Popular Science Monthly/Volume 21/September 1882/Animal Self-Defense
By H. L. FAIRCHILD.
A FIERCE and pitiless struggle for life in the animal world is a stern fact. All creatures are beset by dangers. The negative conditions of cold and hunger and the positive influences of nature's elements are more easily resisted than the innumerable voracious foes. Every animal is predestined food for some other animal. But self-preservation is a universal thought, and endless is the variety of ways whereby life is prolonged.
A few external organs of defense are familiar to every one—as horns, claws, teeth, stings, shells, etc. Many animals depend on weapons and muscular power, a still greater number upon keen senses and fleetness—eternal vigilance. Others rely upon intelligence, cunning, simulation, and deceit; while stupidity, against which even the gods are powerless, may be the saving of others. Some are protected by skill in construction, some by unconscious resemblance, and a host by color, armor, and other passive means. A volume would not exhaust the subject, as there is scarcely a species of animal without some peculiarity for self-preservation.
This brief paper will only treat of defense against enemies; and, although the subject permits of no natural classification, an arbitrary division into passive and active defense will be convenient.
A host of animals of all classes and ranks are more or less defended by a hard covering—the result of natural growth. Such defense, like other modes to be described, is strictly involuntary and passive; and, requiring no intelligent effort, it may be regarded as the lowest. But even in this there is unbounded variety. We will distinguish the following classes:
1. Transformed epidermis constitutes the armor of the lobster, insects, and hard-skinned articulates in general. Also the hair of mammals, the feathers of birds, the scales which cover most fishes, reptiles, and the legs of birds, and the plates of that lizard-like mammal, the
Fig. 1.—Manis (Manis pentadactyla).
manis. 2. Stony secretion of the skin. Here belong the limy shells of mollusks, the tests of sea-urchins, star-fishes, etc.; also those of the chalk-forming rhizopods, and the silica shells of other microscopic animals. 3. True bony armor produced by the skin; as the coat-of-mail of the armadillo, and the scale-armor of the ganoid fishes, the bony pike and sturgeon, for example (also the armor of the group to which
Fig. 2.—Sturgeon (Acipenser).
belong the trunk-fishes. This sort of armor was very common among the most ancient fishes, but it has now gone quite out of fashion. The crocodile and alligator still have this bone armor in great perfection, and covered with epidermic plates—that is, they have a combination of 1 and 3. Altogether they are as well protected as any
Fig. 3.—Ostraciontidæ. Horned Trunk-fish (Ostracion cornutus).
living creature. The armadillo has only its back covered with this bone armor, but, like the hedgehog and the manis, it can roll itself into a ball with the unprotected parts inside. 4. In the turtles the endo- or vertebra-skeleton, is strangely modified and partly expanded upon the outside of the body; so it is literally true that the turtle is inside of his internal skeleton. The ribs are expanded to form the carapax, and the breast-bones to form the plastron of a solid box, within which many species can withdraw their head and limbs. But this is not all. The box is completed by the addition of numerous bony plates developed from the skin, and over all a horny epidermic
Fig. 4.—Armadillo (Chlamyphorus truncatus).
covering. The latter furnishes the beautiful and valuable tortoise-shell. Thus the armor of a turtle is a combination of 1, 3, and 4. One of the land-tortoises, the box-tortoise, deserves particular mention. The plastron, or breast-plate, of this species is divided into two movable parts hinged at a line drawn transversely or across the middle. When its head and feet are withdrawn, each end of the shell is tightly closed, so that no animal can get even a claw inside.
The skin of the rhinoceros is so very tough and thick that it defies ordinary weapons, and is said to resist soft-lead rifle-bullets.
Spines may be either (1) epidermic or (2) a secretion. The first class includes the spines of the echidna, hedgehog, and porcupine; also those of most fishes, lizards, and crabs. To the second class belong those of the globe-fishes, mollusks, rhizopods, and sea-urchins. The spines of the latter group have a remarkable structure. They are attached to the test or shell by a ball-and-socket joint and each moved by independent sets of muscles. While some species have only a very few large club-shaped spines, others have countless thousands of minute needles. The thorn-like spines of the common sea-urchin are also used in locomotion, and it has been happily said that a sea-urchin on its travels is like an animated chestnut-bur.
