Read the book: «Nature's Teachings», page 17

“This insect, so far as my own observation has enabled me to ascertain, does not construct its own burrow, but makes use of any hole which is adapted to its purpose. I once detected a bee entering the hole above the wheel of the sash-line in a summer-house; but its nests are most commonly formed in the holes bored in old willow stumps by Cossus ligniperda (the Goat-moth): formerly they were easily obtained in Battersea Fields, where the willows abounded.

“It is probable that when the parent insect has selected one of these ready-formed tunnels, she enlarges the end used as the depository of the nest, and this is easily effected, as the stumps in question, at the depth of a couple of inches, consist of soft decayed wood.

“The chamber being formed, the bee collects a quantity of down from woolly-stemmed plants, with which she forms an outer coating. She then constructs a number of cells for the reception of the pollen, or food of the larva; they consist of a woolly material, mixed with some glutinous matter which resists the moisture of the food they contain, and in which the larva, being full fed, spins a brown silken cocoon. These bees pass the winter in a larva state, and do not appear until midsummer.

“In one respect, the sexes of this genus differ from most other bees, the males being much larger than the females.”

The reader will see from this account how exact is the analogy between the carpenter’s plane and the jaws of the bee. In consequence of the simile employed by Mr. White, the insect has been popularly known by the title of the Hoop-shaver Bee. It is a tolerably common insect, and abounds in the South of England.

CHAPTER II.
THE SAW AND ITS VARIETIES

Cutting Tools and their working.—Structure of the Edge.—The Kris.—Edge of a Razor.—The Sword and the Apple.—Australian Saw.—Fretwork Saw.—Various Saw-flies.—The Pioneer’s Saw.—Cutting Tools of Trichiosoma.—Side Teeth of the Saws.—The Cordon Saw, or Band Saw.—Tooth-ribbon of Whelks, Slugs, and other Molluscs.—The Dog-whelk, or Purpura.—The Circular Saw.—Sawyer-beetles and their Mode of Work.

STILL keeping to the Cutting Tools and their varieties, we come to the Saw, i.e. the cutting tool set with teeth upon its edge. Now, in plain fact, there is no cutting instrument that does not more or less partake of the character of the Saw; for, in the first place, it is absolutely impossible for man to grind an edge so fine that, when magnified, it will not appear to be deeply notched, and, in the next place, its cutting powers are greatly due to the notches and teeth, and the direction of their points.

We will take both these subjects in turn.

First, as to the notches, or serrated edge. I have now before me two instruments, each the best of their kind, and in both of which the serrations are essential to efficacy. The first is a Malayan dagger, or “kris,” and the second is a surgeon’s lancet, made by Ferguson, of London.

In the kris the edge is intentionally serrated, having been eaten away by means of acids until the required effect was produced. The Malayans know by experience that such an edge is most deadly in a weapon, and that it will cut certain vital parts which a smoother edge might pass without doing any damage.

Now we will take the lancet, and put it under the microscope, when it assumes the most curious resemblance to the kris. Its mirror-like surface looks as if it had been very roughly treated with a coarse file, while its thin and delicate edge, which is perfectly smooth to the eye, and which will pass through a piece of stretched wash-leather without any apparent opposition, becomes as rough and jagged as that of the Malayan weapon.

Take even, for example, the common butcher’s knife, which is perpetually being sharpened on the “steel” that hangs at his belt. The reader may observe that the butcher does not rub the blade of his knife backwards and forwards on the steel, as unskilful persons do. Rapid as is the movement gained by constant practice, any one may see that the blade is always moved in one direction, so as to force the microscopical teeth to point one way, and so to act as a saw when the knife is drawn across the meat.

The power of these teeth or notches may be inferred from a well-known fact. If a razor, no matter how sharp, be pressed upon the human skin without any “draw,” it will indent the skin, but not cut it, while the slightest drawing movement will cause a deep wound. It is the knowledge of this fact that enables an expert swordsman to sever an apple placed on the palm of the bare hand, without even scratching the skin. I have witnessed this feat, and at once saw that it was due to the absence of any “draw” to the cut. The apple was laid on the palm of the hand, which was opened as widely as possible, so as to flatten it. The sword was then brought down on the apple with a sort of chopping movement, so that, although it indented the skin, it did not even inflict a scratch.

