THE SLOE-WEEVIL
No less skilled than the Vine- and Poplar-weevils in the art of
leaf-rolling, the Attelabus and the Apoderus have shown us that, in
spite of a dissimilar equipment, the industry may remain the same; they
have proved that similarity of aptitude is compatible with diversity of
organization. Conversely, different trades may be followed with the
same tools; identity of form does not imply equivalence of instinct.
Who tells us this? Who puts forward this subversive proposition? The
Sloe-weevil (Rhynchites auratus, Scop.) has the audacity to do so.
Rivalling the exploiters of the vine and poplar in metallic lustre, she
possesses, exactly as they do, a curved awl which one would say was
meant for puncturing the stalk of a leaf and then fastening the edges
of the rolled portion; her figure is short and squat, adapted, so it
seems to me, to working in the narrow crease of a fold; she has spiked
sandals which give her a firm hold on slippery surfaces. Any one
acquainted with the cigar-makers has but to see her to call her
straightway by the same generic name. The nomenclators have made no
mistake; they are unanimous in styling her a Rhynchites. Judging the
trade by the worker’s looks, we do not hesitate: we set down this third
Rhynchites as a rival of the others, we class her in the leaf-rollers’
guild.
Well, in this case, we are thoroughly deceived by outward appearances;
we are taken in by an identity of structure. In her habits, the
Rhynchites of the Sloe has nothing in common with the two with whom she
is associated by her classification, which is based solely on the
peculiarities of her form. What is more, until she is seen at work, no
one would suspect her calling. She exploits the fruit of the sloe
exclusively; her grub’s ration is the tiny kernel and its lodging the
small stone of the sloe.
So, unskilled in the trade of her fellows, without any change in her
tools, the kinswoman of the cigar-makers becomes a driller of caskets;
with the same bodkin that serves her relatives for fastening the last
layer of a leaf-roll, she hollows a little cup in the surface of a
shell hard as ivory. The tool that is able to roll a flexible sheet now
wears away the invincible and works like a digger’s pick-axe. And
stranger still: when it has finished its arduous piece of carving, it
sets up above the egg a little miracle whose exquisite delicacy we
shall have occasion to admire.
The grub amazes me no less. It changes its diet. When a denizen of the
vine and the poplar, it eats a leaf; when a denizen of the sloe, it
takes to starchy food. It changes its means of liberation. When they
have attained their full growth and the moment comes for them to go
underground, the first two have nothing in front of them but a yielding
obstacle, the surface layer of the leafy sheath, softened and wasted by
decay; the third, like the Nut-weevil, has to pierce a wall of
exceptional strength.
What singular contrasts might we not discover in facts of this kind, if
we were better-acquainted with the habits of the Rhynchites group? A
fourth example is familiar to me (R. Bacchus, Lin.). Identical in shape
with the manufacturers of cigars and the exploiters of fruit-stones,
worthy, indeed, in all respects of the name of Rhynchites, what does
this Weevil do? Does she roll leaves? No. Does she install her grub in
the casket of a kernel? No.
Her trade is a very simple one, for her method is confined to inserting
her eggs, here, there and everywhere, in the still green flesh of the
apricot. Here there is no difficulty to overcome, and consequently no
art to be displayed by either mother or grub. The rostrum sinks into a
material which offers but a slight resistance; the egg is let down to
the bottom of the wound; and that is all. The establishment of the
family is a most summary proceeding; it reminds us of the practice of
the Larini.
The grub, for its part, has no need for talents of any sort. What would
it do with them? It feeds on the pulp of the fruit, which soon falls to
the ground and is reduced to a jelly. Life is easy in these liquescent
surroundings; the infant is bathed in fermenting pap. When the time
comes for it to take refuge in the subsoil, the jam-sodden grub has no
veil to tear, no wall to break through: the flesh of the apricot has
become a pinch of brown dust.