The hedgehog is one of the best protected of living animals. "Marching securely under the guardianship of its thorn-spiked armor, it recks little of any foe save man. . . . The formidable array of bristling spines with which the back is more or less covered offers a cheval-de-frise of sharp spikes toward any animal that may present itself as an enemy. Another peculiarity is the power possessed by these creatures of rolling themselves into a round ball, by placing the head on the breast, drawing up the legs, and curling the body firmly round the members. By this posture the hedgehogs render themselves invulnerable to almost any animal that may attack them. . . . When in this curious attitude, the hedgehog can not be unrolled by main force, as long as any life remains in the body, for there is an enormously developed muscle, with a very thick margin, which spreads over the back and round the sides, and which, when contracted, holds the creature in so firm an embrace that it will be torn in pieces rather than yield its point."
The spines of this animal are about an inch long, and naturally lie flat on the back, directed toward the tail. But by a peculiar arrangement they are erected when the owner coils himself. In shape the spine "is not unlike a large pin, being sharply pointed at one extremity, and furnished at the other with a round, bead-like head, and rather abruptly bent near the head. If the skin be removed from the hedgehog, the quills are seen to be pinned, as it were, through the skin, being retained by their round heads, which are acted upon by the peculiar muscle which has already been mentioned.
"Protected by this defense, the hedgehog is enabled to throw itself from considerable heights, to curl itself into a ball as it descends, and to reach the ground without suffering any harm from its fall. A hedgehog has been seen repeatedly to throw itself from a wall some twelve or fourteen feet in height, and to fall upon the hard ground without appearing to be even inconvenienced by its tumble. On reaching the ground, it would unroll itself and trot off with perfect unconcern."
The quills upon the "fretful porcupine" are several inches in length. The absurd belief that this animal could throw its quills at an enemy, after the fashion of a lance, arose from the following facts: "Their hold on the skin is very slight, so that, when they have been struck into a foe, they remain fixed in the wound, and, unless immediately removed, work sad woe to the sufferer. For the quill is so constructed that it gradually bores its way into the flesh, burrowing deeper at every movement, and sometimes even causing the death of the wounded creature. In Africa and India leopards and tigers have frequently been killed in whose flesh were pieces of porcupine-quills, that had penetrated deeply into the body, and had even caused suppuration to take place. In one instance a tiger was found to have his paws, ears, and head filled with the spines of a porcupine which he had vainly been endeavoring to kill. . . . If irritated or wounded, the porcupine becomes at once a very unpleasant antagonist, as it spreads out its bristles widely, and rapidly backs upon its opponent."
Many small creatures are undoubtedly protected by offensive fluids or odors, which are not a matter of consciousness or will. In illustration of this method of defense, it will be sufficient to quote the following: "In South America there is a family of butterflies termed Heliconidœ, which are very conspicuously colored and slow in flight, and yet the individuals abound in prodigious numbers, and take no precautions to conceal themselves, even when at rest during the night. Mr. Bates found that these conspicuous butterflies had a very strong and disagreeable odor; so much so, that any one handling them, and squeezing them as a collector must do, has his fingers stained and so infected by the smell as to require time and much trouble to remove it. It is suggested that this unpleasant quality is the cause of the abundance of the Heliconidœ; Mr. Bates and other observers reporting that they have never seen them attacked by the birds, reptiles, or insects, which prey upon other lepidoptera."
Great numbers of animals are permanently colored so as to harmonize with their favorite surroundings. This obscure coloring may be either for the purpose of securing prey, or for concealment. The banded colors of the tiger perfectly blend with the lights and shadows in the jungle-grass. Those forest animals which live on the ground, as game-birds, deer, rabbit, or squirrel, are of brown or neutral hues, which assimilate to the color of dead leaves and tree-trunks; and they are quite impossible to discover as long as they remain motionless. Animals of the desert are dull or rust colored, or of some light tint. Insects, frogs, and lizards, which live among the leaves, are green; those on the ground in dry or rocky places are pale accordingly. Grasshoppers generally have the prevailing hue of the fields where they subsist. Indeed, protective coloration is very common, and any person can find examples.