By the use of the “drawing” movement, the same sword severed a gauze veil laid across it, the two halves floating in opposite directions. By the same cut, I have seen some astonishing feats performed with an Indian sword now in my collection, the objects of attack falling asunder as if by magic, without any apparent force being used.

Having now glanced at the principle of the Saw, we will proceed to some of its details.

The simplest form of Saw in existence is that which is in use among the Australian natives, and consists of obsidian flakes set along one side of a stick. It looks a rude and inefficient affair enough, but it can cut better than might have been thought, as I can testify from experiments on such a saw in my collection.

Many as are the varieties of the Saw, the principle is the same in all, and the chief distinction lies in the shape and arrangement of the teeth, according to the work which they have to do. Watch-spring Saws, for example, which have to cut metal, have their teeth so slight as to be hardly perceptible, and arranged nearly in a line with each other. The Fretwork Saws, which have to cut delicate patterns in wood, with the slightest possible waste of material, are of the same character. Then we have the long curved teeth of the Circular Saws, which tear their way savagely through great tree-trunks, and fill the air with clouds of sawdust. There are also the Tenon Saw, with its thin blade and broad back; the pioneer’s saw for cutting green wood, with its double array of teeth, so as to make a wide “kerf” in which it shall not be clogged; together with many others that we cannot enumerate here.

We will now examine some Saws as found in Nature.

I need scarcely say that some of the best examples of natural saws are furnished by those insects which are known to entomologists as Tenthredinidæ, and to the general world as Saw-flies. These insects are supplied by Nature with a pair of most remarkable saws, which aid them in depositing their eggs. Indeed, without these instruments, the whole race of Saw-flies would long ago have become extinct.

They haunt almost every kind of tree and many plants, and one valuable plant, the Turnip, is so devastated by them, that whole crops are sometimes swept away. As, therefore, the knowledge of the life-history of any insect will tell us whether to protect or destroy it, and the best method of adopting either course, we will cast a hasty glance at some of our commonest Saw-flies, the instruments which they employ, the mode in which they use them, and the analogies between them and the saws made by the hand of man.

In the first place, it must be observed that the use of these saws is to cut grooves in young bark, these grooves being the depositories of their eggs. It follows, therefore, that as a tolerably wide groove is needed, the saw-blade is a tolerably thick one, and the teeth set on the same principle as that which is employed in the saw-sword of the pioneer. When the microscope is applied to the cutting instrument of the Saw-fly, it reveals the fact that there are two horny saws, which work alternately in their grooves, and that they are strengthened by a thick plate of horn on their backs.

The system of toothing is very complicated. Not only are the sides as well as the edges of the saws toothed, but each tooth is furnished with smaller teeth, after the fashion of the shark’s wonderfully effective cutting apparatus. These subsidiary teeth vary greatly in shape and size according to the species, and in some cases each tooth is quite a complicated structure. In Trichiosoma lucorum, for example, a bee-like insect, very common upon hawthorn, the teeth are extremely beautiful. It is difficult to describe them without diagrams, but I will try to give the reader an idea of them.

Each tooth is somewhat of a lancet shape, but is not terminated by a single point. At the tip comes the secondary tooth, which is conical and stands on a footstalk. The cone, however, is not simple, but is made of some seven or eight cutting plates, each smaller than its predecessor, and the last being a sharp conical point. The reader may imagine how effective such a saw would be in cutting green wood, the toothed sides and the subsidiary teeth alike preventing the blades from clogging, while the alternate movement of the saws enables them to do double work in the same time.

Mr. Westwood, who examined these insects very closely, throws out, in his “Modern Classification of Insects,” the idea which forms the subject of this book. Writing of the cutting weapon of the Saw-flies, he remarks that “from its admirable construction it cannot be doubted that a careful examination of its various modifications might furnish ideas for improved mechanical instruments.”

Mr. Gosse, in his “Evenings at the Microscope,” points out that, beautiful and elaborate as these instruments are, they are but the sheaths of a still finer and more delicate pair of saws. These secondary saws have only a few teeth on the edge, and these near the point, whereas the sides are furnished with a number of sharp blades, set on their edges, slightly overlapping each other, and directed backwards. There is a similar structure on the ovipositor of the Sirex, as we shall see when we come to treat of Boring Instruments.

