CHAPTER VII.
LIGHTNING-BUGS.
Gen. Count Dejean, aide-de-camp to Napoleon, was a most enthusiastic collector of beetles; and it is even said of him that he would march his army out of its way to pass through a good collecting locality. At all times during the campaigns which he helped to render famous, his attention was not taken from his favorite occupation; and his military cap was invariably conspicuous from the gorgeous beetles that were there immolated. Every one in the army, from the emperor down to his men, was aware of what was termed his weakness; and the latter were constantly on the lookout for specimens for their commander. At the battle of Wagram, 1809, the general went into the combat with his hat as usual ornamented with beetles, which he had received that morning; and, while standing near the emperor, a shot from the enemy struck him upon the head, knocking him senseless, and destroying his collection,--the hat being completely torn in pieces. The emperor, thinking him fatally wounded, hastened to his side, asking if he was still alive; upon which the general gasped out, “I am not dead; but, alas, my insects are all gone!”
The beetles are among the most interesting of all insects; and a study of them, though casual, will well repay my young readers, who cannot fail to be interested in their peculiarities, their habits, methods of protection and defence, their intelligence in caring for their young, and the wondrous light-emitting power of some species.
In my walks about the San Gabriel Valley, I generally meet a peculiar beetle,--a large, black fellow, who lumbers along in a clumsy manner. If touched, he cannonades me with a fluid of iodine color, which has a most disagreeable odor; so much so, that upon one occasion, my nostrils being in range, I was made temporarily faint by it. The fluid stained my hands like iodine, and caused not a little irritation to the skin. The beetle, then, is a living cannon; the fluid, which is contained in certain glands, being its defence. It can be ejected or thrown two inches, so that it affords quite a protection, and probably would be effective with birds.
Many insects have a curious odor which serves several purposes,--one, in rendering them nauseous to birds and various enemies; and, again, as a means of communication among themselves. Thus, if a community of deaf and dumb persons should decide to identify themselves by certain odors, we would see a practical application of this. One family would carry musk, and be recognized some distance off by it; and so with other perfumes or odors. This is just how some beetles call each other; and in the one referred to both male and female possess the same odor.
Some of the flesh-eating beetles (Plate IX.) exhibit great ingenuity and intelligence in securing a food-supply and an asylum for their young at the same time. To their work is due the fact that the remains of few animals are found at the surface. The moment the latter die, these insects, and especially the grave-diggers (_Necrophorus_), appear. They run about the body, if upon the ground, inspecting it with great interest. If the animal is small, and the earth about it not suitable for its purpose, it is removed to softer ground; and here the beetles begin to dig, undermining the body, until in a very few hours it has disappeared or been completely buried. I have seen a garter snake covered in four hours, and some animals are sunk in this way a foot from the surface. The beetles then feed upon the body, and the female deposits her eggs there,--perhaps thirty white cylindrical objects, which in time hatch; the young being in this way provided with an ample supply of food.
The Egyptian _Scarabæus_, noted for being found in the ancient tombs and monuments, and considered sacred by some of the natives, has an interesting method of caring for its future young. It encloses the eggs in round balls of various material suitable for food; a well is then dug several inches deep, into which the beetles roll the balls, then covering them: so that, when the young appears, it is encased in the food necessary to its existence.
Passing the giant beetles of the tropics, and many others that have features of interest, we come to the forms called lightning-bugs, which, of all their tribe, impress us as marvellous, and which are especially associated with our present subject.
“Sorrowing we beheld The night come on; but soon did night display More wonders than it veiled: innumerous tribes From the wood-cover swarmed, and darkness made Their beauties visible; one while they streamed A bright blue radiance upon flowers which closed Their gorgeous colors from the eye of day; Now motionless and dark, eluded search, Self-shrouded; and anon, starring the sky, Rose like a shower of fire.”
Southey’s description of the South-American fire-flies does not ill apply to the midsummer night festivals held in our own woods and fields of the North, by the diamonds of the night. As twilight deepens, these living lights appear; creeping from beneath the bark of trees, out of the ground, or dropping from some distant limb; darting here and there in streams of light, soaring high in air, twinkling among the leaves; while down in the hollow, where the cat-tails rustle and nod, rises a veritable luminous cloud.