In the old days, the Anthidia, [47] partly weavers of cotton, partly
kneaders of resin, set me a difficult problem. Later came the
Dung-beetles of the pampas, the Phanæi, [48] some preparing, as
preserved foodstuff, cakes of Cow-dung modelled in the shape of a pear,
others sausage-meat kept fresh in clay jars. Both suggested the same
difficulty: can habits and industries which have no mutual connection
be explained as soon as we accept a common origin for these different
manufacturers, who moreover are so much alike in conformation? The
question crops up again, more urgently, with the four Rhynchites.
That the influence of environment may, to some extent, have caused
external modifications; that the light may have accentuated the
colouring; that the quantity of the food may have brought about some
small variation in size; that a warm or cold climate may have thinned
or thickened the fur: all these changes and many others besides I
willingly concede, if that will give any one any pleasure; but, for
pity’s sake, let us take higher ground than this, do not let us reduce
the world of the living to a collection of digestive tubes, an
assortment of bellies that fill and empty themselves.
Let us reflect upon the masterly touch that sets the whole animal
machine in motion; let us question the instincts, the controllers of
form; let us remember that glorious expression of the ancients, mens
agitat molem; and we shall understand the inextricable difficulty that
besets the theorists when they wish to explain how it is that of four
insects, as much alike in shape as so many drops of water, two roll
leaves, another carves fruit-stones, and the fourth profits by the pulp
of a rotten fruit.
If they are affiliated to one another, if they are indeed related, as
their so strongly-marked family-resemblance would seem to affirm, which
of them was the first of the line? Could it be the leaf-roller?
No one, unless he be content with idle fancies, will admit that the
cigar-roller can have tired of her cylinder one day and proceeded, as a
crazy innovator, to make a hole in the casket of a fruit-stone. Such
dissimilar industries do not suggest mutual connection. The first
leaf-rollers, never knowing any lack of leaves, may perhaps have gone
from one tree to others more or less like it; but to give up the art of
leaf-rolling, so easy to acquire, and to become, when nothing compelled
them to, strenuous nibblers of hard wood: that would have been idiotic.
No acceptable reason would explain the desertion of the original trade.
Such follies are unknown in the insect world.
The exploiter of the sloe refuses in her turn to acknowledge herself as
inspiring the cigar-maker:
‘What, I!’ she says, ‘I, give up my little blue plum, so savoury in its
tartness! I, a chaser of goblets, abandon my chisel and, in a moment of
madness, become a folder of leaves! What do you take me for? My grub
dotes on the floury kernel; confronted with any other fare, above all
with the meagre, tasteless roll of my colleague of the poplar, it would
let itself die of hunger. So long as sloes or kindred fruits have
existed, my race, thriving upon them, has never committed the folly of
forsaking them in favour of a leaf. So long as they exist, we shall
remain faithful to them; and, if ever they fail us, we shall perish to
the last grub.’
The lover of the apricot is no less positive. She, who is so easy to
establish in soft pulp, has taken good care not to advise her children
to undertake the laborious task of perforating a shell or rolling a
leaf into a cigar. According to the locality and the abundance of the
fruit, her boldest innovation has been to pass from the apricot to the
plum, the peach, or even the cherry. But how are we to admit that these
lovers of fruit-pulp, well satisfied with their rich living, which has
always been possible, in the old days and to-day alike, can ever have
risked leaving the soft for the hard, the juicy for the dry, the easy
for the difficult?
None of these four is the head of the line. Is the common ancestor then
an unknown species, dumped down, perhaps, in the schist-foliations
whose venerable archives we began by consulting? Even if he were there,
we should be none the wiser. The library of the stones preserves the
forms but not the instincts; it says nothing of industries, because,
let us repeat and again repeat, the insect’s tool tells us nothing of
its trade. With the same rostrum the Weevil may follow very different
callings.
