All insects, however, do not undergo this degree of torpidity. In fact, there are some, though but few, which cannot, at least in our climate, strictly be said to hybernate, understanding by that term passing the winterin one selected situation in a greater or less degree of torpor, without food. Not to mentionCheimatobia brumata, and some other moths, which are disclosed from the pupæ in the middle of winter, and can therefore be scarcely regarded as exceptions to the rule, some insects are torpid only in very severe weather, and on fine mild days in winter come out to eat. This is the case with the larva ofEuprepia fuliginosa[732]; and Lyonet asserts that there are many other caterpillars which eat and grow even in the midst of slight frost[733]. Amongst perfect insects, troops ofTrichocera hiemalis, the gnat whose choral dances have been before described[734], may be constantly seen gamboling in the air in the depth of winter when it is mild and calm, accompanied by the littlePsychoda, so common in windows, severalMuscidæ, spiders, and occasionally someAphodiiandStaphylinidæ: and the societies of ants, as well as their attendant Aphides, are in motion and take more or less food during the whole of that season when the cold is not intense. The younger Huber informs us that ants become torpid only at 2° Reaum. below freezing (27° Fahrenheit), and apparently endeavour to preserve themselves from the cold, when its approach is gradual, by clustering together. When the temperature is above this point they follow their ordinary habits (he has seen them even walk upon the snow), and can then obtain the little food which they require in winter from their cows the Aphides, which, by an admirable provision, become lethargic at precisely the same degree of cold as the ants, and awake at the same period with them[735].
Lastly, there are some few insects which do not seem ever to be torpid, asPodura nivalis, L., and the singular apterous insect recently described by Dalman,Chionea araneoïdes[736], both of which run with agility on the snow itself; and the common hive-bee; though with regard to the precise state in which this last passes the winter, this part of its economy has not been made the subject of such accurate investigation as is desirable.
Many authors have conceived that it is the most natural state of bees in winter to be perfectly torpid at a certain degree of cold, and that their partial reviviscency, and consequent need of food in our climate, are owing to its variableness and often comparative mildness in winter; whence they have advised placing bees during this season in an ice-house, or on the north side of a wall, where the degree of cold being more uniform, and thus their torpidity undisturbed, they imagine no food would be required. So far, however, do these suppositions and conclusions seem from being warranted, that Huber expressly affirms that, instead of being torpid in winter, the heat in a well-peopled hive continues +24° or 25° of Reaumur (86° Fahrenheit), when it is several degrees below zero in the open air; that they then cluster together and keep themselvesin motionin orderto preserve their heat[737]; and that in the depth of winter they do not cease to ventilate the hive by the singular process of agitating their wings before described[738]. He asserts also that, like Reaumur, he has in winter found in the combs brood of all ages; which, too, the observant Bonnet says he has witnessed[739]; and which is confirmed by Swammerdam, who expressly states that bees tend and feed their young even in the midst of winter[740]. To all these weighty authorities may be added that of John Hunter, who, as before noticed, found a hive to grow lighter in a cold than in a warm week of winter; and that a hive from November 10th to February 9th lost more than four pounds in weight[741]; whence the conclusion seems inevitable, that bees do eat in winter.
On the other hand, Reaumur adopts (or rather, perhaps, has in great measure given birth to) the more commonly received notion, that bees in a certain degree of cold are torpid and consume no food. These are his words:—"It has been established with a wisdom which we cannot but admire,—with that wisdom with which every thing in nature has been made and ordained,—that during the greater part of the time in which the country furnishes nothing to bees, they have no longer need to eat. The cold which arrests the vegetation of plants, which deprives our fields and meadows of their flowers, throws the bees into a state in which nourishment ceases to be necessary to them: it keeps them in a sort of torpidity (engourdissement), in which no transpiration from them takes place; or, at least, duringwhich the quantity of that which transpires is so inconsiderable, that it cannot be restored by aliment without their lives being endangered. In winter, while it freezes, one may observe without fear the interior of hives that are not of glass; for we may lay them on their sides, and even turn them bottom upwards, without putting any bee into motion. We see the bees crowded and closely pressed one against the other: little space then suffices for them[742]." In another place, speaking of the custom in some countries of putting bee-hives during winter into out-houses and cellars, he says that in such situations the air, though more temperate than out of doors during the greater part of winter, "is yet sufficiently cold to keep the bees in that species of torpidity which does away their need of eating[743]." And lastly, he expressly says that the milder the weather, the more risk there is of the bees consuming their honey before the spring, and dying of hunger; and confirms his assertion by an account of a striking experiment, in which a hive that he transferred during winter into his study, where the temperature was usually in the day 10° or 12° R. above freezing (59° F.), though provided with a plentiful supply of honey, that if they had been in a garden would have served them past the end of April, had consumed nearly their whole stock before the end of February[744].
