LETTER XXV.

"Happy the Cicadas' lives,Since they all have voiceless wives."

If the GrecianTettixorCicadahad been distinguished by a harsh and deafening note, like those of some other countries, it would hardly have been an object of such affection. That it was not, is clearly proved by the connexion which was supposed to exist between it and music. Thus the sound of this insect and of the harp were called by one and the same name[666]. A Cicada sitting upon a harp was a usual emblem of the science of music, which was thus accounted for:—When tworival musicians, Eunomus and Ariston, were contending upon that instrument, a Cicada flying to the former and sitting upon his harp, supplied the place of a broken string, and so secured to him the victory[667]. To excel this animal in singing seems to have been the highest commendation of a singer; and even the eloquence of Plato was not thought to suffer by a comparison with it[668]. At Surinam the noise of theCicada Tibicenis still supposed so much to resemble the sound of a harp or lyre, that they are called there harpers (Lierman)[669]. Whether the Grecian Cicadæ maintain at present their ancient character for music, travellers do not tell us.

Those of other countries, however, have been held in less estimation for their powers of song; or rather have been execrated for the deafening din that they produce. Virgil accuses those of Italy of bursting the very shrubs with their noise[670]; and Sir J. E. Smith observes that this species, which is very common, makes a most disagreeable dull chirping[671]. Another,Cicada septendecim—which fortunately, as its name imports, appears only once in seventeen years—makes such a continual din from morning to evening that people cannot hear each other speak. They appear in Pennsylvania in incredible numbers in the middle of May[672].—"In the hotter months of summer," says Dr. Shaw, "especially from midday to the middle of the afternoon, the Cicada, τεττιξ, or grasshopper, as we falsely translate it, is perpetually stunning our ears with its most excessively shrill andungrateful noise. It is in this respect the most troublesome and impertinent of insects, perching upon a twig and squalling sometimes two or three hours without ceasing; thereby too often disturbing the studies, or short repose that is frequently indulged, in these hot climates, at those hours. The τεττιξ of the Greeks must have had a quite different voice, more soft surely and melodious; otherwise the fine orators of Homer, who are compared to it, can be looked upon no better than loud loquacious scolds[673]."—An insect of this tribe, and I am told a very noisy one, has been found by Mr. Daniel Bydder, before mentioned, in the New Forest, Hampshire. Previously to this it was not thought that any of these insect musicians were natives of the British Isles.—Captain Hancock informs me that the Brazilian Cicadæ sing so loud as to be heard at the distance of a mile. This is as if a man of ordinary stature, supposing his powers of voice increased in the ratio of his size, could be heard all over the world. So that Stentor himself becomes a mute when compared with these insects.

You feel very curious, doubtless, to know by what means these little animals are enabled to emit such prodigious sounds. I have lately mentioned to you the drum of certain grasshoppers; this, however, appears to be an organ of a very simple structure; but since it is essential to the economy of the Cicadæ that their males should so much exceed all other insects in the loudness of their tones, they are furnished with a much more complex, and indeed most wonderful, apparatus, which I shall now describe. If you look at the underside of the body of a male, the first thing that will strike you is a pair of largeplates of an irregular form—in some semi-oval, in others triangular, in others again a segment of a circle of greater or less diameter—covering the anterior part of the belly, and fixed to the trunk between the abdomen and the hind legs[674]. These are the drum-covers or opercula, from beneath which the sound issues. At the base of the posterior legs, just above each operculum, there is a small pointed triangular process (pessellum)[675], the object of which, as Reaumur supposes, is to prevent them from being too much elevated. When an operculum is removed, beneath it you will find on the exterior side a hollow cavity, with a mouth somewhat linear, which seems to open into the interior of the abdomen[676]: next to this, on the inner side, is another large cavity of an irregular shape, the bottom of which is divided into three portions; of these the posterior is lined obliquely with a beautiful membrane, which is very tense—in some species semi-opake, and in others transparent—and reflects all the colours of the rainbow. This mirror is not the real organ of sound, but is supposed to modulate it[677]. The middle portion is occupied by a plate of a horny substance, placed horizontally and forming the bottom of the cavity. On its inner side this plate terminates in a carina or elevated ridge, common to both drums[678]. Between the plate and the after-breast (postpectus) another membrane, folded transversely, fills an oblique, oblong, or semi-lunar cavity[679]. In some species I have seen this membrane in tension—probably the insect can stretch or relax it at its pleasure. But even all this apparatusis insufficient to produce the sound of these animals;—one still more important and curious yet remains to be described. This organ can only be discovered by dissection. A portion of the first and second segments being removed from that side of the back of the abdomen which answers to the drums, two bundles of muscles meeting each other in an acute angle, attached to a place opposite to the point of the mucro of the first ventral segment of the abdomen, will appear[680]. In Reaumur's specimens these bundles of muscles seem to have been cylindrical; but in one I dissected (Cicada capensis) they were tubiform, the end to which the true drum is attached being dilated[681]. These bundles consist of a prodigious number of muscular fibres applied to each other, but easily separable. Whilst Reaumur was examining one of these, pulling it from its place with a pin, he let it go again, and immediately, though the animal had been long dead, the usual sound was emitted. On each side of the drum-cavities, when the opercula are removed, another cavity of a lunulate shape, opening into the interior of the abdomen, is observable[682]. In this is the true drum, the principal organ of sound, and its aperture is to the Cicada what our larynx is to us. If these creatures are unable themselves to modulate their sounds, here are parts enough to do it for them: for the mirrors, the membranes, and the central portions, with their cavities, all assist in it. In the cavity last described, if you remove the lateral part of the first dorsal segment of the abdomen, you will discover a semi-opaque and nearly semicircular concavo-convex membrane with transverse folds—this is the drum[683]. Each bundle ofmuscles, before mentioned, is terminated by a tendinous plate nearly circular, from which issue several little tendons that, forming a thread, pass through an aperture in the horny piece that supports the drum, and are attached to its under or concave surface. Thus the bundle of muscles being alternately and briskly relaxed and contracted, will by its play draw in and let out the drum: so that its convex surface being thus rendered concave when pulled in, when let out a sound will be produced by the effort to recover its convexity; which, striking upon the mirror and other membranes before it escapes from under the operculum, will be modulated and augmented by them[684]. I should imagine that the muscular bundles are extended and contracted by the alternate approach and recession of the trunk and abdomen to and from each other.

