Chapter XI: Introduction (6)

"I have also some specimens of the cells formed by wasps, which show that the partitions between them are also double, and that the agglutinating substance between them is more easily destroyed than that between the cells of the bee."[AT]

Irregularities in their Workmanship.

Though bees, however, work with great uniformity when circumstances favour their operations, they may be compelled to vary their proceedings. M. Huber made several ingenious experiments of this kind. The following, mentioned by Dr. Bevan, was accidental, and occurred to his friend Mr. Walond. "Inspecting his bee-boxes at the end of October, 1817, he perceived that a centre comb, burthened with honey, had separated from its attachments, and was leaning against another comb so as to prevent the passage of the bees between them. This accident excited great activity in the colony; but its nature could not be ascertained at the time. At the end of a week, the weather being cold, and the bees clustered together Mr. Walond observed, through the window of the box, that they had constructed two horizontal pillars betwixt the combs alluded to, and had removed so much of the honey and wax from the top of each as to allow the passage of a bee: in about ten days more there was an uninterrupted thoroughfare; the detached comb at its upper part had been secured by a strong barrier, and fastened to the window with the spare wax. This being accomplished, the bees removed the horizontal pillars first constructed, as being of no further use."[AU]

A similar anecdote is told by M. Huber. "During the winter," says he, "a comb in one of my bell-glass hives, having been originally insecure, fell down, but preserved its position parallel to the rest. The bees were unable to fill up the vacuity left above it, because they do not build combs of old wax, and none new could be then obtained. At a more favourable season they would have engrafted a new comb on the old one; but now their provision of honey could not be spared for the elaboration of this substance, which induced them to insure the stability of the comb by another process.

"Crowds of bees taking wax from the lower part of other combs, and even gnawing it from the surface of the orifices of the deepest cells, they constructed so many irregular pillars, joists, or buttresses, between the sides of the fallen comb, and others on the glass of the hive. All these were artificially adapted to localities. Neither did they confine themselves to repairing the accidents which their works had sustained. They seemed to profit by the warning to guard against a similar casualty.

"The remaining combs were not displaced; therefore, while solidly adhering by the base, we were greatly surprised to see the bees strengthen their principal fixtures with old wax. They rendered them much thicker than before, and fabricated a number of new connections, to unite them more firmly to each other and to the sides of their dwelling. All this passed in the middle of January, a time that these insects commonly keep in the upper part of their hive, and when work is no longer seasonable."[AV]

M. Huber the younger shrewdly remarks, that the tendency to symmetry observable in the architecture of bees does not hold so much in small details as in the whole work, because they are sometimes obliged to adapt themselves to particular localities. One irregularity leads on to another, and it commonly arises from mere accident, or from design on the part of the proprietor of the bees. By allowing, for instance, too little interval between the spars for receiving the foundation of the combs, the structure has been continued in a particular direction. The bees did not at first appear to be sensible of the defect, though they afterwards began to suspect their error, and were then observed to change their line of work till they gained the customary distance. The cells having been by this change of direction in some degree curved, the new ones which were commenced on each side of it, by being built everywhere parallel to it, partook of the same curvature. But the bees did not relish such approaches to the "line of beauty," and exerted themselves to bring their buildings again into the regular form.

In consequence of several irregularities which they wished to correct, the younger Huber has seen bees depart from their usual practice, and at once lay on a spar two foundation-walls not in the same line. They could consequently neither be enlarged without obstructing both, nor from their position could the edges unite, had they been prolonged. The little architects, however, had recourse to a very ingenious contrivance: they curved the edges of the two combs, and brought them to unite so neatly that they could be both prolonged in the same line with ease; and when carried to some little distance, their surface became quite uniform and level.

"Having seen bees," says the elder Huber, "work both up and down, I wished to try to investigate whether we could compel them to construct their combs in any other direction. We endeavoured to puzzle them with a hive glazed above and below, so that they had no place of support but the upright sides of their dwelling; but, betaking themselves to the upper angle, they built combs perpendicular to one of these sides, and as regularly as those which they usually build under a horizontal surface. The foundations were laid on a place which does not serve naturally for the base, yet, except in the difference of direction, the first row of cells resembled those in ordinary hives, the others being distributed on both faces, while the bottoms alternately corresponded with the same symmetry. I put the bees to a still greater trial. As they now testified their inclination to carry their combs, by the shortest way, to the opposite side of the hive (for they prefer uniting them to wood, or a surface rougher than glass), I covered it with a pane. Whenever this smooth and slippery substance was interposed between them and the wood, they departed from the straight line hitherto followed, and bent the structure of their comb at a right angle to what was already made, so that the prolongation of the extremity might reach another side of the hive, which had been left free.

