Few insects in our climes vie in popular fame with the Glow-worm, that
curious little animal which, to celebrate the little joys of life,
kindles a beacon at its tail-end. Who does not know it, at least by
name? Who has not seen it roam amid the grass, like a spark fallen from
the moon at its full? The Greeks of old called it lampouris, meaning,
the bright-tailed. Science employs the same term: it calls it the
lantern-bearer, Lampyris noctiluca, Lin. In this case the common name
is inferior to the scientific phrase, which, when translated, becomes
both expressive and accurate.
In fact, we might easily cavil at the word "worm." The Lampyris is not
a worm at all, not even in general appearance. He has six short legs,
which he well knows how to use; he is a gad-about, a trot-about. In the
adult state the male is correctly garbed in wing-cases, like the true
Beetle that he is. The female is an ill-favoured thing who knows naught
of the delights of flying: all her life long she retains the larval
shape, which, for the rest, is similar to that of the male, who himself
is imperfect so long as he has not achieved the maturity that comes
with pairing-time. Even in this initial stage the word "worm" is out of
place. We French have the expression "Naked as a worm" to point to the
lack of any defensive covering. Now the Lampyris is clothed, that is to
say, he wears an epidermis of some consistency; moreover, he is rather
richly coloured: his body is dark brown all over, set off with pale
pink on the thorax, especially on the lower surface. Finally, each
segment is decked at the hinder edge with two spots of a fairly bright
red. A costume like this was never worn by a worm.
Let us leave this ill-chosen denomination and ask ourselves what the
Lampyris feeds upon. That master of the art of gastronomy,
Brillat-Savarin, said: "Show me what you eat and I will tell you what
you are."
A similar question should be addressed, by way of a preliminary, to
every insect whose habits we propose to study, for, from the least to
the greatest in the zoological progression, the stomach sways the
world; the data supplied by food are the chief of all the documents of
life. Well, in spite of his innocent appearance, the Lampyris is an
eater of flesh, a hunter of game; and he follows his calling with rare
villainy. His regular prey is the Snail.
This detail has long been known to entomologists. What is not so well
known, what is not known at all yet, to judge by what I have read, is
the curious method of attack, of which I have seen no other instance
anywhere.
Before he begins to feast, the Glow-worm administers an anaesthetic: he
chloroforms his victim, rivalling in the process the wonders of our
modern surgery, which renders the patient insensible before operating
on him. The usual game is a small Snail hardly the size of a cherry,
such as, for instance, Helix variabilis, Drap., who, in the hot
weather, collects in clusters on the stiff stubble and other long, dry
stalks by the road-side and there remains motionless, in profound
meditation, throughout the scorching summer days. It is in some such
resting-place as this that I have often been privileged to light upon
the Lampyris banqueting on the prey which he had just paralysed on its
shaky support by his surgical artifices.
But he is familiar with other preserves. He frequents the edges of the
irrigating ditches, with their cool soil, their varied vegetation, a
favourite haunt of the Mollusc. Here, he treats the game on the ground;
and, under these conditions, it is easy for me to rear him at home and
to follow the operator's performance down to the smallest detail.
I will try to make the reader a witness of the strange sight. I place a
little grass in a wide glass jar. In this I instal a few Glow-worms and
a provision of snails of a suitable size, neither too large nor too
small, chiefly Helix variabilis. We must be patient and wait. Above
all, we must keep an assiduous watch, for the desired events come
unexpectedly and do not last long.
Here we are at last. The Glow-worm for a moment investigates the prey,
which, according to its habit, is wholly withdrawn in the shell, except
the edge of the mantle, which projects slightly. Then the hunter's
weapon is drawn, a very simple weapon, but one that cannot be plainly
perceived without the aid of a lens. It consists of two mandibles bent
back powerfully into a hook, very sharp and as thin as a hair. The
microscope reveals the presence of a slender groove running throughout
the length. And that is all.
