Chapter XX: Letter XXVII: On the Instinct of Insects (1)

The greater part of those surprising facts connected with the manners and economy of insects, of which the relation has occupied the preceding letters, is to be referred, I have told you, to their instinct. But _what_, you will ask, is this instinct?--of what nature is this faculty which produces effects so extraordinary?

To this query I do not pretend to give any satisfactory answer. As I am quite of Bonnet's opinion, that philosophers will in vain torment themselves to define instinct, until they have spent some time in the head of an animal without actually _being_ that animal--a species of metempsychosis through which I have never passed--I shall not attempt to explain what this mysterious energy _is_. It will not, however, I imagine, be very difficult to show what it is _not_; and some observations with this view, followed by an enumeration of peculiarities which distinguish the instincts of insects from those of other tribes of animals, and a short inquiry whether their actions are guided solely by instinct, will form the substance of this letter.

I. It is quite superfluous at this day to controvert the explanations of instinct advanced by some of the philosophers of the old school, such as that of Cudworth, who referred this faculty to a certain _plastic nature_; or that of Des Cartes, who contended that animals are mere _machines_. Nor, I fancy, would you thank me for entering into an elaborate refutation of the doctrine of Mylius, that many of the actions deemed instinctive are the effect of painful corporeal feelings; the cocoon of a caterpillar, for instance, being the result of a fit of the colic, produced by a superabundance of the gum which fills its silk-bags, and which exuding, is twisted round it, by its uneasy contortions, into a regular ball. Still less need I advert to the notable discovery of some pupils of Professor Winckler, that the brain, alias the soul, of a bee or spider, is impressed at the birth of the insect with certain geometrical figures, according to which models its works are constructed,--a position which these gentlemen demonstrate very satisfactorily by a memorable experiment in which they themselves were able to _hear triangles_.

It is as unnecessary to waste any words in refutation of the nonsense (for it deserves no better name) of Buffon, who refers the instinct of societies of insects to the circumstance of a great number of individuals being brought into existence at the same time, all acting with equal force, and obliged by the similarity of their internal and external structure, and the conformity of their movements, to perform each the same actions, in the same place, in the most convenient mode for themselves, and least inconvenient for their companions; whence results a regular, well-proportioned, and symmetrical structure: and he gravely tells us that the boasted hexagonal cells of bees are produced by the reciprocal pressure of the cylindrical bodies of these insects against each other[760]!!

Nor is it requisite to advert at length to the explanations of instinctive actions more recently given by Steffens, a German author (one of the transcendentalists, I conclude, from the incomprehensibility of his book to my ordinary intellect), who says that the products of the vaunted instinct of insects are nothing but "shootings out of inorganic animal masses" (_anorgische anschüsse_)[761]; and by Lamarck[762], who attributes them to certain inherent inclinations arising from habits impressed upon the organs of the animals concerned in producing them, by the constant efflux towards these organs of the nervous fluid, which during a series of ages has been displaced in their endeavours to perform certain actions which their necessities have given birth to. The mere statement of an hypothesis of which the enunciation is nearly unintelligible, and built upon the assumption of the presence of an unseen fluid, and of the existence of the animal some millions of years, is quite sufficient, and would even be unnecessary if it were not of such late origin. Neither shall I detain you with any formal consideration of the hypothesis advanced by Addison and some other authors, that instinct is an immediate and constant impulse of the Deity; which, to omit other obvious objections, is sufficiently refuted by the fact, that animals in their instincts are sometimes at fault, and commit mistakes, which on the above supposition could not in any case happen.

The only doctrine on the subject of instinct requiring any thing like a formal refutation, is that which, contending for the identity of this faculty with reason in man, maintains that all the actions of animals, however complicated, are, like those of the human race, the result of observation, invention, and experience. This theory, maintained by the sceptics, Pythagoras, Plato, and some other ancient philosophers, and in modern times by Helvetius, Condillac, and Smellie, has been by none more ingeniously supported than by Dr. Darwin, who in the chapter treating on instinct, in the first volume of his _Zoonomia_, has brought forward a collection of facts which give it a great air of plausibility. This plausibility, however, is merely superficial; and the result of a rigorous examination by any competent judge is, that the greater part of Dr. Darwin's facts bear more strongly in favour of the dissimilarity of instinct and reason than of their identity: and that those few which seem to support the latter position, are built upon the relations of persons ignorant of natural history, who have confused together distinct species of animals. Thus, because some anonymous informant told him that hive-bees when transported to Barbadoes, where there is no winter, ceased to lay up a store of honey, Dr. Darwin infers that all the operations of these insects are guided by reason and the adaptation of means to an end--a very just inference, if the statement from which it is drawn were accurate; but that it is not so, is known to every naturalist acquainted with the fact that many different species of bees store up honey in the hottest climates; and that there is no authentic instance on record of the hive-bees' altering in any age or climate their peculiar operations, which are now in the coldest and in the hottest regions precisely what they were in Greece in the time of Aristotle, and in Italy in the days of Virgil. Indeed the single fact, depending on the assertions of such accurate observers as Reaumur and Swammerdam, that a bee as soon after it is disclosed from the pupa as its body is dried and its wings expanded, and before it is possible that it should have received any instruction, betakes itself to the collecting of honey or the fabrication of a cell, which operations it performs as adroitly as the most hoary inhabitant of the hive, is alone sufficient to set aside all the hear-say statements of Dr. Darwin, and should have led him, as it must every logical reasoner, to the conclusion, that these and similar actions of animals cannot be referred to any reasoning process, nor be deemed the result of observation and experience.--It is true, it does not follow that animals, besides instinct, have not, in a degree, the faculty of reason also; and as I shall in the sequel endeavour to show, many of the actions of insects can be adequately explained on no other supposition. But to deny, as Dr. Darwin does, that the art with which the caterpillar weaves its cocoon, or the unerring care with which the moth places her eggs upon food that she herself can never use, are the effects of instinct, is as unphilosophical and contrary to fact, as to insist that the eagerness with which, though it has never tasted milk, the infant seeks for its mother's breast, is the effect of reason.

