The accompanying illustration represents the commonest of the group—the Common Shore Crab (Carcinus mænas), which is found plentifully on all our coasts, and even in brackish water far up the estuaries of rivers. It is a very voracious and pugnacious creature, probably the most active of all our crabs, and its movements, whether connected with its feeding, its sports, or its warfare, are always very interesting when observed through clear water. This crab varies considerably in colour, but is usually of the greenish tinge shown in the frontispiece.
Another abundant and well-known species is the Edible Crab (Cancer pagurus), which is as familiar an object in town as on the sea coast. Unlike the common lobster, its natural colour is not considerably changed by boiling, being only turned from a dull to a brighter red.
The finest specimens of this crab are to be caught beyond low-water mark, the usual snare being the basket or pot, baited with fish refuse, but large numbers live among the stones and rocks left exposed at low tide, and sometimes include specimens of considerable size. They should be looked for under large stones that are loosely piled together, or in the narrow chinks of rocks.
It is very interesting to compare the habits of the two common crabs just mentioned. The former, when molested, will run off in great haste, but always retreat with its front to the enemy, and its sharp and powerful pincers far apart and wide open, ready for immediate use in its own defence if necessary. The latter species, on the other hand, though strongly built and provided with formidable claws, seldom runs far, and hardly ever attacks one in the act of pulling it out of its hiding-place; but, on the contrary, doubles all its ten legs under its body as if endeavouring to approach, as nearly as possible, the form of a ball, and will allow itself to be rolled about without showing any signs of life.
The genus Xantho contains two or three species that are common on the Cornish and Devon coasts, and which may be known by their depressed and deeply-grooved carapace and the presence of three or four prominent tubercles on the latero-anterior margins. The abdomen of the female has seven joints, while that of the male has only five. One of these (Xantho florida), shown on [Plate VI.], is a powerfully built crab, as may be seen when, after being disturbed, it pushes its way among the loose stones of the beach, often lifting masses many times its own weight.
On the same plate is also a figure of the pretty Velvet Crab (Portunus puber), also known as the Lady Crab and the Violet Fiddler. The first of these popular names has its origin in the dense covering of close hairs that clothe the carapace, and the last refers to the beautiful violet colouring of parts of the front legs, and, to a lesser extent, of the remaining legs. This is, perhaps, the most ferocious of all our shore crabs, and its attacks, when disturbed, are of such a determined nature that the catching of the larger specimens is quite a lively sport. Though it can hardly be described as an abundant species, yet it sometimes occurs locally in such numbers that it may be found under nearly every stone of any size. In fact, we have searched two or three localities on the south-west coast where this crab is not only extremely numerous, but is at the same time almost the only species to be found; and it seems not unlikely that the pugnacious Lady has been the means of driving the less formidable species from its favourite haunts.
When you disturb a Velvet Crab it will immediately raise itself in a menacing attitude, stretching its brightly coloured pincers as wide apart as possible, and then it will either retreat backwards, or even make a firm stand, ready to strike as soon as it is threatened with an attempted touch. Try to grasp it, and its two powerful weapons of defence are brought together with lightning-like rapidity giving one a decidedly smart blow, possibly followed by a grip of great tenacity for a creature of its size; but, should it miss its aim, its pincers strike together with a sharp click, only, however, to extend at once in preparation for the next attempt.
It will be observed that the walking legs of this crab are all flattened, and that while the first three pairs terminate in sharp, lance-like claws, the last pair are broad and fringed with hairs, thus showing their close relationship to the swimming crabs. In fact, the same genus contains British species which are popularly known as Swimming Crabs.
One of the swimmers is represented in fig. 4 of [Plate VI]. It is generally known as Henslow’s Swimming Crab or the Nipper, the scientific name being Polybius Henslowii. The carapace of this species is quite smooth, thus enabling the crab to move through the water with less resistance, and the walking legs, particularly the last pair, are flattened and fringed for use as paddles. It is said that this crab can raise itself from the bottom to the surface of moderately deep water by means of the swimming feet, and that it preys on fishes which it pursues with some vigour.
Other crabs than those briefly described will reveal themselves to the sea-side collector, but we have not the space to introduce them here. Sufficient information has been given, however, to enable the reader to broadly classify his specimens—a matter of more importance to the young naturalist than the mere naming of species.