The producers of these displays are the lightning-bugs,--beetles belonging to the family _Lampyridæ_ (Plate X., Fig. 7). They are mainly of small size and soft texture; the _larvæ_ being flat and dark colored, and often presenting the appearance of a bit of velvet. They are carniverous in their habits, and can be found under stones and the bark of trees. The velvet-hued _larvæ_ of one species is often seen on the surface of the snow, giving rise to stories of worm showers. The family is divided, generally, into three sub-divisions; and one, the _Lampyrinæ_, is noted for the phosphorescence of many of the species. Numerous species are known throughout the world and in this country, differing much in size; those in Kentucky and other Southern States being somewhat larger than their Northern cousins. In the South and the West-India Islands they are seen to best advantage. In these isles of summer, especially Jamaica, Gosse studied their habits, and observed their nocturnal glories; and to him I am indebted for the following notes relating to the West-India species. He says at all times their sparks, of various degrees of intensity, according to the size of the species, are to be seen, fitfully gleaming by scores about the margins of woods, and in open and cultivated places. He observed about fourteen species, all luminous. _Photuris versicolor_, a large species with drab-colored _elytra_, he found abroad soon after his arrival in December. One flying around the house in the evening, he was struck with its swift and headlong flight and nearly permanent luminosity, which was much more brilliant than that of any species he had at that time seen. The large _Pygolampis_, which he called afterwards _P. xanthophotis_, he did not observe until May, when one flew into his house at Bluefields one evening; and a few nights later he found them in great numbers on the very sea-beach at Sabito. It was conspicuous for the intensity of its light, much exceeding that of _Photuris versicolor_. Sometimes it is only the last segment but two that shows luminosity; but, when excited, the whole hinder part of the abdomen is lighted up with a dazzling glare.
In June, in the woods of St. Elizabeth’s, Gosse had special opportunities for observing the _Lampyridæ_; particularly along the road leading up the mountain from Shrewsbury to Content, where it is cut through the forest, which overhangs it on each side, making it sombre even by day, and casting an impenetrable gloom over the scene by night. The darkness here, however, and especially at one point,--a little dell, which is most obscure,--is studded thick with fire-flies of various species, among which the two large ones above named are conspicuous. _Pygolampis xanthophotis_ he observed only in flight. Its light is of a rich orange color when seen abroad, but when viewed in the light of a candle appears yellow. It is not so deeply tinted as the abdominal light of _Pyrophorus noctilucus_, and is intermittent.
_Photuris versicolor_ is noticeable by its frequent resting on a twig or leaf in the woods, when it will gradually increase the intensity of its light till it glows like a torch; then it gradually fades to a spark, and becomes quite extinct. It thus remains unseen for some time; but in about a minute, or it may be two, it will begin to appear, and gradually increase to its former blaze; then fade again,--strongly reminding the beholder of the revolving light at sea. The light of this species is of a brilliant green hue. Gosse says he has seen a passing _Pyg. xanthophotis_, attracted by the glow of a stationary _Phot. versicolor_, fly upward and play around it; when the intermingling of the green and orange rays had a charming effect.
The smaller species have, some a yellow, and some a green, light. _Pyg. xanthophotis_, when held in the fingers, will frequently illuminate a segment of the abdomen, over which the light plays fitfully, sometimes momentarily clouded, more or less, but generally saturated, as it were, with most brilliant effulgence. This species occasionally comes in at open windows at night, but much more rarely than the _Photuris versicolor_ and the smaller kinds, a dozen or more of which may be seen almost every night, crawling up the walls, or flitting around the room and beneath the ceiling, of these Jamaica homes.
One of our commonest forms in the eastern United States is _Photuris pennsylvanicus_. It is about one-half of an inch in length, has a general yellowish color, with a few stripes or lines of brown or black. Both sexes have wings and quite long _elytra_.
[Illustration:
PLATE X.
1. _Scopelus humboldtii_, showing luminous spots. 2. Mother o’pearl organ from side of same. 3. _Argyropelecus._ 4. Longitudinal section of organs from abdominal region of same. 5. Luminous organ from nasal region of _Ichthyococcus_. 6. Luminous Crustacean. 7. Lampyris. 8. Light cells of same, and trachea (magnified).]
