THE GEOTRUPES: NEST-BUILDING
In September and October, when the first autumn rains soak the ground
and allow the Sacred Beetle to split his natal casket, the
Stercoraceous Geotrupes and the Mimic Geotrupes found their
family-establishments: somewhat makeshift establishments, in spite of
what we might have expected from the name of these miners, so well
styled earth-borers. When he has to dig himself a retreat that shall
shelter him against the rigours of winter, the Geotrupes really
deserves his name: none can compare with him for the depth of the pit
or the perfection and rapidity of the work. In sandy ground, easily
excavated, I have dug up some that were buried over a yard deep. Others
carried their digging farther still, tiring both my patience and my
implements. There you have the skilled well-sinker, the inimitable
earth-borer. When the cold sets in, he will be able to descend to some
stratum where the frost has lost its terrors.
The family-lodging is another matter. The propitious season is a short
one; time would fail, if each individual grub had to be endowed with
one of those mansions. Nothing could be more satisfactory than for the
insect to devote the leisure which the approach of winter gives it to
digging a hole of unlimited depth: this makes the retreat doubly safe;
and for the moment its energies, which are not yet suspended, have no
other outlet. But at laying-time these laborious undertakings are
impossible. The hours pass swiftly. In four or five weeks a numerous
family has to be housed and victualled, which puts the sinking of a
deep pit that requires time and patience quite out of the question.
In any case, precautions will be taken against the dangers of the
surface. Once its family is settled, the unprotected adult insect is
obliged to establish its winter quarters at great depths, whence it
will emerge in spring accompanied by its young ones, like the Sacred
Beetle; but neither the egg nor the grub needs this costly refuge in
the wet season, being well protected by the parents’ industry.
The burrow dug by the Geotrupes for the benefit of her grub is hardly
deeper than that of the Copris or the Sacred Beetle, notwithstanding
the difference of the seasons. Eleven or twelve inches, roughly
speaking, is the most that I find in the fields, where nothing occurs
to restrict the depth. My cages, with their limited thickness of soil,
are less trustworthy in this respect, since the insect has no option
but to use the layer of earth at its disposal. Many a time, however, I
perceive that this layer is not fully traversed down to the floor of
the box, thus furnishing a fresh proof of the slight depth needed.
In the open fields as in the confinement of my cages, the burrow is
always dug under the heap of dung that is being exploited. No outward
sign betrays its presence, concealed as it is beneath the voluminous
droppings of the Mule. It is a cylindrical passage, the same width as
the neck of a claret-bottle, straight and perpendicular in a
homogeneous soil, bent and winding irregularly in rough ground where a
root or stone may bar the way and necessitate an abrupt change of
direction. In my cages, when the layer of earth is insufficient, the
pit, at first vertical, bends at right angles on touching the wooden
floor and is continued horizontally. There is no precise rule therefore
in the boring. The accidents of the soil determine the shape.
At the end of the gallery again there is nothing to remind us of the
spacious hall, the workshop where Copres, Scarabæi and Gymnopleuri
fashion their artistic pears and ovoids, but a mere cul-de-sac of the
same diameter as the nest. A veritable drill-hole, if we make
allowances for the occasional knots and twists inevitable in boring
through stuff that offers more resistance at some places than at
others; a winding channel: that is what the Geotrupes’ burrow is.
The contents of the crude dwelling take the form of a sort of sausage
or pudding, which fills the lower part of the cylinder and fits it
exactly. Its length is not far short of eight inches and its width
about an inch and a half, when the thing belongs to the Stercoraceous
Geotrupes. The dimensions are a little smaller in the work of the Mimic
Geotrupes. In either case, the sausage is nearly always irregular in
shape, now curved, now more or less dented. These imperfections of the
surface are due to the accidents of a stony ground, which the insect
does not always excavate according to the canons of its art, which
favours the straight line and the perpendicular. The moulded material
faithfully reproduces all the irregularities of its mould. The lower
end is rounded off like the bottom of the burrow itself; the upper end
is slightly concave, through being packed more closely in the middle.