Although the saws are made expressly so that they shall not stick in the wood, there are many instances known where female Saw-flies have been found dead on the branches, their saws still in the last groove which they have cut. I am inclined to think that these must be females which have deposited all their eggs, and which have died, as do nearly all insects under similar circumstances. This opinion is strengthened by some observations made by Mr. J. K. Lord on the Cicada, the female of which is furnished with a similar ovipositor:—

“I was curious to watch the female depositing her eggs.

“She first clasps the branch on both sides with her legs, and with the ends of the file very carefully slits up the bark. Then, placing the instrument longitudinally, she files away until she has obtained sufficient length and breadth. The small teeth of the files are now used crosswise of this fissure, until a trench is made in the soft pith.

“When large enough, slowly down the groove in the centre of the instrument glides a small pearly egg, pointed at both ends, and so transparent that the little grub within is clearly discernible. Gently she lays it within its bed, and then drops a thin gummy material on it, to secure it from moisture. This finished, she proceeds to deposit another, and so on, until a sufficient number are produced to fill the fissure; then over all she drags the everted bark. It is easy to perceive where the Cicada has been concealing her brood, by the elevation on the branch.

“In this manner she deposits about seven hundred eggs, going from branch to branch, her marvellous instinct teaching her to select the most suitable wood for the purpose. The time occupied in constructing each nest was from fifteen to twenty minutes. Her earthly mission finished, she drops, fainting and exhausted, from the branch, and dies.

“The male, who is always trilling his refrain, goes on, indifferent, or unconscious, that the task of his faithful spouse is finished, singing even, until his time comes—then he too drops beside her. Thus the songs one by one cease,—not only the Cicada’s, but all the forest choir, and give place to blasts that sigh in mournful music through the leafless trees.”

The Sirex and several of the larger Ichneumon-flies are often found dead in like manner, and I have no doubt from the same cause. An elaborate description of the beautiful double saws of the Cicada is given by Mr. Westwood in the work already quoted, together with illustrations.

The Ribbon Saw, Cordon or Band Saw

Perhaps some of my readers may be acquainted with a saw which has of late years come into extensive use—namely, the Ribbon Saw, Cordon Saw, or Band Saw. This is an endless steel band toothed on one edge, and passing over two wheels. It has the advantage of being of almost any breadth, some being several inches wide, while others are mere narrow ribbons, barely the sixth of an inch wide. The fretwork of pianos and other articles of furniture is cut almost exclusively by the Cordon Saw. A thick piece of wood is cut of the requisite shape, and the upper and under surfaces planed quite true to each other. The pattern is traced on the upper surface, and a very narrow Cordon Saw is then applied to it, cutting completely through the thick block, and adapting itself to all the intricacies of the pattern. The block is then cut into thin slices, so that a number of pieces of fretwork can be made with comparative ease. To those who have been accustomed to cutting fretwork with the slow hand-saw, the Cordon Saw is simply fascinating, the slender steel ribbon cutting through the wood with wonderful rapidity and very little sound.

Beautiful as this invention is, it was long ago anticipated in Nature; and the Cordon Saws, which we shall now see, are armed with teeth many more in number, and far more complicated in detail, than those of any saw made by the hand of man. I allude to the Tooth-ribbon possessed by many of our common molluscs, such as the Limpet, the Whelk, the Periwinkle, the Slug, &c. The last mentioned of these creatures possesses a natural Cordon Saw with nearly twenty-seven thousand teeth, and scarcely a tooth that is not elaborately cut into secondary teeth.

As all these creatures have their teeth differently formed and set, according to the species, it will be impossible to describe them separately. I will therefore restrict myself to the Tooth-ribbon of the common Whelk, a specimen of which is now before me. When viewed through the microscope, it is found to consist of a flat membranous ribbon, on which are set three rows of teeth, those of the outer row being hooked, and those of the inner one plain.

The outer teeth are formed somewhat like the Hebrew letter כ, both of the points being very sharp, and the central part being furnished with two secondary teeth. All these teeth overlap each other, so that some care in manipulation is required before their form can be made out.