Instinct, then, is _not_ the result of a plastic nature; of a system of machinery; of diseased bodily action; of models impressed on the brain; nor of organic shootings-out:--it is not the effect of the habitual determination for ages of the nervous fluid to certain organs; nor is it either the impulse of the Deity, or reason. Without pretending to give a logical definition of it, which while we are ignorant of the essence of reason is impossible, we may call the instincts of animals those unknown faculties implanted in their constitution by the Creator, by which, independent of instruction, observation, or experience, and without a knowledge of the end in view, they are impelled to the performance of certain actions tending to the well-being of the individual and the preservation of the species: and with this description, which is in fact merely a confession of ignorance, we must, in the present state of metaphysical science, content ourselves.

I here say nothing of that supposed connexion of the instinct of animals with their _sensations_, which has been introduced into many definitions of this mysterious power, for two reasons. In the first place, this definition merely sets the world upon the tortoise; for what do we know more than before about the nature of instinct, when we have called it, with Brown, a predisposition to certain actions when certain sensations exist, or with Tucker have ascribed it to the operation of the senses, or to that internal feeling called appetite? But, secondly, this connexion of instinct with bodily sensation, though probable enough in some instances, is by no means generally evident. We may explain in this way the instincts connected with hunger and the sexual passion, and some other particular facts, as the laying of the eggs of the flesh-fly in the flowers of _Stapelia hirsuta_, instead of in carrion their proper nidus, and of those of the common house-fly in snuff[763] instead of dung; for in these instances the smell seems so clearly the guide, that it even leads into error. But what connexion between sensation and instinct do we see in the conduct of the working-bees, which fabricate some of the cells in a comb larger than others, expressly to contain the eggs and future grubs of drones, though these eggs are not laid by themselves, and are still in the ovaries of the queen? So we may plausibly enough conjecture that the fury with which, in ordinary circumstances, at a certain period of the year, the working-bees are inspired towards the drones, is the effect of some disagreeable smell or emanation proceeding from them at that particular time: but how can we explain, on similar grounds, the fact that in a hive deprived of a queen, no massacre of the drones takes place? Lastly, to omit here a hundred other instances, as many of them will be subsequently adverted to, if we may with some show of reason suppose that it is the sensation of heat which causes bees to swarm; yet what possible conception can we form of its being bodily sensations that lead bees to send out scouts in search of a hive suitable for the new colony, several days _before_ swarming?

After these observations on the nature of instinct, generally, I pass on to contrast in several particulars the instincts of insects with those of other animals; and thus to bring together some remarkable instances of the former which have not hitherto been laid before you, as well as to deduce from some of those already related, inferences to which it did not fall in with my design before to direct your attention. This contrast may be conveniently made under the three heads of--the exquisiteness of their instincts--their number--and their extraordinary development.

The instincts of by far the majority of the superior animals are of a very simple kind, only directing them to select suitable food; to propagate their species; to defend themselves and their young from harm; to express their sensations by various vocal modulations; and to a few other actions which need not be particularized. Others of the larger animals, in addition to these simpler instinctive propensities, are gifted with more extensive powers; storing up food for their winter consumption, and building nests or habitations for their young, which they carefully feed and tend.