And now, my friend, what adorable wisdom, what consummate art and skill are displayed in the admirable contrivance and complex structure of this wonderful, this unparalleled apparatus! TheGreat Creatorhas placed in these insects an organ for producing and emitting sounds, which in the intricacy of its construction seems to resemble that which he has given to man, and the larger animals, for receiving them. Here is acochlea; ameatus; and, as it should seem, more than onetympanum.

I am, &c.

We boast of our candles, our wax-lights, and our Argand lamps, and pity our fellow-men who, ignorant of our methods of producing artificial light, are condemned to pass their nights in darkness. We regard these inventions as the results of a great exertion of human intellect, and never conceive it possible that other animals are able to avail themselves of modes of illumination equally efficient; and are furnished with the means of guiding their nocturnal evolutions by actual lights, similar in their effect to those which we make use of. Yet many insects are thus provided. Some are forced to content themselves with a single candle, not more vivid than the rush-light which glimmers in the peasant's cottage; others exhibit two or four, which cast a stronger radiance; and a few can display a lamp little inferior in brilliancy to some of ours. Not that these insects are actually possessed of candles and lamps. You are aware that I am speaking figuratively. But Providence has supplied them with an effectual substitute—a luminous preparation or secretion, which has all the advantages of our lamps and candles without their inconveniences; which gives light sufficient to direct theirmotions, while it is incapable of burning; and whose lustre is maintained without needing fresh supplies of oil or the application of the snuffers.

Of the insects thus singularly provided, the common glow-worm (Lampyris noctiluca) is the most familiar instance. Who that has ever enjoyed the luxury of a summer evening's walk in the country, in the southern parts of our island, but has viewed with admiration these "stars of the earth and diamonds of the night?" And if, living like me in a district where it is rarely met with, the first time you saw this insect, chanced to be, as it was in my case, one of those delightful evenings which an English summer seldom yields, when not a breeze disturbs the balmy air, and "every sense is joy," and hundreds of these radiant worms, studding their mossy couch with mild effulgence, were presented to your wondering eye in the course of a quarter of a mile,—you could not help associating with the name of glow-worm the most pleasing recollections. No wonder that an insect, which chiefly exhibits itself on occasions so interesting, and whose economy is so remarkable, should have afforded exquisite images and illustrations to those poets who have cultivated Natural History.

If you take one of these glow-worms home with you for examination, you will find that in shape it somewhat resembles a caterpillar, only that it is much more depressed; and you will observe that the light proceeds from a pale-coloured patch that terminates the underside of the abdomen. It is not, however, the larva of an insect, but the perfect female of a winged beetle, from which it is altogether so different, that nothing but actual observation could have inferred the fact of theirbeing the sexes of the same insect. In the course of our inquiries you will find that sexual differences even more extraordinary exist in the insect world.

It has been supposed by many that the males of the different species ofLampyrisdo not possess the property of giving out any light; but it is now ascertained that this supposition is inaccurate, though their light is much less vivid than that of the female. Ray first pointed out this fact with respect toL. noctiluca[685]. Geoffroy also observed that the male of this species has four small luminous points, two on each of the two last segments of the belly[686]: and his observation has been recently confirmed by Müller. This last entomologist, indeed, saw only two shining spots; but from the insect's having the power of withdrawing them out of sight so that not the smallest trace of light remains, he thinks it is not improbable that at times two other points still smaller may be exhibited, as Geoffroy has described. In the males ofL. Splendidulaand ofL. hemipterathe light is very distinct, and may be seen in the former while flying[687].—The females have the same faculty of extinguishing or concealing their light—a very necessary provision to guard them from the attacks of nocturnal birds: Mr. White even thinks that they regularly put it out between eleven and twelve every night[688]: and they have also the power of rendering it for a while more vivid than ordinary.

Authors who have noticed the luminous parts of the common female glow-worm, having usually contented themselves with stating that the light issues from thethree last ventral segments of the abdomen[689]; I shall give you the result of some observations I once made upon this subject. One evening, in the beginning of July, meeting with two of these insects, I placed them on my hand. At first their light was exceedingly brilliant, so as to appear even at the junctions of the upper or dorsal segments of the abdomen. Soon after I had taken them, one withdrew its light altogether, but the other continued to shine. While it did this it was laid upon its back, the abdomen forming an angle with the rest of its body, and the last or anal segment being kept in constant motion. This segment was distinguished by two round and very vivid spots of light; which, in the specimen that had ceased to shine, were the last that disappeared, and they seem to be the first parts that become luminous when the animal is disposed to yield its light. The penultimate and antepenultimate segments each exhibited a middle transverse band of yellow radiance, terminated towards the trunk by an obtusely-dentated line; a greener and fainter light being emitted by the rest of the segment.

Though many of the females of theLampyridæare without wings and even elytra, (in which circumstance they differ from all other apterousColeoptera,) this is not the case with all. The female ofPygolampis[690]italica, a species common in Italy, and which, if we may trust to the accuracy of the account given by Mr. Waller in thePhilosophical Transactionsfor 1684, would seemto have been taken by him in Hertfordshire, is winged: and when a number of these moving stars are seen to dart through the air in a dark night, nothing can have a more beautiful effect. Sir J. E. Smith tells us that the beaus of Italy are accustomed in an evening to adorn the heads of the ladies with these artificial diamonds, by sticking them into their hair; and a similar custom, as I have before informed you[691], prevails amongst the ladies of India.

Besides the different species of the genusLampyris, all of which are probably more or less luminous, another insect of the beetle tribe,Elater noctilucus, is endowed with the same property, and that in a much higher degree. This insect, which is called the fire-fly, and is an inch long, and about one-third of an inch broad, gives out its principal light from two transparent eye-like tubercles placed upon the thorax; but there are also two luminous patches concealed under the elytra, which are not visible except when the insect is flying, at which time it appears adorned with four brilliant gems of the most beautiful golden-blue lustre: in fact, the whole body is full of light, which shines out between the abdominal segments when stretched. The light emitted by the two thoracic tubercles alone is so considerable, that the smallest print may be read by moving one of these insects along the lines; and in the West India islands, particularly in St. Domingo, where they are very common, the natives were formerly accustomed to employ these living lamps, which they calledCucuij, instead of candles in performing their evening household occupations. In travelling at night they used to tie oneto each great toe; and in fishing and hunting required no other flambeau[692].—Southey has happily introduced this insect in his "Madoc" as furnishing the lamp by which Coatel rescued the British hero from the hands of the Mexican priests.

