Animal Intelligence Part 14

As soon as the queen has been fertilised, and the services of the drones therefore no longer required, the worker bees fall upon their unfortunate and defenceless brothers to kill them, either by direct stinging or by throwing them out of the hive to perish in the cold. The drones' cells are then torn down, and any remaining drone eggs or pupae destroyed. Generally all the drones--which may number more than a thousand--are slaughtered in the course of a single day. Evidently the object of this ma.s.sacre is that of getting rid of useless mouths; but there is a more difficult question as to why these useless mouths ever came into existence. It has been suggested that the enormous disproportion between the present number of males and the single fertile female refers to a time before the social instincts became so complex or consolidated, and when, therefore, bees lived in lesser communities.

Probably this is the explanation, although I think we might still have expected that before this period in their evolution had arrived bees might have developed a compensating instinct, either not to allow the queen to lay so many drone eggs, or else to ma.s.sacre the drones while still in the larval state. But here we must remember that among the wasps the males do work (chiefly domestic work, for which they are fed by their foraging sisters); so it is possible that in the hive-bee the drones were originally useful members of the community, and that they have lost their primitively useful instincts. But whatever the explanation, it is very curious that here, among the animals which are justly regarded as exhibiting the highest perfection of instinct, we meet with perhaps the most flagrant instance in the animal kingdom of instinct unperfected. It is the more remarkable that the drone-killing instinct should not have been better developed in the direction of killing the drones at the most profitable time--namely, in their larval or oval state--from the fact that in many respects it seems to have been advanced to a high degree of discriminative refinement. Thus, to quote Buchner,--

That the ma.s.sacre of the drones is not performed entirely from an instinctive impulse, but in full consciousness of the object to be gained, is proved by the circ.u.mstance that it is carried out the more completely and mercilessly the more fertile the queen shows herself to be. But in cases where this fertility is subject to serious doubt, or when the queen has been fertilised too late or not at all, and therefore only lays drones' eggs, or when the queen is barren, and new queens, to be fertilised later, have to be brought up from working-bee larvae, then all or some of the drones are left alive, in the clear prevision that their services will be required later... . This wise calculation of consequences is further exemplified in that sometimes the ma.s.sacre of the drones takes place before the time for swarming, as, for instance, when long-continued unfavourable weather succeeds a favourable beginning of spring, and makes the bees anxious for their own welfare. If, however, the weather breaks, and work again becomes possible, so that the bees take courage anew, they then bring up new drones, and prepare them in time for the swarming.

This killing of drones is distinguished from the regular drone ma.s.sacre by the fact that the bees then only kill the developed drones, and leave the drone larvae, save when absolute hunger compels their destruction. Not less can it be regarded as a prudent calculation of circ.u.mstances when the bees of a hive, brought from our temperate climate to a more southern country, where the time of collecting lasts longer, do not kill the drones in August, as usual, but at a later period, suitable to the new conditions.

But the philosophy of drone-killing is, I think, even more difficult in the case of the wasps than in that of the bees. For, unlike the bees, whose communities live from year to year, the wasps all perish at the end of autumn, with the exception of a very few fertilised females. As this season of universal calamity approaches, the workers destroy all the larval grubs--a proceeding which, in the opinion of some writers, strikingly exemplifies the beneficence of the Deity! Now, it does not appear to me easy to understand how the presence of such an instinct in this case is to be explained. For, on the one hand, the individual females which are destined to live through the winter cannot be conspicuously benefited by this slaughter of grubs; and, on the other hand, the rest of the community is so soon about to perish, that one fails to see of what advantage it can be to it to get rid of the grubs.

If the whole human race, with the exception of a few women, were to perish periodically once in a thousand years, the race would profit nothing by destroying, a few months before the end of each millennium, all sick persons, lunatics, and other 'useless mouths.' I have not seen this difficulty with regard to the ma.s.sacring instinct in wasps mentioned before, and I only mention it now in order to draw attention to the fact that there seems to be a more puzzling problem presented here than in the case of the a.n.a.logous instinct as exhibited by bees.

