THE GEOTRUPES: THE LARVA
The egg takes from one to two weeks to hatch, according as it is laid
in October or September. As a rule the hatching takes place in the
first fortnight of October. The larva grows pretty quickly and soon
manifests very different characteristics from those displayed by the
other Dung-beetles. We find ourselves in a new world, full of
surprises. The grub is folded in two, it is bent into a hook, as
required by the narrowness of the cell, which is scooped out gradually
as the inside of the sausage is consumed.
Even so did the grubs of the Sacred Beetle, the Copris and the others
comport themselves; but the larva of the Geotrupes has not the hump
that gave the first-named such an ungainly figure. Its back is curved
regularly. This entire absence of a knapsack, of a putty-bag, points to
different habits. The larva, in fact, is not acquainted with the art of
plugging crevices. If I contrive an opening in the part of the sausage
which it occupies, I do not see it taking note of the hole, turning
round and forthwith repairing the damage with a few pats of a trowel
well supplied with cement. The access of the air does not trouble it
apparently, or rather there is no provision against this in its means
of defence.
You have only to take a glance at its dwelling. What would be the use
of the plasterer’s art of stopping up crannies, when the house simply
cannot crack? Closely moulded in the cylinder of the burrow, the
sausage is preserved from crumbling to dust by the support of its
mould. The Sacred Beetle’s pear, which is free on every side in a large
underground cavity, often swells, splits, peels off. The Geotrupes’
sausage, being packed in a casing, is free from these imperfections.
Besides, if it were to burst, the accident would not be serious, for
now, in autumn and winter, in a soil that is always damp and fresh,
there is no fear of that desiccation which is so greatly dreaded by the
pill-rollers. Hence there is no special industry designed to circumvent
a peril that is unlikely and of little consequence; no excessively
docile intestine to keep the trowel supplied; no ugly hump to act as a
mortar-magazine. The inexhaustible evacuator of our earlier studies
disappears and is replaced by a grub whose motions are more moderate.
Obviously, big eater as the larva is and, moreover, sequestered in a
cell allowing of no communication with the outside, it is utterly
ignorant of what we call cleanliness. Let us not take this to mean that
it is disgustingly filthy, soiled with excrement: we should be making a
grave mistake. Nothing could be neater or glossier than its satiny
skin. We wonder what pains it must take over its toilet, or else what
special grace enables all these eaters of ordure to keep themselves so
clean. Seeing them outside their usual environment, no one would
suspect their sordid life.
We must look elsewhere for any defect in cleanliness, if indeed it is
right to give the name of defect to a quality which, all things
considered, makes for the creature’s good. Language, the one and only
mirror of our thoughts, easily goes astray and becomes treacherous when
attempting to express reality. Let us substitute the larva’s point of
view for our own, let us throw off the man and become the Dung-beetle:
offensive epithets will disappear forthwith.
The grub, that mighty eater, has no relations with the outside world.
What is it to do with the remains of what it has digested? Far from
being embarrassed by them, it takes advantage of them, as do many other
solitaries cabined in a shell. It uses them to keep out the draughts
from its hermitage and to pad it with quilting. It spreads them into a
soft couch, grateful to its delicate skin; it builds them into a
polished niche, a water-tight alcove which will protect the long winter
torpor. I told you that one had but to imagine one’s self a Dung-beetle
for a moment in order to change one’s language utterly. Behold that
which was hateful and burdensome turned into something of value, which
will contribute largely to the grub’s welfare. Onthophagi and Copres,
Scarabæi and Gymnopleuri have accustomed us to this kind of industry.
The sausage is in an upright position, or nearly so. The
hatching-chamber is at the bottom end. As the grub grows, it attacks
the provisions overhead, but does not touch the wall around, which is
of considerable thickness. It has indeed so huge a dish at its disposal
that abstinence becomes no difficult matter. The Sacred Beetle’s grub,
which has no occasion to take precautions against the winter, has a
very skimpy helping. Its little pear is a niggardly ration and is
consumed throughout, all but a slender wall, which the inmate, however,
takes care to thicken and strengthen with a good layer of its mortar.
The grub of the Geotrupes is very differently situated. It is supplied
with a colossal sausage, representing nearly a dozen times as much as
the other provisions. However well endowed it be with stomach and
appetite, it could not possibly consume the whole lot. Besides, the
question of food is not the only one to be considered this time: there
is also the serious matter of the hibernation. The parents foresaw the
severity of the winter and bequeathed their sons the wherewithal to
face it. The giant roly-poly will become a blanket against the cold.
The grub, as a matter of fact, gnaws bit by bit the part above and
scoops out a corridor just wide enough to pass through. In this way, a
very thick wall is left intact, the central part alone being consumed.