Now, how are we to reconcile this contradiction?—for, if Huber be correct in asserting that in frosty weather bees agitate themselves to keep off the cold, and ventilate their hive;—if, as both he and Swammerdam state, they feed their young brood in the depth of winter—it seems impossible to admit that they ever can be inthe torpid condition which Reaumur supposes, in which food, so far from being necessary, is injurious to them. In fact, Reaumur himself in another place informs us, that bees are so infinitely more sensible of cold than the generality of insects, that they perish when in numbers so small as to be unable to generate sufficient animal heat to counteract the external cold, even at 11° R. above freezing[745](57° F.); which corresponds with what Huber has observed (as quoted above) of the high temperature of well-peopled hives, even in very severe weather. We are forced, then, to conclude that this usually most accurate of observers has in the present instance been led into error, chiefly, it is probable, from the clustering of bees in the hives in cold weather; but which, instead of being, as he conceived, an indication of torpidity, would seem to be intended, as Huber asserts, as a preservative against the benumbing effects of cold.
Bees, then, do not appear to pass the winter in a state of torpidity in our climates, and probably not in any others. Populous swarms inhabiting hives formed of the hollow trunks of trees, used in many northern regions, or of other materials that are bad conductors of heat, seem able to generate and keep up a temperature sufficient to counteract the intensest cold to which they are ordinarily exposed. At the same time, however, I think we may infer, that though bees are not strictly torpid at that lowest degree of heat which they can sustain, yet that when exposed tothatdegree they consume considerably less food than at a higher temperature; and consequently that the plan of placing hives in a north aspectin sunny and mild winters may be adopted by the apiarist with advantage. John Hunter's experiment, indeed, cited above, in which he found that a hive grew lighter in a cold than in a warm week, seems opposed to this conclusion; but an insulated observation of this kind, which we do not know to have been instituted with a due regard to all the circumstances that required attention, must not be allowed to set aside the striking facts of a contrary description recorded by Reaumur and corroborated by the almost universal sentiment of writers on bees.—After all, however, on this point, as well as on many others connected with the winter economy of these endlessly-wonderful insects, there is evidently much yet to be observed, and many doubts which can be satisfactorily dispelled only by new experiments.
The degree of cold which most insects in their different states, while torpid, are able to endure with impunity, is very various; and the habits of the different species, as to the situation which they select to pass the winter, are regulated by their greater or less sensibility in this respect. Many insects, though able to sustain a degree of cold sufficient to induce torpidity, would be destroyed by the freezing temperature, to avoid which they penetrate into the earth or hide themselves under non-conducting substances; and there can be little doubt that it is with this view that so many species while pupæ are thus secured from cold by cocoons of silk or other materials. Yet a very great proportion of insects in all their states are necessarily subjected to an extreme degree of cold. Many eggs and pupæ are exposed to the air without any covering; and many, both larvæ and perfectinsects, are sheltered too slightly to be secure from the frost. This they are either able to resist, remaining unfrozen though exposed to the severest cold, or, which is still more surprising, are uninjured by its intensest action, recovering their vitality even after having been frozen into lumps of ice.
The eggs of insects are filled with a fluid matter, included in a skin infinitely thinner than that of hens' eggs, which John Hunter found to freeze at about 15° of Fahrenheit. Yet on exposing several of the former, including those of the silk-worm, for five hours to a freezing mixture which made Fahrenheit's thermometer fall to 38° below zero, Spallanzani found that they were not frozen, nor their fertility in the slightest degree impaired. Others were exposed even to 56° below zero, without being injured[746].