"Varying this experiment in several ways, I saw the bees constantly change the direction of their combs, when I presented to them a surface too smooth to admit of their clustering on it. They always sought the wooden sides. I thus compelled them to curve the combs in the strangest shapes, by placing a pane at a certain distance from their edges. These results indicate a degree of instinct truly wonderful. They denote even more than instinct: for glass is not a substance against which bees can be warned by nature. In trees, their natural abode, there is nothing that resembles it, or with the same polish. The most singular part of their proceeding is changing the direction of the work before arriving at the surface of the glass, and while yet at a distance suitable for doing so. Do they anticipate the inconvenience which would attend any other mode of building? No less curious is the plan adopted by the bee for producing an angle in the combs: the wonted fashion of their work, and the dimensions of the cells, must be altered. Therefore, the cells on the upper or convex side of the combs are enlarged; they are constructed of three or four times the width of those on the opposite surface. How can so many insects, occupied at once on the edges of the combs, concur in giving them a common curvature from one extremity to the other? How do they resolve on establishing cells so small on one side, while dimensions so enlarged are bestowed on those of the other? And is it not still more singular, that they have the art of making a correspondence between cells of such reciprocal discrepance? The bottom being common to both, the tubes alone assume a taper form. Perhaps no other insect has afforded a more decisive proof of the resources of instinct, when compelled to deviate from the ordinary course.

"But let us study them in their natural state, and there we shall find that the diameter of their cells must be adapted to the individuals which shall be bred in them. The cells of males have the same figure, the same number of lozenges and sides, as those of workers, and angles of the same size. Their diameter is 3-1/3 lines, while those of workers are only 2-2/5.

"It is rarely that the cells of males occupy the higher part of the combs. They are generally in the middle or on the sides, where they are not isolated. The manner in which they are surrounded by other cells alone can explain how the transition in size is effected. When the cells of males are to be fabricated under those of workers, the bees make several rows of intermediate cells, whose diameter augments progressively, until gaining that proportion proper to the cells required; and in returning to those of workers, a lowering is observed in a manner corresponding.

"Bees, in preparing the cells of males, previously establish a block or lump of wax on the edge of their comb, thicker than is usually employed for those of workers. It is also made higher, otherwise the same order and symmetry could not be preserved on a larger scale.

"Several naturalists notice the irregularities in the cells of bees as so many defects. What would have been their astonishment had they observed that part of them are the result of calculation? Had they followed the imperfection of their organs, some other means of compensating them would have been granted to the insects. It is much more surprising that they know how to quit the ordinary route, when circumstances demand the construction of enlarged cells; and, after building thirty or forty rows of them, to return to the proper proportions from which they have departed by successive reductions. Bees also augment the dimensions of their cells when there is an opportunity for a great collection of honey. Not only are they then constructed of a diameter much exceeding that of the common cells, but they are elongated throughout the whole space admitting it. A great portion of irregular comb contains cells an inch, or even an inch and a half, in depth.

"Bees, on the contrary, sometimes are induced to shorten their cells. When wishing to prolong an old comb, whose cells have received their full dimensions, they gradually reduce the thickness of its edges, by gnawing down the sides of the cells, until they restore it to its original lenticular form. They add a waxen block around the whole circumference, and on the edge of the comb construct pyramidal bottoms, such as those fabricated on ordinary occasions. It is a certain fact, that a comb never is extended in any direction unless the bees have thinned the edges, which are diminished throughout a sufficient space to remove any angular projection.

"The law which obliges these insects partly to demolish the cells on the edges of the comb before enlarging it, unquestionably demands more profound investigation. How can we account for instinct leading them to undo what they have executed with the utmost care? The wonted regular gradation which may be necessary for new cells, subsists among those adjoining the edges of a comb recently constructed. But afterwards, when those on the edge are deepened like the cells of the rest of the surface, the bees no longer preserve the decreasing gradation which is seen in the new combs."[AW]

The Finishing of the Cells.

While the cells are building they appear to be of a dull white colour, soft, even, though not smooth, and translucent; but in a few days they become tinged with yellow, particularly on the interior surface; and their edges, from being thin, uniform, and yielding, become thicker, less regular, more heavy, and so firm that they will bend rather than break. New combs break on the slightest touch. There is also a glutinous substance observable around the orifices of the yellow cells, of reddish colour, unctuous, and odoriferous. Threads of the same substance are applied all around the interior of the cells, and at the summit of their angles, as if it were for the purpose of binding and strengthening the walls. These yellow cells also require a much higher temperature of water to melt them than the white ones.

It appeared evident, therefore, that another substance, different from wax, had been employed in varnishing the orifices, and strengthening the interior of the cells. M. Huber, by numerous experiments, ascertained the resinous threads lining the cells, as well as the resinous substance around their orifice, to be propolis; for he traced them, as we mentioned in our account of propolis, from the poplar buds where they collected it, and saw them apply it to the cells; but the yellow colour is not imparted by propolis, to which it bears no analogy. We are, indeed, by no means certain what it is, though it was proved by experiment not to arise from the heat of the hives, nor from emanations of honey, nor from particles of pollen. Perhaps it may be ascribed to the bees rubbing their teeth, feet, and other parts of their body, on the surfaces where they seem to rest; or to their tongue (haustellum) sweeping from right to left like a fine pliant pencil, when it appears to leave some sprinkling of a transparent liquid.

