Popular Science Monthly/Volume 16/April 1880/Curious Ways of Getting Food
TO eat and to be eaten would seem the necessity and the end of every living thing. Doubtless every plant may serve as food for some animal; and there is no animal which may not be meat for some other animal. Nature is a vast hunting-ground, where man and beast and every animated being are legitimate prey. Not alone do the carnivorous animals eat the herbivorous. The blood-loving tiger is itself the prey of parasites. Even proud man is living booty. Animals within animals; life within life. There is literal truth in the satirical passage:
Has smaller fleas that on Lira prey;
And these have smaller still to bite 'em,
And so proceed, ad infinitum."
The variety of animal food is, therefore, as broad as animated nature. Hence, we find great variety of means and methods for procuring subsistence. Particularity in food implies especial or efficient means of getting that food. The strange appendages of animals, their form, color, and habits, have to do more with the prehension of food than with any other function. It will be interesting to briefly survey the animal kingdom with reference to this marvelous adaptation. Its origin we will not discuss.
The simplest manner of procuring food is shown by the tapeworm and some other intestinal animals. These feed on the nutritive fluid prepared in the alimentary canal of the animals which they inhabit; and, being destitute of mouth and stomach, absorb the already digested food directly through the skin or body-walls. Probably this absorption does not require will or effort on the part of the parasite, but takes place simply by the physical action known as osmose. It is thus equivalent to the last step in the digestive process of higher animals. Some parasites, as the larva of the tapeworm, which live in the muscles and tissues, imbibe the animal juices by the walls of the body; but here the process as a whole is slightly higher, for this food probably requires more elaboration or digestion.
Any special modification or organ for procuring food is a great advance beyond the method already described. Liquid food is more easily prehended than solid, yet the means are various and remarkable. Even the simplest organs are wonderful in their structure and action.
Those butterflies and moths which take any food at all have a long, slender tube for pumping the nectar of flowers. This "proboscis" is frequently much longer than the insect's body, and when not in use is beautifully coiled under the head. The hummingbird has a long, slender beak for the same purpose, which in some species is curved to fit certain flowers, it is said. Bees and flies lap their food, the former with a hairy tongue, the latter with a proboscis knobbed at the end. The sucker of the leech is furnished with three little saws for cutting the skin of its prey in order to draw its blood. A barbed tube is used by the louse; while the irrepressible mosquito is provided with a whole set of surgical instruments. Its proboscis, which seems so simple to the unaided eye, is found to be a "flexible sheath inclosing six distinct pieces, two of which are cutting-blades or lancets, two notched like a saw with reverted teeth, a tubular canal, and the central one an excessively acute point, which is also tubular."
It is interesting to know how the insect uses so many instruments, as we have all had the pleasure of being the subjects of her surgical skill (for only the female is admitted to the practice of bloodletting). "When the attack is made, the gnat (or mosquito) brings the tip of the organ within its sheath to press upon the skin into which it presently enters, the sheath remaining without and bending into an angle as the lancets descend. When the weapon has penetrated to its base—a distance of one sixth of an inch or more—the lancets move laterally and thus cut the flesh on either side, promoting the flow of blood from the superficial vessels; at the same moment a highly irritative fluid is poured into the wound, which has the effect of diluting the blood and thus rendering it more capable of flowing up the slender central tube into the throat of the insect."
Many aquatic animals, especially the low, fixed forms, depend for subsistence upon the minute organic particles floating in the water. But if the animal can not move in search of food it must have some means of bringing the food to itself. This is frequently accomplished by vibrating hair-like appendages, called cilia, which produce currents in the water. In that immense aggregation of minute animals, the sponge, the canals ramifying through the mass are lined with cilia, which cause constant currents of water to pass in at the small pores and issue at the large openings. Thus "the sponge represents a kind of subaqueous city, where the people are arranged about the streets and roads in such a manner that each can easily appropriate his food from the water as it passes along." Cilia fringe the gills of the bivalve mollusks, like the oyster and scallop, or the clam, which can burrow in the sand and send up into the water a long tube or siphon.
