Part 31

In emergencies the millipede is able to roll itself in a tight ball like its presumed ancestors, the primaeval trilobites. In one Madagascan species this ball is as big as a golf ball. Some millipedes are less than a twentieth of an inch long.

Gigantic millipedes are known from the tree fern swamps of the Carboniferous geological period when the great coal deposits were formed. They were about a foot long and their bodies were covered with long, sharp spines. This apparently was to make them distasteful to the giant amphibians, remotely related to present day frogs and toads, who were the dominant four-footed animals in the world at the time. Thus the millipede has almost as lengthy a history on earth as the more insect-like cockroach of those same forests of 250,000,000 years age.

Bats Have Built-in Radar

Bats “see” with their ears. Echoes of sounds inaudible to man enable the flying mammals to find their way through the almost absolute darkness of deep cavern or jungle. These creatures might be considered inventors of the Navy’s sonar device by which underwater obstacles are located by echoes—or even, in a sense, of radar.

Almost entirely creatures of night and late twilight, bats have small and poorly developed eyes. When one is on the wing it emits an almost constant succession of inaudible “squeaks” at a sound frequency of between 25,000 and 70,000 vibrations a second. The human hearing range reaches only to 30,000. Each squeak, according to measurements by Dr. Donald R. Griffin of Cornell University, lasts about two-hundredths of a second. In ordinary flight over open country it is repeated about ten times a second. By means of the echoes it apparently is possible to detect and avoid any obstacle, even one as small as a strand of silk thread strung across the path, within a distance of ten or twelve feet.

The bat does not hear its own squeaks. Each time one is uttered an ear muscle contracts automatically, thus momentarily shutting off the sound itself so that only the echo can be heard. It is possible that each animal has its individual sound pattern and is guided only by its own echoes. Otherwise, it would seem, there would be complete confusion from the echoes of several hundred bats moving in a flock.

Largest of the bats are northern India’s flying foxes. The body is shaped almost precisely like that of a small fox and is covered with fine, dark-brown hair. The wing spread is about three feet. These flying foxes move in flocks of thousands. They are exclusively fruit eaters and forest dwellers. They are the only bats eaten by man. Their flesh is said to resemble chicken.

Insect-eating bats are prisoners of the air. Once on the wing they must remain in flight all night until they return to the dark caves where they sleep all day, suspended head downwards. Flying from dusk to dawn requires an enormous amount of energy for which a lot of food is required. One of these animals probably must eat about a third of its own weight in insects each night. Thus it is a good friend of the farmer and one of the potent factors in keeping the balance of nature.

If a bat lit on the ground or on any solid object it would be very difficult, perhaps impossible, to get it on the wing again. This is accomplished only by falling from its sleeping place.

The hibernation of temperate zone bats appears very close to complete lifelessness and is probably the most deathlike sleep experienced by any mammal. Animals close to a cave entrance have been found completely coated with ice, as moisture has congealed on the fur. Yet when they wake in the spring they appear none the worse for the experience.

Crabs That Climb Trees

A fantastic race of small, pale hermit crabs are the most numerous and conspicuous animal inhabitants of war-wrecked Pacific islands. The multitudes of these crustaceans may have a considerable role, beneficial and otherwise, in present efforts to cover these white sand wastes with grass and trees.

Of all creatures which start life in the sea, hermit crabs have become best adapted to continual existence on land. Like others of their race they are shell-less and soft-bodied. For protection against enemies and against being dried out by the glaring sun, they live in houses—the abandoned shells of other sea creatures which have been cast ashore. They carry their houses on their backs. When a crab outgrows its shelter it moves to a larger one, changing its dwelling four or five times during a normal lifetime. There is never any housing shortage for those in the small stages of growth. However, the sole refuge for the crab which has reached full size is the “cats-eye,” the shell of a marine snail as much as three inches in diameter with an opalescent pink inner lining which glistens like the eye of a cat. Only the hermits which can find such shells survive.

In searching for food the crabs climb the trunks and branches of kou trees which grow all over the Pacific islands. They eat the bark along the upper side of the branches; most trees show long scars which are the results of past injuries.

