THE NUT-WEEVIL

If a peaceful home, a good stomach and a secure livelihood are enough to bring happiness, then the Nut-weevil is truly a happy creature, more so even than the famous Rat who retired into a Dutch cheese. The hermit of the fabulist1 had kept up certain relations with the world, the source of all his troubles. One day, a deputation from the Rat folk came to ask him for a trifling alms. The recluse listened to their complaints with an unwilling ear; he told them that he could not help them, promised to pray for them and shut the door without further ado.

Hard though he was upon the needs of others, this visit of famished beggars must have disturbed his digestion somewhat: history does not tell us so, but we are at liberty to believe it. The hermit of the naturalist is not subject to these annoyances. Its dwelling is an inviolable cell, a coffer made all in one piece, with neither door nor wicket for distressed bores to come knocking at. Within is absolute quiet, nothing enters of the sounds or cares of the outer world. An excellent lodging, [95]neither too hot nor too cold, peaceful and closed to all. An excellent table, besides, and a sumptuous. What more could any one ask for? The smug inmate waxes big and fat.

We all know the rascal. Which of us, when a boy, cracking a hazel-nut with his strong teeth, has not bitten into something acrid and sticky? Ugh! It’s the nut-maggot! Let us conquer our repugnance and examine the creature closely. It is worth the trouble.

We see a plump and lusty grub bent into a bow, legless and milk-white, except the head, which is capped with a yellowish horn. When taken from its cell and laid on the table, the thing wriggles about, coiling and uncoiling and fidgeting without contriving to shift its place. It is denied the power of locomotion. What would the worm do with that power, boxed up as it is? For that matter, this is a feature common to the Weevil tribe, all of whom are inveterate stay-at-homes in their larval stage. Such is the hermit whose history follows below, the anchorite with the sleek and rounded rump, the larva of the Nut-weevil (Balaninus nucum, Lin.).

The kernel of the hazel-nut is its cake, an abundant provision, which it never or but very seldom finishes entirely, so greatly do the victuals exceed the utmost requirements of obesity. There is plenty to enable one alone to live comfortably for three or four weeks; but it would mean short [96]commons for two. And so the victuals are scrupulously rationed: to each nut its grub, no more.

I have happened on very rare occasions to find two. The late-comer, the offspring of some ill-informed mother, had seated itself at table beside the other, without much profit to itself. There was not much left of the cake; moreover, the still feeble intruder seemed to have had a bad reception from the powerful and jealous owner of the property. There was no doubt about it: the superfluous weakling was doomed to perish. The Weevil knows no more of mutual aid among kinsmen than the Rat in the cheese. Each for himself: such is the savage and bestial law, even in a nutshell.

The dwelling is a perfectly continuous fortification, without a joint or fissure for an invader to slip through. The walnut-tree forms the shell of its fruit out of two halves joined together, with a line of least resistance left between them; the hazel makes its kegs with a single stave, curved into an arch that is equally strong at all points. How did the grub of the Balaninus obtain access to this fortress?

On the surface, smooth as polished marble, the eye perceives nothing to explain the entrance of an exploiter from without. One can picture the surprise and the artless imaginings of those who first remarked the peculiar contents of the intact nut, without any sort of opening to it. The plump [97]maggot, living inside it, could not be an alien. It was therefore born of the fruit itself, under the influence of an unlucky moon. It was a child of putrefaction hatched by a mist.

A faithful custodian of the ancient beliefs, the peasant of to-day always attributes maggoty nuts and other fruits spoiled by insects to the moon and a passing miasma. And this will be so indefinitely, until our country schools yield the place of honour to cheerful, invigorating studies in the fields.

Let us replace these inanities by the reality. The grub is certainly an outsider, an invader; and, if it has made its way in, this is because it has found a passage somewhere. Let us look for this passage, which escaped us at the first examination, with the aid of a magnifying-glass.

