Once while lifting branch coral into my boat on a coral reef, several crabs fell from the olive-hued mass, and like spiders in shape and form, made their way slowly along. Each one was covered with a growth of seaweed. I took a brush and scoured them, producing veritable spider crabs (Fig. 150). The body was pear-shaped; the claws were long and covered with sharp points. These crabs were placed in a tank, and almost immediately began to replace the seaweed which had been rubbed off, evidently being much annoyed at the cleaning process. In redecorating themselves they broke off small bits of seaweed from a branch, placed the broken portion against the mouth, evidently to attach some glutinous matter or animal mucilage, then raising it with an overhand movement, they attached it to the back. This was continually repeated until within a few hours the back of each crab was changed from a smooth surface to a miniature garden. As many times as the seaweed was removed, so many times was it replaced.
The spider crabs range from the beautiful scarlet creatures found in the coral to the giant Macrocheira of Japan, which in large specimens has a spread of legs of twenty feet, some measuring twenty-two feet between the two large biting claws, each of which is ten and a half feet long. This huge crab is very slender, and is slow of movement, its body resembling a rough rock.
Fig. 151.—Crabs that form galls on corals:
a, Cryptochirus (male);
b, Coralliodytes (female);
c, Hapalocarcinus marsupialis (female), that carries its young in a sac or marsupium.
Crabs select singular places for homes. One lives in the sea cucumber; others live in corals, which appear to grow over them, forming a gall (Fig. 151). The little oyster crab found in bivalves is a familiar form. But perhaps the most remarkable home for a crab was the bowl of an old tobacco pipe in which a crab I once owned ensconced itself. This was a hermit crab (Fig. 152). The hermits differ from other crabs in having a long, but soft and totally unprotected tail or abdomen, to preserve which they enter empty shells and drag them about wherever they go. The hermits occur in great variety, and there are marine hermits and land hermits. On the Florida Reef they are found in myriads; every shell alongshore conceals a baby hermit; and almost every nook or cranny affords concealment for a score of them, their red and blue claws forming an attractive contrast to the shell.
Fig. 152.—Hermit crab.
The hermit referred to was first found in a pearly shell and placed in the office, but finally it outgrew this and deserted it for the pipe which some workmen had left on the floor. Every day this old pipe would be clanked and dragged about the room, and once in a while the crab would drag it up a table leg, so reaching the tablecloth and then the table top, where it drank out of a saucer left for the purpose. Later a marine hermit was found in a pipe bowl, proudly dragging the grotesque house about. Anything of this kind would be used by the hermits. One was found in the opening of a spool; and this would roll over and over, carrying the hermit with it. Another took possession of a reed. Among deep-sea sponges the hermits are seen occupying holes in the sponges.
A community of hermits is a laughable sight. They are very pugilistic, and are always fighting. When a hermit outgrows its shell and begins to feel uncomfortable it endeavors to turn out some comrade that has a larger shell, and in the battle arms and claws are often lost. This, however, is not serious, as they grow again. When the hermit finds an empty shell it thrusts in its claws and antennæ, probing it in every direction to see that it is not occupied. When satisfied, it jerks itself out of its own shell, and with the greatest rapidity whisks its soft unprotected body into the new house, where, if it fits, it remains. The shell, when large, is not carried, but dragged about, and when the crab is alarmed or startled it darts backward into the shell, where its large claw and the others constitute almost as good a door as the real operculum of shells. The largest hermits are the marine forms, which enter the large conch shells and drag them about. These hermits are a brilliant red in color. Their claws are very rough.
Closely related to the hermit crabs is the famous cocoanut crab or Birgos of the Spice Islands. This crab is so strong and powerful that, as Professor Van Beneden states, one clinging to a tree, seized a small goat and lifted it from the ground by the ears. The Birgos resembles a huge hermit crab, but has no artificial shell, the soft abdomen being protected by a shell of its own. This large land crab lives mainly on cocoanuts, which it secures by climbing the trees and biting off the stems. Descending, the crab will take the nut and with remarkable discrimination hold it with one claw and with the other tear off the husk, always at the end containing the "eyes." This stripping process, impossible to man without some implement, is remarkable in itself, and tells the story of the muscular strength of the crab. When the "eyes" of the nut are exposed, the crab seizes it by inserting its claws in the holes, and hammers the shell until it is broken. The crabs live at the base of the trees and line their dens with the husk.