Dance of the Ephemeræ.
The Ephemeræ, when they leave the water, rise high into the air, and wing their way perhaps far from the place of their birth. They may often be found wheeling over green fields, or wandering among the forest shades, far from the bubbling stream in whose waters so large a portion of their existence was spent; but morefrequently they are to be found somewhere in the neighbourhood of the stream, enjoying an aërial dance. The feet of the insect are armed with hooks of great minuteness, and by their means the insect attaches itself to a suitable object, sometimes to a wall, sometimes to a twig, or to the trunk of a tree;it does not much matter where. Without at first making the least movement, the insect patiently abides the time when it must withdraw itself from its useless upper garment, and sometimes it has to wait a whole day in this position. The time arrived, the skin splits, and the body of the insect rises gradually out of it; but the difficulty is about the wings. Nevertheless, as we watch the insect, we shall find that it gradually draws them out of their delicate cases, and at length emerges, as perfect in beauty and form as before. The manner in which this is effected is as follows:—although the outer case of the wings is hard and rigid, yet the wings which it covers over are preserved in a soft and moist condition. In proportion, therefore, as the insect disengages itself from the anterior part of the skin, the inner or real wings become contracted, by a number of plaits, into a form nearly cylindrical, which readily admits of their being pulled through the openings lately mentioned; and as soon as the insect is released from its envelope, these plaits unfold, and the wings return to their former shape and dimensions. So exactly does this thin skin, thus cast off, fit all the parts of the insect's body,that it may often be mistaken for the insect itself, when it is found clinging to the place where it has gone through its changes.
Wingless Beetle.
Before we leave the subject of the wings, it must be mentioned that there are some insects which have none. The cut represents a beetle of this class.
If the reader will now take a peep into one of the nurse-boxes in which he may have been rearing butterflies from the pupæ, presuming that several of them have ere this burst from their cases, and are fluttering about anxious for liberty, he will generally detect upon the bottom or sides of the box one or two marks of a somewhat reddish colour; sometimes, indeed, they are very red. These spots are produced by the insect, which, on its emergence from the pupa, generally deposits a drop of fluid from its intestines. Almost all insects perform the same action at this period; but we may well remark with Réaumur, it could scarcely have been supposed, that the excrements of a butterfly should ever have filled the minds of a whole population with terror. Such has, however, been the case, and may, perhaps, yet be indistricts where ignorance and superstition close the minds of the inhabitants against the truths of entomology. "Historians," says Réaumur, "tell us of showers of blood, as having been the cause of terror to nations, and considered as prophetic of fearful events, of the destruction of cities, and revolutions of kingdoms. At the beginning of the month of July, in the year 1608, one of these showers of blood was said to have fallen in the suburbs of Aix, and for some miles around. It turned out that the supposed drops of blood were in reality drops deposited by the butterflies. It is not improbable that other showers of blood recorded by historians, and taking place about the same period of the year, might be accounted for in the same natural and simple manner. Gregory of Tours relates that in the time of Childebert a shower of blood fell in different places in Paris, and particularly in a certain house situated in the territory of Senlis. Another was said to have fallen toward the end of June, in the reign of King Robert. In the year 1533, we are told by another author, a prodigious multitude of butterflies appeared throughout a great portion of Germany, sprinkling plants,leaves, buildings, clothes, and men, with bloody drops, as if it had rained blood."
In the Gentleman's Magazine for the year 1764 we read that "a kind of rain of a red colour, resembling blood, fell in many parts of the Duchy of Cleves, and caused great consternation. Something of the like kind fell also at Rhenen, in the province of Utrecht." A gentleman is reported to have sent a bottle full of it to Dr. Schutte, to know if it contained anything pernicious to health. Dr. Schutte wrote a learned dissertation upon it, and gave it as his opinion that it was caused by the particles which had been raised into the atmosphere by a strong wind, and that it was in no way hurtful to mankind or beasts. Probably butterflies were the real shedders of this blood-like shower, as in the previous cases.[T]
Our next remark about the imago state of insects will, perhaps, create some surprise—Insects in this state, with some apparent exceptions,do not grow larger. When they leave the pupa state, and have all their parts fully developed, they do not subsequently increase in size. We are oftentold by ignorant people that the little house-flies which we watch dancing in our chambers, or scrambling up our windows, are only young flies of the same kind as flesh-flies, and that by-and-by they will grow into a large "Blue-bottle!" This is a sad mistake. Let the reader try. Let a fly be put under a glass, and fed with a little sugar, or honey: in vain will he daily examine it, in the expectation of beholding it increase in size—it will live and die nearly the same little being unaltered to the last. If such persons only knew somewhat of the life of an insect, such an absurd, and, unfortunately, very prevalent mistake would not be committed. We might as reasonably call a trout a young salmon! If we were to examine any number of flies of the house-fly kind, (Musca domestica,) and carefully measure them, or weigh them, we should find them all almost exactly of the same size; which, of course would not be the case if they really grew larger as they grew older.