The search does not take long. The base of the nut displays a wide, rough, light-coloured depression, to which the cup was fastened. On the confines of this area, a little way outside it, is a darker speck. Thus is the entrance to the stronghold; this is the key to the riddle.

The rest follows without further inquiry and is very clearly interpreted by the data provided by the Elephant Weevil. The Nut-weevil also bears a buccal drill, still inordinately long, but this time slightly curved.

I can well imagine the insect, like its relative of the acorns, standing erect on the tripod formed [98]by the tip of its wing-covers and the hinder tarsi; it assumes a posture worthy of portrayal by a fantastic pencil; it plants its instrument perpendicularly; it patiently veers and veers again.

The work is arduous, very arduous, for the nut is selected when nearly ripe, to provide the grub with more savoury and more abundant food; it is thick and tough, much more so than the rind of an acorn. If the Acorn-weevil takes half a day to bore her passage, how long must the Nut-weevil’s task be, how patient her persistence! Perhaps her rod is specially hardened. We can temper our drills till they wear away granite; no doubt the Weevil, in the same way, provides her boring-tool with a bit of triple hardness.

Quickly or slowly, the auger sinks into the base of the nut, where the tissues are softer and milkier; it enters obliquely, making a fairly long journey, to prepare for the grub a column of semolina suited to its first needs. Whether boring into nuts or into acorns, the Balanini make the same delicate preparations for the benefit of their offspring.

At length there comes the placing of the egg, right at the bottom of the shaft. Here the strange method which we already know is repeated. With a hinder rostrum, equal in length to the front one and kept hidden away in the abdomen until the moment comes for using it, the mother inserts her egg at the base of the kernel.

I see these nursery precautions only in my [99]mind’s eye, but I see them very clearly, enlightened as I am by my examination of the nut converted into a cradle and above all by the method of the Acorn-weevil. Still, I might aim at something better than this; I should like to witness the operation: rather a hopeless ambition, I fear.

In my neighbourhood, indeed, the hazel is scarce and its regular exploiter is almost unknown. Nevertheless, let us make the experiment with the six hazel-trees which I planted in the paddock long ago. First of all we must stock them accordingly.

A valley of the Gard, less parched than the Sérignan hills, provides me with a few couples of the insect. They reach me by post at the end of April, when the nut, still quite light in colour, soft and flattish, is beginning to emerge from the cup in which it is sheathed. The kernel is far from formed; there is just a beginning, a promise of a kernel.

In the morning, in glorious weather, I put the strangers on the leaves of my hazels. The journey has not tried them unduly. They look splendid in their modest drab costume. The moment they are free, they half-open their wing-cases, spread their wings, fold them again and once again unfurl them, without taking flight. These are mere muscular exercises, serving to revive their strength after a long imprisonment. I regard these sports in the sunlight as a good omen: my colonists will not run away.[100]

Meantime the nuts are filling out daily and beginning to tempt and entice the children. They are within reach of the smallest, who love to stuff their pockets with them and to crunch them, cracking them between two stones. They receive express injunctions to keep their hands off them. This year, for the sake of the Weevils whose history I wish to learn, the joys of gathering nuts in May will be forbidden.

What sort of ideas can such a prohibition produce in these ingenuous minds? If they were of an age to understand me, I would say:

‘My dears, beware of the great enchantress, Science. If ever one of you—which Heaven forbid—should allow himself to be beguiled by her, let him remember my warning: in exchange for the little secrets which she reveals to us, she demands much graver sacrifices than a handful of nuts.’

The prohibition is understood; the tempting fruit is left almost untouched. For my part, I inspect the nuts assiduously. All my trouble is unavailing: I do not succeed in surprising a Balaninus engaged in her patient task of boring. At the utmost, at sunset, I happen to see one who, hoisted to her full height, is trying to insert her drill. The little that I observe teaches me nothing new; the Acorn-weevil has already shown me as much.