The great Greenland whale subsists on the small animals which swarm in the Arctic seas. But how shall the enormous beast capture sufficient of those tiny creatures? Its apparatus is as remarkable as it is unique—a huge sieve, made of the fringed edges of hundreds of "whalebone" plates, hanging from the roof of the mouth. Filling its cavern-like mouth with water containing the small animals, these are strained out as the water is expelled.
Solid food in mass requires some means of grasping—true prehension; generally accompanied by the power of dividing or crushing—mastication. A most curious method, and but one step higher than shown in the tapeworm, is exhibited by the microscopic amoeba, found in fresh water. An animal without any permanent appendages whatever, a bit of almost structureless protoplasm, it nevertheless moves without limbs, breathes without gills, seizes food without prehensile organs, and digests without a stomach. All the animal functions are performed by the general mass of the body. Its mode of feeling is as follows: When a nutritious particle comes in contact with the body, the surface at that point begins to depress or fall in, and so continues until the surrounding surfaces meet and unite. In other words, the animal wraps itself around the particle, and the bit of food is enveloped in the albuminous body-mass. The nutritive matter is absorbed, and any undigested or waste matter is expelled by a reverse process. Briefly, the amoeba extemporizes a stomach upon the place and at the time it is needed, and is not troubled with that uneasy organ when it is not needed. The ills of dyspepsia are to the amoeba unknown.
The polyp or sea-anemone has numerous grasping arms called tentacles surrounding the mouth, which is at the top of the stump-shaped body. But the muscular power of the soft, watery animal is not sufficient to hold a lively crab or other struggling prey. To supplement this weakness, it is provided with a most marvelous and deadly apparatus. The surfaces of the tentacles, and frequently of the stomach and body-walls, hold countless minute sacs containing beautifully coiled filaments, which are quickly thrown out like so many poisoned darts to pierce and paralyze the victim. The structure and action of these stinging threads is one of the greatest wonders of nature. The weak jelly-fish uses the same means to overpower its prey, which, enveloped and paralyzed by the hundreds of thread-like tentacles, is drawn upward into the digestive cavity. The larger jelly-fishes, with tentacles streaming out to a length of thirty or forty feet, could easily paralyze large animals. It has been suggested that some of the sudden and strange disappearances of bathers may have been caused by these fearful creatures.
Hundreds of little air-pumps are employed by the star-fish. These sucking-disks upon the under side of the flexible rays enable the animal to adhere with surprising power. And it can also protrude its stomach to inwrap prey which is too large to swallow. It is thus able, by turning itself inside out, to suck an oyster from its shell; and, having an especial fondness for these mollusks, it makes great havoc among the oyster-beds.
The tongue is the prehensile organ of the univalve mollusks. Being covered with rows of toothed plates it acts like a rasp, or can be protruded beyond the head to serve as a drill. The vegetable-feeding snails have also a bony plate in the roof of the mouth to aid in cutting. The common garden-snail has not less than 28,000 teeth on its strap-shaped tongue. These mollusks, and all animals hereafter mentioned, have the superior power of vision which, enabling them to discover food or pursue their prey, is of the greatest aid in getting food. The other senses are also aids to prehension.
The devil-fish, so called, the highest of mollusks, is possessor of an apparatus which for terrible efficiency could hardly be surpassed. Its prey is seized by eight long "arms" which surround the mouth, and the grasp is assured by rows of sucking-disks on the inner side of these arms. Indeed, these diminutive air-pumps hold so firmly that an arm will sometimes tear from the head. Some species have in addition two other arras equaling the body in length, which are commonly folded beneath the head, out of the way. As the creature nears its intended prey, these two long arms are quickly projected and seize the victim by means of the suckers, thus serving a purpose similar to a harpoon or lasso. As the victim is drawn nearer, the shorter arms wrap around it and effectually prevent its struggles. Now comes in play another instrument, its powerful, horny jaws, which form a beak shaped like a parrot's inverted. With this terrible weapon it bites its victim in the back of the neck, thus cutting the spinal cord and producing immediate death.