"She beckon'd and descended, and drew outFrom underneath her vest a cage, or netIt rather might be call'd, so fine the twigsWhich knit it, where, confined, two Fire-flies gaveTheir lustre. By that light did Madoc firstBehold the features of his lovely guide."

Pietro Martire tells us that the Cucuij serve the natives of the Spanish West India islands not only instead of candles, but as extirpators of the gnats, which are a dreadful pest to the inhabitants of the low grounds. They introduce a few fire-flies, to which the gnats are a grateful food, into their houses, and by means of these "commodious hunters" are soon rid of the intruders. "How they are a remedy," says this author, "for so great a mischiefe it is a pleasant thing to hear. Hee who understandeth he hath those troublesome guestes (the gnattes) at home, diligently hunteth after the Cucuij. Whoso wanteth Cucuij goeth out of the house in the first twilight of the night, carrying a burning fire-brande in his hande, and ascendeth the next hillock that the Cucuij may see it, and hee swingeth the fire-brande about, calling Cucuius aloud, and beating the ayre with often calling outCucuie, Cucuie." He goes on to observe, that the simple people believe the insect is attracted by their invitations; but that, for his part he is rather inclined to think that the fire is the magnet. Having obtained asufficient number of Cucuij, the beetle-hunter returns home and lets them fly loose in the house, where they diligently seek the gnats about the beds and the faces of those asleep, and devour them[693].—These insects are also applied to purposes of decoration. On certain festival days in the month of June, they are collected in great numbers, and tied all over the garments of the young people, who gallop through the streets on horses similarly ornamented, producing on a dark evening the effect of a large moving body of light. On such occasions the lover displays his gallantry by decking his mistress with these living gems[694]. And according to P. Martire, "many wanton wilde fellowes" rub their faces with the flesh of a killed Cucuius, as boys with us use phosphorus, "with purpose to meet their neighbours with a flaming countenance," and derive amusement from their fright.

BesidesElater noctilucus,E. ignitusand several others of the same genus are luminous. Not fewer than twelve species of this family are described by Illiger in theBerlin Naturalist Society's Magazine[695].

The brilliant nocturnal spectacle presented by these insects to the inhabitants of the countries where they abound cannot be better described than in the language of the poet above referred to, who has thus related its first effect upon the British visitors of the new world:

"..............Sorrowing we beheldThe night come on; but soon did night displayMore wonders than it veil'd: innumerous tribesFrom the wood-cover swarm'd, and darkness madeTheir beauties visible: one while they stream'dA bright blue radiance upon flowers that closedTheir gorgeous colours from the eye of day;Now motionless and dark, eluded search,Self-shrouded; and anon, starring the sky,Rose like a shower of fire."

The beautiful poetical imagery with which Mr. Southey has decorated this and a few other entomological facts, will make you join in my regret that a more extensive acquaintance with the science has not enabled him to spread his embellishments over a greater number. The gratification which the entomologist derives from seeing his favourite study adorned with the graces of poetry is seldom unalloyed with pain, arising from the inaccurate knowledge of the subject in the poet. Dr. Darwin's description of the beetle to which the nut-maggot is transformed may delight him (at least if he be an admirer of the Darwinian style) as he reads for the first time,

"So sleeps in silence the Curculio, shutIn the dark chamber of the cavern'd nut;Erodes with ivory beak the vaulted shell,And quits on filmy wings its narrow cell."

But when the music of the lines has allowed him room for pause, and he recollects that they are built wholly upon an incorrect supposition, the Curculio never inhabiting the nut in its beetle shape, nor employing its ivory or rather ebony beak upon it, but undergoing its transformation under ground, he feels disappointed that the passage has not truth as well as sound.—Mr. Southey, too, has fallen into an error: he confounds the fire-fly of St. Domingo (Elater noctilucus) with a quite different insect, the lantern-fly (Fulgora laternaria) ofMadame Merian; but happily this error does not affect his poetry.

But to return from this digression.—If we are to believe Mouffet, (and the story is not incredible,) the appearance of the tropical fire-flies on one occasion led to a more important result than might have been expected from such a cause. He tells us, that when Sir Thomas Cavendish and Sir Robert Dudley first landed in the West Indies, and saw in the evening an infinite number of moving lights in the woods, which were merely these insects, they supposed that the Spaniards were advancing upon them, and immediately betook themselves to their ships[696]:—a result as well entitling the Elaters to a commemoration feast, as a similar good office the land-crabs of Hispaniola, which, as the Spaniards tell, (and the story is confirmed by an anniversaryFiesta de lôs Cangrejos,) by their clattering—mistaken by the enemy for the sound of Spanish cavalry close upon their heels—in like manner scared away a body of English invaders of the city of St. Domingo[697].

An anecdote less improbable, perhaps, and certainly more ludicrous, is related by Sir J. E. Smith of the effect of the first sight of the Italian glow-worms upon some Moorish ladies ignorant of such appearances. These females had been taken prisoners at sea, and, until they could be ransomed, lived in a house in the outskirts of Genoa, where they were frequently visited by the respectable inhabitants of the city; a party of whom, on going one evening, were surprised to find the house closely shut up, and their Moorish friends in the greatest grief and consternation. On inquiring into the cause,they ascertained that some of thePygolampis italicahad found their way into the dwelling, and that the ladies within had taken it into their heads that these brilliant guests were no other than the troubled spirits of their relations; of which idea it was some time before they could be divested.—The common people in Italy have a superstition respecting these insects somewhat similar, believing that they are of a spiritual nature, and proceed out of the graves, and hence carefully avoid them[698].