What the ancestor of the Rhynchites did we do not know and have no hope
of ever knowing. The theorists, therefore, take their stand only on the
vague and slippery ground of suppositions:
‘Let us admit,’ they say, ‘let us imagine that ... it might be that
...’ and so forth.
My dearly-beloved theorists, this is a most convenient means of
arriving at any conclusion we like. With a bunch of nicely-selected
hypotheses, I will undertake, though no subtle logician, to prove to
you that white is black and that darkness is light.
I am too fond of tangible, indisputable truths; I will not follow you
in your sophistical suppositions. I want genuine facts, well-observed,
scrupulously-tested facts. Now what can you tell us of the genesis of
the instincts? Nothing and again nothing and always nothing.
You think that you have raised a monument of Cyclopæan blocks, and all
that you have built is a house of cards which tumbles to pieces before
the breath of reality. The real Rhynchites—not the imaginary one, but
the insect which any one can observe and question at will—ventures to
tell you so, in her artless sincerity.
She tells you:
‘My manufactures, which are so contrary, cannot be derived one from
another. Our talents are not the legacy of a common ancestress, for, to
leave us such a heritage, the original initiator would have had to be
versed at one and the same time in arts which are mutually
incompatible: that of leaf-rolling, that of piercing fruit-stones and
that of jam-making, to say nothing of the rest, which you don’t yet
know. If she was not capable of doing everything, she must, at least,
in course of time, have given up a first trade and learnt a second,
then a third, then a host of others, the knowledge of which is reserved
for future observers. Well, to practise several industries at the same
time, or even, from specializing in one department, to begin
specializing in some other, quite different department: on my word as a
Rhynchites, all this would seem madness to an animal.’
Thus speaks the Weevil. Let me complete her statement. As the instincts
of the three industrial guilds whose history is here related cannot in
any way be referred to a common origin, the corresponding Rhynchites,
despite their extreme similarity of structure, cannot be ramifications
of the same stock. Each race is an independent medal, struck from a
special die in the workshop of forms and aptitudes. What will it be
then when dissimilarity of form is added to dissimilarity of instincts?
But enough of philosophizing. Let us make the closer acquaintance of
the Sloe-weevil. At the end of July, fattened to a nicety, the grub
leaves its plum-stone and descends into the ground. With its back and
forehead it presses back the surrounding dust and makes itself a
spherical recess, slightly reinforced with a glue furnished by the
builder, to prevent the earth from falling in. Similar preparations for
nymphosis and hibernation are made by the Vine-weevil and the
Poplar-weevil; but these are more forward in their development. Before
September is over, most of them have achieved the adult form. I see
them glittering in the sand of my jars like living nuggets. These
golden globules foresee the rapidly approaching winter: as a rule they
do not stir from their underground quarters. However, enticed by the
hot sunlight, the last of the year, a few Poplar-weevils come up into
the open air to see what the weather is like. At the first breath of
the north-wind, these venturesome ones will take refuge under the
strips of dead bark; perhaps they will even perish.
The guest of the sloe is not in such a hurry. Autumn is drawing to a
close; and my buried captives are still in the larval state. What
matters this delay? They will all be ready when the beloved bush is
covered with blossom. By May, in point of fact, the insect abounds on
the sloes.
This is the time of careless revelry. The fruit is still too small,
with its stone not set and its kernel a transparent jelly; it would not
suit the grub, but it makes a feast for the adult, who, with an
imperceptible movement, without any twisting of the boring-tool, sinks
her drill into the pulp, drives it half-way down, holds it there
motionless and drinks ecstatically. The juice of the sloe pours over
the edge of the well.
This affection for the sour sloe is not exclusive. In my breeding-jars,
even when the regulation fruit is there, Rhynchites auratus very
readily accepts the green cherry and also the orchard plum, as yet
hardly the size of an olive. She refuses absolutely, though they are as
round and as small as sloes, the fruits of the mahaleb cherry, or
Sainte-Lucie cherry, a wilding frequent in the thickets of the
neighbourhood. She finds their drug-like flavour repellent.