As the sheath is bored, the sides are at the same time cemented and
lined with the evacuations of the intestine. Any excess product
accumulates and forms a rampart behind.
So long as the weather remains favourable, the grub moves about in its
gallery; it takes its stand above or below and attacks the provisions
with a tooth that grows daily more languid. Five or six weeks are thus
passed in banqueting; then comes the cold weather, bringing the winter
torpor with it. The grub now digs itself an oval recess, polished by
much wriggling of its body, at the lower end of its case, in the mass
of material which digestion has transformed into a fine paste; it
protects itself with a curved canopy; and it is ready to enjoy its
winter slumbers. It can sleep in peace. If its parents have installed
it underground at an inconsiderable depth to which the frost
penetrates, at any rate they have increased the supply of victuals to
the utmost. The effect of this enormous superfluity is to provide an
excellent dwelling for the bad weather.
In December the grub is full-grown, or not far short of it. If the
temperature only lent a hand, the nymphosis would now be due. But times
are hard; and the grub, in its wisdom, decides to defer the delicate
work of transformation. Sturdy creature that it is, it will be able to
resist the cold much better than the nymph, that frail beginning of a
new life. It therefore has patience and tarries in a state of torpor. I
take it from its cell to examine it.
Convex on top and almost flat below, the larva is a semicylinder bent
into a hook. There is an entire absence of the hump belonging to the
previous Dung-beetles; likewise of any terminal trowel. The plasterer’s
art of repairing crevices being unknown here, there is no need for the
cement-pot or the spreading-utensil. The creature’s skin is smooth and
white, clouded in the hinder half by the dark contents of the
intestines. Sparse hairs, some fairly long, others very short, stand up
on the median and dorsal region of the segments. They apparently serve
to help the grub move about its cell by the mere wriggling of its
hinder part. The head is neither big nor small and is pale-yellow in
colour; the mandibles are large and brown at the tip.
But let us leave these details, which are of no great interest, and say
at once that the creature’s prominent characteristic is supplied by its
legs. The first two pairs are pretty long, especially for an animal
leading a sedentary life in a narrow cabin. They are normally
constructed; and it must be their strength that allows the grub to
clamber about inside its pudding, converted into a sheath by eating.
But the third pair presents a peculiarity of which I know no example
elsewhere.
The limbs forming this pair are rudimentary legs, crippled from birth,
impotent, arrested in their development. They give one the impression
of lifeless stumps. Their length is hardly a third of that of the
others. More remarkable still, instead of pointing downwards like the
normal legs, they shrivel upwards, turning towards the back, and remain
indefinitely in that queer attitude, twisted and stiff. I cannot
succeed in seeing the animal make the slightest use of them.
Nevertheless they show the same joints as the others; but this is all
on a greatly reduced scale, pale and inert. In short, a couple of words
will distinguish the Geotrupes’ larva without any possibility of
confusion: hind-legs atrophied.
This feature is so plain, so striking, so extraordinary that the least
observant among us cannot mistake it. A grub crippled by nature and so
evidently crippled enforces itself on our attention. What do the books
say about it? Nothing, so far as I know. The few which I have with me
are silent on this point. Mulsant, it is true, described the larva of
the Stercoraceous Geotrupes; but he makes no mention of its exceptional
structure. In his anxiety to describe the minutest details of the
organism, has he lost sight of this monstrosity? Labrum, palpi,
antennæ, the number of joints, the hairs: all this is set down and
scrutinized; and the lifeless legs reduced to stumps are passed over in
silence. Are the experts then so busy with the Gnat that they cannot
see the Camel? I give it up.
Observe also that the hind-legs of the perfect insect are longer and
stronger than the middle-legs and vie with the fore-legs in vigour. The
atrophied limbs of the grub, therefore, become the adult’s powerful
pressing-machine; the impotent stumps change into strong
stamping-tools.
Who will tell us the origin of these anomalies now thrice observed
among the dung-workers? The Sacred Beetle, who is sound in every limb
during his infancy, loses his fore-fingers when the adult form appears;
the Onthophagus, who sports a horn on his thorax in his nymphal stage,
drops it and does without the ornament in the end; the Geotrupes, at
first a limping grub, turns his useless stumps into the best of his
levers. The last-named makes progress; the others retrocede. Why does
the cripple become able-bodied and why do the able-bodied become
cripples?
We make chemical analyses of the suns; we surprise the nebulæ in labour
and watch the birth of worlds; and shall we never know why a miserable
grub is born limping? Come, ye divers who fathom life’s mysteries,
descend a little lower into the depths and at least bring us back that
humble pearl, the reply to the problems of the Geotrupes and the Sacred
Beetle!