Besides painting and varnishing their cells in this manner, they take care to strengthen the weaker part of their edifice by means of a mortar composed of propolis and wax, and named _pissoceros_[AX] by the ancients who first observed it, though Réaumur was somewhat doubtful respecting the existence of such a composition. We are indebted to the shrewd observations of Huber for a reconcilement of the Roman and the French naturalists. The details which he has given of his discovery are perhaps the most interesting in his delightful book.

"Soon," he says, "after some new combs had been finished in a hive, manifest disorder and agitation prevailed among the bees. They seemed to attack their own works. The primitive cells, whose structure we had admired, were scarcely recognizable. Thick and massive walls, heavy, shapeless pillars, were substituted for the slight partitions previously built with such regularity. The substance had changed along with the form, being composed apparently of wax and propolis. From the perseverance of the workers in their devastation, we suspected that they proposed some useful alteration of their edifices; and our attention was directed to the cells least injured. Several were yet untouched; but the bees soon rushed precipitately on them, destroyed the tubes, broke down the wax, and threw all the fragments about. But we remarked that the bottom of the cells of the first row were spared; neither were the corresponding parts on both faces of the comb demolished at the same time. The bees laboured at them alternately, leaving some of the natural supports, otherwise the comb would have fallen down, which was not their object: they wished, on the contrary, to provide it a more solid base, and to secure its union to the vault of the hive, with a substance whose adhesive properties infinitely surpassed those of wax. The propolis employed on this occasion had been deposited in a mass over a cleft of the hive, and had hardened in drying, which probably rendered it more suitable for the purpose. But the bees experienced some difficulty in making any impression on it; and we thought, as also had appeared to M. de Réaumur, that they softened it with the same frothy matter from the tongue which they use to render wax more ductile.

"We very distinctly observed the bees mixing fragments of old wax with the propolis, kneading the two substances together to incorporate them; and the compound was employed in rebuilding the cells that had been destroyed. But they did not now follow their ordinary rules of architecture, for they were occupied by the solidity of their edifices alone. Night intervening, suspended our observations, but next morning confirmed what we had seen.

"We find, therefore, that there is an epoch in the labour of bees, when the upper foundation of their combs is constructed simply of wax, as Réaumur believed; and that, after all the requisite conditions have been attained, it is converted to a mixture of wax and propolis, as remarked by Pliny so many ages before us. Thus is the apparent contradiction between these two great naturalists explained. But this is not the utmost extent of the foresight of these insects. When they have plenty of wax, they make their combs the full breadth of the hive, and solder them to the glass or wooden sides, by structures more or less approaching the form of cells, as circumstances admit. But should the supply of wax fail before they have been able to give sufficient diameter to the combs whose edges are rounded, large intervals remain between them and the upright sides of the hive, and they are fixed only at the top. Therefore, did not the bees provide against it, by constructing great pieces of wax mixed with propolis, in the intervals, they might be borne down by the weight of the honey. These pieces are of irregular shape, strangely hollowed out, and their cavities void of symmetry."[AY]

It is remarked by the lively Abbé la Pluche, that the foundations of our houses sink with the earth on which they are built, the walls begin to stoop by degrees, they nod with age, and bend from their perpendicular;--lodgers damage everything, and time is continually introducing some new decay. The mansions of the bees, on the contrary, grow stronger the oftener they change inhabitants. Every bee-grub, before its metamorphosis into a nymph, fastens its skin to the partitions of its cell, but in such a manner as to make it correspond with the lines of the angle, and without in the least disturbing the regularity of the figure. During summer, accordingly, the same lodging may serve for three or four grubs in succession; and in the ensuing season it may accommodate an equal number. Each grub never fails to fortify the panels of its chamber by arraying them with its spoils, and the contiguous cells receive a similar augmentation from its brethren.[AZ] Réaumur found as many as seven or eight of these skins spread over one another: so that all the cells being incrusted with six or seven coverings, well dried and cemented with propolis, the whole fabric daily acquires a new degree of solidity.

It is obvious, however, that by a repetition of this process the cell might be rendered too contracted; but in such a case the bees know well how to proceed, by turning the cells to other uses, such as magazines for bee-bread and honey. It has been remarked, however, that in the hive of a new swarm, during the months of July and August, there are fewer small bees or nurse-bees than in one that has been tenanted four or five years. The workers, indeed, clean out the cell the moment that a young bee leaves its cocoon, but they never detach the silky film which it has previously spun on the walls of its cell. But though honey is deposited after the young leave the cells, the reverse also happens; and accordingly, when bees are bred in contracted cells, they are by necessity smaller, and constitute, in fact, the important class of nurse-bees.

