Part 9

One of the most interesting of these ten-footed crustaceans is the blind crayfish of Mammoth Cave. It is found also in various subterranean streams of the country. The eyestalk of these little creatures is all that remains to tell the story of what was once an eye, and they live and thrive in perfect darkness. The ordinary crayfish of Western streams has a peculiar habit of burrowing, which at times has occasioned great damage in undermining dikes and dams. I once came upon a remarkable crayfish community in Indiana. There had been a flood the day previous, and every log in the neighborhood and the piers of the bridge were covered with crayfish which, in this locality at least, appeared to be endeavoring to escape from too much water. On all sides, some yards from the creek and high above it, the ground was raised into small heaps six or eight inches across, each, as I discovered, being the home of a crayfish, and as far as the eye could see on the prairie were these mounds and heaps, suggestive of the vast numbers of these little animals in this vicinity.

XVI. THE CRABS

Of all the crustaceans, the crabs are the most singular and certainly the most intelligent. Rapid in movement, good swimmers, alert, garbed in extraordinary colors, often in stolen homes, they attract attention at once and are the harlequins and clowns of the animal kingdom. The crabs are distinguished from the rest of the group principally by their very short tails. Their bodies are round, elongated, or oval. They are found almost everywhere, from the deep sea, where they occupy shells and sometimes drag about a luminous sea anemone, to every beach. It is in or near the tropics that the most remarkable crabs are seen.

During a visit to the islands off the coast of Texas, I once found a remarkable crab community. The islands were flat sand banks just above the surface, blown and washed up by the sea, with here and there sand dunes and shrubs, and again vast stretches of sand inhabited only by crabs. The latter were all of one kind, a pale gray, so mimicking the sand in color that it was almost impossible to distinguish one from the other. There were legions of them, the sand in places being fairly riddled with their burrows, into which they darted with inconceivable rapidity. As I walked along the sands they ran ahead in rapidly increasing numbers, then divided and were so quick of foot that it was impossible to run them down. This vast army of crabs was the sanitary corps of the island, devouring every dead fish that came ashore and other animal matter of all kinds.

At Garden Key, Florida, these crabs were found in swarms, rarely entering the water except when driven, and never venturing far from the reach of the highest waves at high tide. They had long, stalked eyes, which seem to follow every movement, and were very comical and interesting creatures to watch and study. On the keys covered with bay cedars were other land crabs (Fig. 147), colored rich red and purple. These crabs lived among the cactuses and bay cedar bushes. When climbing on the former their resemblance in shape and color to the purple fruit was remarkable, and if the crab remained quiet, it was almost impossible to distinguish it. In these bushes a tern, the noddy, had built its rude brush nest, and the young bird and the food brought it by the parents were the objects of marked attention on the part of not only the purple-backed crab but a hungry, starving horde of hermit crabs which climbed the tree and snatched the bits of fish from the young birds, despite the presence of their mother. By crawling beneath the thick brush in heat which was almost suffocating, I watched numbers of these foraging expeditions on the part of the crabs, and I think it possible that some of the larger crabs finally carried off the young birds. This was not an impossible feat, as Professor Mosely, of the Challenger deep-sea dredging expedition, observed the same crab or a very near relative, carry off young birds at St. Paul's Rocks. At Ascension he saw the doughty land crabs stealing young rabbits, dragging them from their holes by main force and devouring them. This crab with gorgeous colors was not very fleet of foot, and when I rose up suddenly in the cactus by a nest they would draw in their legs and cling to a branch, mimicking ripe fruit. The hermits would do the same, and fall to the ground in a shower.

An interesting crab found here is known as Grapsus, also a predatory creature with unequaled courage, preying upon every living thing that it can attack with safety. It is richly colored red and white; its legs are long; it is a racer along the sands, impossible to capture. On the West African coast these crabs, or a near relative, are very large, and so swift that they have been used in sport, horsemen following them at full speed as game.

The ordinary crab of the Eastern shore is highly valued, and vast numbers are shipped from Fort Monroe in Virginia to the northern cities. The trade in "soft shells" is even more important. The latter are caught in various ways. An old colored man of my acquaintance used to tread for them on the mud flats with his bare feet; but he confessed that it was a disagreeable business, as sometimes he stepped on "hard shells" by mistake and was badly bitten.

The English edible crab is of large size and always in demand, resembling the edible crab of the Pacific, which is also very large and greatly esteemed.

That these crabs have a strong homing sense, or an affection for certain localities, was demonstrated some years ago. Two crab fishermen were following their occupation from the same boat, and each as he caught a crab cut upon its swimming claw a private mark so that they could be claimed by the rightful owners at the end of the day. The boat was overtaken by a storm and the crabs were tipped overboard five miles from where they were caught and lost. The following week the two men again began to fish in the original spot, and to their amazement began to catch the marked crabs, which had returned five miles alongshore to the locality of their choice.

The so-called green crab (Fig. 148) is an attractive and active creature, one that can easily be observed. Its quaint stalked eyes, which turn this way and that, and which can be stowed away in little depressions, and its singular method of walking, are very interesting features. When a crab walks on land it is usually endwise, and when it wishes to change its course it is not obliged to turn about but moves its legs in the opposite direction. It can also move directly ahead. These movements are all performed by six legs, which are pointed, the trail of this crab on the sand resembling pin marks on the hard beach. The two front claws are for tearing food and for general defense, while the last pair, widened out at the end in some, are paddles by which the crab swims when it ventures off the bottom.