All these instincts are common to insects, a great proportion of which are in like manner confined to these. But a very considerable number of this class are endowed with instincts of an _exquisiteness_ to which the higher animals can lay no claim. What bird or fish, for example, catches its prey by means of nets as artfully woven and as admirably adapted to their purposes as any that ever fisherman or fowler fabricated? Yet such nets are constructed by the race of spiders. What beast of prey thinks of digging a pit-fall in the track of the animals which serve it for food, and at the bottom of which it conceals itself, patiently waiting until some unhappy victim is precipitated down the sides of its cavern? Yet this is done by the ant-lion and another insect. Or, to omit the endless instances furnished by wasps, ants, the Termites, &c., what animals can be adduced which, like the hive-bee associating in societies, build regular cities composed of cells formed with geometrical precision, divided into dwellings adapted in capacity to different orders of the society, and storehouses for containing a supply of provision? Even the erections of the beaver, and the pensile dwelling of the tailor-bird, must be referred to a less elaborate instinct than that which guides the procedures of these little insects--the complexness and yet perfection of whose operations, when contrasted with the insignificance of the architect, have at all times caused the reflecting observer to be lost in astonishment.

It is, however, in the _deviations_ of the instincts of insects and their _accommodation to circumstances_, that the exquisiteness of these faculties is most decidedly manifested. The instincts of the larger animals seem capable of but slight modification. They are either exercised in their full extent or not at all. A bird, when its nest is pulled out of a bush, though it should be laid uninjured close by, never attempts to replace it in its situation; it contents itself with building another. But insects in similar contingencies often exhibit the most ingenious resources, their instincts surprisingly accommodating themselves to the new circumstances in which they are placed, in a manner more wonderful and incomprehensible than the existence of the faculties themselves. Take a honey-comb, for instance. If _every_ comb that bees fabricate were _always_ made _precisely_ alike--with the same general form, placed in the same position, the cells all exactly similar, or where varying with the variations always alike;--this structure would perhaps in reality be not more astonishing than many of a much simpler conformation. But when we know that in nine instances out of ten the combs in a bee-hive are thus similar in their properties, and yet that in the tenth one shall be found of a form altogether peculiar; placed in a different position; with cells of a different shape--and all these variations evidently adapted to some new circumstance not present when the other nine were constructed,--we are constrained to admit that nothing in the instinct of other animals can be adduced, exhibiting similar exquisiteness: just as we must confess an ordinary loom, however ingeniously contrived, far excelled by one capable of repairing its defects when out of order.

The examples of this variation and accommodation to circumstances among insects are very numerous; and as presenting many interesting facts in their history not before related, I shall not fear wearying you with a pretty copious detail of them, beginning with the more simple.

It is the instinct of _Geotrupes vernalis_ to roll up pellets of dung, in each of which it deposits one of its eggs; and in places where it meets with cow- or horse-dung only, it is constantly under the necessity of having recourse to this process. But in districts where sheep are kept, this beetle wisely saves its labour, and ingeniously avails itself of the pellet-shaped balls ready made to its hands which the excrement of these animals supplies[764].

A caterpillar described by Bonnet, which from being confined in a box was unable to obtain a supply of the bark with which its ordinary instinct directs it to make its cocoon, substituted pieces of paper that were given to it, tied them together with silk, and constructed a very passable cocoon with them.--In another instance the same naturalist having opened several cocoons of a moth (_Cucullia Verbasci_), which are composed of a mixture of grains of earth and silk, just after being finished; the larvæ did not repair the injury in the same manner. Some employed both earth and silk; others contented themselves with spinning a silken veil before the opening[765].

The larva of the cabbage-butterfly (_Pontia Brassicæ_) when about to assume the pupa state, commonly fixes itself to the under-side of the coping of a wall or some similar projection. But the ends of the slender thread which serves for its girth would not adhere firmly to stone or brick, or even wood. In such situations, therefore, it previously covers a space of about an inch long and half an inch broad with a web of silk, and to this extensive base its girth can be securely fastened. That this proceeding, however, is not the result of a blind unaccommodating instinct, seems proved by a fact which has come under my own observation. Having fed some of these larvæ in a box covered by a piece of muslin, they attached themselves to this covering; but as its texture afforded a firm hold to their girth, they span _no_ preparatory web.

_Bombus_[766] _Muscorum_ and some other species of humble-bees cover their nests with a roof of moss. M. P. Huber having placed a nest of the former under a bell glass, he stuffed the interstices between its bottom and the irregular surface on which it rested, with a linen cloth. This cloth, the bees, finding themselves in a situation where no moss was to be had, tore thread from thread, carded it with their feet into a felted mass, and applied it to the same purpose as moss, for which it was nearly as well adapted.--Some other humble-bees tore the cover of a book with which he had closed the top of the box that contained them, and made use of the detached morsels in covering their nest[767].

The larva of _Cossus ligniperda_, which feeds in the interior of trees, previously to fabricating a cocoon and assuming the pupa state, forms for the egress of the future moth a cylindrical orifice, except when it finds a suitable hole ready made. When the moth is about to appear, the chrysalis with its anterior end forces an opening in the cocoon. If the orifice in the tree has been formed by itself, in which case it exactly fits its body, it _entirely_ quits the cocoon, and pushes itself half way out of the hole, where it remains secure from falling until the moth is disclosed. But if the orifice, having been adopted, be larger than it ought to have been, and thus not capable of supporting the pupa in this position, the provident insect pushes itself only _half way_ out of the cocoon, which thus serves for the support which in the former case the wood itself afforded[768].