We are not disposed, however, to go quite so far as an American periodical writer, who says, "Thus we see that the contraction of the cell may diminish the size of a bee, _even to the extinction of life_, just as the contraction of a Chinese shoe reduces the foot even to uselessness."[BA] We know, on the contrary, that the queen-bee will not deposit eggs in a cell either too small or too large for the proper rearing of the young. In the case of large cells, M. Huber took advantage of a queen that was busy depositing the eggs of workers to remove all the common cells adapted for their reception, and left only the larger cells appropriated for males. As this was done in June, when bees are most active, he expected that they would have immediately repaired the breaches he had made; but to his great surprise they did not make the slightest movement for that purpose. In the meanwhile the queen, being oppressed by her eggs, was obliged to drop them about at random, preferring this to depositing them in the male cells, which she knew to be too large. At length she did deposit six eggs in the large cells, which were hatched as usual three days after. The nurse-bees, however, seemed to be aware that they could not be reared there, and though they supplied them with food, did not attend to them regularly. M. Huber found that they had been all removed from the cells during the night, and the business both of laying and nursing was at a complete stand for twelve days, when he supplied them again with a comb of small cells, which the queen almost immediately filled with eggs, and in some cells she laid five or six.

[The accompanying illustration exhibits these three kinds of bees, namely, the Queen, the Drone, and the Worker, together with the cells which they respectively inhabit. Fig. 1 shows the queen-bee as she appears when in command of a hive. When she first issues from the royal cell, she is much smaller in the body, and an inexperienced observer might have some difficulty in distinguishing her from an ordinary worker. But any one who has been accustomed to bees can pick her out as soon as his eyes rest upon her. Her body is rather larger and narrower than those of the workers, and the wings are shorter in proportion, slightly crossing at the tips when she is at rest. Fig. 2 represents the common worker-bee, which, as has already been mentioned, is simply an undeveloped female. Fig. 3 is the male or drone-bee, which is easily distinguishable, even by a novice. He is larger, stouter, and heavier built than the female; his eyes are so enormous that they seem to occupy nearly the entire head, and he has some well-defined tufts of hair on the end of the abdomen. He can even be detected by the ear, as he flies, the deep droning hum being quite unlike the fussy, business-like sound produced by the worker. Fig. 4 represents one of the royal cells, a little reduced in size. In making this cell, the bees lose sight of their habitual economy of wax, and use enough material for fifty ordinary cells. It is probable that the great size of the cell enables the inclosed insect to expand, and so to be capable of becoming the mother as well as the ruler of her subjects. The royal cell is always placed at the edge of a comb, so as not to interfere with the other cells, which contain honey, bee-bread, and grubs; and in each hive there are generally several of these cells in different stages of structure. Figs. 5 and 6 represent the proportionate sizes of the cells which contain the drone and worker bees.]

* * * * *

The architecture of the hive, which we have thus detailed, is that of bees receiving the aid of human care, and having external coverings of a convenient form, prepared for their reception. In this country bees are not found in a wild state; though it is not uncommon for swarms to stray from their proprietors. But these stray swarms do not spread colonies through our woods, as they are said to do in America. In the remoter parts of that continent there are no wild bees. They precede civilization; and thus when the Indians observe a swarm they say, "The white man is coming." There is evidence of bees having abounded in these islands, in the earlier periods of our history; and Ireland is particularly mentioned by the Venerable Bede as being "rich in milk and honey."[BB] The hive-bee has formed an object of economical culture in Europe at least for two thousand years; and Varro describes the sort of hives used in his time, 1870 years ago. We are not aware, however, that it is now to be found wild in the milder clime of Southern Europe, any more than it is in our own island.

The wild bees of Palestine principally hived in rocks. "He made him," says Moses, "to suck honey out of the rock."[BC] "With honey out of the rock," says the Psalmist, "should I have satisfied thee."[BD] In the caves of Salsette and Elephanta, at the present day, they hive in the clefts of the rocks, and the recesses among the fissures, in such numbers as to become very troublesome to visitors. Their nests hang in innumerable clusters.[BE]

We are told of a little black stingless bee found in the island of Guadaloupe, which hives in hollow trees or in the cavities of rocks by the sea-side, and lays "up honey in cells about the size and shape of pigeons' eggs. These cells are of a black or deep-violet colour, and so joined together as to leave no space between them. They hang in clusters almost like a bunch of grapes."[BF] The following are mentioned by Lindley as indigenous to Brazil. "On an excursion towards Upper Tapagippe," says he, "and skirting the dreary woods which extend to the interior, I observed the trees more loaded with bees' nests than even in the neighbourhood of Porto Seguro. They consist of a ponderous shell of clay, cemented similarly to martins' nests, swelling from high trees about a foot thick, and forming an oval mass full two feet in diameter. When broken, the wax is arranged as in our hives, and the honey abundant."[BG]

Captain Basil Hall found in South America the hive of a honey-bee very different from the Brazilian, but nearly allied to, if not the same as, that of Guadaloupe. "The hive we saw opened," he says, "was only partly filled, which enabled us to see the economy of the interior to more advantage. The honey is not contained in the elegant hexagonal cells of our hives, but in wax bags, not quite so large as an egg. These bags or bladders are hung round the sides of the hive, and appear about half full; the quantity being probably just as great as the strength of the wax will bear without tearing. Those near the bottom, being better supported, are more filled than the upper ones. In the centre of the lower part of the hive we observed an irregularly-shaped mass of comb, furnished with cells like those of our bees, all containing young ones in such an advanced state, that, when we broke the comb, and let them out, they flew merrily away."