More remarkable, however, is the protection afforded by what is termed chromatic function. "It consists in the power possessed by many fishes, crustaceans, amphibia, and reptiles, of adapting their general coloring, often by extremely rapid alteration, to the coloring of the surrounding objects, so that they seem to be helped by it in the pursuit of their prey, or especially protected against the attacks of their enemies."
This is very striking in many fishes. It can be readily observed in the common tree-frogs. The chameleon and the devil-fishes are famous for their power of changing color when irritated. The degree of consciousness involved in this is unknown.
The resemblance to inanimate objects of many small animals, especially insects, is one of the most curious things commonly met with. Insects imitate leaves, sticks, dry twigs, stones, lichens, etc., so perfectly as to sometimes deceive the close observer. The most remarkable examples are found in the tropics, where insect-life luxuriates. Wallace thus describes an Indian butterfly (Kallima): "The upper surface of these is very striking and showy, as they are of large size, and are adorned with a broad band of rich orange on a deep-bluish ground. The under side is very variable in color, so that out of fifty specimens no two can be found exactly alike; but every one of them will be some shade of ash, or brown, or ochre, such as are found among dead, dry, or decaying leaves. The apex of the upper wings is produced into an acute point, a very common form in the leaves of tropical shrubs and trees, and the lower wings are also produced into a
Fig. 5. Leaf-Butterfly (Kallima paralekta).
short, narrow tail. Between these two points runs a dark curved line exactly representing the midrib of a leaf, and from this radiate on each side a few oblique lines, which serve to indicate the lateral veins of a leaf. . . . But this resemblance, close as it is, would be of little use if the habits of the insect did not accord with it. If the butterfly sat upon leaves or upon flowers, or opened its wings so as to expose the upper surface, or exposed and moved its head and antennae as many butterflies do, its disguise would be of little avail. We might be sure, however, from the analogy of many other eases, that the habits of the insect are such as still further to aid its deceptive garb: but we are Dot obliged to make any such supposition, since I myself had the good fortune to observe scores of Kallima paralekta, in Sumatra, and to capture many of them, and can vouch for the accuracy of the following details: These butterflies frequent dry forests and fly very swiftly. They were never seen to settle on a flower or a green leaf, but were many times lost sight of in a bush or tree of dead leaves. On such occasions they were generally searched for in vain, for, while gazing intently at the very spot where one had disappeared, it would suddenly dart out, and again vanish twenty or fifty yards farther on; on one or two occasions the insect was detected reposing, and it could then be seen how completely it assimilates itself to the surrounding leaves. It sits on a nearly upright twig, the wings fitting closely back to back, concealing the antennæ and head, which are drawn up between their bases. The little tails of the hind wing touch the branch, and form a perfect stalk to the leaf, which is supported in its place by the claws of the middle pair of feet, which are slender and inconspicuous. The irregular outline of the wings gives exactly the perspective effect of a shriveled leaf. We have thus size, color, form, markings, and habits, all combining together to produce a disguise which may be said to be absolutely perfect: and the protection which it affords sufficiently indicated by the abundance of the individuals which posses it." Fig. 6.—Phasma sp., a wingless orthopterous insect. Of the walking-stick in Wallace says: "Some of these are a foot long and as thick as one's finger, and their whole coloring, form, rugosity, and the arrangement of the head. lees, and antennæ, are such as to render them absolutely identical in appearance with dry sticks. They hang; loosely about shrubs in the forest, and have the extraordinary habit of stretching out their legs unsymmetrically so as to render the deception more complete." The counterfeiting is carried even to the imperfections and injuries of the objects copied. Still speaking of the walking-stick insects, Wallace says: "One of these creatures, obtained by myself in Borneo, was covered over with foliaceous excrescences of a clear olive-green color, so as exactly to resemble a stick grown over by a creeping moss or jungermannia. The Dyak who brought it assured me it was grown over with moss, although alive: and it was only after a most minute examination that I could convince myself it was not so." And of a leaf-butterfly he says: "We find representations of leaves in every stage of decay, variously blotched and mildewed, and pierced with holes, and in many cases irregularly covered with powdery black dots, gathered into patches and spots, so closely resembling the various kinds of minute fungi that grow on dead leaves that it is impossible to avoid thinking at first sight that the butterflies themselves have been attacked by real fungi."