In any case, it is only a brief attempt. The insect is casting about and has not yet found what [101]suits her. Perhaps the perforator of hazel-nuts works at night.

In another respect I have been more fortunate. Some nuts, some of the first colonized, are laid by in my study and subjected to frequent inspections. My diligence is rewarded with success.

At the beginning of August, two larvæ leave their coffers before my eyes. They have no doubt long been chipping with the points of their mandibles, that patient chisel, at the hard wall. The exit-hole is just finished when I take note of the coming departure. A fine dust is falling by way of shavings.

The window of release is distinct from the narrow aperture of the entrance. Perhaps it will not do to obstruct this grating, which ventilates the house, while the grub is still at work. The window aforesaid is situated at the base of the fruit, close to the rough surface by which the nut adheres to its cupule. In this region, where the incipient materials are elaborated until the nut is perfectly ripe, the density is a little less than elsewhere. The point to be perforated is excellently chosen therefore: it is here that the least resistance will be encountered.

Without any preliminary auscultation, without exploratory soundings, the recluse knows the weak point of his prison. Confident of success, he works away with a will. Where the first blow of the pick is struck the others follow; no time is wasted on [102]experiments. Persistence is the strength of the weak.

It is done: daylight enters the coffer. The window is opened, round, widening a little inwards and carefully polished over the whole circumference of its embrasure. Under the burnisher of the mandibles any roughness that might presently increase the difficulty of the emergence has disappeared. The holes in our steel draw-plates are scarcely more accurate.

The comparison with a draw-plate comes in quite aptly here: the larva actually frees itself by a wire-drawing-operation. Like a length of brass wire which is reduced by being passed through an orifice too narrow for its diameter, it escapes through the window in the shell by decreasing its girth. The wire is drawn by an exertion on the part of the workman’s pincers or by the rotation of the machine; it subsequently retains the reduced thickness which the operation has given it. The grub knows another method: it lengthens and thins itself by its own efforts; and, directly it has passed through the narrow orifice, it returns to its natural size. Apart from these differences the resemblance is striking.

The exit-aperture is precisely the same width as the head, which, being rigid, with a horny cap, does not lend itself to deformation. Where the head has passed, the body has to pass, however fat it may be. When the liberation is completed, [103]it is most surprising to see how bulky a cylinder, how corpulent a grub has contrived to make its way through the tiny opening. If we had not witnessed the exodus, we should never have suspected such a feat of gymnastics.

The orifice, we were saying, is exactly fitted to the diameter of the head. Now this inelastic head, by whose size that of the hole has been calculated, represents at most one-third of the width of the body. How does a threefold thickness pass through a single calibre?

Here comes the head, without the least difficulty: it is the pattern to which the door was built. The neck, a little wider, follows: a slight contraction frees it. Next comes the turn of the chest and the plump belly. This is a most arduous operation. The grub has no legs. It has nothing, neither hooks nor stiff bristles, that might give it a purchase. It is a soft roly-poly which has, by its own efforts, to clear the disproportionately narrow passage.

What happens inside the nut escapes me: it is hidden by the opaque shell; what I see outside is very simple and tells me of that which cannot be seen. The creature’s blood rushes from back to front; the humours of the organism change their position and accumulate in the part that has already emerged, which swells into a dropsy, attaining five or six times the diameter of the head.

In this way a large cushion is formed on the [104]kerb of the well, a girdle of energy which, by its dilatation and its intrinsic elasticity, gradually extricates the remaining segments, which are diminished in volume by the shifting of their fluid contents.

It is a slow and very laborious business. The grub, in its free part, bends, draws itself up and sways from side to side. We do the same when forcing a nail from side to side to extract it from its socket. The mandibles gape widely, close and gape again, with no intention of laying hold. These movements represent the yo-heave-hoes with which the exhausted creature accompanies its efforts, like those of sailors hauling on a cable.

‘Yo-heave-ho!’ says the grub; and the sausage rises a peg higher.