Clavigero, in his 'History of Mexico,' evidently describing the same species of bee, says it abounds in Yucatan, and makes the honey of Estabentum, the finest in the world, and which is taken every two months. He mentioned another species of bee, smaller in size, and also without a sting, which forms its nest of the shape of a sugar-loaf, and as large or larger. These are suspended from trees, particularly from the oak, and are much more populous than our common hives.

Wild honey-bees of some species appear also to abound in Africa. Mr. Park, in his second volume of travels, tells us that some of his associates imprudently attempted to rob a numerous hive of its honey, when the exasperated bees, rushing out to defend their property, attacked their assailants with great fury, and quickly compelled the whole company to fly.

At the Cape of Good Hope the bees themselves must be less formidable, or more easily managed, as their hives are sought for with avidity. Nature has there provided man with a singular and very efficient assistant in a bird, most appropriately named the honey-guide (_Indicator major_, Veillot; _Cuculus indicator_, Latham). The honey-guide, it is said, so far from being alarmed at the presence of man, appears anxious to court his acquaintance, and flits from tree to tree with an expressive note of invitation, the meaning of which is both well known to the colonists and the Hottentots. A person thus invited by the honey-guide seldom refuses to follow it onward till it stops, as it is certain to do, at some hollow tree containing a bee-hive, usually well stored with honey and wax. It may be that the bird finds itself inadequate to the attack of a legion of bees, or to penetrate into the interior of the hive, and is thence led to invite an agent more powerful than itself. The person invited, indeed, always leaves the bird a share of the spoil, as it would be considered sacrilege to rob it of its due, or in any way to injure so sacred a bird.

Useful, however, as is the honey-guide, it must always be carefully watched, and the traveller must not follow it without keeping his eyes well open. For although, as a general fact, the bird will lead its followers to honey, it has a strange habit of leading them to the spot where lies hidden some dangerous animal. Sometimes it brings them to a rhinoceros, wallowing in a mud pool. Sometimes it directs them to a solitary buffalo, one of the most dangerous animals that Southern Africa produces, and one which the natives fear but little less than the lion itself. And more than once the too-confiding traveller has followed the honey-guide, and been led to a spot where was lying one of the venomous serpents.

The Americans, who have not the African honey-guide, employ several well-known methods to track bees to their hives. One of the most common though ingenious modes is to place a piece of bee-bread on a flat surface, a tile for instance, surrounding it with a circle of wet white paint. The bee, whose habit it is always to alight on the edge of any plane, has to travel through the paint to reach the bee-bread. When, therefore, she flies off, the observer can track her by the white on her body. The same operation is repeated at another place, at some distance from the first, and at right angles to the bee-line just ascertained. The position of the hive is easily determined, for it lies in the angle made by the intersection of the bee-lines. Another method is described in the 'Philosophical Transactions for 1721.' The bee-hunter decoys, by a bait of honey, some of the bees into his trap, and when he has secured as many as he judges will suit his purpose, he encloses one in a tube, and, letting it fly, marks its course by a pocket-compass. Departing to some distance, he liberates another, observes its course, and in this manner determines the position of the hive, upon the principle already detailed. These methods of bee-hunting depend upon the insect's habit of always flying in a right line to its home. Those who have read Cooper's tale of the 'Prairie' must well remember the character of the bee-hunter, and the expression of "lining a bee to its hive."

In reading these and similar accounts of the bees of distant parts of the world, we must not conclude that the descriptions refer to the same species as the common honey-bee. There are numerous species of social bees, which, while they differ in many circumstances, agree in the practice of storing up honey, in the same way as we have numerous species of the mason-bee and of the humble-bee.

_CHAPTER VII._

CARPENTRY OF TREE-HOPPERS AND SAW-FLIES.

The operations of an insect in boring into a leaf or a bud to form a lodgment for its eggs appear very simple. The tools, however, by which these effects are performed are very complicated and curious. In the case of gall-flies (_Cynips_), the operation itself is not so remarkable as its subsequent chemical effects. These effects are so different from any others that may be classed under the head of Insect Architecture, that we shall reserve them for the latter part of this volume, although, with reference to the use of galls, the protection of eggs and larvæ, they ought to find a place here. We shall, however, at present confine ourselves to those which simply excavate a nest, without producing a tumour.

The first of these insects which we shall mention is celebrated for its song, by the ancient Greek poets, under the name of _Tettix_. The Romans called it _Cicada_, which we sometimes, but erroneously, translate "grasshopper;" for the grasshoppers belong to an entirely different order of insects. We shall, therefore, take the liberty of calling the Cicadæ _Tree-hoppers_, to which the cuckoo-spit insect (_Tettigonia spumaria_, Oliv.) is allied; but there is only one of the true Cicadæ hitherto ascertained to be British, namely, the _Cicada hæmatodes_ (Linn.), which was discovered in the New Forest, Hampshire, by Mr. Daniel Bydder.