A less degree of cold suffices to freeze many pupæ and larvæ, in both which states the consistency of the animal is almost as fluid as in that of the egg. Their vitality enables them to resist it to a certain extent, and it must be considerably below the freezing point to affect them. The winter of 1813-14 was one of the severest we have had for many years, Fahrenheit's thermometer having been more than once as low as 8° when the ground was wholly free from snow; yet almost the first objects which I observed in my garden, in the commencement of spring, were numbers of the caterpillars of the gooseberry-moth (Abraxas grossulariata), which, though they had passed the winter with no other shelter than the slightly projecting rim of some large garden-pots, were alive and quite uninjured; and these and many other larvæ neverin my recollection were so numerous and destructive as in that spring: whence, as well as from the corresponding fact recorded with surprise by Boerhaave, that insects abounded as much after the intense winter of 1709, during which Fahrenheit's thermometer fell to 0, as after the mildest season, we may see the fallacy of the popular notion, that hard winters are destructive to insects[747].
But though many larvæ and pupæ are able to resist a great degree of cold, when it increases to a certain extent they yield to its intensity and become solid masses of ice. In this state we should think it impossible that they should ever revive. That an animal whose juices, muscles, and whole body have been subjected to a process which splits bombshells, and converted into an icy mass that may be snapped asunder like a piece of glass, should ever recover its vital powers, seems at first view little less than a miracle; and, if the reviviscency of the wheel animal (Vorticella rotatoria), and of snails, &c. after years of desiccation, had not made us familiar with similar prodigies, might have been pronounced impossible; and it is probable that many insects when thus frozen never do revive. Of the fact, however, as to several species, there is no doubt. It was first noticed by Lister, who relates that he had found caterpillars so frozen, that when dropped into a glass they chinked like stones, which nevertheless revived[748]. Reaumur, indeed, repeated this experiment without success; and found that when the larvæ ofLasiocampa Pityocampawere frozen into ice by a cold of 15° R. below zero (2° F. belowzero), they could not be made to revive[749]. But other trials have fully confirmed Lister's observations. My friend Mr. Stickney, before mentioned as the author of a valuableEssay on the Grub(larva ofTipula oleracea)—to ascertain the effect of cold in destroying this insect, exposed some of them to a severe frost, which congealed them into perfect masses of ice. When broken, their whole interior was found to be frozen. Yet several of these resumed their active powers. Bonnet had precisely the same result with the pupæ ofPontia Brassicæ, which, by exposing to a frost of 14° R. below zero (0° F.), became lumps of ice, and yet produced butterflies[750]. Indeed, the circumstance that animals of a much more complex organization than insects, namely, serpents and fishes, have been known to revive after being frozen, is sufficient to dispel any doubts on this head. John Hunter, though himself unsuccessful in his attempts to reanimate carp and other animals that had been frozen, confesses that the fact itself is so well authenticated as to admit of no question[751].
On what principle a faculty so extraordinary and so contrary to our common conceptions of the nature of animal life depends, I shall not attempt to explain. Nor can any thing very satisfactory be advanced with regard to the source of the power which many insects in some states, and almost all in the egg state, have of resisting intense degrees of cold without becoming frozen. It is clear that the usual explanation of the same faculty to a less degree in the warm-blooded animals—the constant production of animal heat from the caloric set free inthe decomposition of the respired air—will not avail us here. For, first, the hive-bee, which has the capacity of evolving animal heat in a much greater degree than any other insect, is killed by a cold considerably less than that of freezing. Secondly, many large larvæ, as Reaumur has observed, are destroyed by a less degree of cold than smaller species whose respiratory organization is necessarily on a much less extensive scale. And thirdly, the eggs of insects—in which, though they probably are in some degree acted upon by the oxygen of the atmosphere, nothing like respiration takes place—can endure a much greater intensity of cold than either the larvæ or pupæ produced from them.
Nor can we refer the effect in question to the thinness or thickness—the greater or less non-conducting power—of the skin of the animal. Reaumur found that the subterranean pupæ of many moths perished with a cold of 7° or 8° R. below zero (14° F.), while the exposed pupæ ofPontia Brassicæand other species endured 15° or 16° without injury[752]; (a proof, by the way, that the different economy of these insects, as to their choice of a situation in their state of pupæ, is regulated by their power of resisting cold;) but no difference in the substance of the exterior skin is perceptible. And the eggs of insects have usually thinner skins than pupæ, and yet they are unaffected by a degree of cold much superior.
In the present state, then, of our knowledge of animal physiology, we must confess our ignorance of the cause of these phenomena, which seem never to have been sufficiently adverted to by general speculators on the nature of animal heat. We may conjecture, indeed, eitherthat they are owing to some peculiar and varying attraction for caloric inherent in the fluids which compose the animal, and which in the egg state, like spirit of wine, resist our utmost producible artificial cold; or that, as John Hunter seems to infer with respect to a similar faculty in a minor degree in the hen's egg, the whole are to be referred to some unknown power of vitality. The latter seems the most probable supposition; for Spallanzani found that the blood of marmots, which remains fluid when they are exposed to a cold several degrees below zero of Fahrenheit, freezes at a much higher temperature when drawn from the animal[753]; and it is reasonable to conjecture that the same result would follow if the fluids filling the eggs of insects were collected separately, and then exposed to severe cold.