Along the centre of the tooth-ribbon run successive rows of small, lancet-shaped teeth, six in a row, so that altogether there are eight teeth in each row.

The power of this weapon is astonishing. Some of my readers may be aware that Whelks are carnivorous beings, and that they swarm upon any dead animal which may be found in the sea. Indeed, when we hear of the mutilations which take place on dead corpses after a shipwreck, and which are generally attributed to fishes, we may make up our minds that the real delinquents are the Whelks, together with various crustacea, and that the principal instrument in effecting such mutilation is the tooth-ribbon which has just been described.

The Whelks feed largely upon other molluscs, in spite of their shells. A periwinkle has a peculiarly hard shell, and yet Mr. Rymer Jones saw a Dog-whelk (Purpura lapillus) eat a periwinkle in a single afternoon, first boring a hole through its shell with the tooth-ribbon, and then, by means of the same weapon, licking it, so to speak, out of its shell.

The Periwinkle itself has a similar tooth-ribbon, and so have the Limpet and the pretty Top-shell. These creatures are vegetarians, but they are furnished with similarly armed tongues, and use them in the same way. Nothing is easier than to see these tooth-ribbons in use. When sea-water is kept in glass vessels, a green flocculence is sure to collect upon the glass and to render it opaque.

If, however, a few Periwinkles and Top-shells are placed in the tank, they immediately set to work at this confervoid growth, and by means of the tooth-ribbon sweep off the green substance, leaving the glass nearly clean. This movement can be seen with the naked eye, but with the assistance of a pocket lens the action of the tooth-ribbon is beautifully shown as it issues from its socket, makes its sweeping curve, with the tiny teeth glittering like specks of glass, and then is withdrawn ready for another sweep.

Should sea-water and living Periwinkles not be easily obtained, the same phenomenon may be observed in fresh water, and with the common Pond-snail, which may be caught by thousands in any stream and in most ponds.

The Circular Saw

In one sense the Cordon Saw is a Circular Saw, but we now restrict the name to the tool which has a circular blade, more or less deeply toothed on the edge. The largest and coarsest of these saws are of enormous diameter, have teeth several inches in length, and can cut a large tree-trunk asunder in a wonderfully short time.

There is a huge saw of this kind in Chatham Dockyard. It is kept in a sort of cellar covered with flap doors, where it really has the air of some dread monster lying in wait for prey. A tree-trunk is brought for it to feed upon. The doors slowly open, the saw emerges, revolves so fast that the eye cannot detect the teeth, seizes on the tree-trunk, tears its way through with a scream and roar, and then sinks back into its cellar. I have often watched this saw in action, and have never been able to get over a kind of feeling that it was alive.

Now, if we suppose the saw to be pierced in the centre, and to have teeth on the inside instead of the outside, it would be equally efficacious; and, indeed, we have several tools used for cutting iron bars or pipes, that are constructed on a similar principle, though the cutting tooth revolves slowly instead of rapidly, and is urged by a lever handle.

There is in Nature a Circular Saw of just such a character, the teeth having their points directed inwards, and not outwards.

In tropical America there are several large beetles which, like our Stag-beetle, feed upon the sap of trees, and obtain it by wounding the young branches with their jaws.

One or two of them are pointed out as having the power of cutting a branch completely off by seizing it in their deeply toothed jaws, and flying round and round the branch so as to convert themselves into a circular saw. The late Mr. Waterton showed me a branch which had fallen on his head, and which was said to have been cut off by the Sawyer-beetle, as the insect is called. He did not actually see the insect at work, but he had no doubt that the natives were right who told him that it was the work of beetles’ jaws. Certainly the cut looked exactly as if it had been made in the way described. The branch was somewhat thicker than an ordinary walking-stick.

The truth of this statement has often been denied, but I have ascertained from personal observers that it is literally true. A loud noise is produced by the operation, and, as the female is never seen to perform it, the general idea is that it is a call to its mate.