But there are some insects which, after they leave their pupa, increase within a very short time to a size which could scarcely be believed. In particular, the new-born insects of a tribe of flies which produce the aphis-lion larva before spokenof, are distinguished by this peculiarity. We behold a very little insect emerge from the pupa-case, and in a quarter of an hour we are astonished to find it has grown to a great fly! This sudden increase appears the more marvellous, because during this period the insect takes no nourishment. The wings of this insect, when it is just born, are not more thanone-tenththe size they acquire in that short space of time. The insect is to all appearance firm and plump, and offers a ridiculous contrast to the tiny pupa-case out of which it has emerged. It appears probable that this sudden enlargement is to be accounted for by the insect filling itself with air, and thus causing the various parts so closely packed together, and fitted into one another, in the pupa, to be expanded. The experiment which puts this idea to the test is a very simple one; we need only prick the body of the insect with a fine needle, and we shall hear a slight sound produced by the escape of the air; and in a few seconds the body of the creature shrinks to its former dimensions. It appears, indeed, that the body of the insect is actually larger at this time than at a subsequent period of its life, when it becomesmore flattened and shorter. Another beautiful insect, one of the lace-winged flies, exhibits the same singular phenomenon. Its pupa-case is not larger than a small pea, yet the body of the insect is nearly half-an-inch long, and covers, when its wings and antennæ are expanded, a surface of an inch square. It appears, in fact, almost incredible that it could ever have been contained within so small a compass.
The cases just related may appear to be really exceptions to the rule just laid down, as to the non-increase of insects when once emerged from the pupa; but upon a little consideration it will be found that the exceptions are more apparent than real. The increase in size is not really a process ofgrowth, but is simply owing to the expansion of the body of the insect to its due size, only taking place in a sudden manner by breathing a certain amount of air. The dragon-fly gives us another instance of a similar enlargement soon after leaving the pupa-case.
CHAPTER II.
THE STRUCTURE AND ORGANS OF THE IMAGO.
White Hawthorn Butterfly.
We must now ask the reader's attention to a very important part of the history of the insect—the knowledge of its various parts, and their uses in the insect economy. Men of science would call this the anatomy and physiology of insects; and if there is a desire felt to know and retain the proper terms employed by those versed in this science when they treat of these subjects, it will be well to bear these names in mind. We may, however, convey some notion of the nature of the studies called by these names, by the following illustration. Let us take yonder butterfly as our example, and, arresting it in its zig-zag career over flowers and fields, let us carefully bringit in-doors, and there look closely at its various parts and appendages. There we find two long, delicate, thread-like organs springing from the head; then we come to the head, with its different organs; farther back is a separate portion, distinct from the head, and distinct, also, from the remainder of the body of the insect; at the side of it are the wings; below are the legs; last of all we bring under our notice the remaining division of the insect's body, the abdomen. Now if Anatomy stood at our right hand while we took notice of each part, she would point out all the peculiarities of its structure, and would tell us of how many other parts it was made up, and how all were beautifully and wonderfully put together by the skill of the Great Creator. Further than this, she would, very probably, strongly insist upon our remembering each part by a particular name; and, as we may add, since she is particularly fond of, and learned in, Latin and Greek, we may rest quite assured each name she communicated to us would be in one or other of these classical languages; for example, instead of saying the butterfly was one of the "scale-winged" insects, which would be far too homely for her, she would declare thatit belonged to theLepidoptera, which is the same thing in Greek; and its "head" she would inform us was the "caput," which is the Latin for that word! This done, her strict duties would be exactly fulfilled, and she would summon her sister-science, Physiology, to give us further information about the butterfly. Physiology, who, we may remark, is a far less stern-looking personage than her austere relative, and appears with a countenance which expresses that she has much to tell us which will greatly interest us, would next take up the panting insect. She would tell us to consider attentively the head of the little creature, while we listened to her elegant account of the purposes it was intended to subserve. She would dilate with eloquence upon the exquisite machinery which was compacted into so small a compass as its mouth; and she would render us almost breathless with amazement, as with rising animation she revealed to us the astonishing optical wonders of an insect's eye, telling us, perhaps, that an insect may probably see like the fabled Argus, behind, and before, and on every side, at the same time! Then she would tell us, in order, the nature and uses of each part,and, in a word, give us a minute, but delightful account of everything that is known about the Life of an Insect.