In the diurnal _Lucidota_, often seen flying in shady places, and to be remembered by the peculiar, disagreeable, milky fluid they exude when caught, the luminous organs are feebly developed. In the female they are indicated by yellow spots found on the last ventral segment, and on the last two in the male. In the genus _Pyropyga_ the light organs are inconspicuous, except in one species,--_luteicollis_. In _Pyractomena_, an attractive genus, this peculiar feature is well developed in both sexes, and the light vivid at times. The phosphorescent organs are larger in the male, and situated on the fifth and sixth ventral segments. Close examination will show in the male a large, stigma-like pore on each side, midway between the middle and the side, whose office is not perfectly understood. In the female the lanterns are at the sides of the segments. _P. lucifera_, found from Massachusetts to Texas, has extremely small luminous organs.
In the genus _Photinus_, certain species of which have parts of a roseate tint, the light-emitting organs are larger in the male than in the female, and vary considerably in position in the different species. In the male they cover the entire ventral segments, from the fourth to fifth inclusive; and on the fifth and sixth segments the little impressions or pores referred to are seen in the females. The light-organs occupy the middle portion of the ventral segments, and resemble a flat elevation upon the fifth segment. There are so many exceptions and differences, that the young naturalist will find it a particularly interesting study. Thus in _P. dimissus_ the male has the usual illuminating apparatus, while it is entirely wanting in the female.
In the group _Lampyres_ the lights are bright in the females, but variable in the males. For a long time only the male of the genus _Phengodes_ was known, the female being described as another insect. The mistake was made owing to the fact that the female never attains a development beyond the larval condition, and is the only instance among beetles where the larval female produces fertile eggs. The female is about two inches in length, of a creamy-white hue in the daytime; but at night it presents a truly magnificent appearance, emitting from the sides or margins of the segments a rich green phosphorescent light.
Another light-giver rarely seen is the _larva_ of _Mastinocerus_, a slender, cylindrical form of a pale color. It lives upon snails, and is feebly luminous. Mrs. King thus writes to Dr. le Conte concerning it: “June 4, saw running rapidly over the table, near a lighted lamp, a small Coleopter; it was twisting its abdomen up over its wings, and evidently trying to straighten them out, as they seemed moist and twisted at their ends. The general appearance suggested _Mastinocerus_; and, acting on this thought, I captured it, and sat up till a late hour to be assured of the truth. The insect was in a small phial, and moved quickly. It gave out light conspicuously from the head, feebly from the anal end, and still more so from about the base of the abdomen. The light seen in the head, though visible in the dark as a round spot, yet, when taken into a room obscurely lighted, was invisible from above; but, when the insect was suddenly thrown upon its back, a light no larger than a pin-point was seen just about the junction of the head and prothorax.”
The method of illumination in this group is intermittent, the light appearing as repeated flashes: hence the term “lightning-bugs” in contrast to the steady gleam of the fire-flies or Elaters. Mr. A. E. Eaton has counted the flashes in _Luciola lusitanica_, and found that there were thirty-six in a minute, each flash lasting from one-fourth to one-third of a second.[37]
The light of some species is intense, while that of others is very feeble. By placing detached parts of the luminous organs upon a page, I have been able to make out the type; and, if numbers of living lightning-bugs are confined, they can be utilized as a lamp,--rather a dull one, it must be confessed, unless the numbers are greatly augmented. The _larvæ_, as well as the _imagos_, are often luminous; even the eggs of some emit light.
An examination of the luminous organs during the daytime shows them to be yellowish or whitish patches on the various segments. If the hand is held over them, the light is seen, and in complete darkness they present a magnificent spectacle,--the light dying away, then growing intense, about the spot, so that it appears to be fairly trembling with heat, as if some chemical action was periodically asserting itself, causing the tissues to become suffused with a fiery glow; yet, if the most delicate thermometer is placed against the luminous organs of a large number of these insects, there is not the slightest elevation to show the presence of heat. If now we kill the insect, and remove the luminous matter, it resembles a bit of starch with luminous spots; and pressure, which admits more oxygen, causes a temporary increase in the light.
