Part 41

The white-headed eagle became the national bird of the United States by act of Congress on June 20, 1782. For nearly two centuries it has remained the American symbol of fearlessness and freedom. The same bird—Haleoletus leucocephalus and not the more familiar golden eagle found in the West—had been the supreme totem animal of the Six Nations of the Iroquois from whom many institutions of the new republic indirectly may have been derived.

This eagle still is fairly abundant in the fringes of forest around the Great Lakes, its fishing grounds. Its nest, almost always at the top of a tall sycamore or hickory which is dead or dying, is almost literally a log cabin. The bird sometimes uses sticks six feet long for the outer walls. It grasps large dead branches in its talons, breaks them off by sheer force, and flies away with them. A recently observed nest was nine feet high and six feet in diameter.

The Predatory Mantid

Why does the “praying mantid” pray? The prayerlike pose of this near relative of the cockroach is its normal position both for seizing its victims and for defending itself.

For their size mantids are among the most predatory animals in existence. They are also among the least known of the insects. There are more than 1500 species in the world, mostly tropical. Only 19 are known in the United States which is on the northern fringe of their normal habitat. One of the most remarkable features of the mantid is its front legs, which bear sharp spines and fold in a curious hinged fashion enabling the insect to reach forward, seize a fly or some other victim, and bring it to its mouth. This is the explanation for the seeming attitude of prayer.

Mantids feed entirely on other animals, chiefly insects caught alive. Instances of small birds, lizards and mice being eaten have been reported, probably due to mistaken observations. There is no question that mature individuals of several species can handle any caterpillar, grasshopper, cockroach or other large insect that comes within its range. Their appetite is enormous. An adult mantid has been known to eat ten cockroaches in less than three hours. Bees and wasps usually have no terrors for the predators, although occasionally a mantid is stung while trying to catch a wasp and gives evidence of the injury.

Sometimes the mantid’s front legs are held in a posture of sparring, rather than of prayer. More than once the sight of one of these insects “sparring” with an English sparrow or some other small animal has attracted a crowd on a city street and gotten paragraphs in the local newspapers.

The mantid usually waits motionless until its prey comes within reach but sometimes, supposedly when very hungry, it may stalk another insect. Sometimes the victim is touched lightly with the antennae before the front legs flash forward and make the capture.

These insects have developed considerable camouflage. Some tropical species look like flowers, their colors blending with those of foliage. One species varies in color from white to pale pink and has the practise of crouching among certain blossoms, the petals of which its legs and other body parts resemble. Others have arranged themselves on plants so that they look like blue flowers. Presumably bees and other flower-loving insects thus are lured to their doom. A few tropical mantids have developed a superficial resemblance to other insects of the same environment which are distasteful to birds and monkeys. Some closely resemble large ants.

There is a widespread belief that the male always is eaten by the female after mating. Sometimes this happens, but the male never is a willing victim and quite frequently escapes. The eggs are laid in groups of from a dozen to about 400. They are deposited in layers in the midst of a thick frothy liquid which soon hardens and becomes fibrous. For the most part, each species deposits egg masses of a distinctive shape.

On the whole, they probably are beneficial insects because the greater part of their prey consists of species injurious to gardens. The possibility of propagating them for the control of injurious insects, such as Japanese beetles, has been suggested because of their notoriously big appetites. It would, however, be impossible to restrict them to a specific pest. They would continue to eat about every living creature of the right size that came within reach of their claws, including many beneficial species.

Fireflies as Electricians

The flashing of a field of fireflies is an expensive show. For two generations one of the ideals of science has been to produce artificially “cold light”—radiation confined entirely to those wavelengths to which the retina of the human eye is sensitive without any energy being wasted in the form of heat or invisible light. Could the ideal be attained with the same expenditure of fuel and power as is required for light production at present the world’s bills for illumination would be decreased enormously.

Actually the firefly has attained this ideal in one direction. It emits only visible light. From this point of view the firefly or any other sort of luminescent animal is very efficient indeed. A good part of the total radiation from any man-made source of light—or for that matter from the sun—is invisible infrared, observable only as heat. Possibly the firefly produces some heat in its light production but it is too little to be measured. It is safe to say that within a tiny fraction, 100% of the radiation produced is in the visible spectrum—most of it shorter wave lengths than those which produce the sensation of blue light. This is by far the highest efficiency known to science.

Chemists can duplicate the process to a certain extent. Consequently a great deal of research has been devoted to the light-emitting mechanism, physical and chemical, of the insects. Firefly luminescence is due to the oxidation—that is, the burning—of a chemical substance, luciferin. This reaction, in turn, depends upon a catalyst known as luciferase. The same phenomenon can be brought out by appropriate mixtures of luciferin, luciferase, and oxygen in a test-tube at the proper temperature.