From this it will be manifest that we have hitherto chiefly listened to the voice of Physiology in this little book, although the leading particulars of the Anatomy of the insect in its various stages have also been brought before us. We must now address ourselves for some little time to learn, from the combined sciences of Anatomy and Physiology, the structure and uses of the different organs, and their principal parts, in the insect, in theimagoor perfect state. In order to follow the account we shall have to give the reader, it will be convenient to take some common insect, such as awasp, and fix in the memory the names of the various parts we shall have to distinguish, in thus treating of theimago-insect. A dragon-fly is a good example also. We shall first mention the general arrangement of the insect's structure; and subsequently take up each part separately.
It must first be mentioned, that insects possess nointernalbony skeleton, like that possessed by ourselves and many other animals. If we wereto cut open the dead body of a fly, we should look in vain for anything like the back-bone, or the bones of the legs. But it must not, therefore, be thought that insects have no skeleton at all. Their skeleton is the thick, hard, horny substance which forms their external covering. In the wasp, for instance, it will be easily perceived, on pressing the head or the trunk of the insect between the fingers, that there is a very firm, solid coating, protecting the tender and delicate organs within. It is a very singular fact that the wisdom of the Creator has so ordered this outside coating, that where it is most necessary to be strong, as for example, when an insect has to burrow through the ground, or is in danger of being often crushed, there its thickness is greatest; and again where, as in the case of those insects which live chiefly in the air, this thickening is less necessary, because there is less risk of injury to its body, there the external covering is thinner and softer. So extraordinarily is one insect strengthened in its external coats, that it is scarcely possible to crush it by the hardest squeezing between the thumb and fingers. It has, on this account, been compared to a once famous London character, called "Leather-coatedJack," who used to suffer carriages to be driven over his body without receiving any harm!
In looking at an insect, we perceive that it is naturally divisible into three principal parts: first, there is the head, orcaput; next, the trunk, orthorax; and thirdly, the hinder portion of the body, orabdomen. If we turn to a Latin dictionary, and hunt out the wordinsecta, which is the Latin term for "insect," we shall find that it is derived from a verb which signifies "to be cut in," or "notched." From this we see that the very wordinsecthas arisen from perceiving what we are now alluding to, the natural notching of the body of these creatures into certain portions. We mentioned, however, at page 89, that the insect in thelarvaform had a body which was, in almost every instance, divided intothirteensegments, or parts. It may be asked, Are these all lost in the perfect insect; or are they still to be traced in it? They are still to be traced in it. The head is one, three form the trunk or thorax, and the remaining number constitute the abdomen: but, in order to save disappointment, it must be added, that it is rare to find the full number of segments or distinct parts in theabdomen; we seldom, in fact, find more than seven or eight, the remaining two or one being generally hidden. It is interesting, however, to trace in the perfect insect these indications of its previous larval condition, especially when we remember the strange appearance it underwent while a pupa.
Now the various parts in theheaddivision are, to speak generally, thehead proper, themouth, theeyes, and theantennæ. Entomologists describe a large number of other parts, which would also be mentioned here if this little treatise were intended to give a minute account of the insect's anatomy; and those features which are of most prominence and importance, will be mentioned in addition when we come to speak particularly of these several chief organs.
The middle portion of the insect, orthorax, is divided into three parts—a front, middle, and hinder part; or, in the language of entomology, apro-thorax, ameso-thorax, and ameta-thorax. Attached to the thorax are thewingsand thelegs. The remaining portion, orabdomen, is furnished with organs and appendages, not requiring special mention in this place.
Eyes of a Bee.
Let us consider briefly the organs which are seated in these divisions; and, beginning with the head, let us glean a few particulars upon that most interesting topic—the eyes of insects. We might well fill a volume with this subject alone, for truly it is almost inexhaustible. In the other sections of the animal kingdom, the eyes, though organs of the highest importance, are, nevertheless, simple, and little varied in their number and arrangement. But in insects, whether we consider their number, their structure, their arrangement, or their size, we are lost in amazement at finding these organs assume an importance in the insect's economy, of which we have no parallel elsewhere. Look, for example, at the accompanying representation of the eyes of a bee, and then let us ask whether, in all the world beside, we can find a creature whose two eyes are larger than all the rest of its head put together? What should we think of a quadruped as large as a bull, whose eyes occupied great part of its head, its forehead, and the greater portion of its face? What astonishing powers of sight it would possess!