Mimicry is the resemblance which poorly protected animals bear to others well protected. Several species of edible butterflies imitate the Heliconidæ and others, which are protected by fetid odors; other
Fig. 7.—a, Doliops sp., mimics b, Pachyrhynchus orbifer; c, Doliops curcilioncides, mimics d, Pachyrhynchus sp.; e, Scepastus pachyrhynchoides (a grasshopper), mimics f, Apocyrtus; g, Doliops sp.; mimics h, Pachyrhynchus sp.; i, Phoraspis sp. (a grasshopper), mimics k, a Coccinella. All from the Philippines, of natural size. It is evident that the great similarity of the creatures to those they mimic is less conspicuous in the engraving than in real life, since the exact correspondence in the coloring can not he given here.
butterflies mimic wasps so closely that persons fear to handle them, although the imitation does not extend to the sting. Innocent beetles imitate other beetles which have hard shells or fetid glands. They also mimic bees and wasps. Flies also mimic wasps, and grasshoppers mimic beetles. Some moths almost exactly imitate the form and color of hummingbirds. Wallace states that some harmless snakes mimic poisonous species. And this mimicry is found even among birds.
Active defense implies such organs and methods of defense as are under control of the animal's will, or matters of conscious action. We shall here find much greater variety.
The homes of animals—nests, houses, burrows, etc.—are protection from the storm and for the young as well as from foes. This is a most interesting and extended field, and requires separate treatment.
But many small creatures build individual shells or cases wholly for defense against enemies. These are frequently carried about with the creature, as armor, wherever it goes. A familiar example, found in any brooklet, is seen in the case of the young caddis-fly. To hide and protect itself from the ever-hungry fishes, the larva of this insect incloses its body in a tube formed by gluing together bits of wood, shells, sand, and all sorts of matter that may be found at the bottom of a stream. This case has a silken lining, and out of the end the larva protrudes its head and legs for locomotion, or wholly withdraws out of sight and danger. Other water larvae reside within a bit of hollow straw or plant-stem. Fig. 8.—Caddis-Worm, with its Case. A similar habit characterizes a group of sea-worms, to which belongs the Serpula. Thin tubes may be formed of a limy secretion, or built by cementing sand, shells, etc. One of the tentacles of the Serpula is terminated by an expansion which, when the worm withdraws into its case, serves as a stopper (operculum) to securely close the opening (see Monthly, February, 1882, page 452, Fig. 4). The silk pupa-cases of the moths are very wonderful, even if very common, examples of artificial covering.
The singular hermit-crabs are obliged, on account of their lack of a hard epidermis, to inhabit some empty mollusk-shell. And they are exactly fitted for that sort of life: the tail-fin is changed into hooks for holding the shell; some of the legs are strong levers for dragging its heavy house; and one of its claws is disproportionately large, in order to close the opening of the shell.
Keen senses combined with swiftness of locomotion are the chief reliance of birds and mammals. The rabbit is a fair example. Innocent and timid, entirely without weapons, it is always on the alert. With its large eyes, ears sensitive to the slightest sound, and a delicate sense of smell, it is as difficult to surprise as it is to "catch a weasel asleep." Every deer-stalker knows he must approach his game on the side opposite the wind. Most mammals, especially the herbivorous, scent danger, and flee away. Many of them use their natural weapons only when brought to bay, and in despair. This is true, indeed, of many carnivorous beasts when they are not bold with hunger. Birds rely, for warning of foes, more exclusively upon their eyes.
Excepting from man, the birds and beasts of prey have little to fear. Their offensive weapons are terribly effective. And, besides teeth and claws, the lion and tiger can strike such blows with their paws as will kill a buffalo at a stroke. The cud-chewing mammals have horns which may, with even the most timid, be efficient as a desperate resort. These are of various kinds as regards form, structure, growth, and duration. The principal kinds are represented by those of the deer, giraffe, antelope, and ox. The efficiency of these natural weapons is greater than would be imagined from a knowledge simply of our domestic animals. The water-buffalo of India (to quote from Wood) "is a most fierce and dangerous animal, savage to a marvelous degree, and not hesitating to charge any animal that may arouse its ready ire. An angry buffalo has been known to attack a tolerably sized elephant, and, by a vigorous charge in the ribs, to prostrate its huge foe. Even the tiger is found to quail before the buffalo, and displays the greatest uneasiness in its presence." Of the gaur, Wood says, "These herds ... in their own domains bear supreme rule, neither tiger, rhinoceros, nor elephant daring to attack them." Some antelopes are on occasion quite a match for the lion.
