabs advance with the waves, ever hovering on the extreme verge, and hungrily watchful for their prey. The dashing waves tumble them over in a most unceremonious fashion, but without in the least disturbing their equanimity, and it is amusing to see how cleverly they guard themselves from being washed back into the sea by sticking their hooked legs into the sand, like animated grapnels.
Before watching the habits of the creature, just let us catch one, and examine the marvellous manner in which its form is adapted for the life which it leads.
The legs are so constructed that they permit their owner to move backwards, forwards, or sideways with equal ease, a capability which is of the greatest importance in procuring food, as well as in escaping from foes. The latter contingency is also beautifully provided for by the shape of the body, which is so formed as to enable the creature to burrow beneath the sand with singular rapidity, leaving scarcely a trace of its presence.
To watch the animal thus employed is an interesting sight. The crab half erects itself on its tail, fixes its claws firmly into the ground, and begins to shovel up the sand with the sharp hinder edge of its tail, just as a child digs a hole with its wooden spade. If the sand is wet, three or four vigorous movements are sufficient to sink the crab below the surface, when the next wave washes a quantity of loose sand over the spot, and nearly obliterates the traces of the creature that is lurking below. A practised eye will, however, detect the concealed crab by means of the bubbles that issue from the sand in consequence of the air expressed from the system.
Here we may mention that the proper way to catch a crab without being bitten is to press the fore-finger smartly on the middle of the back, and then to grasp the two side edges with the thumb and middle finger. The claws are thus forced to fold their joints, and their painful bite need not be feared.
Holding the crab in this manner, turn it over, and examine the wonderful manner in which the limbs are packed, and how admirably they accommodate themselves to the habits of the animal. The claws, when folded, exactly bring their extremities to the mouth, so that any food can be carried to the right place, and literally “tucked in.” The mouth itself is an apparatus so complicated that it cannot be described further than a series of jaws and teeth, placed behind each other in regular succession, and opening like horizontal shears.
A creature that depends upon its own exertions to capture the active prey on which it feeds, must necessarily be furnished with powerful eyes, which are capable of extending the faculty of vision over a very large field. These eyes are seen on the front margin of the crab, placed on footstalks, and having a peculiar nacreous lustre on their grey-brown surfaces. On examination with a good pocket-lens, the eyes are seen to be compound, i. e. formed of a great number of facets, each possessing the power of vision, and all communicating with their common optic nerve. The delicate raised lines caused by the serried ranks of these compound eyes are the origin of the peculiar lustre just mentioned. It will be seen, too, that the visual portion of these organs passes partially round the footstalks, so that when the creature protrudes its eyes it can see objects on all sides with equal ease.
Now, replace the crab in the water, and watch it as it exhibits the instinct which has been implanted in its being by its divine Creator.
Advancing with the flowing tide, and ever remaining within a foot or two of the edge, the crab keeps its eager watch for food, and suffers few living things to pass without capturing them. The whole nature of the animal seems to be changed while it is seeking its prey. The timid, fearful demeanour which it assumes when taken at a disadvantage wholly vanishes, and the apparently ungainly crab becomes full of life and spirit, active and fierce as the hungry leopard, and no less destructive among the smaller beings that frequent the same locality.
Now does it show the singular advantages of its ubiquitous mode of progression. Let a tiny fish, a smaller crustacean, or a soft mollusc pass within a reasonable distance, and the crab darts at it with a tigerlike energy, seldom failing to secure its prey. I have seen these crabs run after and catch the black flies that are so common upon the sand, and once saw a burrowing wasp (Odynerus) snapped up as it alighted on a bit of seaweed. Everyone who has walked along a sandy shore at evening is familiar with the shrimp-like sand-hoppers or sand-skippers (Talitrus) that leap about with such untiring energy, and the difficulty of capturing one of these active creatures. Yet I have seen the green crabs give chase to the sand-hoppers, and pounce on them as cats on mice.