CHAPTER III.
BORING TOOLS.—STRIKING TOOLS.—GRASPING TOOLS

The Bradawl and the Gimlet defined.—Natural Bradawls.—The Ichneumon-flies.—A Pimpla engaged in Boring Operations.—Principle of the Wedge.—Resisting Power of Earth.—Pitching Tents in Sand.—Hidden Forces of Nature.—The Aloe-leaf and its Growth.—A cruel Punishment.—Natural Gimlets.—Ovipositor of the Sirex, and its Analogy to a Carpenter’s Gimlet.—The Auger and the Gad-fly.—Striking Tools.—The Hammer.—Origin and Development of the Tool.—The Axe.—The Woodpecker and the Nuthatch.—The Ivory-billed Woodpecker.—Grasping Tools.—Pincers and their Modifications.—Sugar-tongs and Coal-tongs.—Natural Pincers.—Bivalve Molluscs.—The Clam’s Grip.—The Earwig.—Crab and Lobster Claws.

Boring Tools

NEXT in importance to the edged tools which cut, come the pointed tools by which holes can be bored. We have an abundance of such tools, but they can all be reduced to two types, namely, those which, like the Bradawl, are forced between the fibres, and those which, like the Gimlet, cut away the material as they pass through it.

They may, again, be shown to be different modifications of a single principle—i.e. that of the Wedge or Inclined Plane, which, as has already been shown, is identical with that of the screw. The Bradawl is, in fact, a sharp wedge, which is forced through the fibres, sometimes being merely forced between them, and sometimes cutting them, and thus forcing aside the severed fibres.

A natural example of the Bradawl is to be found in various Ichneumon-flies, especially those with very long ovipositors, which are intended for boring into wood.

All the Ichneumons are parasitic, laying their eggs in the larvæ of other insects, mostly those of moths and butterflies. Generally these larvæ exist in the open air, and the Ichneumon-fly has little difficulty in piercing them. But there are some which live either in wood or underground, and, in order to reach their hidden bodies, the Ichneumon is furnished with an extremely long and sharply pointed ovipositor.

This wonderful instrument is not so thick as an ordinary horsehair, although it is composed of three portions, and seems to be utterly inadequate to the task which it has to perform. Ascertaining by its instinct the exact locality of the caterpillar which it desires to pierce, the Ichneumon-fly clings firmly to the tree, bends the body so as to bring the point of the ovipositor against the wood, and, by moving the abdomen backwards and forwards, gradually works the instrument into the wood, sometimes piercing it to a considerable depth.

Mr. Westwood once saw an Ichneumon-fly thus boring its way into a dry post, the wood of which must have been very hard. When she had bored far enough, she partially withdrew the ovipositor, and then re-plunged it into the hole that she had made, as if she were depositing eggs. While engaged in this operation, she stood very high on her long legs, resting only on the extremities of the feet. She belonged to the genus Pimpla.

The principle of the Wedge or Inclined Plane is admirably shown by objects which we pass unheeded every day, and yet afford wonderful examples of the power of the wedge.

Scarcely any vegetable growth is so plentiful as grass, which has been used in that sense by the highest of all authorities, “which to-day is, and to-morrow is cast into the oven.” Grass forces its way everywhere—not only in cultivated grounds, but in the wildest of lands, where there is scarcely any nurture for it. Even among the habitations of mankind the grass will have its way, and clothes deserted housetops with verdure, and forces itself between the stones that pave neglected streets.

Place side by side some of these stones, together with a very young and tender Grass-blade, and it will seem to be impossible that so fragile an object should be able to exert any influence on the solid stone. Let any one try to push a sharp skewer between the stones, and he will find that he has to exert power sufficient to crush a thousand grass-blades. Yet these slight and delicate objects will force themselves between the stones, and sometimes to such an extent as to cover the whole roadway with verdure.

The force which is employed is simply marvellous, and can only be appreciated by those who know the resisting power of earth, however dry and loose it may be. Even sand has so strong a resistance that tents can be pitched in the desert without difficulty. Of course the ordinary tent-peg would be useless, but the desert dwellers can pitch their tents with perfect security. They fasten the tent-rope to a branch or piece of bush, scrape a hole in the sand, put the bush into the hole, cover it up again, and it will withstand almost any strain, though it be only covered with a few inches of sand.

When miners blast rocks with gunpowder, they take advantage of the resisting power of sand. They bore a suitable hole, place a charge of gunpowder at the bottom, and then merely pour loose sand into the hole until it is filled. When the powder explodes, the rock or coal is shattered to pieces, but the sand is not blown out of the hole. This operation is called “tamping.”