The first thing we learn about them is, that some insects possess what are calledsimple eyes, andcompound eyes. The accompanying cut represents in part the head of aflea, and is annexed in order to give a specimen of asimpleeye. The little circle represents the position of the simple eye. All the organs connected with the head are supposed to be cut off. The head of the bee on the preceding page furnishes us with an excellent illustration of acompound eye. All perfect insects are provided with compound eyes, and a large number with simple eyes too; but no imago or perfect insect has simple eyes alone. We see, therefore, that the simple eyes are only additional or supplementary organs to the compound eyes, which are the chief organs of sight in these creatures. These simple eyes are minute lenses generally placed upon the crown of the head, or the forehead; in the bee this is their position; and by means of a pocket-glass, they can be readily seen in this insect, by looking at its head from above. They will be found arranged in a triangular form. Sometimes an insect is furnished with as many as sixteenof these simple eyes; the spider is, among others, thus endowed. But more commonly they are only three in number. Sometimes they are not imbedded in the substance of the head, as might be supposed; but are actually placed upon the end of a little stalk, presenting an appearance as singular, as if at the end of a bull's horn the animal were to possess an eye in addition to his two others. Swammerdam and Réaumur performed some singular experiments upon these eyes in the bee. Réaumur varnished the back of the head, where these eyes are situated, in more than twenty bees, so as, of course, entirely to blind these eyes; but leaving the large compound eye untouched. The bees were then set at liberty within a few paces from the hive, but not one of them knew where to find it again! nor, indeed, did they appear to make any search for it. They flew at random to the adjacent plants, but never to a distance; and though they seemed to have no difficulty in flying, they did not attempt to fly up into the air.
Eye on a stalk.
Eye of the Dragon-Fly.
The compound eyes of insects are, perhaps, among the most wonderful works of the Creator's hands.In those gigantic creatures whose fossilized bones are all now remaining to tell us of their history, themastodon, andmegatherium, and in such vast creatures as the elephant and the whale, we behold the great power, skill, and wisdom of God; but here, in a little object which we may cover with a pin's head or with a large grain of sand, is a more wonderful instance of His infinite and amazing power than all these. The eye of a dragon-fly is a good instance of a compound eye: and of all the beautiful, radiant, gem-like objects that can be selected for inspection through the microscope, this is the most exquisite. Professor Müller, the great German physiologist, has with wonderful patience and care dissected the eye of this insect, and has given a most beautiful account of its structure. On examining the eye of this insect, even with a good pocket magnifying glass, such as those commonly sold by opticians for a few shillings, it will be found to present the appearance of a beautiful net-work, or very fine grating, as is shown in the cut. When a greater magnifying power is employed, it will be seen that each space in this net-work is a six-sided orhexagonalfigure.Now each of these little spaces is filled by a beautiful minute lens of the same shape set in it. On making a perpendicular cut into the eye it has been found to consist of various layers: the outer layer is a hard clear membrane composed of a multitude of six-sided facets, each forming a more or less distinct cone-shaped cylinder, which runs towards the centre of the eye, as seen in the cut. Under this is a layer of coloured matter, sometimes of a violet, or green, or even reddish hue, which is pierced with as many holes as there are facets. Beneath this there is a varnish of a black colour, within which is a second layer of coloured matter; and in the space between this last and the first coloured layer the delicate fibres of the nerve of sight, or optic nerve, run. These fibres then converge together at the back of the eye into a single large nerve, which is connected with the insect's brain, and conveys the impression of sight to that organ.
Magnified section of the Eye and its nerve.
Magnified section of part of the Eye.
Perhaps this account may be followed with some difficulty; let us, therefore, take a single facet, and trace it to its termination. Each facet being in fact a distinct eye, we shall be able, in so doing, to get a clear comprehension of the whole organ, which is after all only made up of a large number of these distinct eyes. Separating, then, one facet from the rest, we find this single eye to consist of several portions: 1. the six-sided facet; 2. the cone-shaped cylinder, clear and transparent; 3. a delicate fibre of nerve connected with the bottom of this cone; and, 4. the large nerve itself. The diagram on the next page will make this perfectly intelligible.
But it may be asked, What of the colouring matter? It exists in three places. 1. The first layer surrounds the cones (2), and separates them from one another, and from the nerve below in part. 2. The second layer surrounds the nerve fibres (3). And, 3. the last layer is at the junction of the nerve fibre (3) with the nerve itself (4).
This apparently complicated mechanism well deserves the reader's attention; nor should the subject be quitted until it is clearly understood.We are unable to enter into further particulars upon the structure and functions of this beautiful apparatus; but it must be added, that the following is the manner in which the ray of light becomes perceived by the insect. It first passes through the facet (a), next enters the cone (b), then strikes upon the nerve (c) which conveys the impression, taking the large nerve (d) to the brain. The colouring layers are intended to prevent any rays of light from passing to other parts of the insect's eye, and so confusing the impressions made upon its senses by external objects.