The insects hitherto adverted to have been beetles, or of the orderColeoptera. But besides these, a genus in the orderHemiptera, calledFulgora, includes several species which emit so powerful a light as to have obtained in English the generic appellation ofLantern-flies. Two of the most conspicuous of this tribe are theF. laternariaandF. candelaria; the former a native of South America, the latter of China. Both, as indeed is the case with the whole genus, have the material which diffuses their light included in a hollow subtransparent projection of the head. InF. candelariathis projection is of a subcylindrical shape, recurved at the apex, above an inch in length, and the thickness of a small quill. We may easily conceive, as travellers assure us, that a tree studded with multitudes of these living sparks, some at rest and others in motion, must at night have a superlatively splendid appearance.—InF. laternaria, which is an insect two or three inches long, the snout is much larger and broader, and more of an oval shape, and sheds a light the brilliancy of which transcends that of any other luminous insect. Madame Merian informs us, that the first discoverywhich she made of this property caused her no small alarm. The Indians had brought her several of these insects, which by day-light exhibited no extraordinary appearance, and she inclosed them in a box until she should have an opportunity of drawing them, placing it upon a table in her lodging-room. In the middle of the night the confined insects made such a noise as to awake her, and she opened the box, the inside of which to her great astonishment appeared all in a blaze; and in her fright letting it fall, she was not less surprised to see each of the insects apparently on fire. She soon, however, divined the cause of this unexpected phenomenon, and re-inclosed her brilliant guests in their place of confinement. She adds, that the light of one of theseFulgoræis sufficiently bright to read a newspaper by: and though the tale of her having drawn one of these insects by its own light is without foundation, she doubtless might have done so if she had chosen[699].—Another species (F. pyrrhorynchus) is figured by Mr. Donovan in hisInsects of India, of which the light, though from a smaller snout than that ofF. laternaria, must assume a more splendidand striking appearance, the projection being of a rich deep purple from the base to near the apex, which is of a fine transparent scarlet; and these tints will of course be imparted to the transmitted light.

In addition to the insects already mentioned, some others have the power of diffusing light, as two species ofCentipedes(Geophilus electricusandphosphoreus), and probably others of the same genus. In these the light is not confined to one part, but proceeds from the whole body.G. electricusis a common insect in this country, residing under clods of earth, and often visible at night in gardens.G?phosphoreus, a native of Asia, is an obscure species, described by Linné, on the authority of C. G. Ekeberg, the captain of a Swedish East Indiaman, who asserted that it dropped from the air, shining like a glow-worm, upon his ship, when sailing in the Indian ocean a hundred miles (Swedish) from the continent. However singular this statement, it is not incredible. The insect may either, as Linné suspects, have been elevated into the atmosphere by wings with which, according to him, one species of the genus is provided; or more probably, perhaps, by a strong wind, such as that which raised into the air the shower of insects mentioned by De Geer as occurring in Sweden in the winter of 1749, after a violent storm that had torn up trees by the roots, and carried away to a great distance the surrounding earth, and insects which had taken up their winter quarters amongst it[700]. That the windmay convey the light body of an insect to the above-mentioned distance from land, you will not dispute when you call to mind that our friend Hooker, in his interestingTour in Iceland, tells us that the ashes from the eruption of one of the Icelandic volcanos in 1755 were conveyed to Ferrol, a distance of upwards of 300 miles[701].—Lastly, to conclude my list of luminous insects, Professor Afzelius observed "a dim phosphoric light" to be emitted from the singular hollow antennæ ofPausus sphærocerus[702]. A similar appearance has been noticed in the eyes ofAcronycta Psi,Cossus ligniperda, and other moths.Chiroscelis bifenestrataof Lamarck, a beetle, has two red oval spots covered with a downy membrane on the second segment of the abdomen, which he thinks indicate some particular organ perhaps luminous[703]: and M. Latreille informs me that a friend of his, who saw one living which was brought from China to the Isle of France in wood, found that theocelliin the elytra ofBuprestis ocellatawere luminous.

But besides the insects here enumerated, others may be luminous which have not hitherto been suspected of being so. This seems proved by the following fact. A learned friend[704]has informed me, that when he was curate of Ickleton, Cambridgeshire, in 1780, a farmer of that place of the name of Simpringham brought to him a mole-cricket (Gryllotalpa vulgaris, Latr.), and toldhim that one of his people, seeing aJack-o'lantern, pursued it and knocked it down, when it proved to be this insect, and the identical specimen shown to him.

This singular fact, while it renders it probable that some insects are luminous which no one has imagined to be so, seems to afford a clue to the, at least, partial explanation of the very obscure subject ofignes fatui, and to show that there is considerable ground for the opinion long ago maintained by Ray and Willughby, that the majority of these supposed meteors are no other than luminous insects. That the large varying lambent flames, mentioned by Beccaria to be very common in some parts of Italy, and the luminous globe seen by Dr. Shaw[705]cannot be thus explained, is obvious. These were probably electrical phenomena: certainly not explosions of phosphuretted hydrogene, as has been suggested by some, which must necessarily have been momentary. But that theignis fatuusmentioned by Derham as having been seen by himself, and which he describes as flitting about a thistle[706], was, though he seems of a different opinion, no other than some luminous insect, I have little doubt. Mr. Sheppard informs me that, travelling one night between Stamford and Grantham on the top of the stage, he observed for more than ten minutes a very largeignis fatuusin the low marshy grounds, which had every appearance of being an insect. The wind was very high: consequently, had it been a vapour, it must have been carried forward in a direct line; but this was not the case. It had the same motions as a Tipula, flying upwards and downwards, backwards and forwards, sometimes appearing as settled,and sometimes as hovering in the air.—Whatever be the true nature of these meteors, of which so much is said and so little known, it is singular how few modern instances of their having been observed are on record. Dr. Darwin declares, that though in the course of a long life he had been out in the night, and in the places where they are said to appear, times without number, he had never seen any thing of the kind: and from the silence of other philosophers of our own times, it should seem that their experience is similar.