The method employed in their capture of all active animals is rather unique. As soon as the crab sees the intended prey, it sits up for a moment, darts at the doomed being, and literally flings itself upon the victim, imprisoning it beneath the body, and hemming it in by means of the legs, which make an impassable cage around. One of the claws is then inserted under the body, and the prisoner picked daintily out as if by a dexterous thumb and finger. One claw then holds the prey, while the other pulls it to pieces and puts the morsels deftly into the mouth. The crab knows the value of time, and loses not a moment in disposing of its prey, tucking it into its voracious maw with amusing dispatch, and looking out the while for a fresh victim. Once I saw a very large sand-hopper make its escape from its pursuer. It gained nothing, however, but a temporary release, for the crab instantly gave chase, secured, and ate it in a few moments.
Fierce and destructive as it may be, the green crab is itself a frequent victim to more powerful foes, and is often doomed, with poetical justice, to undergo the sufferings which it has inflicted upon other beings. None are more terrible enemies than those of its own species, for the crab is an insatiate cannibal, devouring its kindred without the slightest compunction. In all these cases, however, it is needful that the dimensions of slain and slayer should be very disproportionate, as the crab cares not to earn a meal through a fight.
I was lately witness to a very amusing episode, where a large and powerful crab caught sight of a tender little one, as it scuttled over the wet sand. Away started the giant in full chase, and away ran the pigmy, as if knowing that life and death hung on the issue of the race. In spite of the great disproportion in size, the superior activity of the smaller crab prevented its pursuer from gaining much ground; but at last its strength evidently began to fail, and I thought it must inevitably succumb to the terrible foe that pressed so fiercely on its footsteps. Suddenly, however, it darted under a stem of laminaria that was lying on the shore, gathered all its limbs under its shell, and there lay motionless. The pursuer was instantly baffled. It raised itself in the air and surveyed the shore in all directions. Then it prowled about like a cat that has lost a mouse. It even was cunning enough to turn over some bits of seaweed that were lying on the shore, but never thought of searching under the thick stem of the laminaria. At last it gave up the pursuit, returned disconsolately to the sea, shovelled itself under the sand, and I saw it no more. Its intended victim then cautiously looked from its place of shelter, just protruded a claw, then a leg, then looked again, and at last came boldly forth, and went off to catch something on its own account.
As a general rule, the larger the size of the crab the more bellicose is its disposition. The smaller specimens are usually discreet as well as valorous, and if surprised either run away as fast as they can, or burrow into the sand with all speed. But the great, broad-shelled bully of the rocks has had his own way so long that his first impulse is always to show fight, and no sooner does he catch sight of the advancing foe than down goes his tail and up go his claws, and there he sits, defiantly ready for instant combat. It is as well to be cautious about handling such a champion, for he can strike with his claws as swiftly as a serpent darts its armed head, and should he miss his aim the clash of the bony weapons is distinctly audible.
Be it well understood that a bite from such a creature is no trifle, for the claws are enormously powerful, and their tips are sharply toothed, and they hold like the jaws of a bull-dog.
Even this belligerent animal is ofttimes fain to retreat before a foe of greater powers, stronger weapons, and harder shell, the edible crab which figures on our tables, and is known among the seaside population as the punger. Fortunately, however, for our green friend, the punger mostly inhabits a different belt of water, being most commonly found among the rocks at low-water mark, whereas the green crab lives almost wholly above that elevation.
Many persons when walking along the shore have observed a curious series of little marks on the sand, set in rows of five or so in depth, and meandering in seemingly purposeless irregularities. At first the marks appear to be made without any order, but a little examination will show that the same group of marks is repeated at regular intervals. These are the foot-tracks of the green crab, and the distance between the similar lines of marks denotes the size of the animal that made them.
Guided by these tracks, an experienced shore-haunter can often follow the crab to its place of concealment, and bring it to light, whether it be buried in the sand, or lying under the shelter of pendent seaweeds. In attempting this feat, however, it is as well to be quite sure of the direction in which the crab has gone, so as not to be led away from, instead of towards, the hidden crustacean. This object can always be attained by examining the shape of the marks, which are always larger at one end than the other, the larger extremities always pointing in the direction which the crab has taken.
There is much more to be said of these creatures, but failing space will not permit of further description. Should, however, any reader of these lines suffer the annoyance of a wet day at the sea-side, he is hereby recommended to procure a water-proof garment, to betake himself to the shore as the tide is rising, and amuse himself by watching the crabs.