The variations in the procedures of the larva of a little moth described by Reaumur, whose habitation has been before noticed[769]--one of those which constantly reside in a subcylindrical case--are still more remarkable. This little caterpillar feeds upon the elm, the leaves of which serve it at once for food and clothing. It eats the parenchyma or inner pulp, burrowing between the upper and under membranes, of portions of which cut out, and properly sewed together, it forms its case. Its usual plan is, to insinuate itself between the epidermal membranes of the leaf, close to one of the edges. Parallel with this it excavates a cavity of suitable form and dimensions, gnawing the pulp even out of every projection of the serratures, but carefully avoiding to separate the membranes at the very edge, which with a wise saving of labour it intends should form one of the seams of its coat; and as the little miner is not embarrassed with the removal of the excavated materials, which it swallows as it proceeds, a cavity sufficiently large is but the work of a few hours. It then lines it with silk, at the same time pushing it into a more cylindrical shape; and lastly, cutting it off at the two ends and inner side, it sews up the latter with such nicety that the suture is scarcely discoverable; and is now provided with a case or coat exactly fitting its body, open at the two ends, by one of which it feeds and by the other discharges its excrement, having on one side a nicely-joined seam, and the other--that which is commonly applied to its back--composed of the natural marginal junction of the membranes of the leaf.

Such are the ordinary operations of this insect, which, when it is considered that the case is rather fusiform than cylindrical; that the end through which it eats is circular, and the other curiously three-cornered like a cocked-hat; and that consequently its cloth requires to be very irregularly and artfully cut, to be accommodated to such a figure--it must be admitted, are the result of an instinct of no very simple kind. Complicated, however, as these manœuvres seem, our ingenious workman is not confined to them. By way of putting its resources to the test, Reaumur cut off the serrated edge from the nearly-finished coat of one of them, and exposed the little occupant to the day. He expected that it would have quitted its mutilated garment and commenced another; and so it certainly would, had it been guided by an invariable instinct. But he calculated erroneously. Like one of its brother tailors of the biped race, it knew how "to cut its coat according to its cloth," and immediately setting about repairing the injury sewed up the rent. Nor was this all. The scissors having cut off one of the projections intended to enter into the construction of the triangular end of its case, it entirely changed the original plan, and made that end the head which had been first designed for the tail.

On another occasion Reaumur observed one of these larvæ to cut out its coat from the very centre of a leaf, where it is obvious a series of operations wholly different must be adopted, the two membranes composing it necessarily requiring to be cut and sewed on _two_ sides instead of on one only. But what was most striking in this new procedure was the alteration which the caterpillar made in the period of sewing up its garment. When these larvæ cut out their case from the edge of a leaf, they seem aware that, if they were to detach it entirely from the inner side before the process of sewing, lining, &c., is completed, having no support on the exterior edge, it would be liable to fall down; at the same time they could not sew together the membranes composing it at the _inner_ side, without cutting them in part from the leaf. While, therefore, they divide the major part of their inner side from the leaf, they artfully leave them attached to it by one of the large nerves at each end: and these supports they do not cut asunder until the intermediate space has been sewed up, and they are ready to step, with their house on their back, upon the _terra firma_ of the disk of the leaf. In this instance, therefore, the larvæ do not wholly separate their case from the leaf, until it is sewed. But when the same larvæ cut out their materials from the middle of the leaf, where, though completely cut round, they are retained in their situation secure from all danger of falling by the serratures of the incisions made by the jaws of the larvæ, these little tailors vary their mode, and _entirely_ detach the pieces from the surrounding leaf, before they proceed to set a stitch into them[770].

In the preceding instances the variation of instinct takes place in the same individual, but Bonnet mentions a very curious fact in which it occurs in different generations of the same species. There are annually, he informs us, two generations of the Angoumois moth, an insect which has been before mentioned[771], as destructive to wheat: the first appear in May and June, and lay their eggs upon the ears of wheat in the fields; the second appear at the end of the summer or in autumn, and these lay their eggs upon wheat in the granaries. These last pass the winter in the state of larvæ, from which proceeds the first generation of moths. But what is extremely singular as a variation of instinct, those moths which are disclosed in _May_ and _June_ in the granaries, quit them with a rapid flight at sun-set, and betake themselves to the yet unreaped fields, where they lay their eggs; while the moths which are disclosed in the granaries after harvest, stay there, and never attempt to go out, but lay their eggs upon the stored wheat[772].--This is as extraordinary and inexplicable as if a litter of rabbits produced in spring were impelled by instinct to eat vegetables, while another produced in autumn should be as irresistibly directed to choose flesh.