With regard to the immediate source of the luminous properties of these insects, Mr. Macartney, to whom we are indebted for the most recent investigation on the subject, has ascertained that in the common glow-worm, and inElater noctilucusandignitus, the light proceeds from masses of a substance not generally differing, except in its yellow colour, from the interstitial substance (corps graisseux) of the rest of the body, closely applied underneath those transparent parts of the insects' skin which afford the light. In the glow-worm, besides the last-mentioned substance, which, when the season for giving light is passed, is absorbed, and replaced by the common interstitial substance, he observed on the inner side of the last abdominal segment two minute oval sacs formed of an elastic spirally-wound fibre similar to that of the tracheæ, containing a soft yellow substance of a closer texture than that which lines the adjoining region, and affording a more permanent and brilliant light. This light he found to be less under the control of the insect than that from the adjoining luminous substance, which it has the power of voluntarily extinguishing, notby retracting it under a membrane, as Carradori imagined, but by some inscrutable change dependent upon its will: and when the latter substance was extracted from living glow-worms it afforded no light, while the two sacs in like circumstances shone uninterruptedly for several hours. Mr. Macartney conceives, from the radiated structure of the interstitial substance surrounding the oval yellow masses immediately under the transparent spots in the thorax ofElater noctilucus, and the subtransparency of the adjoining crust, that the interstitial substance in this situation has also the property of shining—a supposition which, if De Geer and other authors be correct in stating that this insect has two luminous patches under its elytra, and that the incisures between the abdominal segments shine when stretched, may probably be extended to thewholeof the interstitial substance of its body.—What peculiar organization contributes to the production of light in the hollow projections ofFulgora laternariaandcandelaria, the hollow antennæ ofPausus sphærocerus, and under the whole integument ofGeophilus electricus, Mr. Macartney was unable to ascertain. Respecting this last he remarks, what I have myself observed, that there is an apparent effusion of a luminous fluid on its surface, that may be received upon the hand, which exhibits a phosphoric light for a few seconds afterwards; and that it will not shine unless it have been previously exposed for a short time to the solar light[707].

With respect to the remote cause of the luminous property of insects, philosophers are considerably divided in opinion. The disciples of modern Chemistry have in general, with Dr. Darwin, referred it to the slow combustion of some combination of phosphorus secreted from their fluids by an appropriate organization, and entering into combination with the oxygene supplied in respiration. This opinion is very plausibly built upon the ascertained existence of phosphoric acid as an animal secretion; the great resemblance between the light of phosphorus in slow combustion and animal light; the remarkably large spiracula in glow-worms; and upon the statement, that the light of the glow-worm is rendered more brilliant by the application of heat and oxygene gas, and is extinguished by cold and by hydrogene and carbonic acid gases. From these last facts Spallanzani was led to regard the luminous matter as a compound of hydrogene and carburetted hydrogene gas. Carradori having found that the luminous portion of the belly of the Italian glow-worm (Pygolampis italica) shone in vacuo, in oil, in water, and when under other circumstances where the presence of oxygene gas was precluded, with Brugnatelli ascribed the property in question to the imbibition of light separated from the food or air taken into the body, and afterwards secreted in a sensible form[708]. Lastly, Mr. Macartney having ascertained by experiment that the light of a glow-worm is not diminished by immersion in water, or increased by the application of heat; that the substance affording it, though poetically employed for lighting the fairies'tapers[709], is incapable of inflammation if applied to the flame of a candle or red-hot iron; and when separated from the body exhibits no sensible heat on the thermometer's being applied to it—rejects the preceding hypotheses as unsatisfactory, but without substituting any other explanation; suggesting, however, that the facts he observed are more favourable to the supposition of light being a quality of matter than a substance[710].

Which of these opinions is the more correct I do not pretend to decide. But though the experiments of Mr. Macartney seem fairly to bear him out in denying the existence of any ordinary combination of phosphorus in luminous insects, there exists a contradiction in many of the statements, which requires reconciling before final decision can be pronounced. The different results obtained by Forster and Spallanzani, who assert that glow-worms shine more brilliantly in oxygene gas, and byBeckerheim, Dr. Hulme, and Sir H. Davy, who could perceive no such effect, may perhaps be accounted for by the supposition that in the latter instances the insects having been taken more recently, might be less sensible to the stimulus of the gas than in the former, where possibly their irritability was, as Brown would say, accumulated by a longer abstinence: but it is not so easy to reconcile the experiment of Sir H. Davy, who found the light of the glow-worm not to be sensibly diminished in hydrogene gas[711], with those of Spallanzani and Dr. Hulme, who found it to be extinguished by the same gas, as well as by carbonic acid, nitrous and sulphuretted hydrogene gases[712]. Possibly some of these contradictory results were occasioned by not adverting to the faculty which the living insect possesses of extinguishing its lights at pleasure; or different philosophers may have experimented on different species of Lampyris.

The general use of this singular provision is not much more satisfactorily ascertained than its nature. I have before conjectured—and in an instance I then related it seemed to be so—that it may be a means of defence against their enemies[713]. In different kinds of insects, however, it may probably have a different object. Thus in the lantern-flies (Fulgora), whose light precedes them, it may act the part that their name imports, enabling them to discover their prey, and to steer themselves safely in the night. In the fire-flies (Elater), if we consider the infinite numbers that in certain climates and situations present themselves every where in the night,it may distract the attention of their enemies or alarm them. And in the glow-worm—since their light is usually most brilliant in the female; in some species, if not all, present only in the season when the sexes are destined to meet; and strikingly more vivid at the very moment when the meeting takes place[714]—besides the above uses, it is most probably intended to conduct the sexes to each other. This seems evidently the design in view in those species in which, as in the common glow-worm (L. noctiluca), the females are apterous. The torch which the wingless female, doomed to crawl upon the grass, lights up at the approach of night, is a beacon which unerringly guides the vagrant male to her "love-illumined form," however obscure the place of her abode. It has been objected, however, to this explanation, that—since both larva and pupa, as De Geer observed[715], and the males shine as well as the females—the meeting of the sexes can scarcely be the object of their luminous provision. But this difficulty appears to me easily surmounted. As the light proceeds from a peculiarly organized substance, which probably must in part be elaborated in the larva and pupa states, there seems nothing inconsistent in the fact ofsomelight being then emitted with the supposition of its being destined solely for use in the perfect state: and the circumstance of the male having the same luminous property, no more proves that the superior brilliancy of the female is not intended for conducting him to her, than the existence of nipples and sometimes of milk in man proves that the breast of woman is not meant for the support of her offspring.We often see without being able to account for the fact, except on Sir E. Home's idea, that the sex of the ovum is undetermined[716], traces of an organization in one sex indisputably intended for the sole use of the other.