M. Réaumur was exceedingly anxious to study the economy of these insects; but they not being indigenous in the neighbourhood of Paris, he commissioned his friends to send him some from more southern latitudes, and he procured in this way specimens not only from the South of France and from Italy, but also from Egypt. From these specimens he has given the best account of them yet published; for though, as he tells us, he had never had the pleasure of seeing one of them alive, the most interesting parts of their structure can be studied as well in dead as in living specimens. We ourselves possess several specimens from New Holland, upon which we have verified some of the more interesting observations of Réaumur.

Virgil tells us that in his time "the cicadæ burst the very shrubs with their querulous music;"[BH] but we may well suppose that he was altogether unacquainted with the singular instrument by means of which they can, not poetically, but actually, cut grooves in the branches they select for depositing their eggs. It is the male, as in the case of birds, which fills the woods with his song; while the female, though mute, is no less interesting to the naturalist on account of her curious ovipositor. This instrument, like all those with which insects are furnished by nature for cutting, notching, or piercing, is composed of a horny substance, and is also considerably larger than the size of the tree-hopper would proportionally indicate. It can on this account be partially examined without a microscope, being, in some of the larger species, no less than five lines[BI] in length.

The ovipositor, or auger (_tarière_), as Réaumur calls it, is lodged in a sheath which lies in a groove of the terminating ring of the belly. It requires only a very slight pressure to cause the instrument to protrude from its sheath, when it appears to the naked eye to be of equal thickness throughout, except at the point, where it is somewhat enlarged and angular, and on both sides finely indented with teeth. A more minute examination of the sheath demonstrates that it is composed of two horny pieces slightly curved, and ending in the form of an elongated spoon, the concave part of which is adapted to receive the convex end of the ovipositor.

When the protruded instrument is further examined with a microscope, the denticulations, nine in number on each side, appear strong, and arranged with great symmetry, increasing in fineness towards the point, where there are three or four very small ones, beside the nine that are more obvious. The magnifier also shows that the instrument itself, which appeared simple to the naked eye, is, in fact, composed of three different pieces; two exterior armed with the teeth before mentioned, denominated by Réaumur files (_limes_), and another pointed like a lancet, and not denticulated. The denticulated pieces, moreover, are capable of being moved forwards and backwards, while the centre one remains stationary; and as this motion is effected by pressing a pin or the blade of a knife over the muscles on either side at the origin of the ovipositor, it may be presumed that those muscles are destined for producing similar movements when the insect requires them. By means of a finely-pointed pin carefully introduced between the pieces, and pushed very gently downwards, they may be, with no great difficulty, separated in their whole extent.

The contrivance by which those three pieces are held united, while at the same time the two files can be easily put in motion, is similar to those of our own mechanical inventions, with this difference, that no human workman could construct an instrument of this description so small, fine, exquisitely polished, and fitting so exactly. We should have been apt to form the grooves in the central piece, whereas they are scooped out in the handles of the files, and play upon two projecting ridges in the central piece, by which means this is rendered stronger. M. Réaumur discovered that the best manner of showing the play of this extraordinary instrument is to cut it off with a pair of scissors near its origin, and then, taking it between the thumb and the finger at the point of section, work it gently to put the files in motion.

Beside the muscles necessary for the movement of the files, the handle of each is terminated by a curve of the same hard horny substance as itself, which not only furnishes the muscles with a sort of lever, but serves to press, as with a spring, the two files close to the central piece, as is shown in the lower figure.

M. Pontedera, who studied the economy of the tree-hoppers with some care, was anxious to see the insect itself make use of the ovipositor in forming grooves in wood, but found that it was so shy and easily alarmed, that it took to flight whenever he approached; a circumstance of which Réaumur takes advantage, to soothe his regret that the insects were not indigenous in his neighbourhood. But of their workmanship, when completed, he had several specimens sent to him from Provence and Languedoc by the Marquis de Caumont.

The gall-flies, when about to deposit their eggs, select growing plants and trees; but the tree-hoppers, on the contrary, make choice of dead, dried branches, for the mother seems to be aware that moisture would injure her progeny. The branch, commonly a small one, in which eggs have been deposited, may be recognised by being covered with little oblong elevations caused by small splinters of the wood, detached at one end, but left fixed at the other, by the insect. These elevations are for the most part in a line, rarely in a double line, nearly at equal distances from each other, and form a lid to a cavity in the wood about four lines in length, containing from four to ten eggs. It is to be remarked that the insect always selects a branch of such dimensions that it can get at the pith, not because the pith is more easily bored, for it does not penetrate into it all, but to form a warm and safe bed for the eggs. M. Pontedera says, that when the eggs have been deposited, the insect closes the mouth of the hole with a gum capable of protecting them from the weather; but M. Réaumur thinks this only a fancy, as, out of a great number which he examined, he could discover nothing of the kind. Neither is such a protection wanted; for the woody splinters above mentioned furnish a very good covering.