The voluminous object is put together in layers rather suggestive, as
regards curve and arrangement, of a pile of watch-glasses. Each of them
obviously corresponds with a load of materials gathered in the heap
above the burrow, carried down separately, placed in position on the
previous layer and then vigorously trampled flat. The edges of the
disk, which adapt themselves less well to this work of compression,
remain at a higher level; and all this tends to form something like a
concave lens. These same less-compressed edges give a sort of rind,
which is soiled with earth owing to its contact with the walls of the
tunnel. Altogether, the structure tells us the method of manufacture.
The Geotrupes’ sausage, like our own, is obtained by moulding in a
cylinder. It results from layers introduced one after the other and
duly compressed, especially in the middle, which is more easily
accessible to the manipulator’s legs. Direct observation will presently
confirm these inferences and supplement them with details of
considerable interest, which we should never suspect from simply
examining the work.
Before continuing, let us note how well inspired the insect is in
always boring its burrow under the heap whence the materials for the
sausage are to be extracted. The number of loads successively carried
down and pressed is considerable. Allowing a thickness of a sixth of an
inch for each layer—a figure which is near enough—I see that some fifty
journeys are needed. If the provisions had each time to be fetched from
a distance, the Geotrupes would be unable to cope with her task, which
would be too long and tiring. Her sort of work is incompatible with all
that travelling, after the fashion of the Sacred Beetle’s. She is wise
to settle beneath the heap. She has only to climb up from her well to
find under her feet, at her very door, enough to make her
black-pudding, however large she may wish it to be.
This, it is true, presupposes a copiously supplied workyard. When
toiling on behalf of her grub, the Geotrupes keeps a look-out for one
of this kind and accepts no purveyors except the Horse and the Mule,
never the Sheep, who is too niggardly. It is not a question here of the
quality of the foodstuffs; it is a question of quantity. My cages, in
fact, tell me that the Sheep would have the preference, if she were
more generous. What she does not give normally I create artificially by
piling sheaf upon sheaf. Beneath this extraordinary treasure, the like
of which is never offered by the fields, my captives work with a zest
that shows how well they appreciate the windfall. They enrich me with
more sausages than I know what to do with. I arrange them in strata in
great pots, so that, when winter comes, I may study the actions of the
larva; I lodge them separately in glass tubes and test-tubes; I pack
them in tins. The shelves of my study are crammed with them. My
collection reminds me of an assortment of potted meats.
The unfamiliarity of the material involves no change in the structure.
Because of its finer grain and greater plasticity, the surface is more
regular and the inside more homogeneous; and that is all.
At the lower end of the sausage, which end is always rounded off, is
the hatching-chamber, a circular cavity which could hold a fair-sized
hazel-nut. The respiratory needs of the germ demand that the side-walls
should be thin enough to allow the air to enter freely. Inside, I catch
the gleam of a greenish, semifluid plaster, a simple exudation from the
porous mass, as in the Copris’ ovoids and the Sacred Beetle’s pears.
In this round hollow lies the egg, without adhering in any way to the
surrounding walls. It is a white, elongated ellipsoid and is of
remarkable bulk in proportion to the insect. In the case of the
Stercoraceous Geotrupes, it measures seven to eight millimetres in
length by four at its widest point. [49] The egg of the Mimic Geotrupes
is a little smaller.
This little hollow contrived in the substance of the sausage, at the
lower end, does not agree at all with what I have read about the
Geotrupes’ nest-building. Quoting an old German writer, Frisch, [50] an
author whom the poverty of my library does not allow me to consult,
Mulsant, [51] speaking of the Stercoraceous Geotrupes, says:
‘At the bottom of her perpendicular gallery, the mother builds,
usually with earth, a sort of nest, or egg-shaped shell, open at
one side. On the inner wall of this shell she glues a whitish egg,
the size of a grain of wheat.’
What can this shell be, usually made of earth and open at one side so
that the grub may reach the column of provisions overhead? I am at an
utter loss to know. Shell, especially made of earth, there is none, nor
any opening. I see and see again, as often as I wish, a round cell,
closed everywhere and built at the lower end of the food-cylinder, but
nothing else, nothing that even vaguely resembles the structure
described.