A common habit, especially of the undersized individuals, is cleverly to tear off and eat only the ovaries and stamens of blossoming plants. “These are certainly not isolated acts,” says a Pacific Science Board report, “but ones perfected by practice and perhaps instinct. The crabs probably decimate the flora, feeding particularly on tender seedlings. They largely are responsible for the paucity of different kinds of plants on some islands. The seeds of any new kinds of plants washing to its shores are subject to their inspection and, if palatable, sacrificed to their appetite. The foreign plants now being introduced as seeds and seedlings must not only surmount the drastic condition of drought and salinity but also the hurdle of these voracious animals.”

In the spring the females carry their numerous maroon colored eggs attached to their abdomens. When do they return to the ocean to allow these eggs to hatch their free-swimming larvae that resemble so closely the shrimp-like ancestor of all hermit crabs? Where do they throw off the hard, non-expanding shells they have requisitioned as they increase in size, in burrows on land or in the ocean? How, with gills adapted for respiration in water, have they perfected respiration on land? Questions such as these are still unanswered.

The Ferocious Centipede

“Natives of Brazil call the centipede the ambua. These creatures of a thousand legs, some of which are more than a foot long, bend as they crawl along and are reckoned very poisonous. In their going it is observable that on each side of their bodies every leg has its motion, one regularly after the other; being numerous, their legs have a kind of undulation and thereby communicate to the body a swifter progression than one would imagine where so many short feet are to take so many short steps that follow one another, rolling on like the waves of the sea.”

The eighteenth century British naturalist Charles Owen was not alone in considering the millipedes and centipedes as kinds of snakes; nor in being confused, as naturalists still are, at their curious, complicated way of moving. There had been highly exaggerated reports. The Spaniard Ulloa, Columbus' gold assayer, described some centipedes he saw on the northern coast of South America as a yard long and six inches wide. Their bite, he contended, was fatal.

“In the Kubbo-Kale valley,” reported British naturalist H. S. Wood in 1935, “I saw a centipede ten inches long. Its general color was electric blue with bright coral red fangs. It was the most terrible thing I have seen in my tramps through the forest.” Wood was stung by one of these Indian centipedes; he described the sensation as “exactly like that of a third degree burn.”

These animals are neither snakes, insects nor worms. They constitute an independent and intermediate order of animal life. They are considered a little nearer to the spiders than to true insects. They have retained the ways of life of the ancestral worm.

Most of the centipedes are active, ferocious, flesh-eating animals. Their poison fangs are deadly to their normal prey—earthworms and insects. Some of the larger species do not hesitate to attack lizards and small mice. A bite, however painful, probably never is fatal to a human. All are land animals which creep or crawl under logs and bark. They usually remain in seclusion during the day but come out of their retreats at night when they wander over the ground and attract attention to themselves by their phosphorescence. A few have been described as sea dwellers but these do not actually live in the water. They crawl along the shore and are submerged by each tide. Some or completely blind, others have many eyes.

The centipedes are among the most repulsive of all animals, yet there are accounts of South American Indian children who drag very large ones out of the earth and eat them. Religious fanatics among North African Arabs swallow them alive as proof of their supernatural powers.

Tropical America has many varieties with varied and curious habits, like the Nicaraguan species described by Thomas Belt:

“Among the centipedes was one which had a singular method of securing prey. It is about three inches long and sluggish in its movements but from its tubular mouth it is able to discharge a viscid fluid to a distance of about three inches, which stiffens with exposure to the air to the consistency of a spider’s web, but stronger. With this it can envelope and capture its prey, just as a fowler throws his net over a bird.

“Some of the other centipedes have phosphorescent spots in the head, which shine brightly at night, casting a greenish light for a little distance in front of them. I think these lights may serve to dazzle or allure the insects on which they prey.”

Centipedes have been observed attacking earthworms. One may grapple with its victim for several hours before killing it. Then it sucks the blood.

A fairly familiar visitor in the southern United States is a house centipede which thrives in damp basements and sometimes invades ground floors. It is a wormlike creature, about an inch long, with fifteen pairs of long legs. In the female the last pair are twice as long as the rest of the body. The animal is yellowish grey with white bands on its legs. It is poisonous, but its jaws are weak and it seldom bites human beings. Despite the evil reputation of its race, this centipede should be a welcome guest for it feeds on cockroaches, flies, spiders, moths, and other domestic pests. It is a fast runner but often stops suddenly, remains absolutely motionless for a moment, and then darts for concealment.