While the extracting pad is swelling and straining every muscle, it is evident that the part still in the shell is draining itself of its humours as far as it possibly can, making them flow into the part released. It is this that makes the wire-drawing action feasible.

One more effort of leverage from the inflated girdle; one more yawn:

‘Heave-ho!’

That has done the trick. The grub glides over the shell and drops.

One of the nuts which have just afforded me this sight was gathered on its branch a few hours before. The grub, then, would have fallen to the ground [105]from the height of the hazel-bush. Allowing for the proportions, such a fall would for us mean a terrible crash; for the grub, so plastic and supple, it is a trifle. It matters little to the larva whether it tumbles into the world from the top of the bush or whether it quietly changes its lodgings a little later, when the nut, fallen of its own ripeness, is lying on the ground.

Without delay, as soon as free, it explores the soil within a restricted radius, seeks a point easy to dig, finds it, does a little spade-work with its jaws, wriggles its rump and buries itself. At no very great depth a spherical cavity is made by pressing back the dusty soil. Here the grub will spend the winter and await the resurrection of the spring.

Were I so presumptuous as to advise the Balaninus, better-versed than any one in its business as a Weevil, I should say:

‘To leave your nut now is an act of folly. Later, when the April festival is here and the hazels replace their drooping catkins by the pink pistils of their nascent fruit, well and good; but to-day, in this time of blazing sunshine, which drives the most gallant workers to idleness, what is the use of deserting a home in which you can sleep so comfortably throughout the slack summer season? Where will you find a better lodging than the shell of a hazel-nut when the autumn rains come and the winter frosts? In what more peaceful solitude [106]could the delicate work of the transformation be effected? Besides, the subsoil is full of dangers. It is damp and cold; its roughness makes it painful to the touch for a skin as fine as yours. A formidable enemy lurks there, a cryptogam that implants itself upon any buried larva. In my jars I have great difficulty in protecting the buried larvæ which I am trying to rear. Sooner or later white tufts form upon the glass wall, thread-like fluffs whose lower portion will clasp and drain a poor grub turned into a scrap of plaster: it is the mycelium of one of the Sphæriaceæ whose allotted field of exploitation is the bodies of insects undergoing nymphosis underground. In the nut, a hygienic cell, free from devastating germs, nothing of the sort is to be feared. Why leave it?’

These arguments the Balaninus meets with a refusal. It shifts its quarters, and it is right. On the ground, where the nut is lying, it has reason, to begin with, to dread the Field-mouse, a great hoarder of nuts. He collects in his stone-heap everything yielded by his nightly rounds; then, at his leisure, with a patient tooth, he pierces a small hole in the shell and extracts the kernel.

The hazel-nut is a welcome find, a savoury morsel. If emptied by the Weevil, it is only the more valuable: instead of its usual contents it contains the grub of the Balaninus, a rich saveloy which makes a pleasant change from a farinaceous diet. So, for fear of the Field-mouse, we go underground.[107]

A still more important motive urges this departure. True, it would be pleasant to sleep in the impregnable castle of the nut-shell; but the delivery of the future insect has also to be thought of. The larva of the Capricorn, throwing caution to the winds, leaves the interior of the oak and comes to the surface, risking the investigations of the Woodpecker; it runs into danger to prepare an exit for the great horned Beetle, who could not make his way out unaided.

A similar precaution is necessary for the Weevil-larva. While possessing the full strength of its mandibles, without waiting for the torpor during which the accumulated fats will be remoulded into a new organism, it pierces the coffer from which the adult would be incapable of escaping by her own efforts; it comes out and buries itself in the ground. The future is wisely provided against; from its present catacomb the adult will be able without hindrance to ascend to the light of day.

We were saying that, if the Weevil assumed her final shape in the nut, she would be incapable of effecting her own release. Yet with her drill she is very well able to perforate the shell when the egg has to be installed. Why should she be prevented from doing in the inverse direction what she is able to perform inwards from without? A little reflection will show us the tremendous difficulty.