Which of the two is responsible for the imaginary construction? Can the
German entomologist have sinned through superficial observation? Or did
the Lyons entomologist misinterpret the older author? I lack the
necessary documents to bring the mistake home to the right person. Is
it not pathetic to see these masters, who are so punctilious about a
joint of the palpi, so cantankerous about the first claim to some
barbaric appellation, almost indifferent when they come to treat of
habits and industry, which are the supreme expression of an insect’s
life? Nomenclators’ entomology is making enormous strides: it
overwhelms us, swamps us. The other, biologists’ entomology, the only
interesting branch of the science, the only one really worthy of our
attention, is neglected to such an extent that the commonest species
has no history or calls for serious revision of the little that has
been written about it. Vain lamentations: things will go on in the same
old way for a long time to come.
To return to the Geotrupes’ sausage. Its shape is diametrically
opposite to that which we have studied in the case of the Copris and
the Sacred Beetle, who are sparing of material but very generous with
their labour, taking great care to give their work the shape best
suited to preserve it against dryness. With their ovoids and their
spheres surmounted by a neck, they are able to keep the modest
family-ration fresh. The Geotrupes knows nothing of these scientific
methods. More primitive in her ways, she sees well-being only in
overabundance. Provided that the gallery be crammed with food, she
little cares how shapeless her pile may be.
Instead of avoiding dryness, she appears to go in search of it. Just
look at the sausage. It is inordinately long and clumsily put together.
There is no compact, impermeable rind; and there is an excessive amount
of surface, touching the earth for the whole length of the cylinder.
This is exactly what is needed to bring about quick desiccation; it is
the converse of the problem of the smallest surface, solved by the
Sacred Beetle and the others. Then what becomes of my views on the
shape of those provisions, views so well founded, according to our
logic? Can I have been taken in by a blind geometry, which achieves a
rational result by chance?
To any one who says so let the facts reply. Here is their answer: the
manufacturers of spheres build their nests at the height of the summer,
when the ground is parched; the manufacturers of cylinders build theirs
in the autumn, when the earth becomes saturated with rain. The first
have to guard their family against the danger of bread too hard to eat.
The second know nothing of starvation through desiccation; their
provisions, potted in cool earth, retain indefinitely the proper degree
of softness. The moistness, not the shape, of the sheath is the
safeguard of the ration inside it. The rainfall at this time of the
year is in inverse ratio to that of summer; and this is enough to
render useless the precautions taken in the dog-days.
Let us probe deeper and we shall see that the cylinder is preferable to
the sphere in autumn. When October and November come, the rains are
frequent and persistent; but a day’s sunshine is enough to dry the soil
to the shallow depth where the Geotrupes’ nest lies. It is a serious
matter not to lose the enjoyment of this fine day. How will the grub
benefit by it?
Imagine the larva enclosed in the big ball which the copious quantity
of food placed at its disposal might well supply. Once saturated with
moisture by a shower, this sphere would retain it stubbornly, for its
form is that of least evaporation and of least contact with the
sun-warmed soil. In vain, within twenty-four hours, will the surface
layer of the ground be restored to its normal coolness: the globular
mass will retain its excess of water, for lack of adequate contact with
the sun- and air-dried earth. In the too-humid and too-thick recess,
the provisions will go musty; the heat from outside will be
inopportune, as will the air; and the larva will derive little
advantage from this late autumn sun, whose tardy rays ought to ripen it
to perfection and give it the necessary vigour to brave the trials of
winter.
What was a good quality in July, when it was necessary to guard against
excessive dryness, becomes a bad one in October, when excessive damp is
to be avoided. The cylinder is therefore substituted for the sphere.
The new shape, with its exaggerated length, fulfils the converse
condition of that beloved by the pill-makers: here, with a similar
volume, the surface is developed to its extreme limits. Is there a
reason for this complete change? No doubt; and I seem to perceive it.