Spring is, of course, the period when insects shake off the four or five months' sleep which has sweetly banished winter from their calendar, quit their dormitories, and again enter the active scenes of life. It is impossible to deny that the increased temperature of this season is the immediate cause of their reappearance; for they leave their retreats much earlier in forward than in backward springs. Thus in the early spring of 1805 (to me a memorable one, since in it I began my entomological career, and had anxiously watched its first approaches in order to study practically the science of which I had gained some theoretical knowledge in the winter,) insects were generally out by the middle of March; and before the 30th, I find, on referring to my entomological journal, that I had taken and investigated (I scarcely needadd, not always with a correct result,) fifty-eight coleopterous species: while in the last untoward spring (1816) I did not observe even a bee abroad until the 20th of April; and the first butterfly that I saw did not appear until the 26th.
There are, however, circumstances connected with this reappearance, which seem to prove that somethingmorethan the mere sensation of warmth is concerned in causing it. I shall not insist upon the remarkable fact which Spallanzani has noticed, that insects reappear in spring at a temperature considerably lower than that at which they retired in autumn; because it may be plausibly enough explained by reference to their increased irritability in spring, the result of so long an abstinence from food, and their consequent augmented sensibility to the stimulus of heat. But if the mere perception of warmth were the sole cause of insects ceasing to hybernate, then we might fairly infer, that species of apparently similar organization, and placed in similar circumstances, would leave their winter quarters at the same time. This, however, is far from being the case. Reaumur observed that the larvæ ofMelitæa Cinxiaquitted their nest a full month sooner than those ofArctia chrysorrhea[754]. The reason is obvious; but cannot be referred to mere sensation. The former live on grass, and on the leaves of plantain, which they can meet with at the beginning of March—the period of their appearance: the latter eat only the leaves of trees which expand a month later. It might, indeed, be still contended, that this fact is susceptible of explanation by supposing that the organization of these two species of larva, though apparently similar,is yet in fact different, that of the one being constituted so as to be acted upon by a less degree of heat than that of the other: and this solution would be satisfactory if the torpidity of these larvæ were uninterrupted up to the very period at which they quit their nest. But facts do not warrant any such supposition. You have seen[755]that the temperature of a mild day even in winter awakens many insects from their torpidity, though without inducing them to leave their hybernacula; and it is therefore highly improbable that the larvæ ofA. chrysorrheashould not often have their torpid state relaxed during the month of March, when we have almost constantly occasional bright days elevating the thermometer to above 50°. Yet as they still do not, like the larvæ ofM. Cinxia, leave their nest, it seems obvious that something more than the sensation of heat is the regulator of the movements of each. Not, however, to detain you here unnecessarily, I shall not enlarge at present on this point, but shall pass on, in concluding this letter, to advert to the causes which have been assigned for the hybernation and torpidity of animals, and to state my own ideas on the subject, which will equally apply to the termination of this condition in spring.
The authors who have treated on these phenomena have generally[756]referred them to the operation of cold upon the animals in which they are witnessed, but actingin a different manner. Some conceive that cold combined with a degree of fatness arising from abundance of food in autumn, produces in them an agreeable sensation of drowsiness, such as we know, from the experience of Sir Joseph Banks and Dr. Solander in Terra del Fuego, as well as from other facts, is felt by man when exposed to a very low temperature; yielding to which, torpidity ensues. Others, admitting that cold is the cause of torpidity, maintain that the sensations which precede it are of a painful nature; and that the retreats in which hybernating animals pass the winter are selected in consequence of their endeavours to escape from the disagreeable influence of cold.
I have before had occasion to remark[757]the inconclusiveness of many of the physiological speculations of very eminent philosophers, arising from their ignorance of Entomology, which observation forcibly applies in the present instance. The reasoners upon torpidity have almost all confined their view to the hybernating quadrupeds, as the marmot, dormouse, &c. and have thus lost sight of the far more extensive series of facts supplied by hybernating insects, which would often at once have set aside their most confidently-asserted hypotheses. If those who adopt the former of the opinions above alluded to, had been aware that numerous insects retire to their hybernacula (as has been before observed) on some of the finest days at the close of autumn, they could never have contended that this movement, in which insects display extraordinary activity, is caused by the agreeabledrowsinessconsequent on severe cold; and the very same fact is equally conclusive against the theory, that it is toescape the pain arising from a low temperature that insects bury themselves in their winter quarters.