To place the egg in position, a fine tube, of the thickness of the drill, is sufficient. To give passage [108]to the solid adult Weevil would demand a comparatively enormous opening. The material to be pierced is very hard, so hard that the larva, with the powerful gouges of its mandibles, bores a hole only just big enough to allow the head to pass. The rest of the body has to follow by dint of exhausting efforts.

How could the insect open a sufficiently large door with its delicate foil, when the far better-equipped grub has so much difficulty in boring a moderate porthole? Could she not, by making a ring of perforations, remove a round disk of the requisite size? Strictly speaking, this would be possible, with a prodigious expenditure of patience, a quality which insects can hardly be said to lack.

But here length of time is not enough: the boring-tool is absolutely unmanageable inside the nut-shell. It is so long that, to implant it at the point to be drilled, the Weevil, when she works outside, is obliged to stand erect. For lack of space under the low ceiling of the shell, this position and the alternate tacking about become impossible.

However patient she herself may be and however well-armed we suppose the tip of her drill to be, the Weevil, prevented from employing her auger by the narrowness of the premises, would perish in her coffer. She would die a victim to her inordinate machinery, which serves excellently well for pushing the egg into place, but which would be [109]very unwieldy if the prisoner had to effect her own delivery.

Given a less exaggerated rostrum, just a short and powerful punch, the Weevil, methinks, would not abandon the nut while she was still in the larva stage, the danger of the Field-mouse notwithstanding. It is a delightful laboratory for the remodelling-process of the metamorphosis. The shell, it is true, lies on the surface of the soil, unsheltered and exposed to the north-wind. But what does the cold matter, provided that we keep dry? The insect has little to fear from the frosts. Its slumbers are all the sweeter when the torpor attending the renewal of its being is increased by the torpor due to a low temperature.

I am persuaded of it: if she carried a less cumbersome drill, the Balaninus would not change her quarters the moment the kernel of her hazel-nut was consumed. My conviction is based on the habits of other Weevils, in particular Gymnetron thapsicola, Germ., who exploits the capsules of a mullein, Verbascum thapsus, Lin., the shepherd’s club, a frequent denizen of the tilled fields. As cells these capsules are, though less in volume, almost the equivalent of the hazel-nut.

They consist of strong shells, formed of two pieces closely joined, with no communication whatever with the outside world. A Weevil of humble size and modest attire takes possession of them in May and June as lodgings for her larvæ, which [110]gnaw the placenta of the fruit, laden with unripe seeds.

In August the plant is withered, scorched by the sun, but still standing and topped with its compact spike of capsules. Open some of these shells, almost as solid as cherry-stones. Inside is the Weevil in the adult state. Open them in winter: the Gymnetron has not gone. Open them for the last time in April: the little Weevil is still at home.

Meanwhile, fresh mulleins have sprouted hard by; they flower; their shells attain the right degree of ripeness: the time has come to leave, to go and establish one’s family. Not till then does the solitary demolish her hermitage, her capsule, which has protected her so faithfully hitherto.

And how does she do so? It is quite simple. Her rostrum is a short bradawl, easily wielded therefore, even in the confined space of a cell. The shell, moreover, is not too strong. It is a very dry vellum wrapper rather than a hard wooden wall. The recluse drives her short-handled pick into it; she stabs and thumps and brings the wall crumbling down. And now hurrah for the joys of the sun! Hurrah for the yellow flowers, with stamens all bristling with violet hairs!

Considering their tools, in one case of exaggerated length under a too low ceiling, in another short and suited to the space available in the cell, are not both these insects happily inspired, the first [111]in leaving her nut prematurely, while the grub’s powerful shears enable her to do so, the second in spending three parts of the year in the security of her shell, quitting it only at the time of the wedding on the friendly plant? Thus do we see the impeccable logic of the instincts revealed, even in the humblest creatures.