At times the crabs appear to migrate. I have seen the bottom of a bay on the Virginian coast so covered that it was impossible to wade without stepping upon a crab. In the island of Jamaica certain land crabs march to the sea to deposit their eggs, at which time they appear more or less indifferent to danger, and move on, despite the attacks of birds and various animals, including man.

The crabs known as fiddlers (Fig. 149) are common up and down the Atlantic coast, especially in the warmer portions. A most interesting colony lived north of Fernandina, Florida. Some years ago a plank walk led across their domain, and one could stand and watch their ludicrous maneuvers. The fiddler is not over an inch in length. It is of a dark ivory hue, and its eyes are perched on long stalks, so that it can bury itself in the mud and thrust its eyes upward, and thus in perfect safety observe everything that is going on. The right claw of this crab is half as long again as its entire body--a colossal weapon framed for an animal five or ten times its size. Indeed, it is so large as to be almost useless, for a large amount of strength is required to operate so gigantic an implement. To emphasize the undue size of this claw, the left one is a dwarf, being too small to act as a defensive weapon. How so small a crab can use so strange a pair of weapons was a puzzle, until by watching them, I discovered that the crab uses its large claw as a bogy, brandishing it fiercely, which gives it a very ferocious appearance. The movement of the claw back and forth is called fiddling, hence the name of the crab, which appears to be constantly fiddling. Where hundreds are seen, all fiddling and menacing one another at the same time, the sight is laughable.

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.

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.

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.

In ancient times crablike creatures existed, eight or nine feet in length. These are represented to-day by the quaint horseshoe or king crabs (Fig. 153). They are found in shallow water in Northern waters, and resemble a horseshoe with a long, sharp spike or spine--the tail of this strange animal.

XVII. LUMINOUS CRABS

One of the interesting experiences of Nordenskiöld in the Arctic Ocean was wading through the sludge, as the soft snow water along the beach is called, and seeing each footprint turn into a mass of light, caused by the phosphorescence of a small crustacean called Metridia. The light was bluish white, of great intensity, and although at times the cold was so severe that mercury would freeze, yet everywhere this marvelous light blazed. Even drops and splashes of the water seemed to be molten metal, but were merely alive with this minute light giver resembling Cyclops. In the Pacific, especially in summer, the exhibition of what might be called "crab light" is marvelous, and this is often true in the Atlantic. The light following the splash of an oar, the spray hurled aside by the cut water, the foaming water around a propeller, and the strange shifting specter which follows the rudder, are caused more or less by minute crustaceans which have the faculty of emitting light without heat.

Along the beach beneath seaweed, we shall find Gammarus, a long, very small, but mighty jumper, that at night emits a red light. Many of the near relatives of this little creature are phosphorescent, and perhaps the most beautiful of all is one named Idotea phosphorea. It is a yellowish spotted little creature found in pools alongshore. It darts about among the weed, and would rarely, if ever, be noticed during the day; but at night the entire animal seems permeated with a golden light which marks it in vivid lines against the dark bottom, and flashes and miniature meteors indicate it as it dashes across the little pool, its ocean world.

The most beautiful of all crustaceans is the one known as Sapphirina. I have seen the ocean filled with them; some red, others blue or yellow, purple or green, all known gems being imitated by these matchless gems of the sea, which in daylight vie with the most brilliant iridescence in producing wonderful displays. No more beautiful scene can be imagined than that embracing these living gems, standing out in brilliant tints against the deep blue of the ocean. These gems also have the gift of phosphorescence and at night appear in a new guise.

One of the singular long-legged spider crabs of the deep sea, Colossendeis, is said to be phosphorescent. Giglioli, the Italian naturalist, describes a crab which gives a golden purple light, the latter appearing from the thorax. The little shrimp, Mysis, which carries its young in a pouch, from which it is called the opossum shrimp, is not phosphorescent, but its young in what is called the zoëa stage are luminous. The odd-shaped little creature, which is the mantis shrimp in one of its stages, is brilliantly luminous, not over its entire body, but in the eyestalks. Some of the deep-sea crabs have luminous eyes, strange monsters wandering in the abysmal regions of the deep sea.

While most of these crabs have the light in only one place, one discovered by Sir Joseph Banks was luminous over its entire surface. Exactly what the luminous matter is, is not known, but in some instances it can be scraped off and will render the hands luminous when rubbed upon them. According to A. M. Norman, naturalist of the Porcupine expedition, the crustacean Ethusa, found at a depth of eighteen hundred feet, is blind, its eyestalk being spiny, and the eye replaced by a smooth, round termination which is supposed to be a light-emitting organ. Aristeus has phosphorescent eyes, which blaze with the yellow fire of a cat's eye, and this is true of many other crustaceans. Some have luminous backs; others have fiery bands upon the legs, while almost every portion of the body of some species is the seat of this wonderful light. That the lights are of some use there can be little doubt. In one little creature Dr. Gunther found a brilliant light stationed between its eyes, which certainly was a light to illumine its way in the deep, dark bed of the ocean.

XVIII. THE INSECTS

Among the best-known and attractive members of the lower animal kingdom are the insects, represented by the gorgeous butterflies, the iridescent beetles, the fierce spiders, and many others. The crustaceans may almost be called the insects of the ocean, as in general appearance they closely resemble these animals; but the real insects are higher forms.

The skeleton (Fig. 154) of an insect is divided into three distinct parts instead of two. The head is distinct from the body, as in the crabs, and the skeleton, like that of the crabs, is external, and formed of a horny substance called chitin. As in the crabs, the body is made up of rings, or segments: four in the head generally, three in the thorax, and ten or eleven in the abdomen. It is interesting to glance at the various parts of insects, and later on, in reading about the many species, to note the many different purposes to which each is adapted.