When the weather is severe, what becomes of the larva in the retreat
which it has succeeded in making at the far end of its box? The
exceptional cold of January and February 1895 will answer this
question. My cages, always left in the open air, had repeatedly
undergone a drop in temperature of some ten degrees below
freezing-point. In this arctic weather, I conceived a wish to go in
search of information and learn how things were progressing in my
unprotected cages.
I could not manage it. The bed of earth, wetted by the earlier rains,
had become a compact block throughout, which I should have had to break
up like a stone with a hammer and chisel. Extraction by violent means
was not practicable: I should have endangered everything with my
hammering. On the other hand, if any life remained in the frozen mass,
I should have placed it in jeopardy by changing the temperature too
suddenly. It was better to await the very slow natural thaw.
Early in March I inspect the cages again. This time there is no ice
left. The earth is yielding and easy to dig. All the adult Geotrupes
have died, bequeathing me a fresh supply of sausages, almost as
plentiful as that which I had gathered and placed in safety in October.
They have all perished; there is not a single survivor. Is cold or old
age to blame?
At this very time and later, in April and May, when the new generation
is wholly in the larval or at most in the nymphal stage, I often find
adult Geotrupes busy in their scavenging-works. The old ones therefore
see a second spring; they live long enough to know their children and
to work with them, as do the Scarabæi, the Copres and others. These
early ones are veterans. They have escaped the hardships of winter
because they have been able to bury themselves far enough underground.
Mine, kept captive between a few boards, have died for want of a
sufficiently deep pit. At a time when they needed three feet of earth
to shelter themselves, they had less than twelve inches. It was cold,
therefore, that killed them, rather than age.
The low temperature, while fatal to the adult, has spared the larva.
The few sausages left in position after my October diggings contain the
grub in excellent condition. The protecting sheath has fulfilled its
office to perfection: it has preserved the sons from the catastrophe
that caused the death of the parents.
The other cylinders, fashioned in the course of November, contain
something even more remarkable. In their hatching-chamber, at the
bottom, they hold an egg, all plump and shiny and as healthy-looking as
though it had been laid that day. Can life still exist there? Is it
possible, after the best part of the winter has been passed in a block
of ice? I dare not believe it. The sausage itself has not an attractive
appearance. It is darkened by fermentation, smells musty and does not
suggest food worth having.
At all events, I will take the precaution of bottling the miserable
puddings, after ascertaining that the egg is there in each case. I was
well-advised. The fresh aspect of the germs, after wintering under such
rude conditions, did not belie them. The hatching was soon effected;
and early in May the late arrivals were almost as well-developed as
their seniors, hatched in the autumn.
Some interesting facts are revealed by this piece of observation. First
of all, the laying-period of the Geotrupes is a fairly long one,
lasting from September to some time in November. At that date the first
hoar-frosts begin; the soil is not warm enough to hatch the eggs; and
the last ones, unable to hatch as swiftly as their predecessors, wait
for the return of the fine weather. A few mild April days are enough to
reawaken their suspended vitality. Then the usual evolution goes on,
and this so rapidly that, notwithstanding a delay of five or six
months, the backward larvæ are very nearly as big as the others by May,
when the first nymphs appear.
Secondly, the Geotrupes’ eggs are capable of enduring the trials of
severe cold unscathed. I do not know the exact temperature inside the
frozen block which I tried to tackle with a mason’s chisel. Outside,
the thermometer sometimes fell to ten degrees below freezing-point;
and, as the cold period lasted a long time, we may believe that the
layer of earth in my boxes was equally cold. Now the Geotrupes’
puddings were enclosed in that frozen mass turned to a block of stone.
A generous allowance must no doubt be made for the non-conductivity of
these puddings composed of thready materials; the wall of dung did, to
a certain extent, protect the larva and the egg against the biting
cold, which, if experienced direct, would have been fatal. No matter:
in that atmosphere the dung-cylinders, damp at the start, must in the
long run have acquired the hardness of stone. In their
hatching-chamber, in the tunnel made by the larva, the temperature
undoubtedly sank below freezing-point.
Then what became of the grub and the egg? Were they really frozen?
Everything seems to tell us so. That this most delicate of all delicate
things, a germ, a rudiment of life in a blob of glair, should harden,
turn into a bit of stone and then resume its vitality and continue its
evolution after thawing seems inadmissible. And yet circumstances
confirm it. We should have to credit the Geotrupes’ sausages with
athermanous properties unequalled by any other substance to regard them
as a sufficient protection against such intense and lasting
refrigeration. What a pity that we could derive no information from the
thermometer in this instance! After all, if complete freezing is
unproven, one point has been established for certain: the egg and the
grub of the Geotrupes can support and survive very low temperatures in
their protecting sheath.