The grubs hatch from these eggs (of which, M. Pontedera says, one female will deposit from five to seven hundred), issue from the same holes through which the eggs have been introduced, and betake themselves to the ground to feed on the roots of plants. They are not transformed into chrysalides, but into active nymphs, remarkable for their fore limbs, which are thick, strong, and furnished with prongs for digging; and when we are told, by Dr. Le Ferve, that they make their way easily into hard stiff clay, to the depth of two or three feet, we perceive how necessary to them such a conformation must be.

Saw-flies.

An instrument for cutting grooves in wood, still more ingeniously contrived than that of the tree-hopper, was first observed by Vallisnieri, an eminent Italian naturalist, in a four-winged fly, most appropriately denominated by M. Réaumur the _saw-fly_ (_Tenthredo_) of which many sorts are indigenous to Great Britain. The grubs from which these flies originate are indeed but too well known, as they frequently strip our rose, gooseberry, raspberry, and red currant trees of their leaves, and are no less destructive to birch, alder, and willows; while turnips and wheat suffer still more seriously by their ravages. These grubs may readily be distinguished from the caterpillars of moths and butterflies by having from sixteen to twenty-eight feet, by which they usually hang to the leaf they feed on, while they coil up the hinder part of their body in a spiral ring. The perfect flies are distinguished by four transparent wings; and some of the most common have a flat body of a yellow or orange colour, while the head and shoulders are black.

In order to see the ovipositor, to which we shall for the present turn our chief attention, a female saw-fly must be taken, and her belly gently pressed, when a narrow slit will be observed to open at some distance from the apex, and a short, pointed, and somewhat curved body, of a brown colour and horny substance, will be protruded. The curved plates which form the sides of the slit are the termination of the sheath, in which the instrument lies concealed till it is wanted by the insect. The appearance of this instrument, however, and its singular structure, cannot be well understood without the aid of a microscope.

The instrument thus brought into view is a very finely-contrived saw, made of a horny substance, and adapted for penetrating branches and other parts of plants where the eggs are to be deposited. The ovipositor-saw of the insect is much more complicated than any of those employed by our carpenters. The teeth of our saws are formed in a line, but in such a manner as to cut in two lines parallel to, and at a small distance from, each other. This is effected by slightly bending the points of the alternate teeth right and left, so that one-half of the whole teeth stand a little to the right, and the other half a little to the left. The distance of the two parallel lines thus formed is called the _course_ of the saw, and it is only the portion of wood which lies in the course that is cut into sawdust by the action of the instrument. It will follow that in proportion to the thinness of a saw there will be the less destruction of wood which may be sawed. When cabinet-makers have to divide valuable wood into very thin leaves, they accordingly employ saws with a narrow course, while sawyers who cut planks use one with a broad course. The ovipositor-saw being extremely fine, does not require the teeth to diverge much; but from the manner in which they operate, it is requisite that they should not stand, like those of our saws, in a straight line. The greater portion of the edge of the instrument, on the contrary, is towards the point somewhat concave, similar to a scythe, while towards the base it becomes a little convex, the whole edge being nearly the shape of an Italic _f_.

The ovipositor-saw of the fly is put in motion in the same way as a carpenter's hand-saw, supposing the tendons attached to its base to form the handle, and the muscles which put it in motion to be the hand of the carpenter. But the carpenter can only work one saw at a time, whereas each of these flies is furnished with two, equal and similar, which it works at the same time--one being advanced and the other retracted alternately. The secret, indeed, of working more saws than one at once is not unknown to our mechanics; for two or three are sometimes fixed in the same frame. These, however, not only all move upwards and downwards simultaneously, but cut the wood in different places; while the two saws of the ovipositor work in the same cut, and consequently, though the teeth are extremely fine, the effect is similar to a saw with a wide set.

It is important, seeing that the ovipositor-saws are so fine, that they be not bent or separated while in operation--and this, also, nature has provided for, by lodging the backs of the saws in a groove, formed by two membranous plates, similar to the structure of a clasp-knife. These plates are thickest at the base, becoming gradually thinner as they approach the point, which the form of the saws requires. According to Vallisnieri, it is not the only use of this apparatus to form a back for the saws, he having discovered, between the component membranes, two canals, which he supposes are employed to conduct the eggs of the insect into the grooves which it has hollowed out for them.

The teeth of a carpenter's saw, it may be remarked, are simple, whereas the teeth of the ovipositor-saw are themselves denticulated with fine teeth. The latter, also, combines at the same time the properties of a saw and of a rasp or file. So far as we are aware, these two properties have, never been combined in any of the tools of our carpenters. The rasping part of the ovipositor, however, is not constructed like our rasps, with short teeth thickly studded together, but has teeth almost as long as those of the saw, and placed contiguous to them, on the back of the instrument, resembling in their form and setting the teeth of a comb, as may be seen in the figure. Of course, such observations are conducted with the aid of a microscope.