When the egg is at stake, I cannot induce the mother to accept the
cultivated plum. In time of dearth, the ordinary cherry seems to be
less repugnant. Whereas the mother’s stomach is satisfied with any sort
of astringent pulp, the grub’s clamours for a sweet kernel in a small
casket which does not offer too much resistance. That of the cherry,
seasoned with prussic acid and rather bitter, is accepted only with
hesitation; that of the plum, contained in a stone whose strong walls
would oppose too great an obstacle first to the entry and then to the
exit of the grub, is absolutely disdained. Therefore the pregnant
mother, thoroughly versed in her household affairs, refuses for her
family any stone fruit other than the sloe.
Let us watch her at work. During the first fortnight of June, the
egg-laying is in full swing. At this period the sloes begin to assume a
purple hue. They are hard, about as large as a pea, which is not far
from their final size. The stone is woody and resists the knife; the
kernel has acquired consistency.
The fruits attacked show two kinds of pit, turned brown by the decayed
tissues. Some, the more numerous, are shallow funnels nearly always
filled up with a drop of hardened gum. At these points the insect has
simply made a meal and has not gone deeper than about half the
thickness of the pulpy layer. Later, the exudations from the wound have
filled the cavity with a gummy plug.
The other cavities, which are wider and form irregular polygons,
penetrate to the stone. The opening measures nearly four millimetres;
[49] and the walls, instead of slanting like those of the food-pits,
rise vertically from the exposed stone. Let us note yet another detail
whose importance we shall see presently: it is rare to find any gum in
them, though the other cavities usually contain it. These pits, which
are free from obstruction, are family establishments. I count two,
three, four on the same sloe; sometimes only one. Very often they are
accompanied, where the Weevil has fed, by funnel-shaped surface
erosions.
The larger pits descending to the stone form a sort of irregular
crater, in the centre of which there is always a little cone of brown
pulp. Not infrequently the magnifying-glass reveals a fine perforation
at the top of this central cone; at other times the orifice is closed,
but in a careless fashion, which makes one suspect a connection with
the depths below.
Cut this cone down the axis. At its base is a tiny hemispherical cup
hollowed in the thickness of the stone. Here, on a bed of fine dust due
to the work of erosion, lies a yellow egg, oval and about a millimetre
[50] long. Above the egg, like a protecting roof, rises the cone of
brown pulp, pierced throughout its length by a fine channel, which is
sometimes free and sometimes half obstructed.
The structure of the work tells us how the operation is conducted. In
the fleshy layer of the sloe the mother, eating the substance, or
discarding it if there be more than her appetite calls for, first makes
a pit with perpendicular walls and lays a suitable surface of the stone
absolutely bare. Then, in the centre of this area, she chases with her
graver a little cup sinking half-way through the thickness of the
shell. Here, on a soft bed of raspings, the egg is laid. Lastly, as a
defensive device, the mother erects above the cup and its contents a
pointed roof, a cone of pulp obtained from the walls of the pit.
The insect works very well in captivity, if given plenty of space,
sunlight and a twig covered with sloes. It is easy to watch the
proceedings of the egg-laying mother; but the result of diligent
observation amounts to very little.
Almost the whole day, the mother remains clinging to one spot on the
fruit, motionless, with her rostrum driven into the pulp. As a rule,
there is no movement on her part, nothing to betray any effort.
From time to time a male visits her, climbs on her back, throws his
legs around her and, himself swaying from side to side, rocks her very
gently to and fro. Without permitting herself to be diverted from her
serious labours, the female thus embraced passively yields to the
rolling motion. Perhaps it is a means of whiling away the long hours
needed for establishing an egg.
To see more than this is very difficult. The rostrum does its work in
the hidden seclusion of the pulp and, as the pit opens and widens, the
digger covers it with the fore-part of her body. The hollow is ready.