I am, &c.

If insects can boast of enjoying a greater variety of food than many other tribes of animals, this advantage seems at first sight more than counterbalanced in our climates, by the temporary nature of their supply. The graminivorous quadrupeds, with few exceptions, however scanty their bill of fare, and their carnivorous brethren, as well as the whole race of birds and fishes, can at all seasons satisfy, in greater or less abundance, their demand for food. But to the great majority of insects, the earth for nearly one half of the year is a barren desert, affording no appropriate nutriment. As soon as winter has stripped the vegetable world of its foliage, the vast hosts of insects that feed on the leaves of plants must necessarily fast until the return of spring: and even the carnivorous tribes, such as the predaceous beetles, parasiticHymenoptera,Sphecina, &c. would at that period of the year in vain look for their accustomed prey.

How is this difficulty provided for? In what mode has the Universal Parent secured an uninterrupted succession of generations in a class of animals for the mostpart doomed to a six months' deprivation of the food which they ordinarily devour with such voracity? By a beautiful series of provisions founded on the faculty, common also to some of the larger animals, of passing the winter in a state of torpor—by ordaining that the insect shall live through that period, either in an incomplete state of its existence when its organs of nutrition are undeveloped, or, if the active epoch of its life has commenced, that it shall seek out appropriatehybernacula, or winter quarters, and in them fall into a profound sleep, during which a supply of food is equally unnecessary.

In two of the four states of existence common to insects, in which different tribes pass the winter, namely, the egg and the pupa state, the organs for taking food (except in some cases in the latter) are not developed, and consequently the animal is incapable of eating. The existence of insects in these states during the winter, differs from their existence in the same form in summer only in the greater length of its term. In both seasons food is alike unnecessary, so that their hybernation in these circumstances has little or nothing analogous to that of larger animals. With this, however, strictly accords their hybernation in the larva and imago states, in which their abstinence from food is solely owing to the torpor that pervades them, and the consequent non-expenditure of the vital powers.—I shall attend to the peculiarities of their hybernation in each of these states in the order just laid down; premising that we have yet much to learn on this subject, no observations having been instituted respecting the state in which multitudes of insects pass the winter.

It is probable that some insects of almost every order hybernate in theeggstate: though that these must be comparatively few in number, seems proved from two considerations: first, That the majority of insects assume the imago, and deposit their eggs in the summer and early part of autumn, when the heat suffices to hatch them in a short period: and secondly, That the eggs of a very large proportion of insects require for their due exclusion and the nutriment of the larvæ springing from them, conditions only to be fulfilled in summer, as all those which are laid in young fruits and seeds; in the interior and galls of leaves; in insects that exist only in summer, &c. &c. The insects which pass the winter in the egg state are chiefly such as have several broods in the course of the year, the females of the last of which lay eggs that, requiring more heat for their development than then exists, necessarily remain dormant until the return of spring.

The situation in which the female insect places her eggs in order to their remaining there through the winter, is always admirably adapted to the degree of cold which they are capable of sustaining; and to the ensuring a due supply of food for the nascent larvæ. Thus, with the former view,Acrida verrucivoraand many other insects whose eggs are of a tender consistence, deposit them deep in the earth out of the reach of frost; and with the latter,Trichoda Neustria,Lasiocampa castrensis,Hypogymna dispar, and some other moths, departing from the ordinary instinct of their congeners, which teaches them to place their eggs upon theleavesof plants, fix theirs to the stem and branches only. That this variation of procedure has reference to the hybernation ofthe eggs of these particular species, is abundantly obvious. Insects whose eggs are to be hatched in summer, usually fix them slightly to the leaves upon which the larvæ are to feed. But it is evident that, were this plan to be adopted by those whose eggs remain through the winter, their progeny might be blown away along with the leaf to which they are attached, far from their destined food. These, therefore, choose a more stable support, and carefully fasten them, as has just been observed, either to the trunk or branches of the tree, whose young leaves in spring are to be the food of the excluded larvæ. The latter plan is followed by the female ofTrichoda Neustria, which curiously gums her eggs in bracelets round the twigs of the hawthorn, &c. But another provision is demanded. Were these eggs of the usual delicate consistence, and to be attached with the ordinary slight gluten, they would have a poor chance of surviving the storms of rain and snow and hail to which for six or eight months they are exposed. They are therefore covered with a shell much more hard and thick than common; packed as closely as possible to each other; and the interstices are filled up with a tenacious gum, which soon hardens the whole into a solid mass almost capable of resisting a penknife. Thus secured, they defy the elements and brave the blasts of winter uninjured.—The female ofHypogymna dispar, whose eggs have a more tender shell, glues them in an oval mass to the stem of a tree (whence the German gardeners call the larvæStamm-raupe), and then covers them with a warm non-conducting coat of hairs plucked from her own body, equally impervious to cold and wet.

Another of those beautiful relations between objects atfirst sight apparently unconnected, which at every step reward the votaries of Entomology, is afforded by the coincidence between the period of the hatching in spring of eggs deposited before winter, and of the leafing of the trees upon which they have been fixed, and on whose foliage the larvæ are to feed: which two events, requiring exactly the same temperature, are always simultaneous. Of this fact I have had a striking exemplification the last spring (1816). On the 20th of February, observing the twigs of the birches in the Hull Botanic Garden to be thickly set, especially about the buds, with minute oval black eggs of some insect with which I was unacquainted, I brought home a small branch and set it in a jar of water in my study, in which is a fire daily, to watch their exclusion. On the 28th of March I observed that a numerous brood of Aphides (notA. Betulæ, as the wings were without the dark bands of that species) had been hatched from them, and that two or three of the lower buds had expanded into leaves, upon the sap of which they were greedily feasting. This was full a month before either a leaf of the birch appeared, or the egg of an Aphis was disclosed in the open air.—To view the relation of which I am speaking with due admiration, you must bear in mind the extremely different periods at which many trees acquire their leaves, and the consequent difference demanded in the constitution of the eggs which hybernate upon dissimilar species, to ensure their exclusion, though acted upon by thesametemperature, earlier or later, according to the early or late foliation of these species. There is no visible difference between the conformation of the eggs of the Aphis of the birch and those of the Aphis of the ash; yet in thesameexposurethose of the former shall be hatched, simultaneously with the expansion of the leaves, nearly a month earlier than those of the latter: thus demonstrably proving that the hybernation of these eggs is not accidental, but has been specially ordained by the Author of nature, who has conferred on those of each species a peculiar and appropriate organization.