It is, however, into the history of the hive-bee that we must look for the most striking examples of variation of instinct; and here, as in every thing relating to this insect, the work of the elder Huber is an unfailing source of the most novel and interesting facts.

It is the ordinary instinct of bees to lay the foundation of their combs at the top of the hive, building them perpendicularly _downwards_; and they pursue this plan so constantly, that you might examine a thousand (probably ten thousand) hives, without finding any material deviation from it. Yet Huber in the course of his experiments forced them to build their combs perpendicularly upward[773]; and, what seems even more remarkable, in an horizontal direction[774].

The combs of bees are always at an uniform distance from each other, namely about one third of an inch, which is just wide enough to allow them to pass easily and have access to the young brood. On the approach of winter, when their honey-cells are not sufficient in number to contain all the stock, they _elongate_ them considerably, and thus increase their capacity. By this extension the intervals between the combs are unavoidably contracted; but in winter well-stored magazines are essential, while from their state of comparative inactivity spacious communications are less necessary. On the return of spring, however, when the cells are wanted for the reception of eggs, the bees contract the elongated cells to their former dimensions, and thus re-establish the just distances between the combs which the care of their brood requires[775]. But this is not all. Not only do they elongate the cells of the old combs when there is an extraordinary harvest of honey, but they actually give to the new cells which they construct on this emergency a much greater _diameter_ as well as a greater depth[776].

The queen-bee in ordinary circumstances places each egg in the centre of the pyramidal bottom of the cell, where it remains fixed by its natural gluten: but in an experiment of Huber, one whose fecundation had been retarded, had the first segments of her abdomen so swelled that she was unable to reach the bottom of the cells. She therefore attached her eggs (which were those of males) to their lower side, two lines from the mouth. As the larvæ always pass that state in the place where they are deposited, those hatched from the eggs in question remained in the situation assigned them. But the working-bees, as if aware that in these circumstances the cells would be too short to contain the larvæ when fully grown, _added to their length_, even before the eggs were hatched[777].

Bees close up the cells of the grubs, previously to their transformation, with a cover or lid of wax: and in hanging its abode with a silken tapestry before it assumes the pupa state, the grub requires that the cell should not be too short for its movements. Bonnet having placed a swarm in a very flat glass hive, the bees constructed one of the combs parallel to one of the principal sides, where it was so straight that they could not give to the cells their ordinary depth. The queen, however, laid eggs in them, and the workers daily nourished the grubs, and closed the cells at the period of transformation. A few days afterwards he was surprised to perceive in the lids, holes more or less large, out of which the grubs partly projected, the cells having been too short to admit of their usual movements. He was curious to know how the bees would proceed. He expected that they would pull all the grubs out of the cells, as they commonly do when great disorders in the combs take place. But he did not sufficiently give credit to the resources of their instinct. They did not displace a single grub--they left them in their cells: but as they saw that these cells were not deep enough, they closed them afresh with lids much more convex them ordinary, so as to give to them a sufficient depth; and from that time no more holes were made in the lids.

The working bees, in closing up the cells containing larvæ, invariably give a convex lid to the large cells of drones, and one nearly flat to the smaller cells of workers: but in an experiment instituted by Huber to ascertain the influence of the size of the cells on that of the included larvæ, he transferred the larvæ of workers to the cells of drones. What was the result? Did the bees still continue blindly to exercise their ordinary instinct? On the contrary, they now placed a nearly _flat_ lid upon these large cells, as if well aware of their being occupied by a different race of inhabitants[778].

On some occasions bees, in consequence of Huber's arrangements in the interior of their habitations, have begun to build a comb nearer to the adjoining one than the usual interval; but they soon appeared to perceive their error, and corrected it by giving to the comb a gradual curvature, so as to resume the ordinary distance[779].

In another instance, in which various irregularities had taken place in the form of the combs, the bees, in prolonging one of them, had, contrary to their usual custom, begun two separate and distant continuations, which in approaching instead of joining would have interfered with each other, had not the bees, apparently foreseeing the difficulty, gradually bent their edges so as to make them join with such exactness that they could afterwards continue them conjointly[780].

In constructing their combs, bees, as you have been before told, in my letter on the habitations of insects, form the first range of cells--that by which the comb is attached to the top of the hive--of a different shape from the rest. Each cell instead of being hexagonal is pentagonal, having the fifth broadest side fixed to the top of the hive, whence the comb is much more securely cemented to that part, than if the first range of cells had been of the ordinary construction. For some time after their fabrication, the combs remain in this state; but at a certain period the bees attack the first range of cells as if in fury, gnaw away the sides without touching the lozenge-shaped bottoms; and having mixed the wax with propolis, they form a cement well known to the ancients under the names of _Mitys_, _Commosis_ and _Pissoceros_, which they substitute in the place of the removed sides of the cells, forming of it thick and massive walls and heavy and shapeless pillars, which they introduce between the comb and the top of the hive so as to agglutinate them firmly together. Huber, who first in modern times witnessed this remarkable modification of the architecture of bees, observed, that not only are they careful not to touch the bottoms of the cells, but that they do not remove at once the cells on both sides of the comb, which in that case might fall down; but they work alternately, first on one side and then on the other, replacing the demolished cells as they proceed, with mitys, which firmly fixes the comb to its support.