Every one, again, knows how firm are gate-posts, and how they resist the weight, jarring, and leverage of a heavy gate, all because they are sunk a little way into the earth.

Considering, therefore, that such fragile things as young grass-blades can force their way through the superincumbent weight, we can but be amazed at the aggregate of active force which is in full operation in every pasture field and garden lawn.

As far as I know, not being much of a botanist, every seed that springs up does so on the wedge principle, though the form of the wedge may be varied.

A terrible example of the force which is exercised by this principle among the vegetables is shown in some parts of the world where the Aloe flourishes in a wild state. In our colder clime the Aloe, though it does live in the open air, is a slow-growing plant. But, in its own land, it shoots up with a surprising vigour, and its sharply pointed and saw-edged leaves are said to grow to the extent of six inches in a single night.

Taking advantage of this rapid, and, at the same time, powerful growth, the natives, when they want to punish a man with more than ordinary severity, tie him hand and foot, and bind him to the earth just over a sprouting aloe plant, and leave him there. In twenty-four hours the man is nearly certain to be dead, the aloe-leaf having forced itself completely through his body. Or, if he be not actually dead, he lives in frightful tortures, which are continually increased by the flinty point and notches forcing themselves slowly, but surely, through the body.

For an example of the Gimlet we may take the ovipositor of the Sirex, an insect which I believe has no popular name. It is coloured much after the same manner as the hornet, and is often mistaken for that insect by those who are not versed in entomology. And, as its long and straight ovipositor is generally taken for a hornet’s sting, the insect assumes a double terror to the ignorant.

Now, the real fact is, that in its larval stage of existence the Sirex feeds upon the wood of the fir-tree—a diet which, to our ideas, is about as unsatisfactory as can well be imagined. In order that the young Sirex may be within reach of food, the egg must be introduced deeply into the body of the tree, and, for the egg to be so received, a channel must be cut for it.

This is done by means of the marvellously formed ovipositor. Many admirable descriptions have been given of the head of this instrument and its boring powers, but I am not aware that any one has noticed the secondary cutting blades that are set along the shaft of the principal borer, and which answer exactly the same purpose as the spiral cutting edge of the gimlet or auger.

Not being desirous of repeating my own observations in different words, I transfer to these pages a short account of the ovipositor of the Sirex, as examined by me when writing my work on British Insects, entitled “Insects at Home,” and published by Messrs. Longmans and Co.:—

“I very strongly recommend any of my readers who may obtain a female Sirex to disengage the actual borer from its two-bladed sheath, and examine it with the aid of a microscope. A half-inch object-glass will give quite a sufficient power.”

“It is straight, stiff, and elastic, as if made of steel, and, if bent, will spring back to its proper form with the elasticity of a Toledo rapier.

“But the borer possesses an auxiliary cutting apparatus which places it far above the rymer in point of efficacy. Even with an ordinary magnifying lens, it is easy to see that the end of the borer is developed into a sharp head, very much resembling that of a boarding-pike, and that the outline of the shaft is broken into a series of notches.

“The half-inch glass, however, discloses a marvellous example of mechanical excellence. The head of the borer is then seen to be armed with long, sharp teeth, slightly curved inwards, and acting just as does the carpenter’s ordinary centrebit.

“So much for the head of the borer: we will now turn to the shaft.

“It appears that, in order to make a clean-cut hole for the reception of the egg, the shaft of the borer has to finish the task which the head begins. Accordingly, it is armed on each of its sides with a series of hard, sharp-edged ridges, running diagonally across it, and acting exactly as do the sharp ridges of a coffee-mill.”

In point of fact, the ovipositor of the Sirex is the natural type of the improved gimlet of the present day. Instead, however, of having a single, spiral, sharp-edged groove running along the whole length of the shaft, it has a series of small, sharp blades, set exactly in the same line as is taken by the spiral groove, and acting in exactly the same manner—i.e. by cutting out successive portions of wood, and, by the diagonal position of the blades, throwing out the debris as fast as it is cut.

I cannot but think that, if any modern tool manufacturer could take as his model the saw-like ovipositor of the Tenthredinidæ, and the auger-like ovipositor of the present insect, he would produce a series of most valuable implements, possessing powers far beyond those of ordinary tools.