The art of rolling a leaf

The Life and Love of the Insect by Jean-Henri Fabre, is part of the HackerNoon Books Series. You can jump to any chapter in this book here. LEAF-ROLLERS

CHAPTER XIV. LEAF-ROLLERS

The attainments of the Curculionid mother are, generally speaking, limited to inserting her eggs at places where the grubs will find suitable nourishment and occasionally varying the diet with a botanical judgment of marvellous certainty. She displays little or no industry. The niceties of the feeding-bottle or the baby-linen do not concern her. To this rough conception of the duties of maternity, I know but one exception, the attribute of certain Weevils, who, in order to endow their young with an alimentary preserve, possess the art of rolling a leaf, which serves as board and lodging in one.

Among these manufacturers of vegetable sausages, the most skilful is the Poplar Weevil (Rhynchites Populi, Lin.), who is modest in proportions, but resplendent in attire. Her back is clad in gleaming gold and copper; her back is indigo blue. Would you see her at work, you need but visit the lower twigs of the common black poplar, at the edge of the meadows, about the end of May.

Whereas, up at the top, the fond spring breezes shake the majestic green distaff and set the leaves quivering on their flattened stalks, down below, in a zone of calmer air, the tender shoots of the year remain quiescent. Here, especially, far from the wind-tossed heights opposed to [185]labour, the Rhynchites works. And, as the workshop is just at a man’s height, nothing is more easy than to observe the roller’s actions.

Easy, yes, but distressing, under a blazing sun, if one would follow the insect in all the detail of its methods and the progress of its work. Moreover, this involves a great deal of walking, which takes up time; and, again, it is not favourable to precise observations, which require an indefinite amount of leisure and assiduous visits at all hours of the day. It would, therefore, be greatly preferable to study the animal comfortably at home; but it is above all things necessary that she should lend herself to this plan.

The Rhynchites fulfils the condition excellently well. She is a peaceable enthusiast and works on my table with the same zest as in her poplar-tree. A few tender shoots, planted in fresh sand, under a woven-wire cover, and renewed as soon as they begin to fade, take the place of the tree in my study. The Weevil, not in the least intimidated, devotes herself to her industry even under the lens of my magnifying-glass and supplies me with as many scrolls as I could wish for.

Let us watch her at work. She picks the leaf which she proposes to roll from the young shoots sprouting in sheaves at the base of the trunk, but picks it not among the lower leaves, which are already the correct green and of a firm texture, nor yet among the terminal leaves, which are in a fair way of growing. Above, they are too young, not wide enough; below, they are too old, too tough, too hard to manage.

The leaf selected belongs to the intermediate rows. As yet of a doubtful green, in which yellow predominates, soft and glossy with varnish, it has, or has very nearly, [186]the final dimensions. Its denticulations swell into delicate glandular pads, whence oozes a little of the viscous matter that tars the buds at the moment when their bracts become disjoined.

A word now on the equipment in respect of tools. The legs are supplied with double claws shaped like the meat-hooks of a steel-yard. The lower side of the tarsi carries a thick tuft of white bristles. Thus shod, the insect clambers very nimbly up the most slippery vertical walls; it can stand and run like a fly, with its back downwards, on the ceiling of a glass bell. This characteristic alone is enough to suggest the subtle sense of equilibrium which the Weevil’s work will demand.

The curved and powerful beak or rostrum, without being exaggerated in size, spreads at the tip into a spatula ending in a pair of fine, shear-like mandibles. It makes an excellent bodkin, which plays the first or leading part in the whole work. The leaf, in fact, cannot be rolled in its actual condition. It is a live blade which, owing to the afflux of the sap and the tonicity of the tissues, would resume its flat formation in proportion as the insect endeavoured to curve it. The dwarf insect has not the strength to master a piece of these dimensions, to roll it up so long as it retains the elasticity of life. This is evident to our eyes; it is evident also to the eyes of the Weevil.

How is she to obtain the degree of inert suppleness required in the circumstances? We ourselves would say:

“We must pluck the leaf, let it fall to the earth, and manipulate it on the ground when it is rightly withered.”

The Curculionid is cleverer than we at this sort of business and does not share our opinion. What she says to herself is:

“On the ground, amid the obstruction of the grass, my labours would be impracticable. I want elbow-room; I want the thing to hang in the air, where there are no obstacles of any kind. And there is a more serious consideration: my grub would refuse a rank, dried-up sausage; it insists on food that retains a certain freshness. The scroll which I intend for its consumption must be not a dead leaf, but an impaired leaf, not altogether deprived of the juices with which the tree supplies it. I must wean my joint, but not kill it outright, so that the dying leaf may remain in its place for the few days during which the extreme youth of the worm lasts.”