How different is the method employed by the Laodicea! This worm inverts or protrudes its gullet as a sort of proboscis, provided at the end with little teeth for grasping. Like the star-fish, to seize its food, it turns itself inside out.
Biting insects and most articulates have horny jaws moving horizontally. Poison fangs are sometimes added, as in the centiped. The claws of the crab and lobster are transformed legs; one frequently used as an anchor, while the other holds the prey.
Every one is familiar with the skillful trap which the spider sets for his victims. This wily creature sometimes builds a concealed lair whence it can spring upon its prey. Others, that spin no web, have a curious fashion of fastening a thread to whatever object they stand on at the instant they pounce on their prey, in order that the victim,
which is frequently larger than the spider, may not fly away with its captor. It does fly to the extent of the thread, but the poison soon takes effect, and the cruel spider deliberately winds up its anchor cable and recovers its footing.
A relative of the dragon-flies, the ant-lion, when in the larval state, digs a conical pitfall, at the bottom of which it lies buried, with only its strong jaws projecting. Here it patiently waits for an ant or some small creature to tumble in. If the struggling animal seems likely to clamber out, the ant-lion hurls sand at it to bring it within reach of the fatal jaws, where it is surely lost.
Ants sometimes undertake the dairy business. Being exceedingly fond of a milky fluid which exudes from two tubes situated on the hinder part of the bodies of certain plant-lice, called aphides, to procure it they resort to measures strangely intelligent for even the proverbially wise ant. They have been known to build mud stables in which the aphides were kept as stalled milch-cows. To cause the flow of milk, the ants irritate or rub the tubes with their antennae.
With few exceptions fishes depend upon their numerous teeth for seizing food. The sturgeon is toothless, and draws in its food by suction. A single long tooth is used by the hag-fish to transfix its victim, while it bores the flesh with a long, spiny tongue. The angler lies half concealed by sand and weeds, with its enormous mouth agape ready to seize any small fish which may incautiously venture near. Upon its nose is a long, flexible spine, with shiny tip, which, waving in the water, decoys small fry to their death.
King of fishes, by virtue both of size and ferocity, is the rapacious shark. This terror of the sea has its mouth armed with hundreds of teeth, triangular in outline and serrated on the edges. There are several rows, and, as the outer old teeth drop away, others rise into position to take their places.
In Japan is found a beautiful fish which has a sort of gun for bringing down insects. It does not have to wait, like other fishes, for the fly to fall into the water by accident. Seeing one lighted near the water, the chætodon gently approaches, and, aiming its beak, blows a drop of water with unerring aim, knocks the unsuspecting fly off its perch into the stream, and devours it, doubtless with a relish begotten of its skill as a sportsman. An air-gun with a drop of water for a bullet! It is said the Japanese amuse themselves by watching their captive chætodons shoot the flies presented to them.
Most reptiles use teeth for prehending food, like the fishes. Some, however, as the toad and chameleon, employ the tongue, which, being rooted in front and free behind, besides being very extensile, is thrown out and over with great quickness and precision. A sticky saliva causes the insect to adhere.
Poison-fangs of serpents are helps to procure food as well as weapons; and the power of charming is a very strange and effective way of obtaining food.
The alligator will approach a large animal which may be standing at the water's edge, and, by a quick blow of its powerful tail, knock the unsuspecting creature into the water. In deep water it is at the mercy of the reptile, which kills it by drowning. The nostrils of the alligator and crocodile are so placed as to be out of water, while the prey held in the jaws is beneath the surface.