The mother withdraws and turns round. For a moment I catch a glimpse of
the bare stone at the bottom of the crater, with a tiny cup in the
centre of the denuded area. As soon as the egg is laid in this cup, the
insect turns round again and nothing more is visible until the work is
completed.
How does the pregnant mother contrive to raise above the egg a
protective heap, a cone, an obelisk somewhat irregular in shape, but
very curious with its narrow ventilating-shaft? Above all, how does she
manage to make this communicating passage in the soft mass? These are
details which we can scarcely hope to detect, so discreetly does the
insect work. We must be content to know that the rostrum alone, without
the aid of the legs, digs the crater and erects the central cone.
In the heat of June, less than a week is enough for the hatching. By
good fortune, solicited, so far as that goes, by attempts that come
near to exhausting my small stock of patience, I witness an interesting
sight. I have a new-born grub before my eyes. It has just cast the skin
of the egg; it is very busily wriggling in its powdery cup. Why so much
excitement? For this reason: to reach the kernel, its ration, the tiny
creature has to finish the pit and turn it into an entrance-window.
A stupendous task for a speck of albumen. But this feeble speck boasts
a set of carpenter’s tools; its mandibles, a pair of fine chisels,
received the necessary temper while their owner was still in the egg.
The grub sets to work immediately. By the following day, through a tiny
aperture which would hardly admit the point of a fair-sized needle, it
has entered into the promised land and is in possession of the kernel.
Another stroke of luck partly tells me the use of the central cone
pierced chimney-fashion. The mother, while sinking the pit in the flesh
of the sloe, drinks the juices that ooze out and eats the pulp. This is
the most direct manner of getting rid of the refuse without
interrupting her work. When she is digging in the surface of the stone,
the cup intended to receive the egg, she leaves in place the fine dust
resulting from her labours, an excellent material as bedding for the
egg but useless as food.
And what does the maggot in its turn do with its sawdust as it deepens
the pit in order to reach the kernel? To scatter the rubbish round
about is impossible: there is no room; to put it away in its stomach is
even less feasible: it cannot make its first mouthfuls of this dry
flour while waiting for the milk-food of a kernel.
The new-born grub has a better method. With a few heaves of its back,
it thrusts the litter of rubbish outside, through the chimney in the
cone. I have indeed caught sight of a white, powdery speck at the top
of the central cone. This tunnelled cone therefore is a lift which
carries away the rubbish of the excavation.
But the use of the curious building cannot be limited to this: the
ever-thrifty insect has not gone to the pains of building a tall,
hollow obelisk with the sole object of preparing a thoroughfare for the
atoms of dust that hamper the grub in its labours. The same result
could be obtained with less trouble; and the Weevil is too sensible to
construct the complex when the single would suffice. Let us look at
things more closely.
Evidently the egg, laid in a cup on the surface of the stone, needs a
protecting roof. Moreover, the grub, which will presently be working at
the bottom of its cup to reach the kernel, will require a refuse-shoot
in its restricted quarters. A small, shallow dome, with a window to get
rid of the sweepings, would, it seems, fulfil all the requisite
conditions. Then why the luxury of this pyramidal chimney which rises
to the topmost level of the pit, as a cone in eruption rises in the
centre of a volcanic crater?
The craters in the sloes have their lava, that is, their flow of gum,
which trickles from the various points injured and then hardens into
blocks. This flood stops up every hole at which the insect has merely
fed. The large pits with the central cones, on the other hand, have no
gum or show only a few scanty drops of it on their walls.
The mother, it is obvious, has taken certain precautions to defend the
home of the egg against the inroads of the gum. In the first place, she
has enlarged the cavity to keep the egg at a due distance from the
treacherous wall oozing with viscidity; she has moreover dug the pulp
down to the stone and has thoroughly stripped a perfectly clean surface
from which nothing dangerous can now exude.