When a female saw-fly has selected the branch of a rose-tree, or any other, in which to deposit her eggs, she may be seen bending the end of her belly inwards, in form of a crescent, and protruding her saw, at the same time, to penetrate the bark or wood. She maintains this recurved position so long as she works in deepening the groove; but when she has attained the depth required, she unbends her body into a straight line, and in this position works upon the place lengthways, by applying the saw more horizontally. When she has rendered the groove as large as she wishes, the motion of the tendons ceases, and an egg is placed in the cavity. The saw is then withdrawn into the sheath for about two-thirds of its length, and at the same moment a sort of frothy liquid, similar to a lather made with soap, is dropped over the egg, either for the purpose of gluing it in its place or sheathing it from the action of the juices of the tree. She proceeds in the same manner in sawing out a second groove, and so on in succession, till she has deposited all her eggs, sometimes to the number of twenty-four. The grooves are usually placed in a line, at a small distance from one another, on the same branch; but sometimes the mother-fly shifts to another, or to a different part of the branch, when she is either scared or finds it unsuitable. She commonly, also, takes more than one day to the work, notwithstanding the superiority of her tools. Réaumur has seen a saw-fly make six grooves in succession, which occupied her about ten hours and a half.

The grooves, when finished, have externally little elevation above the level of the bark, appearing like the puncture of a lancet in the human skin; but in the course of a day or two the part becomes first brown and then black, while it also becomes more and more elevated. This increased elevation is not owing to the growth of the bark, the fibres of which, indeed, have been destroyed by the ovipositor-saw, but to the actual growth of the egg; for when a new-laid egg of the saw-fly is compared with one which has been several days enclosed in the groove, the latter will be found to be very considerably the larger. This growth of the egg is contrary to the analogy observable in the eggs of birds, and even of most other insects; but it has its advantages. As it continues to increase, it raises the bark more and more, and consequently widens, at the same time, the slit at the entrance; so that, when the grub is hatched, it finds a passage ready for its exit. The mother-fly seems to be aware of this growth of her eggs, for she takes care to deposit them at such distances as may prevent their disturbing one another by their development.

Another species of saw-fly, with a yellow body and deep violet-coloured wings, which also selects the rose-tree, deposits her eggs in a different manner. Instead of making a groove for each egg, like the preceding, she forms a large single groove, sufficient for about two dozen eggs. These eggs are all arranged in pairs, forming two straight lines parallel to the sides of the branch. The eggs, however, though thus deposited in a common groove, are carefully kept each in its place; for a ridge of the wood is left to prevent those on the right from touching those on the left--and not only so, but between each egg of a row a thin partition of wood is left, forming a shallow cell.

The edges of this groove, it will be obvious, must be farther apart than those which only contain a single egg, and, in fact, the whole is open to inspection; but the eggs are kept from falling out, both by the frothy glue before mentioned, and by the walls of the cells containing them. They were observed also, by Vallisnieri, to increase in size like the preceding.

[In the middle of summer, plenty of these grooves may be seen, by looking at the under lid of leaf-stalks or delicate young twigs. Row upon row of the grooves are sometimes found, so the all-destructive power of the insects must indeed be great. The larvæ, when full fed, dispose of themselves in various ways. Those of the gooseberry-fly, for example (_Nematus Ribesii_), after they have stripped the bush of its leaves, either seek the ground or remain on the branches, and spin a series of cocoons, attaching them to each branch by their ends. Those, therefore, who wish to destroy these little pests, must know both localities of the cocoons, or they will allow one half to escape while destroying the other.]

This insect has a flat yellow body and four pellucid wings, the two outer ones marked with brown on the edge. In April it issues from the pupa, which has lain under ground from the preceding September. The female of the gooseberry saw-fly does not, like some of the family, cut a groove in the branch to deposit her eggs;--"of what use, then," asks Réaumur, "is her ovipositor-saw?" In order to satisfy himself on this point, he introduced a pair of the flies under a bell-glass along with a branch bent from a red-currant bush, that he might watch the process. The female immediately perambulated the leaves in search of a place suited to her purpose, and passing under a leaf began to lay, depositing six eggs within a quarter of an hour. Each time she placed herself as if she wished to cut into the leaf with her saw; but, upon taking out the leaf, the eggs appeared rather projecting than lodged in its substance. The caterpillars are hatched in two or three weeks; and they feed in company till after midsummer, frequently stripping both the leaves and fruit of an extensive plantation. The caterpillar has six legs and sixteen pro-legs, and is of a green colour mixed with yellow, and covered with minute black dots raised like shagreen. In its last skin it loses the black dots and becomes smooth and yellowish white. The Caledonian Horticultural Society have published a number of plans for destroying these caterpillars.

[Another remarkable mode of disposing of the pupa is shown in the accompanying illustration; it represents the nest of an exotic saw-fly, named _Deilocenes Ellisii_. In this instance, the numerous larvæ unite in spinning for themselves a common envelope of considerable strength; it is seen as it appears when attached to the branch of a tree. The material of which it is composed is the tough silken fibre spun by the larvæ of so many insects, which may be seen in perfection in the cocoons of the Microgaster. Two species of this curious group will be described in a future page.