The only solution which has suggested itself to my mind is the possibility that in earlier times, or in other climates, wasps may have resembled bees in living through the winter, and that the grub-slaying instinct is in them a survival of one which was then, as in the case of the bees now, a clearly beneficial instinct.

For some days before swarming begins, there is a great excitement and buzzing in the hive, the temperature of which rises from 92 to 104.

Scouts having been previously sent out to explore for suitable quarters wherein to plant the new colony, these now act as guides. The swarm leaves the hive with their queen. The bees which remain behind busy themselves in rearing out the pupae, which soon arriving at maturity, also quit the hive in successive swarms. According to Buchner, 'secondary swarms with young queens send out no scouts, but fly at random through the air. They clearly lack the experience and prudence of the older bees.' And, regarding the behaviour of the scouts sent out by primary swarms, this author says:--

M. de Fraviere had the opportunity of observing the manner in which such an examination is carried on, and with what prudence and accuracy. He placed an empty beehive, made in a new style, in front of his house, so that he could exactly watch from his own window what went on inside and out without disturbance to himself or to the bees. A single bee came and examined the building, flying all round it and touching it. It then let itself down on the board, and walked carefully and thoroughly over the interior, touching it continually with its antennae so as to subject it on all sides to a thorough investigation. The result of its examination must have been satisfactory, for after it had gone away it returned accompanied by a crowd of some fifty friends, which now together went through the same process as their guide. This new trial must also have had a good result, for soon a whole swarm came, evidently from a distant spot, and took possession. Still more remarkable is the behaviour of the scouts when they take possession of a satisfactory hive or box for an imminent or approaching swarm.

Although it is not yet inhabited they regard it as their property, watch it and guard it against stranger bees or other a.s.sailants, and busy themselves earnestly in the most careful cleansing of it, so far as this cleansing is impossible to the setter up of the hive. Such a taking possession sometimes occurs eight days before the entrance of the swarm.

_Wars._--As with ants, so with bees, the great cause of war is plunder; and facts now well substantiated by numberless observers concerning 'robber-bees' indicate a large measure of intelligence. These aim at lessening their labour in collecting honey by plundering the store of other hives. The robberies may be conducted singly or in concert. When the thieving propensity is developed only in individual cases, the thieves cannot rely on force in plundering a foreign state, and so resort to cautious stealth. 'They show by their whole behaviour--creeping into the hive with careful vigilance--that they are perfectly conscious of their bad conduct; whereas the workers belonging to the hive fly in quickly and openly, and in full consciousness of their right.' If such solitary burglars are successful in obtaining plunder, their bad example leads other members of their own community to imitate them; thus it is that the whole bee-nation may develop marauding habits, and when they do this they act in concert to rob by force. In this case an army of bees precipitates itself upon the foreign hive, a battle ensues, and if successful in overcoming resistance, the invaders first of all search out the queen-bee and put her to death, whereby they disorganise their enemies and plunder the hive with ease. It is observed that when this policy is once successful, the spirit of aggrandis.e.m.e.nt is encouraged, so that the robber-bees 'find more pleasure in robbery than in their own work, and become at last formidable robber-states.' When an invaded hive is fairly overcome by the invaders killing the queen, the owners of the hive, finding that all is lost, not only abandon further resistance, but very often reverse their policy and join the ranks of their conquerors.

They a.s.sist in the tearing down of their cells, and in the conveyance of the honey to the hive of their invaders. 'When the a.s.sailed hive is emptied, the next ones are attacked, and if no effective resistance is offered, are robbed in similar fas.h.i.+on, so that in this way a whole bee-stand may be gradually destroyed.' Siebold observed the same facts in the case of wasps (_Polistes gallica_). If, however, the battle turns in favour of the defenders, they pursue the flying legions of their enemies to a distance from their home. It sometimes happens that the plundered hive offers no resistance at all, owing to the robbers having visited the same flowers as the robbed, and so probably (having much the same smell) not being recognised as belonging to a different community.