This is not yet enough: though distant and rising perpendicularly from
the stripped area, the walls of the pit still give cause for alarm. In
some sloes under certain conditions, they will perhaps yield a
superabundance of gum. The only means of averting the danger is to
raise above the egg a barricade as high as the brink of the crater and
capable of arresting the flow. This is the reason for the central cone.
If there is a copious eruption, the gum will fill the ringed space, but
at least it will not cover the spot where the egg lies. The tall,
insubmersible obelisk is therefore almost ingeniously-contrived
defensive structure.
This obelisk is hollow along its axis. We have seen it serving as a
lift for the rubbish which the young grub throws out when deepening its
natal basin and converting it into a passage which gives access to the
kernel. But this is a very secondary function; it has another of
greater importance.
Every egg breathes. In its cup with the sawdust mattress, the Weevil’s
egg needs a supply of air, a very moderate supply, no doubt, but it
must have some. Through the passage in its conical roof the air reaches
it and is renewed, even if bad luck has filled the crater with gum.
Every living creature breathes. The maggot has entered the stone of the
fruit by making an opening such as our finest drills could not equal
for precision. It is now in a sealed casket, an air-tight barrel,
tarred, moreover, with gummy pulp. Yet it must have air, even more than
the egg.
Well, ventilation is effected by the shaft which the grub has driven
through the thickness of the stone. However tiny the air-hole, it is
big enough provided it be not clogged. There is no need to fear
anything of the sort, even with an excess of gum. Above the ventilator
rises the defensive cone, continuing, by means of its tunnel, the
communication with the outer world.
I wanted to know how anchorites more vigorous than the hermit of the
sloe would behave in an exceedingly limited and renewable atmosphere. I
must have them in the period of repose which precedes the
metamorphosis. The insect has then completed its growth; it is no
longer feeding; it is almost inert. It is living as cheaply as it can
and may be compared with a germinating seed. Its need of air is reduced
to the lowest possible limit.
Indifferent as to choice, I use what I have within reach and first of
all the larvæ of the Brachycerus, the Weevil that feeds on garlic. A
week ago they abandoned their cloves and went down into the earth,
where, motionless in their hollows, they are making ready for the
transformation. I place six of them in a glass tube, sealed at one end
by the blow-pipe. I divide them one from the other by means of cork
partitions, so as to allow each a cell comparable in capacity with the
natural lodging. Thus stocked, the tube receives a first-rate cork
covered with a layer of sealing-wax. It is absolutely closed. No
gaseous exchanges are possible between the inside and the outside; and
each larva is strictly limited to the small quantity of atmosphere
which I have meted out to it approximately, according to the capacity
of the underground cells.
Similar tubes are prepared, some with Cetonia-grubs taken from the
shells in which they were awaiting metamorphosis and others with nymphs
of the same species. What will become of these various prisoners, whose
life is latent, suspended, demanding a minimum of ventilation?
The sight that greets my eyes a fortnight later is conclusive. My tubes
contain only a horrible mess of corpses. Evaporation was impossible; no
fresh air came to cleanse the premises and vivify the larvæ and nymphs;
and all have perished, all have become putrid.
The casket of the sloe, despite its air-tight condition, is not so
close a receptacle as my glass prisons. Gaseous exchanges are effected,
since the kernel, itself a living body, continues to thrive. But what
suffices to maintain the life of a seed must be insufficient for the
much more active life of the insect. The larva of the Weevil, during
the few weeks which it spends nibbling its kernel, would thus be in
great jeopardy if it had no other resources for breathing than the air
in the sloe-stone, so limited in quantity and so scantily renewed.
Everything seems to prove that if the air-hole, the work of its chisel,
were to be plugged with a drop of gum, the recluse would perish, or at
least drag out a languishing existence and would be incapable of
migrating underground at the proper time. This suspicion is worth
confirming.