Now that dryness is no longer to be feared, will not this kind of
shape, with its large surface, enable the mass of foodstuff to get rid
of its superfluous moisture more readily? Should it rain, its wide area
certainly will make it liable to more rapid saturation; but also, when
the fine weather returns, the surplus water will soon disappear thanks
to the extensive contact with a quickly-drained soil.
Let us conclude by enquiring how the roly-poly is manufactured. To
watch the performance in the fields appears to me a very difficult, not
to say impracticable undertaking. With my cages, success is certain,
provided that we exercise a little patience and dexterity. I let down
the board which keeps the artificial soil in place at the back. This
now reveals its vertical surface, which I explore bit by bit with the
point of a knife until I strike a burrow. If the operation be
cautiously conducted, without the disturbance due to an ill-calculated
landslip, the labourers are discovered at their toil, paralysed, it is
true, by the sudden flood of light and as it were petrified in the
attitude of work. The arrangement of the workshop and the materials,
the position and posture of the workers enable us easily to reconstruct
the scene, though it be abruptly suspended and not renewed so long as
our inspection lasts.
One fact, to begin with, thrusts itself upon our attention, a fact of
deep interest and so exceptional that this is the first example with
which my entomological studies have presented me. In each burrow laid
bare I always find two collaborators, a pair: I find the male lending
the mother his assistance. The household duties are divided between the
two. My notes give the following scene, to which we can easily restore
its animation according to the pose of the immobilized actors.
The male is at the back of the gallery, squatting on a length of
sausage measuring barely an inch. He occupies the basin formed through
the stuff’s being packed more tightly in the centre of each stratum.
What was he doing before the violation of his home? His attitude tells
us clearly: with his sturdy legs, especially the hind-legs, he was
pressing down the last layer placed in position. His mate occupies the
upper floor, almost at the opening of the burrow. I see her holding
between her legs a great lump of material which she has just gathered
at the bottom of the heap surmounting the house. The scare caused by my
intrusion has not made her let go. Hanging up there, above space,
braced against the walls of the pit, she clasps her burden with a sort
of cataleptic obstinacy. The nature of the interrupted work is easily
guessed: Baucis was carrying down to Philemon, the stronger of the two,
the wherewithal to continue the arduous work of piling and trampling.
After laying the egg and surrounding it with those delicate precautions
of which a mother alone possesses the secret, she had handed over the
construction of the cylinder to her companion, confining herself to
playing the humble part of a caterer’s man.
Similar scenes, observed during different phases of the work, enable me
to draw a general picture. The sausage begins with a short, wide casing
which closely lines the bottom of the burrow. In this bag, with its
yawning mouth, I find the two sexes in the midst of materials crumbled
and possibly weeded before being pressed, so that the grub may have
first-class victuals within its reach as soon as it starts feeding. The
couple between them plaster the walls and increase their thickness
until the cavity is reduced to the size needed for the
hatching-chamber.
This is the moment for laying the egg. Withdrawing discreetly, the male
waits with materials ready to close the cell that has just been filled.
The closing is done by bringing the edges of the sack nearer together
and adding a ceiling, a hermetically cemented lid. This is the delicate
part of the work, calling for knack much more than strength. The mother
alone attends to it. Philemon is now a mere journeyman-mason: he passes
the mortar, without being allowed on the ceiling, which his brutal
pressure might cause to fall in.
Soon the roof, duly thickened and reinforced, has nothing more to fear
from pressure. Then the ruthless stamping begins, the rough work which
transfers the leading part to the male. In the Stercoraceous Geotrupes
the difference in size and vigour between the sexes is striking. Here
indeed we have a very exceptional case: Philemon belongs to the
stronger sex. He is distinguished by his portly figure and muscular
energy. Take him in your hand and squeeze. I defy you to stand it, if
your skin is at all sensitive to pain. With his sharp-toothed and
convulsively stiffened legs, he digs into your flesh; he slips like an
irresistible wedge into the spaces between your fingers. It is more
than you can bear; and you have to let the creature go.