All these experiments have shown that, considering the amount of oxygen necessary, it is a very wasteful process. It is far less efficient than most means of producing artificial light known to man—one percent compared with the 4.54 percent of the carbon filament; 17.17 percent of the acetylene flame, or 60 percent of the sodium arc light. To illuminate houses or streets with firefly light would be a very expensive procedure indeed.

Dr. N. D. Maluf of Yale University quotes a calculation that “an area of firefly light six feet in diameter on the ceiling of a room nine feet high would give ample illumination for reading or drawing on a table three feet high.” This would hardly interest an illuminating engineer. The light can, however, be used in an emergency. During the Spanish-American War Major General W. C. Gorgas is reputed to have used the light from a bottle of fireflies to perform an emergency operation. The average householder would rebel at the monthly bills.

The actual light from a single firefly is very minute indeed, averaging little more than 25 thousandths of a candle power. The combined courtship efforts of a whole field full of the insects would hardly light a single room enough for sewing or reading. The insect will sometimes glow steadily with a light as low as two hundred-thousandths of candle power intensity.

Among fireflies, flashing is essentially a courtship phenomenon, yet there is no discernible difference between the quality of the light of male and female insects. What actually happens is that the flash of the female in response to the signal of the male is timed almost exactly at a trifle over two seconds. The male is instinctively aware of this time interval, so that he does not become confused with the signals of other males. In a large group of the insects the flashes of the two sexes tend to become synchronized, producing a field of light.

The Mollusk Vampire of Hell

Black demon of the realm of everlasting dark is Vampyrotouthis infernalis. Most nightmarish of living animals, this “vampire of hell” has a midnight-black body about two inches long, red-brown round face on a head almost as large as the rest of the body, red eyes an inch in diameter encircled by narrow bands of pinkish-orange, rows of ivory white teeth, ten wriggling, ever-probing tentacles extending from the head. On the sides of the neck are two powerful, flashing lights each of which is a cluster of about 50 tiny phosphorescent nodules. The entire body is covered with hundreds of tiny lights.

Fortunately nobody is likely to meet this horror of an hallucination-damned maniac’s ravings on a lonely road passing a graveyard at night. It is a mollusk, a close relative of the octopus and the squid but belonging to neither family, which lives in abysses of sub-tropical seas all around the world, far below the depths reached by the most penetrating green rays of the sun. Only its relatively small size and restricted habitat prevent it from being the most fearsome, loathsome creature on this planet.

The “vampire” is a living fossil, survivor out of the demonic seas of 200,000,000 years ago which found shelter from the inexorable scythe with which time mows down demons by retreating further and further into the dark. Imprints of quite similar sea animals, probably denizens of warm, shallow waters, have been found in English rocks.

Up to now about a hundred individuals have been taken from the deep sea, mostly by scientific expeditions. Of these, nearly two-thirds have come from the Atlantic off the Florida coast and near Bermuda. There are several in the Smithsonian collections. The fantastically terrible little mollusk was first taken in the Indian Ocean by Dr. Carl Cuhn of the German Valdavia expedition about 75 years ago. Until quite recently all specimens obtained have been in poor condition and there has been considerable difficulty in classifying them. The job has been complicated by the fact that the vampire apparently undergoes a series of metamorphoses which have been mistaken for different species. During the past ten years, however, they have been studied intensively by Dr. Grace Pickford of the Bingham Oceanographic Laboratory of Yale and their fearsome reality has been established beyond question.

Naturally, since the living animal cannot be observed, essentially little is known of its habits and ways of life. Certainly it is a voracious carnivore like all others of its race and preys upon every other creature of the depths in its size range. It seems to be confined exclusively to a depth of about 1,500 meters. This is the level of the sea where, for some reason oceanographers are unable to fathom, the oxygen content of the water is lowest. It goes up immediately both above and below. The vampire, apparently, cannot stand too much oxygen. Its eggs sink to about 2,000 meters where they reach their suspension level. As soon as the little mollusks hatch they rise to their natural habitat.

The vampire has powerful tentacles but its fin muscles indicate that it is a weak swimmer. It probably lurks in the abysmal darkness for its prey to come within reach of the probing tentacles. Even with its enormous eyes and its many lights it hardly can distinguish moving objects very well and presumably is not particular about what living things it eats. Its usual victims probably are fishes and smaller mollusks. It is unlikely that the creature has many natural enemies it need fear. Unlike the octopuses, its nearest relations, it has no ink sac from which to discharge a black cloud around its body for its own concealment.

Climbing and Flying Frogs

A family of frogs that climb trees, burrow and are learning to fly are the tree frogs of Mexican tropical forests. Various members of the family are at different stages in their physical adaptation to tree life. They constitute a striking example of evolution at work as a race struggles to shake itself free from one environment and conquer another despite considerable odds.