CURIOSITIES RESPECTING INSECTS.—(Continued.)

Luminous Insects.

Many insects are possessed of a luminous preparation or secretion, which has all the advantages of our lamps and candles, without their inconveniences; which gives light sufficient to direct our motion; which is incapable of burning; and whose lustre is maintained without needing fresh supplies of oil, or the application of snuffers.

Of the insects thus singularly provided, the common Glow-worm (Lampyris noctiluca) is the most familiar instance.—This insect in shape somewhat resembles a caterpillar, only it is much more depressed; and the light proceeds from a pale-coloured patch that terminates, the under side of the abdomen.

It has been supposed by many, that the males of the different species of lampyris do 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 to (L. noctiluca.) Geoffrey also observed, that the male of this species has four small luminous points, two on each of the two last segments of the belly: and his observation has been recently confirmed by Miller. This last entomologist, indeed, saw only two shining spots; but from the insects 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 Geoffrey has described. In the males of L. splendidula, and of L. hemiptera, the light is very distinct, and may be seen in the former while flying. 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, and they have also the power of rendering it for a while more vivid than ordinary.

Though many of the females of the different species of lampyris are without wings, and even elytra, (in Coleoptera,) this is not the case with all. The female of L. Italica, a species common in Italy, and which, if we may trust to the accuracy of the account given by Mr. Waller, in the Philosophical Transactions for 1684, would seem to 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. Dr. Smith says, 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 prevails amongst the ladies of India.

Besides the golden species of the genus Lampyris, 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 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 those living lamps, which they called cucuij, instead of candles, in performing their evening household occupations. In travelling at night, they used to tie one to each great toe; and in fishing and hunting, required no other flambeau.—Pietro Martire’s Decades of the New World, quoted in Madoc, p. 543. 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 out,
From underneath her vest, a cage, or net
It rather might be called, so fine the twigs
Which knit it, where, confined, two fire-flies gave
Their lustre. By that light did Madoc first
Behold the features of his lovely guide.”

Pietro Martire tells us, that 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 that he has 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 Cucuie aloud, and beating the ayre with often calling out, Cucuie, 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 a sufficient 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.—Martire ubi supr. Colonies, i. 128. 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 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.—Walton’s Present State of the Spanish Colonies. And according to P. Martire, “many wanton wilde fellowes” rub their faces with “the flesh of a killed cucuij,” as boys with us use phosphorus, “with purpose to meet their neighbours with a flaming countenance,” and derive amusement from their fright.

Besides Elater noctilucus, E. ignitus, and several others of the same genus, are luminous: not fewer than twelve species of this family are described by Illiger in the Berlin Naturalist Society’s Magazine.

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 British visitors of the new world:

“——————————sorrowing we beheld
The night come on: but soon did night display
More wonders than it veil’d; innumerable tribes
From the wood-cover swarm’d, and darkness made
Their beauties visible; one while they stream’d
A bright blue radiance upon flowers that clos’d
Their gorgeous colours from the eye of day;
Now motionless and dark, eluding search,
Self-shrouded; and anon starring the sky,
Rose like a shower of fire.”

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 Thos. Cavendish and Sir John 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: a result as well entitling the elatera to a commemoration feast, as a similar good office by the land-crabs of Hispaniola, which, as the Spaniards tell, (and the story is confirmed by an anniversary Fiesta de los Cangrejos,) by their clattering being mistaken for the sound of Spanish cavalry close upon their heels, in like manner scared away a body of English invaders from the city of St. Domingo.—Walton’s Hispaniola, i. 39.

An anecdote less improbable, perhaps, and certainly more ludicrous, is related by Sir James Smith, of the effect of the first sight of the Italian fire-flies 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 the Lampyris Italica had 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; and some time elapsed before they could be divested of this idea. 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.—Tour on the Continent, 2d ed. iii. 85.

The insects hitherto adverted to have been beetles, or of the order Coleoptera. But, besides these, a genus in the order Hemiptera, called Fulgora, includes several species, which emit so powerful a light, as to have obtained in English the generic appellation of lantern-flies. Two of the most conspicuous of this tribe are the F. lanternaria and F. 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. In F. candelaria this 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 during the night have a superlatively splendid appearance.

In F. lanternaria, 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. Madam Merian informs us, that the first discovery she made of this property caused her no small alarm. The servants had brought her several of these insects, which by day-light exhibited no extraordinary appearance, and she inclosed them in a box till she should have an opportunity of drawing them, placing them 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 these fulgora was sufficiently bright to read a newspaper by. Another species, F. pyrrhorynchus, is described by Donovan, in his Insects of India; of which the light, though from a smaller snout than that of F. lanternaria, must assume a more splendid and 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.

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 in Elater noctilucus and ignitus, 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 glowworm, 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 sacks, formed of an elastic spirally-wound fibre, similar to that of the trachea, 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, not by retracting it under a membrane, as Carradori imagined, but by some inscrutable change which depends upon its will: and when the latter substance was extracted from living glowworms, it afforded no light, while the two sacks in like circumstances shone uninterruptedly for several hours. Mr. Macartney conceives, from the radiated structure of interstitial substance surrounding the oval yellow masses immediately under the transparent spot in the thorax of Elater 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 over its elytra, and that the incisures between the abdominal segments shine when stretched, may probably be extended to the whole of the interstitial substance of its body.

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 oxygen 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 glowworms; and upon the statement, that the glowworm is rendered more brilliant by the application of heat and oxygen gas, and is extinguished by cold and by hydrogen and carbonic acid gases. From these last facts, Spallanzani was led to regard the luminous matter as a compound of hydrogen and carburetted hydrogen gas. Carradori having found that the luminous portion of the belly of the Italian glowworm, lampyris Italica, shone in vacuo, in oil, in water, and when under other circumstances where the presence of oxygen gas was precluded,—with Brugnatelli, ascribed the property in question to the imbibition of light, separated from the food or air taken in the body, and afterwards secreted in a sensible form.[15] Lastly, Mr. Macartney having ascertained, by experiment, that the light of a glowworm 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,[16] 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 hypothesis 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.

Which of these opinions is the more correct, is left for future philosophers to decide.The general use of this singular provision is not much more satisfactorily ascertained than its nature. It is conjectured that it may be a means of defence against its enemies. 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, enable 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 glowworm, since their light is usually more brilliant in the female, it is most probably intended to conduct the sexes to each other.

Thine is an unobtrusive blaze,
Content in lowly shades to shine;
And much I wish, while yet I gaze,
To make thy modest merit mine!
Mrs. Opie.