The object of this substitution of mitys for wax seems clear. While the combs are new and only partially filled with honey, the first range of cells, originally established as the base and the guide for the pyramidal bottoms of the subsequent ones, serves as a sufficient support for them. But when they contain a store of several pounds, the bees seem to foresee the danger of such a weight proving too heavy for the thin waxen walls by which the combs are suspended, and providently hasten to substitute for them thicker walls, and pillars of a more compact and viscid material.

But their foresight does not stop here. When they have sufficient wax, they make their combs of such a breadth as to extend to the sides of the hive, to which they cement them by constructions approaching more or less to the shape of cells. But when a scarcity of wax happens before they have been able to give to their combs the requisite diameter, a large vacant space is left between the edges of these combs, which are only fixed by their upper part, and the sides of the hive; and they might be pulled down by the weight of the honey, did not the bees ensure their stability by introducing large irregular masses of wax between their edges and the sides of the hive.--A striking instance of this art of securing their magazines occurred to Huber. A comb, not having been originally well fastened to the top of his glass hive, fell down during the winter amongst the other combs, preserving, however, its parallelism with them. The bees could not fill up the space between its upper edge and the top of the hive, because they never construct combs of old wax, and they had not then an opportunity of procuring new: at a more favourable season they would not have hesitated to build a new comb upon the old one; but it being inexpedient at that period to expend their provision of honey in the elaboration of wax, they provided for the stability of the fallen comb by another process. They furnished themselves with wax from the other combs, by gnawing away the rims of the cells more elongated than the rest, and then betook themselves in crowds, some upon the edges of the fallen comb, others between its sides and those of the adjoining combs; and there securely fixed it, by constructing several _ties_ of different shapes between it and the glass of the hive; some were pillars, others buttresses, and others beams artfully disposed and adapted to the localities of the surfaces joined. Nor did they content themselves with repairing the accidents which their masonry had experienced; they provided against those which might happen, and appeared to profit by the warning given by the fall of one of the combs to consolidate the others and prevent a second accident of the same nature. These last had not been displaced, and appeared solidly attached by their base; whence Huber was not a little surprised to see the bees strengthen their principal points of connexion by making them much thicker than before with old wax, and forming numerous ties and braces to unite them more closely to each other and to the walls of their habitation.--What was still more extraordinary, all this happened in the middle of January, at a period when the bees ordinarily cluster at the top of the hive, and do not engage in labours of this kind[781].

You will admit, I think, that these proofs of the resources of the architectural instinct of bees are truly admirable. If, in the case of the substitution of mitys for the first range of waxen cells, this procedure _invariably_ took place in _every_ bee-hive at a _fixed_ period--when, for example, the combs are two-thirds filled with honey--it would be less surprising: but there is nothing of this invariable character about it. It does not, as Huber expressly informs us[782], occur at any marked and regular period, but appears to depend on several circumstances not always combined. Sometimes the bees content themselves with bordering the sides of the upper cells with propolis alone, without altering their form or giving them greater thickness. And it is not less remarkable that, from the instances last cited, it appears that they are not confined to one kind of cement for strengthening and supporting their combs, but avail themselves of propolis, wax, or a mixture of both, as circumstances direct.

Not to weary you with examples of the modifications of instinct we are considering, I shall introduce but three more:--the first, of the mode in which bees extend the dimensions of an old comb; the second, of that which they adopt in constructing the male cells and connecting them with the smaller cells of workers; and the last, of the plan pursued by them when it becomes necessary to bend their combs.

You must have observed that a comb newly made becomes gradually thinner at its edges, the cells there, on each side, progressively decreasing in length: but in time these marginal cells, as they are wanted for the purposes of the hive, are elongated to the depth of the rest. Now suppose bees, from an augmentation of the size of their hive, to have occasion to extend their combs either in length or breadth, the process which they adopt is this: They gnaw away the tops of the marginal cells until the combs have resumed their original lenticular form, and then construct upon their edges the pyramidal lozenge-shaped bottoms of cells, upon which the hexagonal sides are subsequently raised, as in their operation of cell-building. This course of proceeding is invariable: they never extend a comb in any direction whatever, without having first made its edges thinner, diminishing its thickness in a portion sufficiently large to leave no angular projection.--Huber observes, and with reason, in relating this surprising law which obliges bees partially to demolish the cells situated upon the edges of the combs, that it deserves a more close examination than he found himself competent to give it: for, if we may to a certain point form a conception of the instinct which leads these animals to employ their art of building cells, yet how can we conceive of that which in particular circumstances forces them to act in an opposite direction, and determines them to _demolish_ what they have so laboriously constructed[783]?