The luminous organs are similar in structure to the fat body of the insect, and are made up of light-emitting cells (Plate X., Fig. 8), surrounded by a maze of _tracheæ_, or air-tubes. In explanation of the light, it has been suggested that the cells secrete phosphuretted hydrogen, which becomes luminous upon contact with oxygen which reaches it through the minute air-tubes. Regarding _Luciola Italica_, Professor Emery says that the male _Luciolæ_ gave out light in two distinct modes: in the night, when they are brisk and fly about, the light increases and decreases at short, regular intervals, so that it seems to twinkle. If one of them is caught flying, or disturbed in its rest by day, it shines less than at the maximum of its intensity when on the wing, but without intermission. It is remarked, however, that the luminous plates do not shine uniformly over their whole extent; but that sometimes one spot, and sometimes another, glows more strongly. If such a specimen is examined under the microscope, we perceive, on a dark background, bright, luminous rings, which are not, however, uniformly brilliant, but display certain more intense points, which flash up, and again disappear, or continue to shine on faintly for a time, re-appearing afterward in full splendor. These changes take place without any regular succession.[38]
The common lightning-bugs of Europe are _Lampyris noctiluca_ (Plate IX., Fig. _d_) and _L. splendidula_ (Fig. _a_). Their life history is an interesting study, and a brief description will apply to all. In early spring we find the little yellow eggs, perhaps gleaming with the wonderful phosphorescence, and thus finding protection, attached to blades of grass or other objects just above ground. The _larva_ (Plate IX., Fig. _c_), a long, narrow, flat creature, soon appears and begins a predatory life; even being provided with an apparatus for removing the mucus of its victim. About the month of April it attains its full vigor, and during the summer changes to the pupa form, or hibernates all winter, entering a deep sleep, and assuming its new shape the following spring. We see the light from the very first in the eggs of some; then in the _larva_, there appearing like little sacs on the under surface, one on each side of the middle line, so arranged that the insect can hide them by retracting the body, and causing them to blaze out when the abdomen is extended. Nothing in all nature is more wonderful than the changes through which these and other insects pass before attaining adult growth.
The _larva_ is a busy little creature, full of life; but, when about to change, it becomes lethargic and quiet, as if impressed with the importance of the coming metamorphosis. Finally it wriggles out of its old skin, and becomes a _pupa_, also luminous; exceedingly lively, yet with its motions restricted. It moves its _antennæ_ and legs, and pushes itself along by movements of the abdomen. Finally the perfect insect appears, with its wondrous array of lights, so little understood, and which, if accompanied with the ordinary amount of heat attendant upon such a display, would soon roast or fry its possessor. As to the use of the lights, we can only conjecture. It has been shown that one insect recognized the other by it, and thus it may be a sign language; while, according to others, it is a warning to birds and other enemies.
Mr. Darwin thus refers to the lightning-bug of South America: “All the fire-flies which I caught here (at Rio) belonged to the _Lampyridæ_ (in which family the English glow-worm is included), and the greater number of specimens were of _Lampyris occidentalis_. I found that this insect emitted the most brilliant flashes when irritated; in the intervals, the abdominal rings were obscured. The flash was almost co-instantaneous in the two rings, but it was just perceptible first in the anterior one. The shining matter was fluid and very adhesive; little spots, where the skin had been torn, continued bright with a slight scintillation, whilst the uninjured parts were obscured. When the insect was decapitated, the rings remained uninterruptedly bright, but not so brilliant as before. Local irritation with a needle always increased the vividness of the light. The rings in one instance retained their luminous property nearly twenty-four hours after the death of the insect. From these facts it would appear probable that the animal has only the power of concealing or extinguishing the light for short intervals, and that at other times the display is voluntary. On the muddy and wet gravel walks, I found the _larvæ_ of _Lampyris_ in great numbers. They resembled in general form the female of the English glow-worm. These _larvæ_ possessed but feeble luminous powers; and on the slightest touch they feigned death, and ceased to shine; nor did irritation excite any fresh display.”
[Illustration:
PLATE XI.
LUMINOUS BEETLE. (_Pyrophorus noctilucus._)
In burrow of Mole Cricket.]