A much greater number of insects pass the winter in thepupathan in the egg state; probably nine-tenths of the extensive orderLepidoptera, many inHymenoptera, and several in other orders. In placing these pupæ in security from the too great cold of winter and the attacks of enemies, the larvæ from which they are to be metamorphosed exhibit an anxiety and ingenuity evidently imparted to them for this express design. A few are suspended without any covering, though usually in a sheltered situation. But by far the larger number are concealed under leaves, in the crevices or in the trunk of trees, &c., or inclosed in cocoons of silk or other materials which will be described to you in a subsequent letter, and often buried deep under ground out of the reach of frost.—One reason why so many lepidopterous insects pass the winter as pupæ, has been plausibly assigned by Rösel, in remarking that this is the case with all the numerous species which feed on annual plants. As these have no local habitation, dying one year and springing up from seed in another quarter the next, it is obvious that eggs deposited upon them in autumn would have no chance of escaping destruction; and that even if the larvæ were to be hatched before winter, and to hybernate in that state, they would have no certainty of being in the neighbourhood of their appropriate foodthe next spring. By wintering in the pupa state, these accidents are effectually provided against. The perfect insect is not ready to break forth until the food of the young, which are to proceed from its eggs, is sprung up.

To the insects which hybernate in thelarvastate, of course belong, in the first place, all those which exist under that form more than one year; as manyMelolonthæ,Elateres,Cerambyces,Buprestes, and several species ofLibellula,Ephemera, &c. There are also many larvæ which, though their term of life is not a year, being hatched from the egg in autumn, necessarily pass the winter in that state, as those of severalAnobiaand other wood-boring insects; ofSemasia Wœberanaand others of the same family; of the second broods of several butterflies, &c. Many of these residing in the ground or in the interior of trees need no other hybernacula than the holes which they constantly inhabit; some, as the aquatic larvæ, merely hide themselves in the sides or muddy bottom of their native pools; while others seek for a retreat under moss, dead leaves, stones, and the bark of decaying trees. Most of these can boast of no better winter quarters than a simple unfurnished hole or cavity; but a few, more provident of comfort, prepare themselves an artificial habitation. With this view the larva ofCossus ligniperda, as formerly observed in describing the habitations of insects[717], forms a covering of pieces of wood lined with fine silk; those ofHepiolus Humuli,Xylina radicea, and some other moths, excavate under a stone a cavity exactly the size of their bodies, to which they give all round a coating of silk[718],and the larvæ ofPieris Cratægiinclose themselves in autumn in cases of the same material[719], and thus pass the cold season in small societies of from two to twelve, under a common covering formed of leaves. Bonnet mentions a trait of the cleanliness of these insects which is almost ludicrous. He observed in one of these nests a sort of sack containing nothing but grains of excrement; and a friend assured him that he had seen one of these caterpillars partly protrude itself out of its case, the hind feet first, to eject a similar grain; so that it would seem the society have on their establishment a scavenger, whose business it is to sweep the streets and convey the rejectamenta to one grand repository[720]! This, however singular, is rendered not improbable from the fact that beavers dig in their habitations holes solely destined for a like purpose[721].

A very considerable number of insects hybernate in theperfectstate, chiefly of the ordersColeoptera,Hemiptera,Hymenoptera, andDiptera, and especially of the first.Vanessa Urticæ,Io, and a few other lepidopterous species, with a small proportion of the other orders, occasionally survive the winter; but the bulk of these are rarely found to hybernate as perfect insects. Of coleopterousinsects, Schmid, to whom we are indebted for some valuable remarks on the present subject[722], says that he never found or heard of any Entomologist finding a hybernating individual of the common cockchafer (Melolontha vulgaris) or of the stag-beetle (Lucanus Cervus); and suggests that it is only those insects which exist but a short period as larvæ, as most of the tribe of weevils, lady-birds, &c., that survive the winter in the perfect state; while those which live more than one year in the larva state, as the species just mentioned, are deprived of this privilege.

Towards the close of autumn the whole insect world, particularly the tribe of beetles, is in motion. A general migration takes place: the various species quit their usual haunts, and betake themselves in search of secure hybernacula. Different species, however, do not select precisely the same time for making this change of abode. Thus many lady-birds, field-bugs, and flies, are found out of their winter quarters even after the commencement of frost; while others, as Schmid has remarked, make good their retreat long before any severe cold has been felt: in fact, I am led to believe, from my own observations, that this is the case with the majority of coleopterous insects; and that the days which they select for retiring to their hybernacula, are some of the warmest days of autumn, when they may be seen in great numbers alighting on walls, rails, path-ways, &c. and running into crevices and cracks, evidently in search of some object very different from those which ordinarily guide their movements. I have noticed this assemblage in different years, but more particularly in the last autumn (1816).Walking on the banks of the Humber on the 14th of October about noon,—the day bright, calm, and deliciously mild, Fahrenheit's thermometer 58° in the shade,—my attention was first attracted by the path-ways swarming with numerous species of rove-beetles (Staphylinus,Oxytelus,Aleochara, &c.), which kept incessantly alighting, and hurrying about in every direction. On further examination I found a similar assemblage, with the addition of multitudes of other beetles,Halticæ,Nitidulæ,Rhyncophora,Cryptophagi, &c. on every post and rail in my walk, as well as on a wall in the neighbourhood; and on removing the decaying mortar and bark, I found that some had already taken up their abode in holes, from their situation with their antennæ folded, evidently meant for winter quarters. I am not aware that any author has noticed this remarkable congregation of coleopterous insects previously to hybernating, which it is so difficult to explain on any of the received theories of torpidity, except the pious Lesser, who so expressly alludes to it, and without quoting any other authority, that he would seem to have derived the fact from his own observation[723].