The horn of the rhinoceros is very different from those of the ruminants. Its peculiar situation on the nose makes it a very ugly and efficient weapon. It is placed on the middle of an arch of bone, the latter being free at one end so as to give elasticity. Many animals, particularly the horse tribe, make excellent use of the feet. Of the use of the hind-feet, the mule is a striking but somewhat threadbare illustration. The elk and related animals strike with the fore-feet, and are able to cope with a dog or wolf.
The ostrich and the secretary-bird also kick; and the latter, as is also true of many birds, gives heavy blows with its wing.
The kangaroo uses his hind-feet less to kick than to cut and disembowel his antagonist. The bear employs much the same tactics. He hugs and crushes his antagonist with his fore-legs, and strikes and tears with either foot.
The elephant uses his great weight to literally crush his foe. But his weapon is his elongated nose.
Another example of the nose used as a weapon is found in the sword-fish. Here the bones of the skull are produced to form a thick beak, or sword, which points forward directly in a line with the body. With this lance, five or six feet long, the fish is able to pierce even through a ship's bottom. The British Museum is said to contain a sword imbedded in the planking of a ship. Accounts have been given of the sword-fish attacking and even killing the whale.
The saw-fish, a sort of shark, has a similar beak, not sharp pointed, however, but blunt and armed with teeth on either edge. It can be used as a lance, and has been deeply driven into a ship's timbers. It is used mainly for striking, and, if the animal attacked is moving, the effect is a saw-cut. It then acts as a veritable saw. But it seems absurd for an animal to carry teeth on the outside of his nose.
With another shark the tail is a weapon, as it is with the whale also. The tail of the thrasher is extremely large, and can deal severe blows. The thrashers have been known to attack the whale when the latter is at the surface. It is conjectured that the thrashers and the sword-fish form a conspiracy against the whale, and, while the latter prevent the whale from diving, the former leap out of the water and bring their huge tails down on the naked back of the whale with a tremendous slap that can be heard a long way. Probably the whale is . more frightened than hurt.
Some rays or skates have the tail long and whip-like. It is covered with sharp spines, and forms an effective instrument for either striking or grasping. These spines produce severe inflammation, and are greatly dreaded by fishermen. The larger ones are much used by savages for edging weapons. It is supposed that the whip-ray seizes an enemy, or its prey, with its tail, and kills it by the cutting spines on its tail, and by pressing it against the barbed spine situated on its back. These spines are commonly used as spear or arrow heads by the savages of the South Sea.
Some small creatures have forceps or jaws as weapons. Those of the lobster are modified feet, while those of the beetle are mouth-parts.
The most elaborate organs of defense are found in the lower forms of life. And at near the lowest point in the animal scale we find an apparatus exceedingly complex and efficient. This is the "nettling-threads," "lasso-cells," or cnidæ which give the hydra, jelly-fish, and
Fig. 9.—Lasso-Cell, containing Barbed Filament. (After Gosse.)
polyps their power of stinging. They are also possessed by the crinoids, some naked sea-snails, and some sea-worms. Like many other weapons, they are used to subdue prey as well as to repel enemies. These creatures are soft and delicate, and would seem to be the easiest food for other animals. The cnidæ are probably their only defense, but they seem quite sufficient. A chapter would be required to give a full description of these wonderful weapons. The instrument consists of a hollow filament, coiled in a sac, the whole of microscopic size. The sacs are commonly on the surface of the tentacles and other free surfaces of the body. In some species they are collected in thread-like magazines which are shot out of the body-walls. Upon irritation this hollow thread is thrown out of the sac to a great length, by eversion. It is turned inside out, and then exposes a barbed surface. They penetrate the soft tissues of the animal attacked, and convey a poison fatal to small animals. Any bather who has ever been stung by a jelly-fish can give a satisfactory account of the effect of these weapons. There is no doubt that a man would be completely and quickly paralyzed if entangled, in a nude state, among the tentacles of the larger jelly-fishes.