The thieves, when they find such to be the case, may become so bold as to stop the bees that are returning to the hive with their loads, of which they deprive them at the entrance of the hive. This is done by a process which one observer, Weygandt,[56] calls 'milking,' and it seems that the milking bee attains the double advantage of securing the honey from the milked one and disarming suspicion of the other bees by contracting its smell and entering the hive loaded, into which it is admitted without opposition to continue its plunder.

Sometimes robber-bees attack their victims in the fields at a distance from the hives. This sort of highway robbery is generally conducted by a gang of four or five robber-bees which set upon a single honest bee, 'hold him by the legs, and pinch him until he unfolds his tongue, which is sucked in succession by his a.s.sailants, who then suffer him to depart in peace.'

It is strange that hive-bees of dishonest temperaments seem able to coax or wheedle humble-bees into the voluntary yielding of honey.

'Humble-bees have been known to permit hive-bees to take the whole honey that they have collected, and to go on gathering more, and handing it over, for three weeks, although they refuse to part with it, or seek refuge in flight, when wasps make similar overtures.'[57]

Besides theft and plunder, there are other causes of warfare among bees, which, however, are only apparent in their effects. Thus, for some undiscernible reason, duels are not infrequent, which generally end in the death of one or both combatants. At other times, equally without apparent reason, civil war breaks out in a hive, which is sometimes attended with much slaughter.

_Architecture._--Coming now to the construction of the cells and combs, there is no doubt that here we meet with the most astonis.h.i.+ng products of instinct that are presented in the animal kingdom. A great deal has been written on the practical exhibition of high mathematical principles which bees display in constructing their combs in the form that secures the utmost capacity for storage of honey with the smallest expenditure of building material. The shortest and clearest statement of the subject that I have met with is the following, which has been given by Dr.

Reid:--

There are only three possible figures of the cells which can make them all equal and similar, without any useless interstices. These are the equilateral triangle, the square, and the regular hexagon.

Mathematicians know that there is not a fourth way possible in which a plane may be cut into little s.p.a.ces that shall be equal, similar, and regular, without useless s.p.a.ces. Of the three figures, the hexagon is the most proper for convenience and strength. Bees, as if they knew this, make their cells regular hexagons.

Again, it has been demonstrated that, by making the bottoms of the cells to consist of three planes meeting in a point, there is a saving of material and labour in no way inconsiderable. The bees, as if acquainted with these principles of solid geometry, follow them most accurately. It is a curious mathematical problem, at what precise angle the three planes which compose the bottom of a cell ought to meet, in order to make the greatest possible saving, or the least expense of material and labour. This is one of the problems which belong to the higher parts of mathematics. It has accordingly been resolved by some mathematicians, particularly by the ingenious Maclaurin, by a fluctionary calculation, which is to be found in the Transactions of the Royal Society of London. He has determined precisely the angle required, and he found, by the most exact mensuration the subject would admit, that it is the very angle in which the three planes in the bottom of the cell of a honeycomb do actually meet.[58]

Marvellous as these facts undoubtedly are, they may now be regarded as having been satisfactorily explained. Long ago Buffon sought to account for the hexagonal form of the cells by an hypothesis of mutual pressure.

Supposing the bees to have a tendency to build tubular cells, if a greater number of bees were to build in a given s.p.a.ce than could admit of all the parallel tubes being completed, tubes with flat sides and sharp angles might result, and if the mutual pressure were exactly equal in all directions, these sides and angles would a.s.sume the form of hexagons. This hypothesis of Buffon was sustained by such physical a.n.a.logies as the blowing of a crowd of soap-bubbles in a cup, the swelling of moistened peas in a confined s.p.a.ce, &c. The hypothesis, however, as thus presented was clearly inadequate; for no reason is a.s.signed why the mutual pressure, even if conceded to exist, should always be so exactly equal in all directions as to convert all the cylinders into perfect hexagons--even the a.n.a.logy of the soap-bubbles and the moistened peas failing, as pointed out by Brougham and others, to sustain it, seeing that as a matter of fact bubbles and peas under circ.u.mstances of mutual pressure do not a.s.sume the form of hexagons, but, on the contrary, forms which are conspicuously irregular. Moreover, the hypothesis fails to account for the particular prismatic shape presented by the cell base. Therefore it is not surprising that this hypothesis should have gained but small acceptance. Kirby and Spence dispose of it thus:--'He (Buffon) gravely tells us that the boasted hexagonal cells of the bee are produced by the reciprocal pressure of the cylindrical bodies of these insects against each other!!'[59] The double note of admiration here may be taken to express the feelings with which this hypothesis of Buffon was regarded by all the more sober-minded naturalists. Yet it turns out to have been not very wide of the mark. As is often the case with the gropings of a great mind, the idea contains the true principle of the explanation, although it fails as an explanation from not being in a position to take sufficient cognizance of all the facts. Safer it is for lesser minds to restrain their notes of exclamation while considering the theories of a greater; however crude or absurd the latter may appear, the place of their birth renders it not impossible that some day they may prove to have been prophetic of truth revealed by fuller knowledge. Usually in such cases the final explanation is eventually reached by the working of a yet greater mind, and in this case the undivided credit of solving the problem is to be a.s.signed to the genius of Darwin.