In the household he performs the function of an hydraulic press. We
subject our packs of fodder to the action of the press in order to
reduce their cumbrous bulk; he likewise compresses and reduces the
stringy materials of his sausage. It is most often the male that I find
at the top of the cylinder, a top excavated to form a deep basket. This
basket receives the load brought down by the mother; and, like the
labourer trampling on the grapes at the bottom of the vintage-tub, the
Geotrupes presses and amalgamates his materials with the convulsive
effort of his galvanic movements. The operation is so well conducted
that the new load, at first not unlike a voluminous mass of coarse
lint, becomes a compact layer uniform with the one before it.
The mother, however, does not abdicate her rights: I find her now and
then at the bottom of the basin. Perhaps she has come to see how the
work is going on. Her touch, which is better-suited for the delicate
part of the rearing, will more readily discover the mistakes that need
correcting. Very likely also she comes to relieve her husband in these
exhausting compressive operations. She herself is strong, sturdy in the
legs and capable of working turn and turn about with her valiant
companion.
However, her usual place is at the top of the gallery. I find her there
at one time with the armful which she has just gathered, at another
with a heap made up of several loads placed in reserve for the work
down below. As and when it is wanted, she draws upon the heap and
gradually carries the materials down to be pressed by the male.
Between this temporary warehouse and the basin at the bottom there is a
long empty space, the lower part of which supplies us with another bit
of information as to the progress of the work. The walls are lavishly
coated with a wash extracted from the most plastic portion of the
materials. This detail is not without value. It tells us that, before
packing the food-sausage layer by layer, the insect begins by cementing
the rough and porous wall of the mould. It putties its well to protect
the grub against the damp which might ooze through in the rainy season.
Finding it impossible by pressure to harden the skin of the
tightly-packed sausage to the requisite degree, it adopts a means
unknown to the Beetles that labour in large workshops; it coats the
earthy casing with cement. In this way it avoids, so far as lies in its
power, the risk of drowning on rainy days.
This waterproofing is done at intervals, as the cylinder grows in
length. The mother appears to me to attend to it whenever her warehouse
of provisions is sufficiently stocked to give her the time. While her
companion is pressing, she, an inch higher up, is plastering.
At last the combined efforts of husband and wife result in a cylinder
of the regulation length. The greater part of the well above remains
empty and uncemented. Nothing tells me that the Geotrupes trouble about
this unoccupied area. Scarabæi and Copres shoot into the
entrance-passage to the underground chamber a portion of the rubbish
extracted; they build a barricade in front of the dwelling. The
sausage-makers seem to be unfamiliar with this precaution. All the
burrows which I inspect are empty in the upper part. There is no sign
of excavated earth put back and pressed into position; there is merely
a little fallen rubbish, coming either from the dung-heap above or from
the crumbling walls.
This neglect might well be ascribed to the thick roof that surmounts
the house. Remember that the Geotrupes generally settle under the
copious provender which the Horse and the Mule bestow upon them. Under
such a shelter, is it really necessary to bolt one’s door? Besides, the
rough weather looks after the closing for them. The roof falls in, the
earth slips and the yawning pit soon fills up without the assistance of
those who dug it.
Just now my pen ventured to write the names of Philemon and Baucis. As
a matter of fact, the Geotrupes couple do in certain respects recall
the peaceful mythological household. What is the male, in the insect
world? Once the wedding has been celebrated, he is an incompetent, an
idler, a good-for-nothing, a drug in the market whom others shun and
sometimes even get rid of by atrocious means. The Praying Mantis [52]
tells us tragic enough things in this connection.
Now here, by a very curious exception, the sluggard becomes a toiler;
the lover of the moment a faithful husband; the careless parent a
serious paterfamilias. The brief meeting changes into a lasting
partnership. Married life, domestic life comes into being: a glorious
innovation; and the pioneer is a Dung-beetle! Go downwards: there is
nothing resembling it; go upwards: for a long time there is still
nothing. We have to mount to the top of the scale.
Take that little fish of our brooks, the Stickleback. The male knows
very well how to build out of algæ and different water-weeds a nest, a
snuggery, in which the female will come and spawn; but he knows nothing
of work shared in common. The cares of a family in which the mother
takes little interest fall upon him alone. No matter: there is one step
gained, a great one and especially a very remarkable one among fishes,
who are so supremely indifferent to family-affection and substitute an
appalling fecundity for the trouble of breeding. Fabulous numbers make
good the voids due to the lack of industry in the parents, even in the
mother, a mere bag for eggs.