Since the occasion presents itself, let me say a few more words on the
insect’s powers of resisting cold. Some years ago, while looking for
Scolia-cocoons in a heap of mould, I had made a large collection of the
grubs of Cetonia aurata. [54] I placed my loot in a flower-pot with a
few handfuls of decayed vegetable matter, just enough to cover the
insects’ backs. I intended to draw upon them for certain enquiries
which I was making at the time. The pot remained in the open air; and I
forgot all about it. A cold snap came, accompanied by sharp frost and
snow. Then I remembered my Cetoniæ, so ill-protected against this kind
of weather. I found the contents of the pot hardened into a
conglomeration of earth, dead leaves, ice, snow and shrivelled grubs.
It was a sort of almond-rock, in which the larvæ stood for the almonds.
Sorely tried by the cold as they were, the colony ought to have
perished. But no: when the thaw arrived, the frozen larvæ came to life
again and began to swarm about as though nothing unusual had happened.
The insect’s powers of endurance are less great than the larva’s. As
the organization becomes more refined, it loses its robustness. My
cages, which went through such a bad time in the winter of 1895,
provided me with a striking instance. A few species—Scarabæi, Copres,
Pilularii and Onthophagi—were represented at the same time by newcomers
and old stagers. All the Geotrupes, without an exception, died in the
earthy bed which had turned into a block of stone; the Minotaurs also
succumbed, every one of them. And yet both find their way up north and
are not afraid of cold climates. On the other hand, the southern
species, the Sacred Beetle, the Spanish Copris and Pilularius
flagellatus, the younger generation as well as the veterans, withstood
the winter better than I dared hope. Many of them died, it is true;
they formed the majority; but at any rate there were survivors whom I
marvelled to see recovering from their icy paralysis, trotting about
under the first kisses of the sun. In April, those specimens which have
escaped from freezing resume their labours. They teach me that, when at
liberty, Copres and Scarabæi have no need to retire to winter quarters
at great depths underground. A moderate screen of earth, in some
sheltered nook, is enough for them. Less skilful diggers than the
Geotrupes, they are better provided with the power to resist a passing
spell of cold.
We will end this digression by remarking, as so many others have done,
that agriculture cannot reckon on the cold weather to rid it of its
dread enemy, the insect. Very hard frosts, lasting a long time and
penetrating well beneath the surface of the soil, can destroy various
species which are not able to go down low enough; but a great many
survive. Moreover, the grub and especially the egg in many cases defy
our severest winters.
The first five days of April put an end to the torpor of the larvæ of
both Geotrupes, snuggling on the bottom floor of their cylinder, in a
temporary cell. Activity returns, bringing with it a last flicker of
appetite. The remains of the autumn banquet are plentiful. The grub
makes use of them no longer for greedy feasting, but just as a midnight
snack between two slumbers, that of winter and the deeper sleep of the
metamorphosis. Hence the sides of the sheath are attacked
spasmodically. Breaches yawn, sections of wall come tumbling down, and
soon the edifice is nothing but an unrecognizable ruin.
The lower portion of the original sausage remains, however, with its
walls intact for a length of an inch or two. Here, in a thick layer,
the grub’s excreta are accumulated, held in reserve for the final work.
In the centre of this mass a hollow is dug, carefully polished inside.
With the excavated rubbish the grub builds not just a canopy, like that
with which the winter alcove was protected, but a solid lid, with a
rough outer surface, in appearance not unlike the work of the Cetoniæ
when they wrap themselves in a shell of mould. This lid, with what is
left of the pudding, forms a habitation which would remind us pretty
closely of the Cockchafer’s dwelling, were it not truncated in the
upper part, which moreover is most often topped by a few remnants from
the destroyed cylinder.
The grub is now shut in for the transformation, motionless, with its
body emptied of all dross. In a few days a blister appears on the
dorsal surface of the last abdominal segments. This swells, spreads and
gradually extends as far as the thorax. It is the work of excoriation
beginning. Distended by a colourless liquid, the blister gives an
uncertain glimpse of a sort of milky cloud, the first blurred outline
of the new organism.
The thorax splits in front, the cast skin is slowly pushed backwards,
and at last we have the nymph, all white, half-opaque and
half-crystalline. I obtain my first nymphs about the beginning of May.
Four or five weeks later, the perfect insect arrives, white on the
wing-cases and belly, while the rest of the body already possesses the
normal colouring. The chromatic evolution is quickly completed; and,
before the end of June, the Geotrupes, now perfectly matured, emerges
from the soil at twilight and flies off to start on his scavenger’s job
without delay. The laggards, those whose egg has gone through the
winter, are still in the white nymphal stage when their elders effect
their release. Not before September is nigh will they burst their natal
shell and, in their turn, sally forth to aid in the cleansing of the
fields.