I therefore prepare a handful of sloes; I myself bring about what would
have happened naturally but for the mother’s precautions. I deluge the
crater and its central cone with a drop of thick solution of gum
arabic. My sticky preparation takes the place of the product of the
sloe-bush. The drop hardens; I add others until the top of the cone
disappears in the thickness of the varnish. As for the rest of the
fruit, I leave it as it was.
This done, let us wait, but leave the sloes in the open air, as they
are, on the bush. There the gummy concretions will not grow soft—which
would not fail to happen in a glass jar—merely by means of the moisture
supplied by the fruits themselves.
By the end of July, the sloes left in their natural state give me the
first emigrants; the exodus goes on through part of August. The means
of exit is a round hole, very cleanly cut, similar to that made by the
Nut-weevil. Just like the grub of the last-named, the emigrant passes
itself through the draw-plate and releases itself by a feat of
gymnastics in which it dilates the part of the body already extracted
with the humours forced out of the part still imprisoned.
The exit-door is sometimes one with the narrow entrance; more often it
is beside it; but it is never, absolutely never, outside the bare space
that forms the bottom of the crater. The grub seems to loathe finding
the soft pulp of the sloe in front of its mandibles. Admirably adapted
for chiselling hard wood, the tool would perhaps become clogged in a
sticky mess. This needs a spoon to remove it, not a gouge. At all
events, the exit is always made at some point of the floor thoroughly
cleaned by the mother, where there is neither gum nor fleshy pulp to
hamper the proper working of the tool.
What is happening at the same time with the gummy sloes? Nothing
whatever. I wait a month: nothing yet. I wait two, three, four months:
nothing, still nothing. Not a grub comes out of my prepared sloes. At
last, in December, I decide to see what has been going on inside. I
crack the stones whose air-holes I have blocked with gum.
Most of them contain a dead maggot, which has dried up while quite
young. Some hide a live larva, well developed, but lacking in strength.
You can see that the creature has suffered not from want of food, for
the kernel is almost entirely consumed, but from another unsatisfied
need. Lastly, a small number show me a live grub and an exit-hole made
in the regular manner. These lucky ones, immured by the gum perhaps
when they were already full-grown, had the strength to perforate the
casket; but, finding on top of the wood the hateful varnish, which is
the result of my perfidy, they obstinately refused to bore any farther.
The gummy barrier stopped them short; and it is not their habit to seek
their freedom in another direction. Away from the bare floor, the
bottom of the crater, they would infallibly come upon the pulp, which
is no less detestable than the gum. In short, of the collection of
larvæ subjected to my stratagems, not one has thriven; the sealing with
gum has been fatal to them.
This result puts an end to my hesitations: the cone set up in the
centre of the pit is necessary to the existence of the grub sequestered
in the stone. Its tunnel is a ventilating-shaft.
Each species certainly possesses its peculiar method of maintaining a
connection with the outside world, when the larva lives under
conditions in which the renewal of the air would be too difficult or
even impossible if no precautions were taken. Generally, a fissure, a
corridor, more or less unobstructed and the usual work of the grub, is
enough to ventilate the dwelling. Sometimes it is the mother herself
who sees to these hygienic requirements; and then the method employed
is strikingly ingenious. While on this subject, let us recall the
wonderful devices of the Dung-beetles.
The Sacred Beetle models her grub’s loaf in the form of a pear; the
Spanish Copris [51] shapes it like an egg. It is compact, homogeneous
and as air-tight as stucco-work. To breathe in these lodgings would
unquestionably be a very difficult thing; but the danger is provided
against. Look at the small end of the pear and the top of the ovoid.
After ever so little reflection, you will be seized with surprise and
admiration.