Certain Toads attempt the duties of paternity; and then we have nothing
more till we come to the bird, that paragon of the domestic virtues.
Here we find married life in all its moral beauty. A contract turns the
couple into two collaborators, both equally zealous for the prosperity
of the family. The father takes just as much part as the mother in the
building of the nest, the quest of provisions, the distribution of each
mouthful and the supervision of the youngsters as they try their wings
preliminary to their first flight.
Standing still higher in the animal scale, the mammal carries on the
wonderful example without adding to it; on the contrary, it often
simplifies things. Man remains and has no prouder title to nobility
than his unwearying care for the family, that alliance which is never
dissolved. To our shame, I admit, a few individuals deny their
responsibility and sink below the level of the Toad.
The Geotrupes rivals the bird. The nest is the joint production of
husband and wife. The father puts the various layers together and
compresses them; the mother plasters the walls, fetches fresh loads and
places them under the presser’s feet. This home, the outcome of the
couple’s efforts, is also a storehouse of provisions. Here we see no
mouthfuls distributed to the children from day to day, but the
food-problem is solved none the less: the united labours of the two
partners result in the sumptuous sausage. Father and mother have done
their duty splendidly; they bequeath to the grub an eminently
well-furnished larder.
A pair that continue to exist as such, a couple that join forces and
unite their industry for their offspring’s welfare, certainly represent
enormous progress, perhaps the greatest in the animal kingdom. One day,
in the midst of the isolated existences, the household appeared, the
invention of an inspired Dung-beetle. How is it that his magnificent
acquirement is the property of a few, instead of extending all around,
from one species to another, throughout the guild? Can it be that
Scarabæi and Copres would have nothing to gain, in saving of time and
labour, if the mother, instead of working alone, had an assistant?
Things would move faster, so it seems to me, and a more numerous family
would be permissible, a possibility not to be despised when one has an
eye to the prosperity of the species.
How, on his side, did the Geotrupes think of combining the two sexes in
building the nest and stocking the larder? The abrupt transformation of
the usual airy paternity of the insect into something that rivals
motherhood in tenderness is so serious and so rare an event that we
long to discover the cause of it, if indeed we may hope to do so with
the sorry means of information at our disposal. One idea occurs to us
at once: may there not be some connection between the male’s superior
size and his liking for hard work? Endowed with greater robustness and
vigour than the mother, he who is usually so lazy has become a zealous
helper; the love of work has come from a surplus of unspent strength.
Take care: this apparent explanation will not hold water. The two sexes
of the Mimic Geotrupes scarcely differ in size; the advantage is often
even in the female’s favour; and nevertheless the male lends assistance
to his companion: he is as eager a well-sinker, as energetic a presser
as his big stercoraceous kinsman.
And here is a still more conclusive argument: among the Anthidia, [53]
those Bees who weave cotton-stuffs or knead resin, the male, though
much larger than the female, is an absolute idler. He, so strong, so
stout of limb, take part in the work! Never! Let the mother, the feeble
mother, wear herself out while he, powerful fellow that he is, frolics
among the speedwell and the lavender.
It is not physical strength, therefore, that has made the Geotrupian
paterfamilias into a worker devoted to his children’s welfare. And this
is as much as our investigations tell us. To pursue the problem would
be a vain endeavour. The origin of faculties escapes us. Why is this
gift bestowed here and that gift there? Who knows? Can we indeed ever
hope to know?
One point alone stands out clearly: instinct is not dependent on
structure.
The Geotrupes have been known from time immemorial; conscientious
entomologists, peering through their magnifying-glasses, have examined
them down to their smallest details; and no one has yet suspected their
marvellous privilege of keeping house in common. Above the monotonous
level of the ocean suddenly emerge the headlands of lonely little
islands, scattered here and there, whose existence none can suspect
until geography has added them to her charts. Even so do the peaks of
instinct rear their crests above the ocean of life.