The stings of insects are more familiar, but still very wonderful. In the sting of the honey-bee "we see an apparatus beautifully contrived to enter the flesh of an enemy; two spears finely pointed, sharp-edged, and saw-toothed, adapted for piercing, cutting, and tearing; the reversed direction of the teeth gives the weapon a hold on the flesh, and prevents it from being readily drawn out. Here is an elaborate store of power for the jactation of the javelins, in the numerous
Fig. 10.—Barbed Case of Everted Settling-Thread. (After Gosse.)
muscular bands; here is a provision made for the precision of the impulse; and, finally, here is a polished sheath for the reception of the weapons and their preservation when not in actual use. All this is perfect; but something still was wanting to render the weapons effective, and that something your experience has proved to be supplied." This is the poison, which has also a complex apparatus for its secretion and ejection. This sting is a modified ovipositor, and possessed only by the females, or neuters, which are undeveloped females. The male insect is always a mild and inoffensive creature.
Scorpion-stings are similar to those of insects in position and use, but are unlike in origin and development.
The poison-fangs of venomous snakes are modified teeth. They are so attached that when not in use they lie in a fold in the upper jaw. The poisonous snakes have broad heads, on account of the muscles which control the fangs and the large glands which secrete the venom. The latter is a sort of saliva, probably charged with fermenting organisms, which are harmless in the food-canal, but which in the blood multiply with amazing rapidity. The poison is conveyed to the wound by a groove in the side of the fang.
The fangs of spiders represent the antennæ of insects. They are tubular, for conveying venom, and jointed. The point or terminal joint when not in use shuts into the basal joint, like the blade of a pocket-knife into its handle. The fangs of the scorpion are modified feet.
Certain fishes have the power of storing a large quantity of electricity, which is used at will to paralyze and kill prey or enemies. The electric eel can kill small fishes at a distance, it is said, of fifteen feet; and they sometimes kill the horses which are driven into the pools for the purpose of exhausting and capturing the eels. The electricity, is stored in a peculiar tissue of large cells or tubes which act like a battery of so many Leyden-jars. Apparently nervous force is here converted into electricity. After giving several shocks, the creature is exhausted for a time. Fig. 11.—The Torpedo, with its Electrical Apparatis displayed. b, branchiæ; c, brain; e, electric organ; g, cranium; me, spinal cord; n, nerves to the pectoral fins; nl, nervi laterales; np, branches of pneumogastric nerves going to the electric organ; o, eye. Besides those creatures which are passively offensive by their odors, there are others which can at will expel fluids to offend and deter enemies. The skunk need only be named, and the point will be fairly grasped by the reader. Some reptiles have the power to expel an offensive fluid from glands in the skin. The toad and salamander are examples. This fluid is acrid and biting, and intensely irritating to delicate skin, as the mucous membrane of the mouth or eye. The abundance of this viscid yellow fluid in the salamander probably led to the ancient notion that this little amphibian could withstand and extinguish fire. The water-beetle (Dytiscus) also expels a nauseating fluid.
It is very curious to find how some weak and lowly creatures succeed in frightening away their powerful foes. They assume a virtue which they do not possess. The attitudes of some insects may also protect them, as the habit of turning up the tail, by the harmless rove-beetles, no doubt leads other animals, besides children, to the belief that they can sting. The curious attitude assumed by sphinx caterpillars is probably a safeguard, as well as the blood-red tentacles which can suddenly be thrown out from the neck by the caterpillars of all the true swallow-tailed butterflies."
Many creatures produce sounds for the same purpose. The cat spits. Snakes hiss. The porcupine rattles his quills. "Even the preliminary rustle of the quills with which a porcupine generally prepares every attack is sufficient to make an ordinary horse flee in terror." Perhaps the sounds produced by certain naked sea-snails are in some degree for defense.