Drones, or male bees, are more bulky than the workers; and you have been told, in speaking of the habitations of insects, that the cells which bees construct for rearing the larvæ of the former, are larger than those destined for the education of the larvæ of the latter. The diameter of the cells of drones is always 3-1/3 lines (or twelfths of an inch); that of those of workers 2-2/5 lines: and these dimensions are so constant in their ordinary cells, that some authors have thought they might be adopted as an universal and invariable scale of measure, which would have the great recommendation of being every where at hand, and at all events would be preferable to our _barley-corns_. Several ranges of male cells, sometimes from thirty to forty, are usually found in each comb, generally situated about the middle. Now as these cells are not isolated, but form a part of the entire comb, corresponding on its two faces--by what art is it that the bees unite hexagonal cells of a small, with others of a larger diameter, without leaving any void spaces, and without destroying the uniformity and regularity of the comb? This problem would puzzle an ordinary artist, but is easily solved by the resources of the instinct of our little workmen.

When they are desirous of constructing the cells of males below those of workers, they form several ranges of intermediate or transition cells, of which the diameter augments progressively, until they have reached that range where the male cells commence; and in the same manner, when they wish to revert to the modelling of the cells of workers, they pass by a gradually decreasing gradation to the ordinary diameter of the cells of this class.--We commonly meet with three or four ranges of intermediate cells before coming to those of males; the first ranges of which participate in some measure in the irregularity of the former.

But it is upon the construction of the _bottoms_ of the intermediate ranges of cells that this variation of their architecture chiefly hinges. The bottoms of the regular cells of bees are, as you are aware, composed of _three_ equal-sized rhomboidal pieces; and the base of a cell on one side of the comb is composed of portions of the bases of _three_ cells on the other; but the bottoms of the intermediate cells in question (though their orifices are perfectly hexagonal) are composed of _four_ pieces, of which two are hexagonal and two rhomboidal; and each, instead of corresponding with three cells on the opposite side, corresponds with _four_. The size and the shape of the four pieces composing the bottom, vary; and these intermediate cells, a little larger than the third part of the three opposite cells, comprise in their contour a portion of the bottom of the fourth cell. Just below the last range of cells with regular pyramidal bottoms, are found cells with bottoms of four pieces, of which three are very large, and one very small, and this last is a rhomb. The two rhombs of the transition cells are separated by a considerable interval; but the two hexagonal pieces are adjacent and perfectly alike. A cell lower, we perceive that the two rhombs of the bottom are not so unequal: the contour of the cell has included a greater portion of the opposite fourth cell. Lastly, we find cells in pretty considerable number, of which the bottom is composed of four pieces perfectly regular--namely, two elongated hexagons and two equal rhombs, but smaller than those of the pyramidal bottoms. In proportion as we remove our view from the cells with regular tetrahedral bottoms, whether in descending or from right to left, we see that the subsequent cells resume their ordinary form; that is to say, that one of their rhombs is gradually lessened until it finally disappears entirely; and the pyramidal form re-exhibits itself, but on a larger scale than in the cells at the top of the comb. This regularity is maintained in a great number of ranges, namely, those consisting of male cells; afterwards the cells diminish in size, and we again remark the tetrahedral bottoms just described, until the cells have once more resumed the proper diameter of those of workers.

It is, then, by encroaching in a small degree upon the cells of the other face of the comb, that bees at length succeed in giving greater dimensions to their cells; and the graduation of the transition cells being reciprocal on the two faces of the comb, it follows that on both sides each hexagonal contour corresponds with four cells.--When the bees have arrived at any degree of this mode of operating, they can stop there and continue to employ it in several consecutive ranges of cells: but it is to the intermediate degree that they appear to confine themselves for the longest period, and we then find a great number of cells of which the bottoms of four pieces are perfectly regular. They might, then, construct the whole comb on this plan, if their object were not to revert to the pyramidal form with which they set out.--In building the male cells, the bees begin their foundation with a block or mass of wax thicker and higher than that employed for the cells of workers, without which it would be impracticable for them to preserve the same order and symmetry in working on a larger scale.