In fact, the great source of the confused and unsatisfactory reasoning which has obtained on this subject, is, that no author, as far as my knowledge extends, has kept steadily in view, or indeed has distinctly perceived, the difference between torpidity and hybernation; or, in other words, between thestatein which animals pass the winter, and theirselectionof asituationin which they may become subject to that state.
That the torpidity of insects, as well as of other hybernating animals, is caused by cold, is unquestionable. However early the period at which a beetle, for example, takes up its winter quarters, it does not suffer that cessation of the powers of active life which we understand by torpidity, until a certain degree of cold has been experienced; the degree of its torpidity varies with the variations of temperature; and there can be no doubt that, if it were kept during winter from the influence of cold, it would not become torpid at all—at least this has proved the fact with marmots and dormice thus treated; and the Aphis of the rose (A. Rosæ), which becomes torpid in winter in the open air[758], retains its activity and gives birth to a numerous progeny upon rose trees preserved in greenhouses and warm apartments.
But, can we, in the same way, regard mere cold as the cause of thehybernationof insects? Is it wholly owing to this agent, as most writers seem to think—to feelings either of a pleasurable or painful nature produced by it—thatpreviouslyto becoming torpid they select or fabricate commodious retreats precisely adaptedto the constitution and wants of different species, in which they quietly wait the accession of torpidity and pass the winter? In my opinion, certainly not.
In the first place, if sensations proceeding from cold lead insects to select retreats for hybernating, how comes it that, as above shown, a large proportion of them enter these retreats before any severe cold has been felt, and on days considerably warmer than many that preceded them? If this supposition have any meaning, it must imply that insects are so constituted that, when a certain degree of cold has been felt by them, the sensations which this feeling excites impel them to seek out hybernacula. Now the thermometer in the shade on the 14th of October 1816, when I observed vast numbers thus employed, was at 58°:—this then, on the theory in question, is a temperature sufficiently low to induce the requisite sensations. But it so happens, as I learn from my meteorological journal (which registers the greatest and least daily temperature as indicated by a Six's thermometer), that on the 31st of August 1816 the greatest heat was not more than 52°, or six degrees lower than on the 14th of October: yet it was six weeks later that insects retired for the winter!
But it may be objected, that it is perhaps not so much the precise degree of cold prevailing on the day when insects select their hybernacula, that regulates their movements, as the lower degree which may have obtained for a few nights previously, and which may act upon their delicate organization so as to influence their future proceedings. Facts, however, are again in direct opposition to the explanation; for I find that, for a week previously to the 14th of October 1816, the thermometerwas never lower at night than 48°, while in the first week of August it was twice as low as 46°, and never higher than 50°.[759]
As a last resource, the advocates of the doctrine I am opposing, may urge, that possibly insects may even have their sensations affected by the cold some daysbeforeit comes on, in the same way as we know that spiders and some other animals are influenced by changes of weather previously to their actual occurrence. But once more I refer to my meteorological journal; and I find that the average lowest height of the thermometer, in the week comprising the latter end of October and beginning of November 1816, was 431⁄7°; while in the week comprising the same days of the month of the end of August and beginning of September it was only 445⁄7°—a difference surely too inconsiderable to build a theory upon.
I have entered into this tedious detail, because it is of importance to the spirit of true philosophizing to showwhat little agreement there often is between facts and many of the hypotheses, which authors of the present day are, from their determination to explain every thing, led to promulgate. But in truth there was no absolute need for imposing this fatigue upon your attention; for the single notorious consideration that in this climate, as well as in more southern ones, we not unfrequently have sharp night-frosts in summer, and colder weather at that season than in the latter end of autumn and beginning of winter, and yet that insectsdohybernate at the latter period, but donotat the former, is an ample refutation of the notion that mere cold is the cause of the phenomenon. If, indeed, the hybernacula of insects were simply the underside of any dead leaf, clod, or stone, that chanced to be in the neighbourhood of their abode, it might still be contended, that such situations werealwaysresorted to by them on the occurrence of a certain degree of cold, but that they remained in them only when its continuance had induced torpidity: and it seems to have been in this view that most reasoners on this subject have regarded the hybernation of the larger animals, to which they have exclusively directed their attention. But had they been acquainted (as surely the investigators of such a question ought to have been) with the economy of the class of insects, in which not merely a few species, as among quadrupeds, but ninety-nine hundredths of the whole, in our climates, hybernate, they would have known that their hybernacula are in general totally distinct from their ordinary retreats in casual cold weather; and that many of them even fabricate habitations requiring considerable time and labour, expressly for the purpose of their winter residence—whichlast fact in particular, on their theory, admits of no satisfactory explanation. We may say, and truly, that the sensation of fatigue causes man to lie down and sleep; but we should laugh at any one who contended that this sensation forced him first to make a four-post bedstead to repose upon.