There—and there only—you will see, not the air-tight paste of the rest
of the work, but a stringy plug, a disk of coarse velvet bristling with
tiny fibres, a round piece of loosely-made felt through which the
gaseous exchanges can be effected. A filter takes the place of the
solid material. The mere appearance is enough to tell us the function
of this part. If doubts occurred to our minds, here is something to
dispel them: I cover the fibrous expanse with several coats of varnish;
I deprive the filter of its porousness, without interfering with any
other part. Now let us see what happens. When the time comes for the
emergence, with the first autumn rains, let us break open the pills.
They contain nothing but shrivelled corpses.
An egg is killed if you varnish it: when placed under the sitting Hen
it remains a lifeless pebble. The chicken has died in the germ. So
perish the Sacred Beetle, the Copris and the rest when we varnish the
circular disk of felt which acts as a ventilator.
This method of the porous plug is recognized as being so efficacious
that it is in general use among the pill-makers of the remotest
regions. The Splendid Phanæus and Bolbites onitoides, both from Buenos
Aires, [52] employ it as zealously as the Dung-beetles of Provence.
One of the dwellers in the pampas uses another process, prescribed by
the material which she manipulates. This is Phanæus Milon, a ceramic
artist and meat-packer. With very fine clay she fashions a gourd in the
middle of which she places a round meat-pie made from the sanies of a
corpse. The grub for which these victuals are intended hatches in an
upper story, separated from the larder by a clay partition.
How will this grub breathe, first in its cell upstairs and then in the
lower room, when it has perforated the floor and reached the cold
pasty? The house is a piece of pottery, an earthenware jar whose wall
sometimes measures a finger’s-breadth in thickness. Air cannot possibly
pass through such a casing. The mother, who knew this, made
arrangements accordingly. Along the gourd’s neck she contrived a narrow
passage through which a flow of air is possible. Without resorting to
obstruction by means of varnish or anything else, we see quite plainly
that this minute tunnel is a ventilating-shaft.
Exposed on her fruit to the danger from the gum, the Weevil excels the
meat-packer of the pampas in her delicate precautions. Over the spot
where the egg lies, she raises an obelisk, the equivalent of the
gourd’s neck in the work of the Phanæus; to give the germ air, she
leaves the axis of the nipple hollow, as does the potter. In either
case, the new-born grub has a tough job to begin with: in the one it
chisels the fruit-stone; in the other it pierces the earthenware
partition. And now both have reached their goal: the first its kernel,
the second its meat-pie. Behind them they have left a round port-hole
which continues the tunnel made by the mother. Thus communication
between the inside of the establishment and the outer atmosphere is
assured.
The comparison cannot be carried farther, so greatly does the ingenuity
of the Rhynchites, in danger of being stifled by the gum, surpass that
of the other Beetle, who is perfectly safe in his clay pot. The Weevil
has to reckon with the terrible exudations which threaten to submerge
and stifle her larva. The mother, therefore, in the first place, builds
up the defensive cone, the ventilating-shaft, to a height which the
gummy flood will not reach; then, around this rampart of fruit-pulp,
she makes a wide moat which keeps at a distance the wall sweating the
dangerous substance. If the eruption is too violent, the viscous fluid
will collect in the crater without imperilling the breathing-hole.
If the Rhynchites and her competitors in means of defence against the
dangers of asphyxia have taught themselves their trade by degrees, by
passing from an unsuccessful to another, more satisfactory method; if
they are really the creatures of their achievements, do not let us
hesitate, though we deal a blow to our self-conceit: let us recognize
them as engineers capable of teaching a lesson to our own graduates;
let us acclaim the microcephalous Weevil as a powerful thinker, a
wonderful inventor.
You dare not go to that length; you prefer to appeal to the hazards of
chance. But what a wretched resource is chance when we are considering
such rational contrivances! As well throw the letters of the alphabet
up in the air and expect them to form a given line of a poem as they
fall!
Instead of bamboozling our minds with such tortuous conceptions, how
much simpler, and above all how much more truthful, to say:
‘Matter is governed by a sovereign order.’
This is what the Sloe-weevil, in her humble way, tells us.