The insect repeatedly taps the Snail's mantle with its instrument. It
all happens with such gentleness as to suggest kisses rather than
bites. As children, teasing one another, we used to talk of "tweaksies"
to express a slight squeeze of the finger-tips, something more like a
tickling than a serious pinch. Let us use that word. In conversing with
animals, language loses nothing by remaining juvenile. It is the right
way for the simple to understand one another.
The Lampyris doles out his tweaks. He distributes them methodically,
without hurrying, and takes a brief rest after each of them, as though
he wished to ascertain the effect produced. Their number is not great:
half a dozen, at most, to subdue the prey and deprive it of all power
of movement. That other pinches are administered later, at the time of
eating, seems very likely, but I cannot say anything for certain,
because the sequel escapes me. The first few, however--there are never
many--are enough to impart inertia and loss of all feeling to the
Mollusc, thanks to the prompt, I might almost say lightning, methods of
the Lampyris, who, beyond a doubt, instils some poison or other by
means of his grooved hooks.
Here is the proof of the sudden efficacy of those twitches, so mild in
appearance: I take the Snail from the Lampyris, who has operated on the
edge of the mantle some four or five times. I prick him with a fine
needle in the fore-part, which the animal, shrunk into its shell, still
leaves exposed. There is no quiver of the wounded tissues, no reaction
against the brutality of the needle. A corpse itself could not give
fewer signs of life.
Here is something even more conclusive: chance occasionally gives me
Snails attacked by the Lampyris while they are creeping along, the foot
slowly crawling, the tentacles swollen to their full extent. A few
disordered movements betray a brief excitement on the part of the
Mollusc and then everything ceases: the foot no longer slugs; the front
part loses its graceful swan-neck curve; the tentacles become limp and
give way under their own weight, dangling feebly like a broken stick.
This condition persists.
Is the Snail really dead? Not at all, for I can resuscitate the seeming
corpse at will. After two or three days of that singular condition
which is no longer life and yet not death, I isolate the patient and,
though this is not really essential to success, I give him a douche
which will represent the shower so dear to the able-bodied Mollusc. In
about a couple of days, my prisoner, but lately injured by the
Glow-worm's treachery, is restored to his normal state. He revives, in
a manner; he recovers movement and sensibility. He is affected by the
stimulus of a needle; he shifts his place, crawls, puts out his
tentacles, as though nothing unusual had occurred. The general torpor,
a sort of deep drunkenness, has vanished outright. The dead returns to
life. What name shall we give to that form of existence which, for a
time, abolishes the power of movement and the sense of pain? I can see
but one that is approximately suitable: anaesthesia. The exploits of a
host of Wasps whose flesh-eating grubs are provided with meat that is
motionless though not dead have taught us the skilful art of the
paralysing insect, which numbs the locomotory nerve-centres with its
venom. We have now a humble little animal that first produces complete
anaesthesia in its patient. Human science did not in reality invent
this art, which is one of the wonders of latter-day surgery. Much
earlier, far back in the centuries, the Lampyris and, apparently,
others knew it as well. The animal's knowledge had a long start of
ours; the method alone has changed. Our operators proceed by making us
inhale the fumes of ether or chloroform; the insect proceeds by
injecting a special virus that comes from the mandibular fangs in
infinitesimal doses. Might we not one day be able to benefit from this
hint? What glorious discoveries the future would have in store for us,
if we understood the beastie's secrets better!
What does the Lampyris want with anaesthetical talent against a
harmless and moreover eminently peaceful adversary, who would never
begin the quarrel of his own accord? I think I see. We find in Algeria
a beetle known as Drilus maroccanus, who, though non-luminous,
approaches our Glow-worm in his organization and especially in his
habits. He, too, feeds on Land Molluscs. His prey is a Cyclostome with
a graceful spiral shell, tightly closed with a stony lid which is
attached to the animal by a powerful muscle. The lid is a movable door
which is quickly shut by the inmate's mere withdrawal into his house
and as easily opened when the hermit goes forth. With this system of
closing, the abode becomes inviolable; and the Drilus knows it.