The site chosen by different perfect insects for their hybernacula is very various. Some are content with insinuatingthemselves under any large stone, a collection of dead leaves, or the moss of the sheltered side of an old wall or bank. Others prefer for a retreat the lichen or ivy-covered interstices of the bark of old trees, the decayed bark itself, especially that near the roots, or bury themselves deep in the rotten trunk; and a very great number penetrate into the earth to the depth of several inches. The aquatic tribes, such asDytisci,Hydrophili, &c. burrow into the mud of their pools; but some of these are occasionally met with under stones, bark, &c. In every instance the selected dormitory is admirably adapted to the constitution, mode of life, and wants of the occupant. Those insects which can bear considerable cold without injury, are careless of providing other than a slight covering; while the more tender species either enter the earth beyond the reach of frost, or prepare for themselves artificial cavities in substances such as moss and rotten wood, which conduct heat with difficulty, and defend them from an injuriously low temperature. It does not appear that any perfect insect has the faculty of fabricating for itself a winter abode similar to those formed of silk, &c. by some larvæ. Schmid, indeed, has mentioned findingRhagium mordaxandInquisitorin such abodes, constructed, as he thought, of the inner bark of trees; but these, as Illiger has suggested, were more probably the deserted dwellings of lepidopterous larvæ, of which the beetles in question had taken possession[724].—Most insects place themselves in their hybernacula in the attitude which they ordinarily assume when at rest; but others choose a position peculiar to their winter abode. So most of the ground-beetles(Eutrechina) adhere by their claws to the under side of the stone, which serves for their retreat, their backs being next to the ground; in which posture, probably, they are most effectually protected from wet.Gyrohypnus sanguinolentus, and other rove-beetles of the same genus, coils itself up like a snake, with the head in the centre.

The majority of insects pass the winter in perfect solitude. Occasionally, however, several individuals of one species, not merely of such insects asAnchomenus prasinus, a beetle,Pyrrhocoris apterus, a bug, &c., which usually in summer also live in a sort of society, but of others which are never seen thus to associate, asHaltica oleracea,Carabus intricatus, and severalCoccinellæ, &c. are found crowded together. This is perhaps often more through accident than design, as individuals of the same species are frequently met with singly; yet that it is not wholly accidental, seems proved by the fact that such assemblages are generally of the same genus and even species. Sometimes, however, insects of dissimilar genera and even orders are met with together. Schmid once in February found the rareLomechusa strumosatorpid in an ant-hill in the midst of a conglomerated lump of ants, with which it was closely intertwined[725].

By far the greater proportion of insects pass the winter only in one or other of the several states of egg, pupa, larva, or imago, but are never found to hybernate inmorethan one. Some species, however, depart from this rule. ThusAphis Rosæ,Cardui, and probably many others of the genus, hybernate both in the egg and perfectstate[726];Cinthia Cardui,Gonepteryx Rhamni, and some other species, usually in the pupa, but often in the perfect state also; andVanessa Io, according to the accurate Brahm, in the three states of egg, pupa, and imago[727]. It is probable that in these instances the perfect insects are females, which, not having been impregnated, have their term of life prolonged beyond the ordinary period.

The first cold weather, after insects have entered their winter quarters, produces effects upon them similar to those which occur in the dormouse, hedgehog, and others of the larger animals subject to torpor. At first a partial benumbment takes place; but the insect if touched is still capable of moving its organs. But as the cold increases all the animal functions cease. The insect breathes no longer, and has no need of a supply of air[728]; its nutritive secretions cease, and no more food is required; the muscles lose their irritability[729]; and it has all the external symptoms of death. In this state it continues during the existence of great cold, but the degree of its torpidity varies with the temperature of the atmosphere. The recurrence of a mild day, such as we sometimes have in winter, infuses a partial animation into the stiffened animal: if disturbed, its limbs and antennæ resume their power of extension, and even the faculty of spirting out their defensive fluid is re-acquired by many beetles[730]. But however mild the atmosphere in winter, the great bulk of hybernating insects, as if consciousof the deceptious nature of their pleasurable feelings, and that no food could then be procured, never quit their quarters, but quietly wait for a renewal of their insensibility by a fresh accession of cold.

On this head I have had an opportunity of making some observations which, in the paucity of recorded facts on the hybernation of insects, you may not be sorry to have laid before you. The 2nd of December 1816 was even finer than many of the preceding days of the season, which so happily falsified the predictions that the unprecedented dismal summer would be followed by a severe winter. The thermometer was 46° in the shade; not a breath of air was stirring; and a bright sun imparted animation to troops of the winter gnat (Trichocera hiemalis), which frisked under every bush; to numerousPsychodæ; and even to the flesh-fly, of which two or three individuals buzzed past me while digging in my garden. Yet though these insects, which I shall shortly advert to as exceptions to the general rule, were thus active, the heat was not sufficient to induce their hybernating brethren to quit their retreats. Removing some of the dead bark of an old apple-tree, I soon discovered several insects in their winter quarters. Of the little beetleLebia quadrinotata, DuftschmidFaun. Austr.(Carabus punctomaculatus, Ent. Brit.), I found six or eight individuals, and all so lively, that though remaining perfectly quiet in their abode until disturbed, they ran about with their ordinary activity as soon as the covering of bark was displaced. The same was the case with a colony of earwigs. Two or three individuals ofLebia quadrimaculatashowed more torpidity. When first uncovered, their antennæ werelaid back; and it was only after the sun had shone some seconds upon them that they exhibited symptoms of animation, and after stretching out these organs began to walk. Close by them lay a single weevil (Anthonomus Pomorum), but in so deep a sleep that at first I thought it dead. It gave no sign of life when placed on my hand, quite hot with the exercise of digging; and it was only after being kept there some seconds, and breathed upon several times, that it first slowly unfolded its rostrum, and then its limbs. It deserves remark, that all these insects, thus differently affected, were on the same side of the tree, under a similar covering of bark, and apparently equally exposed to the sun, which shone full upon the covering of their retreat[731].

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