The mother, therefore, having made her selection, takes up her stand on the stalk of the leaf and there patiently drives in her rostrum, turning it with a persistency that denotes the great importance of this thrust of the bodkin. A little wound opens, a fairly deep wound, which soon becomes a point of mortification.

It is done: the sap-conduits are cut and allow only a scanty proportion to ooze through to the edge. At the injured point, the leaf gives way under the weight; it bends vertically, withers a little and soon acquires the requisite flexibility. The moment has come to work it.

That bodkin-thrust represents, although much less scientifically, the prick of the hunting Hymenopteron’s sting. The latter wants for her offspring a prey now dead, now paralyzed; she knows, with the thoroughness of a consummate anatomist, at what points it behoves her to insert the sting to obtain either sudden [188]death or merely a cessation of movement. The Rhynchites requires for her young a leaf rendered flexible ad hoc, half-alive, paralyzed in a fashion, a leaf that can easily be shaped into a scroll; she is wonderfully familiar with the little leaf-stalk, the petiole, in which the vessels that dispense the foliaceous energy are collected in a tiny bundle; and she inserts her drill there, there only and never any elsewhere. Thus, at one blow, without much trouble, she effects the ruin of the aqueduct. Where can the beaked insect have learnt her astute trade as a drier-up of wells?

The leaf of the poplar is an irregular rhombus, a spear-head whose sides widen into pointed pinions. The manufacture of the scroll begins with one of those two lateral corners, the right or left indifferently. Notwithstanding the hanging posture of the leaf, which makes the upper or lower surface equally easy of access, the insect never fails to take its position on the upper side. It has its reasons, dictated by the laws of mechanics. The upper surface of the piece, which is smoother and more flexible, has to form the inside of the scroll; the lower surface, which has greater elasticity because of its powerful veins, must occupy the outside. The statics of the small-brained Weevil agree with those of the scientists.

See her at work. She stands on the rolling-line, with three of her legs on the part already rolled and the three opposite on the part still free. Solidly fixed, on both sides, with her claws and tufts, she obtains a purchase with the legs on the one side, while making her effort with the legs on the other. The two halves of the machine alternate like motors, so that, at one time, the formed cylinder rolls over the free blade and, at another, the free blade moves and is laid upon the scroll already made.[189]

There is nothing regular, however, about these alternations, which depend upon circumstances known to the animal alone. Perhaps they merely afford a means of resting for a little while without stopping a work that does not allow of interruption. In the same way, our two hands mutually relieve each other by taking it in turns to carry the burden.

It is impossible to form an exact image of the difficulty overcome, without watching, for hours on end, the obstinate straining of the legs, which tremble with exhaustion and threaten to spoil everything if one of them let go at the wrong moment, or without seeing with what prudence the roller never releases one claw until the five others are firmly fixed. On the one side are three points of support, on the other three points of traction; and the six are shifted, one by one, little by little, without for a moment allowing their connected mechanical system to flag. A single instant of forgetfulness or weariness would cause the rebellious piece to unroll its scroll and escape from the manipulator’s grasp.

The work is accomplished, moreover, in an uncomfortable position. The leaf hangs very much on the slant or even vertically. Its surface is varnished, is smooth as glass. But the worker is shod accordingly. With her tufted soles, she scales the polished perpendicular; with her twelve meat-hooks, she tackles the slippery floor. Yet this fine set of tools does not rid the operation of all its difficulties. I find it no easy matter to follow the progress of the rolling with the magnifying-glass. The hands of a watch do not move more slowly. The insect stands for a long time, at the same point, with its claws firmly fixed; it is waiting for the leaf to be mastered and to cease resistance. Here, of course, there [190]is no gumming-process to catch hold and keep the fresh surfaces glued together. The stability depends purely upon the flexion acquired. And so it is not unusual for the elasticity of the piece to overcome the efforts of the worker and partly to unroll the more or less forward work. Stubbornly, with the same impassive slowness, the insect begins all over again, replaces the insubordinate piece. No, the Weevil is not one to allow herself to be upset by failure: she knows too well what patience and time will do.

The Rhynchites usually works backwards. When her line is finished, she is careful not to abandon the fold which she has just made and return to the starting-point to begin another. The part last folded is not yet fastened sufficiently; if left to itself too soon, it might easily rebel and flatten out again. The insect, therefore, persists at this extreme point, which is more exposed than the rest; and then, without letting go, makes her way backwards to the other end, still with patient slowness. In this way, an added firmness is imparted to the fold; and the next fold is prepared. At the end of the line there is a fresh prolonged halt, followed by a fresh backward motion. Even so does the husbandman’s plough-share alternate its work on the furrows.