In the second place, if we grant for a moment that it is cold which drives insects to their hybernacula, there are other phenomena attending the state of hybernation which on this supposition are inexplicable. If cold led insects to enter their winter quarters, then they ought to be led by the cessation of cold to quit them. But, as has been before observed, we have often days in winter milder than at the period of hybernating, and in which insects are so roused from their torpidity as to run about nimbly when molested in their retreats; yet though their irritability must have been increased by a two or three months inactivity and abstinence, they do not leave them, but quietly remain until a fresh accession of cold again induces insensibility.
In short, to refer the hybernation of insects to the mere direct influence of cold, is to suppose one of the most important acts of their existence given up to the blind guidance of feelings which in the variable climates of Europe would be leading them into perpetual and fatal errors—which in spring would be inducing them to quit their ordinary occupations, and prepare retreats and habitations for winter to be quitted again as soon as a few fine days had dispelled the frosty feel of a May week; and in a mild winter's day, when the thermometer, as is often the case, rises to 50° or 55°, would lure them to an exposure that must destroy them. It is not,we may rest assured, to such a deceptious guide that the Creator has intrusted the safety of so important a part of his creatures: their destinies are regulated by feelings far less liable to err.
What, you will ask, is this regulator? I answerInstinct—that faculty to which so many other of the equally surprising actions of insects are to be referred; and which alone can adequately account for the phenomena to be explained. Why, indeed, should we think it necessary to go further? We are content to refer to instinct, the retirement of insects into the earth previously to becoming pupæ, and the cocoons which they then fabricate; and why should we not attribute to the same energy, their retreat into appropriate hybernacula, and the construction by many species of habitations expressly destined for their winter residence! The cases are exactly analogous; and the insect knows no more that its hybernaculum is to protect it from too severe a degree of cold during winter, than does the full-fed caterpillar when it enters the earth that it shall emerge a glorious butterfly.
I am, &c.
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. Butwhat, 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 actuallybeingthat animal—a species of metempsychosis through which I have never passed—I shall not attempt to explain what this mysterious energyis. It will not, however, I imagine, be very difficult to show what it isnot; 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 certainplastic nature; or that of Des Cartes, who contended that animals are meremachines. 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 tohear 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 symmetricalstructure: 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 andsome 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 hisZoonomia, 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 veryjust 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, thoughit has never tasted milk, the infant seeks for its mother's breast, is the effect of reason.
Instinct, then, isnotthe 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 theirsensations, 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 generallyevident. 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 ofStapelia 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 daysbeforeswarming?
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 anexquisitenessto 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 itconceals 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 thedeviationsof the instincts of insects and theiraccommodation 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. Ifeverycomb that bees fabricate werealwaysmadepreciselyalike—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 ofGeotrupes vernalisto 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 beingconfined 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 spannopreparatory web.
Bombus[766]Muscorumand some other species of humble-bees cover their nests with a roof of moss. M. P. Huberhaving 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 ofCossus 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, itentirelyquits 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 onlyhalf wayout 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 constantlyreside 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 veryirregularly 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 ontwosides 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 theycould not sew together the membranes composing it at theinnerside, 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 theterra firmaof 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, andentirelydetach 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 extremelysingular as a variation of instinct, those moths which are disclosed inMayandJunein 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 perpendicularlydownwards; 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, theyelongatethem 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 greaterdiameteras 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 thepupa 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 nearlyflatlid uponthese 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 thelozenge-shaped bottoms; and having mixed the wax with propolis, they form a cement well known to the ancients under the names ofMitys,CommosisandPissoceros, 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 ofwax 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 severaltiesof 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 whichmight 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].