A single facet separated, and magnified.
The number of these facets, or, if we choose to call them so, distinct eyes, varies in different insects. In some there are comparatively few, in others an amazing multitude. The following list of their number is given by Müller, as observed by various entomologists:—
According to the calculations of another author there cannot be fewer than 34,650 in the compound eye of a butterfly. Amazing thought! each of this immense host is considered to be a separate eye, receives separate impressions of light, and has a separate structure and organization, both perfect in their kind.
It is not difficult to remove the compound eye of an insect; and in so doing it will be found that each lens is as clear as crystal. The ingenious Réaumur actually succeeded in removing one and adjusting it to a lens; and he found that he could see through the insect's eye very distinctly, only he says the surrounding objects appeared to be greatly multiplied. There is a common optical toy which is ground into a number of facets which communicates this appearance to objects when seen through it, and thus furnishes us with a good illustration of the endless confusion of images which would have perplexed the insect, had not the various beautiful contrivances of which we have spoken been adjusted to prevent it.
But we must guard against a very natural mistake which might arise upon the subject of the eyes of insects from supposing them in any degree comparable to those of higher animals as regards their motions. When man, or an animal, wishes to look at any object, they do so by causing several muscles to be brought into action which move the eyes round so as to receive the rays of light from the particular point where this object is placed; and so admirably arranged is the mechanism by which these movements are effected, that they are as well provided for all the purposes of sight with two eyes as with twenty. In insects no such apparatus exists; the eyes are quite immovable; they are, in fact, set in the head like a gem in a lady's ring, and are altogether removed from the control of the insect. In order to obviate the annoyance and inconvenience which would result from this arrangement, their eyes are formed on the wonderful principles already mentioned, and, instead of insects being furnished with two eyes, they are provided with many thousands! They are thus enabled to enjoy not only the same extent and range of vision with ourselves, but even a much larger.
Insects are also furnished with a contrivance by which they can see objects at a little distance, and objects at a great distance—it may be at the same time; which is more than can be strictly said of ourselves. In men and animals there is a very exquisite apparatus arranged within the eye, by means of which it can accommodate itself to objects close at hand, or again to others at the greatest distance. We can see at one moment a pin at our feet, and at the next the summit of a hill some thirty or forty miles off. Now the laws of light are such, that, to effect this properly, we must have some apparatus in the eye to arrange its focal capacity, so as to receive and concentrate the lines of light proceeding from such different points as the distance of a few inches, and that of many miles. What this apparatus may be is not as yet very satisfactorily determined. But in insects the same result is obtained by a very curious provision.—Some of their eyes are short-sighted, and some long-sighted.The simple eyes are supposed, by Professor Müller, to be the short-sighted eyes, and the compound eyes the long-sighted ones.
The number ofcompoundeyes in insects doesnot often exceed two, these being made up, it will not be forgotten, by multitudes of single eyes. But in a few, whose habits require that they should be endowed with extraordinary means of vision, there are as many as four. If the reader would betake him to the brook-side, and creep noiselessly along its margin some summer afternoon, until he comes to a quiet glassy pool where the water seems to have forgotten itself and fallen asleep, so still, so silent, and so smooth does it lie, reflecting all the lustre of the deep-blue sky overhead, he will surprise a dancing party of insects busy waltzing at a wonderful rate, now skimming hither, now shooting across the glassy pavement on which they sport, now joining together and wheeling round and round, and again, as the king-fisher comes fluttering down the river as though on some errand of immense importance, breaking up their party and flying into a thousand holes and corners to wait until all is quiet. Let him exercise his activity and patience, and catch one of these giddy insects, which are known to entomologists by the name of theGyrinus Natator, and he will have a good example of an insect provided with four compound eyes, so that it cansee not only before and behind, but upward into the sky, and downward into the clear cool waters on whose surface its happy life is spent. Some insects, like Cyclops of old, are furnished only with one eye; and some, it is said, are quite blind—creatures that never feel the blessed influences of the pleasant sunlight. Like the simple eyes, the compound eyes are sometimes fixed on the end of a little footstalk, so as to give the insect somewhat the appearance of being furnished with a pair of opera glasses, or short telescopes.