Birds have not great variety of organs or methods of prehension. Beaks, claws, tongues, and keen senses complete the list of means. The woodpecker drills a hole into the tree to secure the larva which by some mysterious power it knows is buried there; and its barbed tongue is used to draw the worm from its hole. The slender, forked tongue of hummingbirds is used to grasp and draw minute insects from the depths of flowers. The long beaks of some birds are used to penetrate the sand or mud in search of worms. Birds of prey grasp with their talons. Their sight is wonderful, enabling them to discover their quarry at a great distance, and to strike it without error, not-withstanding the velocity of their approach. The sense of smell would seem remarkably developed in certain carrion-eating birds. The secretary-bird kills the poisonous serpents which are its diet by kicking them, while our domestic fowls scratch for a living.
In variety of prehensile means mammals far surpass any equal group of the animal kingdom. Owing to our familiarity, however, these peculiarities seem less interesting; but, if we could divest ourselves of preknowledge, or see them with a new vision, we should be astonished and delighted by the various contrivances and the curious adaptations. The tongue is the chief or only prehensile organ of many animals. Here belong the ox and all the cud-chewers. Of these the giraffe is the strangest. Intended to browse, it has an extremely long neck, mounted on equally long legs and shoulder-blades; yet, lest it should still fail of reaching its dinner, the tongue is proportionately long and remarkably prehensile; being able to select the sweetest foliage, or extend so slenderly at the tip as to enter a hole the size of a quill. Its lingual dexterity is sometimes exercised to the discomfiture of visitors at the menagerie. The toothless ant-eater breaks down the hard mounds of the ants or termites with its powerful claws, and sweeps the insects into its mouth with an immensely long, worm-like tongue; or it may thrust the tongue directly into the ant-holes. The insects adhere by means of a glutinous saliva, as in the case of the toad.
The hog uses his nose for getting food, and the star-nosed mole has a similar contrivance. The lips are employed by the horse; and we find both nose and upper lip prolonged as a proboscis in the tapir and shrew. But the elephant is, of course, the great example of immense proboscis. The whole makeup of the animal is queer, and to a stranger would be absurd. The small boy who described the elephant as "a large beast with a tail at both ends" had the elements of a naturalist. As the neck of the huge creature does not permit great motion of the head, the trunk supplies the deficiency. The tusks are also chiefly food-gatherers; used as picks and spades for uprooting trees and digging succulent roots. The tusks of the walrus are certainly locomotive and defensive organs, but it is suggested that perhaps they are also used to raise algæ from the rocks of the sea-bottom.
The greater number of mammals depend wholly upon the jaws and teeth for grasping food. A full description of these organs more properly belongs to the subject of eating food. Gnawing animals, like the rabbit, have the four front teeth, incisors, acting as chisels. In the hippopotamus the prehensile teeth form tremendous shears for cutting plant-stems.
Beasts of prey use jaws or feet, or both; but, to bring the prey within reach of either organ, requires keen senses to discover, and
craftiness and speed to catch them. Animals of the dog tribe seize with the jaws; those of the cat tribe use all four feet. The supple paw, with its retractile claws, is highly fitted for grasping and tearing, as well as for silent, stealthy tread. The cat's tongue is armed with spiny, recurved papillae, to lap blood or scrape flesh from bones.
Monkeys also employ all their feet for grasping; and, in common with those mammals that can sit on their hind-limbs, such as the squirrel, rat, kangaroo, and bear, carry food to the mouth with the fore-limbs; and some monkeys use the sensitive tips of their long tails to draw fruit from crevices or holes. The strainer of the Greenland whale has been described. A shovel-bill is the appliance of the duck-mole.
Only reference can here be made to the adaptation of mammals to the element in which their food exists. The whale, seal, hippopotamus, and duck-mole, find sustenance in the water. In the ground bur-rows the mole; the squirrel and sloth inhabit the trees, while the bat searches the air. Thus every element contains representatives of this highest animal group.
Prehension of food is so various in means and methods that no universal laws regarding it can be formulated. It can not form a basis of classification, seeming to have little or no discovered relation to animal rank. However, the subject is of greatest interest; and together with the adaptations of animals in other directions, has received in recent years much merited attention, chiefly in behalf of development theories. But, whether these remarkable adaptations of animals to peculiar food and surroundings be the result of variation and development, or of special creation, they are equally wonderful.