Fixed to the surface of the shell by an adhesive apparatus whereof the
Lampyris will presently show us the equivalent, he remains on the
look-out, waiting, if necessary, for whole days at a time. At last the
need of air and food obliges the besieged non-combatant to show
himself: at least, the door is set slightly ajar. That is enough. The
Drilus is on the spot and strikes his blow. The door can no longer be
closed; and the assailant is henceforth master of the fortress. Our
first impression is that the muscle moving the lid has been cut with a
quick-acting pair of shears. This idea must be dismissed. The Drilus is
not well enough equipped with jaws to gnaw through a fleshy mass so
promptly. The operation has to succeed at once, at the first touch: if
not, the animal attacked would retreat, still in full vigour, and the
siege must be recommenced, as arduous as ever, exposing the insect to
fasts indefinitely prolonged. Although I have never come across the
Drilus, who is a stranger to my district, I conjecture a method of
attack very similar to that of the Glow-worm. Like our own Snail-eater,
the Algerian insect does not cut its victim into small pieces: it
renders it inert, chloroforms it by means of a few tweaks which are
easily distributed, if the lid but half-opens for a second. That will
do. The besieger thereupon enters and, in perfect quiet, consumes a
prey incapable of the least muscular effort. That is how I see things
by the unaided light of logic.
Let us now return to the Glow-worm. When the Snail is on the ground,
creeping, or even shrunk into his shell, the attack never presents any
difficulty. The shell possesses no lid and leaves the hermit's
fore-part to a great extent exposed. Here, on the edges of the mantle,
contracted by the fear of danger, the Mollusc is vulnerable and
incapable of defence. But it also frequently happens that the Snail
occupies a raised position, clinging to the tip of a grass-stalk or
perhaps to the smooth surface of a stone. This support serves him as a
temporary lid; it wards off the aggression of any churl who might try
to molest the inhabitant of the cabin, always on the express condition
that no slit show itself anywhere on the protecting circumference. If,
on the other hand, in the frequent case when the shell does not fit its
support quite closely, some point, however tiny, be left uncovered,
this is enough for the subtle tools of the Lampyris, who just nibbles
at the Mollusc and at once plunges him into that profound immobility
which favours the tranquil proceedings of the consumer.
These proceedings are marked by extreme prudence. The assailant has to
handle his victim gingerly, without provoking contractions which would
make the Snail let go his support and, at the very least, precipitate
him from the tall stalk whereon he is blissfully slumbering. Now any
game falling to the ground would seem to be so much sheer loss, for the
Glow-worm has no great zeal for hunting-expeditions: he profits by the
discoveries which good luck sends him, without undertaking assiduous
searches. It is essential, therefore, that the equilibrium of a prize
perched on the top of a stalk and only just held in position by a touch
of glue should be disturbed as little as possible during the onslaught;
it is necessary that the assailant should go to work with infinite
circumspection and without producing pain, lest any muscular reaction
should provoke a fall and endanger the prize. As we see, sudden and
profound anaesthesia is an excellent means of enabling the Lampyris to
attain his object, which is to consume his prey in perfect quiet.
What is his manner of consuming it? Does he really eat, that is to say,
does he divide his food piecemeal, does he carve it into minute
particles, which are afterwards ground by a chewing-apparatus? I think
not. I never see a trace of solid nourishment on my captives' mouths.
The Glow-worm does not eat in the strict sense of the word: he drinks
his fill; he feeds on a thin gruel into which he transforms his prey by
a method recalling that of the maggot. Like the flesh-eating grub of
the Fly, he too is able to digest before consuming; he liquefies his
prey before feeding on it.