In order to ascertain by what means the bee found its way to the hive, whether by seeing it through its compound eyes, or otherwise, Réaumur performed an interesting experiment similar in character to the one before mentioned. He covered with a red varnish, which was quite opaque, the compound eyes of a number of bees taken from the same hive. He then shut them up in a box with several other bees from the same hive which he left untouched. The box was only a few paces distant from the hive from which the bees were taken. He then opened the lid of the box, and those which had not been blinded instantly flew out of it, and entered their habitation. Thosewhose eyes had been varnished appeared not to care to leave the box at all, and seemed very unwilling to make any attempt to fly; some of them, indeed, flew about from one side to another, but did not go far. Réaumur then threw several of them up into the air, and they immediately began to soar higher and higher, until at length they went out of sight altogether! Réaumur compares the poor insect's manœuvres to those of a crow, whose head and eyes mischievous boys have covered with a paper bonnet: the bird flies upward until its strength is exhausted, when it drops again to the earth. Not only did those bees which he threw up into the air thus soar until they were lost to view, but all the most active of those which were left in the box did so likewise, and Réaumur saw them no more. Not one could find its way to the hive. From this experiment, and from the preceding one, it is evident that both the compound and the simple eyes are necessary to enable the insect to see perfectly; for when either was varnished over, the bees could not find their way to their home again. Réaumur imagines that the cause of the wheeling flight of bees, sometimes observed, now in this direction, now in the opposite,may arise from their eyes becoming perhaps in part obscured by the pollen, or yellow powder of the flowers into which they plunge, the bee thereby becoming partly blind-folded. These experiments are so interesting that they deserve repeating, and it might be tried whether the result would be different if only one eye were blinded. Other variations of the experiments will also suggest themselves.
Although not organs of sufficient size to give their colouring the requisite distinctness and amount of surface which would render it very conspicuous in our estimation, the eyes of insects are often exquisitely beautiful, and vie almost with precious stones in lustre. Their most common colour is black, or brown; but the eyes of many flies glow with fiery colours, some banded with green and purple, some variously figured black and red. Some again glitter like burnished gold shaded with the softest green; and some blaze with a play of colours, like the diamond set in jet. The eye of the dragon-fly, in particular, is a lustrous crystalline object of extreme beauty.
Peacock Butterfly.
We have dwelt as long as our limits will permit on this wonderful apparatus of vision in insects:let us now turn our thoughts for a little space to a pair of organs which are, perhaps, of all others the most characteristic of the insect tribes: these are theAntennæ. We need scarcely explain what these are, or point them out to the reader, since they are so familiar to most persons, but under the erroneous, or, at any rate, the questionable expression—"the feelers." We have an excellent specimen ofantennæin those of the butterflies, in which insects they are very long and elegant organs. They are attached to the head by means of a beautiful joint, called a ball and socket, the same as is often adapted to garden watering engine-pipes, so as to enable them to be moved about in all directions. They are never found absent in the perfect insect, and are manifestly organs of considerable importance inthe insect economy. As to their structure,—when examined under a microscope, antennæ are found to be composed of a variable number of small round pieces, covered with a horny or leathery skin, but within being softer and hollow, so as to form a series of tubes placed end to end, all connected together in such a manner as to admit of free movement between each joint, so that the insect can bend them into any shape it may find expedient for its purposes. But it must not be supposed that all antennæ are similar in form, or there would be a risk of their being continually mistaken by the reader for some other organ. The cut on the next page will, at a glance, exhibit the astonishing variety of form assumed by these organs. The common cockchafer is possessed of antennæ as strikingly different in form from those of the butterfly, as if they were really distinct organs intended and adapted to serve different purposes. Some are long and thread-like, some resemble a necklace of pearls, some are notched like a saw, some have a resemblance to a fan, some are like a club, some resemble a fork, and some a feather; in short, their variety of form is almost endless: and they differ as much in length and inthickness; for while the antennæ of some insects are as long as, or even longer than, their bodies, those of others are very short, and little prominent; and while some are as thin and fine as the finest hair, others are nearly as thick as the true body of the insect. Let us now ask what is the use of these singular organs of the insect?
Various Antennæ.