Mr. Waterhouse pointed out 'that the form of the cell stands in close relation to the presence of adjoining cells.' Starting from this fact, Mr. Darwin says,--

Let us look to the great principle of gradation, and see whether Nature does not reveal to us her method of work. At one end of a short series we have humble-bees, which use their old coc.o.o.ns to hold honey, sometimes adding to them short tubes of wax, and likewise making separate and very irregular rounded cells of wax. At the other end of the series we have the cells of the hive-bee, placed in a double layer... . In the series between the extreme perfection of the cells of the hive-bee and the simplicity of those of the humble-bee we have the cells of the Mexican _Melipona domestica_, carefully described and figured by Pierre Huber... . It forms a nearly regular waxen comb of cylindrical cells, in which the young are hatched, and, in addition, some large cells of wax for holding honey. These latter cells are nearly spherical and of nearly equal sizes, and are aggregated into an irregular ma.s.s. But the important thing to notice is, that these cells are always made at that degree of nearness to each other that they would have intersected or broken into each other if the spheres had been completed; but this is never permitted, the bees building perfectly flat cells of wax between the spheres which thus tend to intersect.

Hence each cell consists of an outer spherical portion; and of two, three, or more flat surfaces, according as the cell adjoins two, three, or more other cells. When one cell rests on three other cells, which, from the spheres being nearly of the same size, is very frequently and necessarily the case, the three flat surfaces are united into a pyramid; and this pyramid, as Huber has remarked, is manifestly a gross imitation of the three-sided pyramidal base of the cell of the hive-bee... .

Reflecting on this case, it occurred to me that if the Melipona had made its spheres at some given distance from each other, and had made them of equal sizes, and had arranged them symmetrically in a double layer, the resulting structure would have been as perfect as the comb of the hive-bee. Accordingly I wrote to Prof.

Miller of Cambridge, and this geometer has kindly read over the following statement, drawn up from his information, and tells me that it is strictly correct.

This statement having fully borne out his theory, Mr. Darwin continues:--

Hence we may safely conclude that, if we could slightly modify the instincts already possessed by the Melipona, and in themselves not very wonderful, this bee would make a structure as wonderfully perfect as that of the hive-bee. We must suppose the Melipona to have the power of forming her cells truly spherical, and of equal sizes; and this would not be very surprising, seeing that she already does so to a certain extent, and seeing what perfectly cylindrical burrows many insects make in wood, apparently by turning round on a fixed point. We must suppose the Melipona to arrange her cells in level layers, as she already does her cylindrical cells; and we must further suppose--and this is the greatest difficulty--that she can somehow judge accurately at what distance to stand from her fellow-labourers when several are making their spheres; but she is already so far able to judge of distance that she always describes her spheres so as to intersect to a certain extent; and then she unites the points of intersection by perfectly flat surfaces. By such modifications of instinct, which in themselves are not very wonderful--hardly more wonderful than those which guide a bird to make its nest,--I believe that the hive-bee has acquired through natural selection her inimitable architectural powers.[60]