This is how things happen: a Snail has been rendered insensible by the
Glow-worm. The operator is nearly always alone, even when the prize is
a large one, like the common Snail, Helix aspersa. Soon a number of
guests hasten up--two, three, or more--and, without any quarrel with
the real proprietor, all alike fall to. Let us leave them to themselves
for a couple of days and then turn the shell, with the opening
downwards. The contents flow out as easily as would soup from an
overturned saucepan. When the sated diners retire from this gruel, only
insignificant leavings remain.
The matter is obvious. By repeated tiny bites, similar to the tweaks
which we saw distributed at the outset, the flesh of the Mollusc is
converted into a gruel on which the various banqueters nourish
themselves without distinction, each working at the broth by means of
some special pepsine and each taking his own mouthfuls of it. In
consequence of this method, which first converts the food into a
liquid, the Glow-worm's mouth must be very feebly armed apart from the
two fangs which sting the patient and inject the anaesthetic poison and
at the same time, no doubt, the serum capable of turning the solid
flesh into fluid. Those two tiny implements, which can just be examined
through the lens, must, it seems, have some other object. They are
hollow, and in this resemble those of the Ant-lion, who sucks and
drains her capture without having to divide it; but there is this great
difference, that the Ant-lion leaves copious remnants, which are
afterwards flung outside the funnel-shaped trap dug in the sand,
whereas the Glow-worm, that expert liquifier, leaves nothing, or next
to nothing. With similar tools, the one simply sucks the blood of his
prey and the other turns every morsel of his to account, thanks to a
preliminary liquefaction.
And this is done with exquisite precision, though the equilibrium is
sometimes anything but steady. My rearing-glasses supply me with
magnificent examples. Crawling up the sides, the Snails imprisoned in
my apparatus sometimes reach the top, which is closed with a glass
pane, and fix themselves to it with a speck of glair. This is a mere
temporary halt, in which the Mollusc is miserly with his adhesive
product, and the merest shake is enough to loosen the shell and send it
to the bottom of the jar.
Now it is not unusual for the Glow-worm to hoist himself up there, with
the help of a certain climbing-organ that makes up for his weak legs.
He selects his quarry, makes a minute inspection of it to find an
entrance-slit, nibbles at it a little, renders it insensible and,
without delay, proceeds to prepare the gruel which he will consume for
days on end.
When he leaves the table, the shell is found to be absolutely empty;
and yet this shell, which was fixed to the glass by a very faint
stickiness, has not come loose, has not even shifted its position in
the smallest degree: without any protest from the hermit gradually
converted into broth, it has been drained on the very spot at which the
first attack was delivered. These small details tell us how promptly
the anaesthetic bite takes effect; they teach us how dexterously the
Glow-worm treats his Snail without causing him to fall from a very
slippery, vertical support and without even shaking him on his slight
line of adhesion.
Under these conditions of equilibrium, the operator's short, clumsy
legs are obviously not enough; a special accessory apparatus is needed
to defy the danger of slipping and to seize the unseizable. And this
apparatus the Lampyris possesses. At the hinder end of the animal we
see a white spot which the lens separates into some dozen short, fleshy
appendages, sometimes gathered into a cluster, sometimes spread into a
rosette. There is your organ of adhesion and locomotion. If he would
fix himself somewhere, even on a very smooth surface, such as a
grass-stalk, the Glow-worm opens his rosette and spreads it wide on the
support, to which it adheres by its own stickiness. The same organ,
rising and falling, opening and closing, does much to assist the act of
progression. In short, the Glow-worm is a new sort of self-propelled
cripple, who decks his hind-quarters with a dainty white rose, a kind
of hand with twelve fingers, not jointed, but moving in every
direction: tubular fingers which do not seize, but stick.
The same organ serves another purpose: that of a toilet-sponge and
brush. At a moment of rest, after a meal, the Glow-worm passes and
repasses the said brush over his head, back, sides and hinder parts, a
performance made possible by the flexibility of his spine. This is done
point by point, from one end of the body to the other, with a
scrupulous persistency that proves the great interest which he takes in
the operation. What is his object in thus sponging himself, in dusting
and polishing himself so carefully? It is a question, apparently, of
removing a few atoms of dust or else some traces of viscidity that
remain from the evil contact with the Snail. A wash and brush-up is not
superfluous when one leaves the tub in which the Mollusc has been
treated.