Various lizards abash their enemies by expansion, protrusion, or erection of appendages. The iguana has a bag beneath the neck which it puffs up. The frilled lizard of Australia has a sort of Elizabethan collar about its neck which it can suddenly expand, to astonish and put to flight the approaching enemy. And the basilisk of South America has fin-like appendages upon its back and tail which it can erect if annoyed. The chameleon inflates his body with air, that he may appear to be a much bigger creature than he really is. From this sprang the belief that the chameleon lived on air.
The phosphorescence of animals is a subject not yet fully explained. But without doubt it is partly defensive.
One of the most queer and ludicrous methods of protection is seen in the bombardier beetles. In description of this, listen to Pouchet: "They alarm their enemies by means of real artillery. These coleoptera when threatened suddenly expel from their intestines a whitish acid vapor, the explosion of. which as it issues produces a certain sound, a slight detonation, which carries disorder among the aggressors. This explosion may even be repeated a certain number of times. Hence, when one of these insects is pursued by an enemy, it fires off its artillery anew. The instinct of defense is so inherent in the tribe of bombardiers that, at the sound of a cannon-shot from one of them, all the others fire at the same time; there is a running fire along the whole line. The sound produced by these coleoptera is intense enough to startle those who do not know the ruse."
Truthfulness is not an inherent virtue of animal character. Many are the tricks, deceits, and devices by which they selfishly seek advantage. A common artifice is that of feigning death in order to escape the reality. "Playing 'possum" is a dodge not confined to those higher animals to which we in our condescension grant the possession of a degree of intelligence. The larva of the dytiscus, knowing the preference of fishes for living active prey, when seized immediately becomes flaccid and limp. The fish, supposing he has seized only a carcass, drops it in disgust, and the dytiscus makes the most of his opportunity. When the insect becomes a hard-skinned beetle, it, of course, loses this power, and then employs a disgusting fluid, as before mentioned.
Every collector of insects becomes familiar with species which have the habit of quietly dropping from the plants on which they feed to the ground, upon the least alarm.
Hunters are familiar with many wiles by which pursued animals endeavor to elude their pursuers and throw them off the scent. The fox has the habit of doubling on his track, of walking fences, and going into water. Wood thus describes the habit of a South African antelope, the duyker-bok: "If the sportsman should happen to overtake this buck, it will lie still, watching him attentively, and will not move until it is aware that it is observed. It will then jump up and start off, making a series of sharp turns and dives, sometimes over bushes and at others through them. When it conceives that it is observed, it will crouch in the long grass or behind a bush, as though it were going to lie down. This conduct is, however, nothing but a ruse for the purpose of concealing its retreat, as it will then crawl along under the foliage for several yards, and, when it has gone to some distance in this sly manner, it will again bound away."
When a slug or naked snail enters a bee-hive, the bees fall upon him and sting him to death, as a matter of course. But what to do with the carcass then becomes a vital question. And now is exhibited the wonderful intelligence of the social insects. The body is too large for the bees to move; but if left it will breed pestilence. They cover it with wax; they embalm it, as did nations of old their dead. But a shelled snail entering the hive is invulnerable to their weapons, so they cement his shell to the bottom of the hive. It is a sentence of imprisonment for life, with no hope of pardon. Yet such manifestations of thought we call "instinct," because we wish to monopolize "intelligence."
Oddest of all defensive methods is that of snapping off the tail. The blind-worm, or slow-worm, is a little snake-like lizard common in
Fig. 12.—Blind-Worm (Anguis fragilis).
the Old World. When alarmed it contracts its muscles in such manner and degree as to break its tail off at a considerable distance from the end. But how can this aid it? The detached tail then dances about very lively, holding the attention of the offender, while the lizard himself slinks away. And for a considerable time the tail retains its capability of twisting and jumping every time it is struck. The lizard will then grow another tail, so as to be prepared for another adventure. There are other lizards which have a similar power, though in less degree. The American glass-snake, so called, is one.
Semper describes certain snails of the Philippine Islands which do the same thing: u Every species (Helicarion) that I personally examined possessed the singular property ... of shedding their tails when they are seized somewhat roughly, at a little way behind the shell. This they do by whisking the tail up and down with extraordinary rapidity, almost convulsively, till it drops off; if the creature is held by the tail it immediately falls to the ground, where it easily hides among the leaves. ... These snails at first constantly escaped me and my collectors in this way, and not unfrequently we had nothing but the tail left in our hand."