Mr. Darwin next tested this theory by the experiment of introducing into beehives plates of wax, and observing that the bees worked upon these plates just as the theory required. That is to say, they made their cells by excavating a number of little circular pits at equal distances from one another, so that by the time the pits had acquired the width of an ordinary cell, the sides of the pits intersected. As soon as this occurred the bees ceased to excavate, and instead began to build up flat walls of wax on the lines of intersection. Other experiments with very thin plates of vermilion-coloured wax showed that the bees all worked at about the same rate, and on opposite sides of the plates, so that the common bottoms of any two opposite pits were flat. These flat bottoms 'were situated, as far as the eye could judge, exactly along the planes of imaginary intersection between the basins on the opposite sides of the ridge of wax;' so that if the plate of wax had been thick enough to admit of the opposite basins being deepened (and widened) into cells, the mutual intersection of _adjacent_ as well as _opposite_ bottoms would have given rise, as in the first experiment with the thick plate of wax, to the pyramidal bottoms. Experiments with the vermilion wax also showed, as Huber had previously stated, that a number of individual bees work by turns at the same cell; for by covering parts of growing cells with vermilion wax, Mr. Darwin--

Invariably found that the colour was most delicately diffused by the bees--as delicately as a painter could have done it with his brush--by atoms of the coloured wax having been taken from the spot on which it had been placed, and worked into the growing edges of the cells all round.

Such, omitting details, is the substance of Mr. Darwin's theory. In summary he concludes,--

The work of construction seems to be a sort of balance struck between many bees, all instinctively standing at the same relative distance from each other, all trying to sweep equal spheres, and then building up, or leaving ungnawed, the planes of intersection between these spheres.

This theory, while serving as a full and simple explanation of all the facts, has, as we have seen, been so fully substantiated by observation and experiment, that it deserves to be regarded as raised to the rank of a completed demonstration. It differs from the theory of Buffon in two important particulars: it embraces all the facts, and supplies a cause adequate to explain them. This cause is natural selection, which converts the random 'pressure' in Buffon's theory into a precisely regulated principle. Random pressure alone could never produce the beautifully symmetrical form of the hexagonal cell with the pyramidal bottom; but it could and must have produced the intersection of cylindrical cells among possibly many extinct species of bees, such as the Melipona. Whenever this intersection occurred in crowded nests, it must clearly have been of great benefit in securing economy of precious wax; for in every case where a flat wall of part.i.tion between two adjacent cells did duty instead of a double cylindrical wall of separate cells, there wax should have been saved. Thus we can see how natural selection would have worked towards the developing of an instinct to excavate cells near enough together to produce intersection; and once begun, there is no reason why this instinct should not have been perfected by the same agency, till we meet with its ideal perfection in the hive-bee. For as Mr. Darwin observes,--

With respect to the formation of wax, it is known that bees are often hard pressed to get sufficient nectar; and I am informed by Mr. Tegetmeier that it has been experimentally proved that from twelve to fifteen pounds of dry sugar are consumed by a hive of bees for the secretion of a pound of wax; so that a prodigious quant.i.ty of fluid nectar must be collected and consumed by the bees in a hive for the secretion of the wax necessary for the construction of their combs.

Moreover, many bees have to remain idle for many days during the process of secretion... . Hence it would continually be more and more advantageous to our humble-bees if they were to make their cells more and more regular, nearer together, and aggregated into a ma.s.s, like the cells of Melipona; for in this case a large part of the bounding surface of each cell would serve to bound the adjoining cell, and much labour and wax would be saved. Again, from the same cause, it would be advantageous to the Melipona if she were to make her cells closer together, and more regular in every way than at present; for then, as we have seen, the spherical surfaces would wholly disappear and be replaced by plane surfaces; and the Melipona would make a comb as perfect as that of the hive-bee. Beyond this stage of perfection in architecture, natural selection could not lead; for the comb of the hive-bee, as far as we can see, is absolutely perfect in economising labour and wax.