Irregularities (to use the language of Huber, from whom the above details are abstracted,) have often been observed in the cells of bees. Reaumur, Bonnet and other naturalists cite them as so many examples of imperfections. What would have been their astonishment if they had been aware that part of these anomalies are _calculated_; that there exists as it were a moveable harmony in the mechanism by which the cells are composed! If, in consequence of the imperfection of their organs or of their instruments, bees occasionally constructed some of their cells unequal, or of parts badly put together, it would still manifest some talent to be able to repair these defects, and to compensate one irregularity by another: but it is far more astonishing that they know how to quit their ordinary routine when circumstances require that they should build male cells; that they should be instructed to vary the dimensions and the shape of each piece so as to return to a regular order; and that, after having constructed thirty or forty ranges of male cells, they again leave the regular order on which these were formed, and arrive by successive diminutions at the point from which they set out. How should these insects be able to extricate themselves from such a difficulty--from such a complicated structure? how pass from the little to the great, from a regular plan to an irregular one, and again resume the former? These are questions which no known system can explain[784].

Here again, as observed in a former instance, the wonder would be less, if _every_ comb contained a _certain_ number of transition and of male cells, constantly situated in _one_ and the _same_ part of it: but this is far from being the case. The event which alone, at whatever period it may happen, seems to determine the bees to construct male cells, is the oviposition of the queen. So long as she continues to lay the eggs of workers not a male cell is founded; but as soon as she is about to lay male eggs, the workers seem aware of it, and you then see them form their cells irregularly, impart to them by degrees a greater diameter, and at length prepare suitable ranges of cradles for all the male race[785].--You must perceive how absurd it would be to refer this astonishing variation of instinct to any mere change in the _sensations_ of the bees; and to what far-fetched and gratuitous suppositions we must be reduced, if we adopt any such explanation. We can but refer it to an instinct of which we know nothing; and so referring it, can we help exclaiming with Huber, "Such is the grandeur of the views and of the means of ordaining wisdom, that it is not by a minute exactness that she marches to her end, but proceeds from irregularity to irregularity, compensating one by another: the admeasurements are made on high, the apparent errors appreciated by a divine geometry; and order often results from partial diversity. This is not the first instance which science has presented to us of preordained irregularities which astonish our ignorance, and are the admiration of the most enlightened minds: So true it is, that the more we investigate the general as well as particular laws of this vast system, the more perfection does it present[786]."

It is observed by M. P. Huber, in his appendix to the account of his father's discoveries relative to the architecture of bees, that in general the form of the prisms or tubes of the cells is more essential than that of their bottoms, since the tetrahedral-bottomed transition cells, and even those cells which being built immediately upon wood or glass, were entirely without bottoms, still preserved their usual shape of hexagonal prisms. But a remarkable experiment of the elder Huber shows that bees can alter even the form of their cells when circumstances require it, and that in a way which one would not have expected.

Having placed in front of a comb which the bees were constructing, a slip of glass, they seemed immediately aware that it would be very difficult to attach it to so slippery a surface: and instead of continuing the comb in a straight line, they _bent it at a right angle_, so as to extend beyond the slip of glass, and ultimately fixed it to an adjoining part of the wood-work of the hive which the glass did not cover. This deviation, if the comb had been a mere simple and uniform mass of wax, would have evinced no small ingenuity; but you will bear in mind that a comb consists on each side, or face, of cells having between them bottoms in common: and if you take a comb, and having softened the wax by heat, endeavour to bend it in any part at a right angle, you will then comprehend the difficulties which our little architects had to encounter. The resources of their instinct, however, were adequate to the emergency. They made the cells on the _convex_ side of the bent part of the comb much _larger_, and those on the _concave_ side much _smaller_ than usual; the former having three or four times the diameter of the latter. But this was not all. As the bottoms of the small and large cells were as usual common to both, the cells were not regular prisms, but the small ones considerably wider at the bottom than at the top, and conversely in the large ones!--What conception can we form of so wonderful a flexibility of instinct? How, as Huber asks, can we comprehend the mode in which such a crowd of labourers, occupied at the same time on the edge of the comb, could agree to give to it the same curvature from one extremity to the other; or how they could arrange together to construct on one face cells so small, while on the other they imparted to them such enlarged dimensions?--And how can we feel adequate astonishment that they should have the art of making cells of such different sizes correspond[787]?

* * * * *

After this long but I flatter myself not wholly uninteresting enumeration, you will scarcely hesitate to admit that insects, and of these the bee pre-eminently, are endowed with a much more exquisite and flexible instinct than the larger animals. But you may be here led to ask, Can all this be referred to instinct? Is not this pliability to circumstances--this surprising adaptation of means for accomplishing an end--rather the result of _reason_?

You will not doubt my allowing the appositeness of this question, when I frankly tell you, that so strikingly do many of the preceding facts seem at first view the effect of reason, that in my original sketch of the letter you are now reading, I had arranged them as instances of this faculty. But mature consideration has convinced me (though I confess the subject has great difficulties) that this view was fallacious; and that though some circumstances connected with these facts may, as I shall hereafter show, be referable to reason, the facts themselves can only be consistently explained by regarding them as I have here done, as examples of variations of particular instincts:--and this on two accounts.