If the Glow-worm possessed no other talent than that of chloroforming
his prey by means of a few tweaks resembling kisses, he would be
unknown to the vulgar herd; but he also knows how to light himself like
a beacon; he shines, which is an excellent manner of achieving fame.
Let us consider more particularly the female, who, while retaining her
larval shape, becomes marriageable and glows at her best during the
hottest part of summer. The lighting-apparatus occupies the last three
segments of the abdomen. On each of the first two it takes the form, on
the ventral surface, of a wide belt covering almost the whole of the
arch; on the third the luminous part is much less and consists simply
of two small crescent-shaped markings, or rather two spots which shine
through to the back and are visible both above and below the animal.
Belts and spots emit a glorious white light, delicately tinged with
blue. The general lighting of the Glow-worm thus comprises two groups:
first, the wide belts of the two segments preceding the last; secondly,
the two spots of the final segments. The two belts, the exclusive
attribute of the marriageable female, are the parts richest in light:
to glorify her wedding, the future mother dons her brightest gauds; she
lights her two resplendent scarves. But, before that, from the time of
the hatching, she had only the modest rush-light of the stern. This
efflorescence of light is the equivalent of the final metamorphosis,
which is usually represented by the gift of wings and flight. Its
brilliance heralds the pairing-time. Wings and flight there will be
none: the female retains her humble larval form, but she kindles her
blazing beacon.
The male, on his side, is fully transformed, changes his shape,
acquires wings and wing-cases; nevertheless, like the female, he
possesses, from the time when he is hatched, the pale lamp of the end
segment. This luminous aspect of the stern is characteristic of the
entire Glow-worm tribe, independently of sex and season. It appears
upon the budding grub and continues throughout life unchanged. And we
must not forget to add that it is visible on the dorsal as well as on
the ventral surface, whereas the two large belts peculiar to the female
shine only under the abdomen.
My hand is not so steady nor my sight so good as once they were; but,
as far as they allow me, I consult anatomy for the structure of the
luminous organs. I take a scrap of the epidermis and manage to separate
pretty nearly half of one of the shining belts. I place my preparation
under the microscope. On the skin a sort of white-wash lies spread,
formed of a very fine, granular substance. This is certainly the
light-producing matter. To examine this white layer more closely is
beyond the power of my weary eyes. Just beside it is a curious
air-tube, whose short and remarkably wide stem branches suddenly into a
sort of bushy tuft of very delicate ramifications. These creep over the
luminous sheet, or even dip into it. That is all.
The luminescence, therefore, is controlled by the respiratory organs
and the work produced is an oxidation. The white sheet supplies the
oxidizable matter and the thick air-tube spreading into a tufty bush
distributes the flow of air over it. There remains the question of the
substance whereof this sheet is formed. The first suggestion was
phosphorus, in the chemist's sense of the word. The Glow-worm was
calcined and treated with the violent reagents that bring the simple
substances to light; but no one, so far as I know, has obtained a
satisfactory answer along these lines. Phosphorus seems to play no part
here, in spite of the name of phosphorescence which is sometimes
bestowed upon the Glow-worm's gleam. The answer lies elsewhere, no one
knows where.
We are better-informed as regards another question. Has the Glow-worm a
free control of the light which he emits? Can he turn it on or down or
put it out as he pleases? Has he an opaque screen which is drawn over
the flame at will, or is that flame always left exposed? There is no
need for any such mechanism: the insect has something better for its
revolving light.
The thick air-tube supplying the light-producing sheet increases the
flow of air and the light is intensified; the same tube, swayed by the
animal's will, slackens or even suspends the passage of air and the
light grows fainter or even goes out. It is, in short, the mechanism of
a lamp which is regulated by the access of air to the wick.