The problem, then, as to the origin and perfection of the cell-making instinct appears thus to have been fully and finally solved. I shall now adduce a few facts to show that while the general instinct of building hexagonal cells has doubtless been acquired by natural selection in the way just explained, it is nevertheless an instinct not wholly of a blind or mechanical kind, but is constantly under the control of intelligent purpose. Thus Mr. Darwin observes,--

It was really curious to note in cases of difficulty, as when two pieces of comb met at an angle, how often the bees would pull down and rebuild in different ways the same cell, sometimes recurring to a shape which they had at first rejected.[61]

Again, Huber saw a bee building upon the wax which had already been put together by her comrades. But she did not arrange it properly, or in a way to continue the design of her predecessors, so that her building made an undesirable corner with theirs. 'Another bee perceived it, pulled down the bad work before our eyes, and gave it to the first in the requisite order, so that it might exactly follow the original direction.' Similarly, to quote Buchner,--

All the cells have not the same shape, as would be the case if the bees in building worked according to a perfectly instinctive and unchangeable plan. There are very manifold changes and irregularities. Almost in every comb irregular and unfinished cells are to be found, especially where the several divisions of a comb come together. The small architects do not begin their comb from a single centre, but begin building from many different points, so as to progress as rapidly as possible, and so that the greatest number may work simultaneously; they therefore build from above downwards, in the shape of flat truncated cones or hanging pyramids, and these several portions are afterwards united together during the winter budding.

At these lines of junction it is impossible to avoid irregular cells between the pressed together or unnaturally lengthened ones. The same is true more or less of the pa.s.sage cells, which are made to unite the large cells of the so-called drone wax with the smaller ones of the working bees, and which are generally placed in two or three rows. The cells also which they usually build from the combs to the gla.s.s walls of their hives, in order to hold them up, show somewhat irregular forms. Finally, in places where special conditions of the situation do not otherwise permit, it may be observed that the bees, far from clinging obstinately to their plan, very well understand how to accommodate themselves to circ.u.mstances not only in cell-building, but also in making their combs. F. Huber tried to mislead their instinct, or rather to put to the proof their reason and cleverness in every possible way, but they always emerged triumphant from the ordeal. For instance, he put bees in a hive the floor and roof of which were made of gla.s.s, that is of a body which the bees use very unwillingly for the attachment of their combs, on account of its smoothness. Thus the possibility of building as usual from above downwards, and also from below upwards, was taken away from them; they had no point of support save the perpendicular walls of their dwelling. They thereupon built on one of these walls a regular stratum of cells, from which, building sideways, they tried to carry the comb to the opposite side of the hive. To prevent this Huber covered that side also with gla.s.s. But what way out of the difficulty was found by the clever insects? Instead of building further in the projected direction, they bent the comb round at the extreme point, and carried it at a right angle towards one of the inner sides of the hive which was not covered with gla.s.s, and there fastened it. The form and dimensions of the cells must necessarily have been altered thereby, and the arrangement of their work at the angle must have been quite different from the usual. They made the cells of the convex side so much broader than those of the concave that they had a diameter two or three times as great, and yet they managed to join them properly with the others. They also did not wait to bend the comb until they came to the gla.s.s itself, but recognised the difficulty beforehand,[62] which had been interposed by Huber while they were building with a view to overcome the first difficulty.

_Special Habits._

_The Mason-Bee._--This insect closes the roof of its larval cell with a kind of mortar, which sets as hard as stone. A little hole, closed only with soft mud, is, however, left in one part of the roof as a door of exit for the matured insect. It is said that when a mason-bee finds an old and deserted nest, it saves itself the trouble of making a new one--utilising the ready-made nest after having well cleaned it. In Algiers the mason-bees have been observed in this way to utilise empty snail-sh.e.l.ls. According to Blanchard, some individuals avoid the labour of making their own nests or houses for their young, by possessing themselves of their neighbours' houses either by craft or by force.

'Does the mason-bee act like a machine,' says E. Menault, 'when it directs its work according to circ.u.mstances, possesses itself of old nests, cleanses and improves them, and thereby shows that it can fully appreciate the immediate position? Can one believe that no kind of reflection is here necessary?'

