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.]