Excitement can set the attendant air-duct in motion. We must here
distinguish between two cases: that of the gorgeous scarves, the
exclusive ornament of the female ripe for matrimony, and that of the
modest fairy-lamp on the last segment, which both sexes kindle at any
age. In the second case, the extinction caused by a flurry is sudden
and complete, or nearly so. In my nocturnal hunts for young Glow-worms,
measuring about 5 millimetres long (.195 inch.--Translator's Note.), I
can plainly see the glimmer on the blades of grass; but, should the
least false step disturb a neighbouring twig, the light goes out at
once and the coveted insect becomes invisible. Upon the full-grown
females, lit up with their nuptial scarves, even a violent start has
but a slight effect and often none at all.
I fire a gun beside a wire-gauze cage in which I am rearing my
menagerie of females in the open air. The explosion produces no result.
The illumination continues, as bright and placid as before. I take a
spray and rain down a slight shower of cold water upon the flock. Not
one of my animals puts out its light; at the very most, there is a
brief pause in the radiance; and then only in some cases. I send a puff
of smoke from my pipe into the cage. This time the pause is more
marked. There are even some extinctions, but these do not last long.
Calm soon returns and the light is renewed as brightly as ever. I take
some of the captives in my fingers, turn and return them, tease them a
little. The illumination continues and is not much diminished, if I do
not press hard with my thumb. At this period, with the pairing close at
hand, the insect is in all the fervour of its passionate splendour, and
nothing short of very serious reasons would make it put out its signals
altogether.
All things considered, there is not a doubt but that the Glow-worm
himself manages his lighting apparatus, extinguishing and rekindling it
at will; but there is one point at which the voluntary agency of the
insect is without effect. I detach a strip of the epidermis showing one
of the luminescent sheets and place it in a glass tube, which I close
with a plug of damp wadding, to avoid an over-rapid evaporation. Well,
this scrap of carcass shines away merrily, although not quite as
brilliantly as on the living body.
Life's aid is now superfluous. The oxidizable substance, the
luminescent sheet, is in direct communication with the surrounding
atmosphere; the flow of oxygen through an air-tube is not necessary;
and the luminous emission continues to take place, in the same way as
when it is produced by the contact of the air with the real phosphorus
of the chemists. Let us add that, in aerated water, the luminousness
continues as brilliant as in the free air, but that it is extinguished
in water deprived of its air by boiling. No better proof could be found
of what I have already propounded, namely, that the Glow-worm's light
is the effect of a slow oxidation.
The light is white, calm and soft to the eyes and suggests a spark
dropped by the full moon. Despite its splendour, it is a very feeble
illuminant. If we move a Glow-worm along a line of print, in perfect
darkness, we can easily make out the letters, one by one, and even
words, when these are not too long; but nothing more is visible beyond
a narrow zone. A lantern of this kind soon tires the reader's patience.
Suppose a group of Glow-worms placed almost touching one another. Each
of them sheds its glimmer, which ought, one would think, to light up
its neighbours by reflexion and give us a clear view of each individual
specimen. But not at all: the luminous party is a chaos in which our
eyes are unable to distinguish any definite form at a medium distance.
The collective lights confuse the light-bearers into one vague whole.
Photography gives us a striking proof of this. I have a score of
females, all at the height of their splendour, in a wire-gauze cage in
the open air. A tuft of thyme forms a grove in the centre of their
establishment. When night comes, my captives clamber to this pinnacle
and strive to show off their luminous charms to the best advantage at
every point of the horizon, thus forming along the twigs marvellous
clusters from which I expected magnificent effects on the
photographer's plates and paper. My hopes were disappointed. All that I
obtain is white, shapeless patches, denser here and less dense there
according to the numbers forming the group. There is no picture of the
Glow-worms themselves; not a trace either of the tuft of thyme. For
want of satisfactory light, the glorious firework is represented by a
blurred splash of white on a black ground.