_The Tapestry-Bee._--The so-called tapestry-bee digs holes for her larvae three or four inches deep in the earth, and lines the walls and floor of the chamber with petals of the poppy laid perfectly smooth. Several layers of petals are used, and when the eggs are introduced the chamber is closed by drawing all the leaves together at the top. Loose earth is then piled over the whole structure in order to conceal it. The so-called rose-bee (_Megachile centuncularis_) displays very similar habits.[63]

_The Carpenter-Bee._--This was first observed and described by Reaumur.[64] It makes a long cylindrical tube in the wood of beams, palings, &c. This it divides into a number of successive chambers by part.i.tions made of agglutinated saw-dust built across the tube at right angles to its axis. In each chamber there is deposited a single egg, together with a store of pollen for the nourishment of the future larva.

The larvae hatch out in succession and in the order of their age--_i.e._ the dates at which they were deposited. To provide for this, the bee bores a hole from the lower cell to the exterior, so that each larva, when ready to escape from its chamber, finds an open way from the tube.

The larvae have to cut their own way out through the walls of their respective chambers, and it is remarkable that they always cut through the wall that faces the tubular pa.s.sage left by the parent; they never bore their way out in the opposite direction, which, were they to do so, would entail the destruction of all the other and immature larvae.

_The Carding-Bee._--This insect surrounds its nest with a layer of wax, and then with a thick covering of moss. For this purpose a number of bees co-operate, and in order to save time each bee does not find and carry its own moss, but, with a division of labour similar to that which we have already noticed in the case of certain ants, a row of bees is formed, and the bits of moss pa.s.sed from one to another along the line. There is a long pa.s.sage to the nest, through which the moss has to be pa.s.sed, and it is said that at the mouth of the tunnel a guard is stationed to drive away ants or other intruders.

_Wasps._--These usually construct their nests of wood-dust, which they sc.r.a.pe off the weather-worn surfaces of boards, palings, &c., and work into a kind of paper with their saliva. If they happen to find any real paper, they perceive that it so much resembles the product of their own manufacture that they utilise it forthwith. The wasps do not require any special cells or chambers for the storage of honey, as they do not lay up any supply for the winter. The cells which they construct are therefore used exclusively for the rearing of larvae. In form these cells are sometimes cylindrical or globular, but more usually hexagonal, like those of the hive-bee. Although the mode of building is different from that employed by the bees, there can be little doubt that if it were as carefully investigated Mr. Darwin's theory of transition from the cylindrical to the hexagonal form would be found to apply here also, seeing that both forms so frequently occur in the same nest.

_The Mason-Wasp._--The habits of this insect are described by Mr. Bates.

It constructs its nest of clay. Each pellet that the insect brings it lays on the top of its nest-wall, and then spreads it out with its jaws, and treads it smooth with its feet. The nest, which is suspended on the branch of a tree, is then stocked with spiders and insects paralysed by stinging. The victims, not being wholly deprived of life, keep fresh until required as food of the developing larvae.

_The Butcher-Wasps._--These also paralyse their prey in a similar manner, and for a similar purpose. Fabre removed from a so-called sphex-wasp a killed gra.s.shopper, which it was conveying to its nest and had momentarily laid down at the mouth of the burrow--as these insects always do on returning with prey, in order to see that nothing has intruded into the burrow during their absence. Fabre carried the dead or paralysed gra.s.shopper to a considerable distance from the hole. On coming out the insect searched about until it found its prey. It then again carried it to the mouth of its burrow, and again laid it down while it once more went in to see that all was right at home. Again Fabre removed the gra.s.shopper, and so on for forty times in succession--the sphex never omitting to go through its fixed routine of examining the interior of its burrow every time that it brought the prey to its mouth.

Mr. Mivart, in his 'Lessons from Nature,' points to the instinct of this animal in the stinging of the ganglion of its prey as one that cannot be explained on Mr. Darwin's theory concerning the origin of instincts. In my next work, which will have to deal with this theory, I shall consider Mr. Mivart's difficulty, and also the difficulty first pointed out by Mr. Darwin himself as to why neuter insects, separated as they appear to be from the possibility of communicating by heredity any instinctive acquirements of the individual to the species, should present any instincts at all.

_General Intelligence._

Beginning with Sir John Lubbock's observations on this head, I shall first quote his statements with regard to way-finding:--