From a hint which has before been dropped, it is probable that the answer to this question will be readily anticipated. Various facts appear to show that they may be the insect'sears! "Can it be that such is their function?" some may exclaim, calling to mind that ears in other creatures are so different in appearance and structure from these organs. There have been many opinions on the subject, and some have maintained views completely opposed to this idea. But the greater number of entomologists seem to consider this astheir most probable function. If they are not ears, we are not able to point to any other organs in the head which are. From a number of facts it is certain, that insects can hear; from which it is equally certain, that they must possess special organs. We may, therefore, until the contrary is shown with respect to them, fairly be allowed to consider the antennæ as these organs. The opinions of Messrs. Kirby and Spence on this point are conveyed in the following words:—"They conceive that antennæ by a peculiar structure may collect notices from the atmosphere, receive touches or vibrations, and communicate them to the sensorium (or brain), which, though not precisely to be called hearing, may answer the same purpose." The late celebrated Dr. W. F. Erichson of Berlin, by means of the microscope, has discovered in all insects, and especially in those most remarkable for their powers of smelling, that these organs are furnished with a number of fine pores, clothed with membrane, which he regards as organs of smell.[U]
Every one has heard of M. Pelisson, the prisoner at the Bastile, and his spider companionsof the cell. This gentleman had, by patient training, engaged the attention of a spider, which used every day to come and listen to a solo on his violin, after which it would make its retreat again to its home. Now it is clear, that this little insect not only heard, but even enjoyed, the notes of his instrument; which would have been impossible, had it possessed no ears. Then again, every one must have noticed the start which a fly will make if some sharp noise be made near it, and how actively it will move its legs, and seem to be put all on thequi vive. A little every-day observation will furnish us with many similar instances. "A little moth," writes one of the last-mentioned authors, "was reposing on my window; I made a quiet, not loud, but distinct noise; the antenna nearest to me immediately moved towards me. I repeated the noise at least a dozen times, and it was followed every time by the same motion of that organ; till at length the insect, being alarmed, became more agitated and violent in its motions. In this instance it could not betouch; since the antenna was not applied to a surface, but directed towards the quarter from which the sound came, as if to listen." Can we question thatthe merry grasshopper, chirping all day in the field, is heard by its mate? or that the cricket on the hearth sings for its fellows, or only to pleaseourears? or does the tap of the death-tick beetle, formerly commemorated, draw forth no answering tap from its companion on the other side of the post? All these instances, and countless more that might be mentioned, indicate, beyond a question, that insects have the faculty of hearing, and render it extremely probable that the antennæ are the organs by which this function is performed.
But it is probable that they serve another and not less important purpose. The country folk, who are generally very weather-wise, and whose sayings always deserve a great deal of attention, because they are very commonly founded both upon observation of facts, and experience, will always assure us that the high flight of swallows in their search after insects is a certain token of fair weather; their low flight of approaching wet. Why is this? Can insects foretell the state of the weather? and if so, by what means? That insects have a meteorometrical power of foretelling the state of the weather, appears beyond a doubt. To select a few instances.Bees, our exemplars in so many points, might be consulted with advantage, and would often give us better information as to whether an over-coat or an umbrella would be probably required, than the not always trustworthy barometer. When engaged in their daily labours, if a change of weather to rain is at hand, although the sun may yet shine and the sky remain clear and calm, they foresee it, and return suddenly to their hives. Hence in weather of an unsettled description they never undertake journeys far from home, but make short excursions to and from their hives, being never absent long at a time; and if we find a bee wandering far from its hive, it may be taken, on the other hand, as a pretty sure prognostic that top-coat and umbrella may be left at home forthatday at least. Ants, as we have already noticed, possess the same faculty of weather-wisdom, never allowing their larvæ to be caught in a shower. The abundance of insects in our houses in wet weather, is a familiar observation; we are assured that in hot countries their excessive numbers, during the rainy season, make these little creatures almost as terrible as a plague to all who are within—climbing upthe walls, scrambling into the dishes, drowning themselves in the soup-tureens, or putting out the lights with their bodies. In hot and sultry weather, when a black cloud or two in the far horizon give token of a coming storm, insects abound in the air; but as the heavens grow black, they disappear; and before a drop of rain has actually fallen, we may look in vain for them.
That the antennæ are the organs by which this knowledge of coming events with regard to the weather is obtained by the insects, appears probable. They may, perhaps, perceive by their delicate surfaces, changes in theelectricalcondition of the air, which are quite insensible to ourselves: and as all change of weather is preceded and accompanied by changes of electrical balance of one kind or another in the air, they may be thus forewarned of the coming danger. The following is the manœuvre of a large number of insects of the beetle tribe. When they are about to move from any station where they have been at rest, the first thing they usually do before they move a step, is to bring forward and expand their antennæ, which have previously been folded up out of the way. They open them aswidely as possible, so as to expose them to all the influences of the air, and then, if they be satisfied, they unfold their wings and take their flight. We might compare this proceeding with that of one of ourselves looking up at the direction of the wind, or tapping the weather-glass in the hall, previous to setting out for the day! Too much stress, however, it must be added, is not to be laid upon this point; for while it is unquestionable that insects have knowledge of the weather, it is of course very difficult to ascertain with certainty whether it is by means of their antennæ, or by the general feeling of their bodies; analogous, perhaps, to what rheumatic persons feel when the wind goes round to thenorth-east.