The beacons of the female Glow-worms are evidently nuptial signals,
invitations to the pairing; but observe that they are lighted on the
lower surface of the abdomen and face the ground, whereas the summoned
males, whose flights are sudden and uncertain, travel overhead, in the
air, sometimes a great way up. In its normal position, therefore, the
glittering lure is concealed from the eyes of those concerned; it is
covered by the thick bulk of the bride. The lantern ought really to
gleam on the back and not under the belly; otherwise the light is
hidden under a bushel.
The anomaly is corrected in a very ingenious fashion, for every female
has her little wiles of coquetry. At nightfall, every evening, my caged
captives make for the tuft of thyme with which I have thoughtfully
furnished the prison and climb to the top of the upper branches, those
most in sight. Here, instead of keeping quiet, as they did at the foot
of the bush just now, they indulge in violent exercises, twist the tip
of their very flexible abdomen, turn it to one side, turn it to the
other, jerk it in every direction. In this way, the searchlight cannot
fail to gleam, at one moment or another, before the eyes of every male
who goes a-wooing in the neighbourhood, whether on the ground or in the
air.
It is very like the working of the revolving mirror used in catching
Larks. If stationary, the little contrivance would leave the bird
indifferent; turning and breaking up its light in rapid flashes, it
excites it.
While the female Glow-worm has her tricks for summoning her swains, the
male, on his side, is provided with an optical apparatus suited to
catch from afar the least reflection of the calling signal. His
corselet expands into a shield and overlaps his head considerably in
the form of a peaked cap or a shade, the object of which appears to be
to limit the field of vision and concentrate the view upon the luminous
speck to be discerned. Under this arch are the two eyes, which are
relatively enormous, exceedingly convex, shaped like a skull-cap and
contiguous to the extent of leaving only a narrow groove for the
insertion of the antennae. This double eye, occupying almost the whole
face of the insect and contained in the cavern formed by the spreading
peak of the corselet, is a regular Cyclops' eye.
At the moment of the pairing the illumination becomes much fainter, is
almost extinguished; all that remains alight is the humble fairy-lamp
of the last segment. This discreet night-light is enough for the
wedding, while, all around, the host of nocturnal insects, lingering
over their respective affairs, murmur the universal marriage-hymn. The
laying follows very soon. The round, white eggs are laid, or rather
strewn at random, without the least care on the mother's part, either
on the more or less cool earth or on a blade of grass. These brilliant
ones know nothing at all of family affection.
Here is a very singular thing: the Glow-worm's eggs are luminous even
when still contained in the mother's womb. If I happen by accident to
crush a female big with germs that have reached maturity, a shiny
streak runs along my fingers, as though I had broken some vessel filled
with a phosphorescent fluid. The lens shows me that I am wrong. The
luminosity comes from the cluster of eggs forced out of the ovary.
Besides, as laying-time approaches, the phosphorescence of the eggs is
already made manifest through this clumsy midwifery. A soft opalescent
light shines through the integument of the belly.
The hatching follows soon after the laying. The young of either sex
have two little rush-lights on the last segment. At the approach of the
severe weather they go down into the ground, but not very far. In my
rearing-jars, which are supplied with fine and very loose earth, they
descend to a depth of three or four inches at most. I dig up a few in
mid-winter. I always find them carrying their faint stern-light. About
the month of April they come up again to the surface, there to continue
and complete their evolution.
From start to finish the Glow-worm's life is one great orgy of light.
The eggs are luminous; the grubs likewise. The full-grown females are
magnificent lighthouses, the adult males retain the glimmer which the
grubs already possessed. We can understand the object of the feminine
beacon; but of what use is all the rest of the pyrotechnic display? To
my great regret, I cannot tell. It is and will be, for many a day to
come, perhaps for all time, the secret of animal physics, which is
deeper than the physics of the books.