There is a still more singular use of the antennæ, which deserves to be mentioned. These organs appear to be the principal instruments ofspeech, if we may use such a term, or, at any rate, of the communication of intelligence. When the soldier ants go out upon their expeditions, and have left the nest, previously to setting off, they touch each other with their antennæ and forehead on the trunk; and this is their signal for marching, for as soon as ever a soldier feels this tap, he immediatelyputs himself in motion. When, also, they have any discovery to communicate, they strike with them those that they meet, in a particularly impressive manner; and if a hungry ant wants to be fed, it touches with its two antennæ, moving them very rapidly, those of the individual from which it expects its meal. They appear to salute one another by gently tapping each other's antennæ, as we should shake hands on meeting an old friend!
M. Huber has related an account of some interesting experiments of his on a hive of bees, which strikingly proves that the antennæ are really organs for the transmission of intelligence. He wished to ascertain whether, when they had lost a queen, they discovered the sad event by their smell, their touch, or any unknown cause; for such a loss, in the course of a single hour, is made known in some way or other to the whole hive. In order to ascertain this, he first divided a hive by a grate which kept the two portions a few parts of an inch separated from each other, so that the bees could not come at each other, although any scent could easily have passed. In that part in which there was no queen, the bees were soon in great agitation; and as they did notdiscover where she was confined, in a short time they began to construct royal cells, after which they grew more calm. Mr. Huber next separated them by a partition through which they could pass their antennæ, but not their heads. In this case, the bees all remained tranquil, neither intermitting the care of the brood, nor abandoning their other employments; nor did they begin any royal cell. The means they adopted to assure themselves that their queen was safe, and to communicate with her, was to pass their antennæ through the openings of the grate, A most curious spectacle thus presented itself; an infinite number of those organs might be seen at once, as it were inquiring in all directions; and the queen was observed answering these anxious inquiries of her dutiful subjects in the most marked manner; for she was always fastened by her feet to the grate, crossing her antennæ with those of the inquirers.
While we have been anxious to show that the function of feeling is not the important and principal office of these singular organs, it would be far from correct to state that the antennæ are not occasionally employed, to use the popular term, as "feelers." All who have paid any attentionto the motions of insects must have seen the antennæ actually employed as it were in exploring the number or nature of objects immediately around. From these and the preceding remarks, it becomes manifest, that, next to the organs of sight, the antennæ are most important and useful appendages to the body of the insect. When we consider the various purposes they serve, we become much perplexed to understand how it is possible for one organ to fulfil such varied duties; nor can it be explained. We are unable to conceive of the senses of insects except by comparing them with our own; and in our case there are no organs which can receive, and, at the same time, communicate, intelligence. Our ears, eyes, nose, and the other organs of the senses, have only one function severally assigned to them; and had they more, there would probably be no little confusion in our perceptions of external things. Such confusion does not probably exist in the insect; but it is very possible that its perceptions are somewhat different from ours.
Before we leave the region of the head, we have the important task to fulfil, of describing the mouth of the insect: this part is more complicatedthan the organs we have as yet seen, and requires, therefore, a considerable degree of our careful attention to enable us to do justice to it, and to carry in the mind a clear view of this interesting portion of an insect's structure. "If," writes Mr. Westwood, "a beetle, and a butterfly, a house-fly, or an aphis, be examined whilst feeding, a totally different apparatus will be found in each, although perfectly adapted for the mode of feeding. The beetle is employed in gnawing and tearing in pieces hard or fleshy substances: its instruments of manducation are, therefore, horny and robust. The butterfly, on the contrary, has to seek its food at the bottom of the tubes of flowers; and here in the glowing beams of the sun it revels in its existence, and sips the most delicious nectar. It is necessary for this purpose that it should be provided with a long and slender instrument; but, from the very structure of this apparatus, it is essential for its defence, that, so soon as the insect has ceased feeding, the instrument should be lodged in a place of safety. It is, therefore, rolled up in a beautiful spiral direction, and laid to rest between a pair of hairy appendages, which will defend it from injury. If we observe a commonfly sipping up a drop of spilt wine, or revelling upon a morsel of sugar, it will be found that its mouth is totally unlike either of the former: it is short, thick, and fleshy, and acts as a sucker, the nutriment ascending through the canal which runs upward into the throat. The aphides and all their brethren have a mouth differently constructed, being a long and slender pointed canal, of a fleshy, or leathery substance, but furnished internally with several slender bristles, which the insect employs as lancets to wound its prey. In the flea, again, the structure is quite different."