Less frequently, when, no doubt, the leaf is found to be so limp as to entail no risk, the insect abandons the fold which it has just made, without going over it again in the opposite direction, and quickly scrambles to the starting-point to contrive a new one.

There we are at last. Coming and going from top to bottom and from bottom to top, the insect, by dint of stubborn dexterity, has rolled its leaf. It is now on the [191]extreme edge of the border, at the lateral corner opposite to that whereat the work commenced. This is the keystone upon which the stability of the rest depends. The Rhynchites redoubles her cares and patience. With the end of her rostrum, expanded spatulawise, she presses, at one point after the other, the edge to be fixed, even as the tailor presses the recalcitrant edges of a seam with his iron. For a long, a very long time, without moving, she pushes and pushes, awaiting the proper adhesion. Point by point, the whole of the corner welt is fastidiously sealed.

How is adhesion obtained? If only some thread or other were brought into play, one would readily look upon the rostrum as a sewing-machine planting its needle perpendicularly into the stuff. But the comparison is not allowable: there is no filament employed in the work. The explanation of the adherence lies elsewhere.

The leaf is young, we said; the fine pads of its denticulations are glands whence ooze liquid beads of glue. These drops of viscous matter are the gum, the sealing-wax. With the pressure of its beak, the insect makes it gush more plentifully from the glands. It then has only to hold the signet in position and wait for the impress to acquire consistency. Taken all round, it is our method of sealing a letter. If it hold ever so little, the leaf, losing its elasticity gradually as it withers, will soon cease to fly back and will of itself retain the scroll-form imposed upon it.

The work is done. It is a cigar of the diameter of a thick straw and about an inch long. It hangs perpendicularly from the end of the bruised and bent stalk. It has taken the whole of a day to make. After a short spell of rest, the mother tackles a second leaf and, working [192]by night, obtains another scroll. Two in twenty-four hours are as much as the most diligent can achieve.

Now what is the roller’s object? Would she go to the length of preparing preserves for her own use? Obviously not: no insect, where itself alone is concerned, devotes such care and patience to the preparation of food. It is only in view of the family that it hoards so industriously. The Rhynchites’ cigar forms the future dowry.

Let us unroll it. Here, between the layers of the scroll, is an egg; often there are two, three, or even four. They are oval, pale-yellow and like fine drops of amber. Their adhesion to the leaf is very slight; the least jerk loosens them. They are distributed without order, pushed more or less deeply in the thickness of the cigar and always isolated, singly. We find them in the centre of the scroll, almost at the corner where the rolling begins; we come upon them between the different layers and even near the edge which is sealed in glue with the signet of the rostrum.

Without interrupting her work on the scroll, without relaxing the tension of her claws, the mother has laid them between the lips of the fold in formation, as she felt them coming, one by one, duly matured, at the end of her oviduct. She procreates in the midst of her toil in the factory, between the wheels of the machine that would be thrown out of gear if she snatched a moment’s rest. Manufacture and laying go hand-in-hand. Short-lived, with but two or three weeks before her and an expensive family to settle, the Rhynchites would fear to waste her time in churching.

This is not all: on the same leaf, not far from the scroll that is being laboriously rolled, we almost always find the male. What is he doing there, the idler? Is he watching [193]the work as a mere inquisitive onlooker, who happened to be passing and stopped to see the machinery go round? Is he interested in the business? Does he ever feel inclined to lend a helping hand, in case of need?

One would say so. From time to time, I see him take his stand behind the manufacturer, in the groove of the fold, hang on to the cylinder and join for a little in the work. But this is done without zeal and awkwardly. Half a turn of the wheel, or hardly; and that’s enough for him. After all, it is not his business. He moves away, to the other end of the leaf; he waits, he looks on.

Let us give him credit for this attempt: paternal assistance in the settling of the family is very rare among insects; let us congratulate him on the help he gives, but not beyond measure: his was an interested aid. It is to him a means of declaring his flame and urging his merits.

And, in fact, after several refusals, notwithstanding the advances made by a brief collaboration at the scroll, the impatient one is accepted. Things happen in the work-yard. For ten minutes, the rolling is suspended; but the workwoman’s legs, stubbornly contracted, are careful not to let go: were their effort to cease, the scroll would unroll at once. There must be no interruption of work for this brief diversion, the animal’s only pleasure.

The stopping of the machine, which is always held tight so as to keep the recalcitrant roll in subjection, does not last long. The male withdraws to a slight distance, without quitting the leaf, and the task is resumed. Sooner or later, before the seals are put upon the work, a new visit is paid by the dawdler, who, under pretence of assisting, plants his claws for a moment into the rolling piece, plucks up courage and renews his exploits with the [194]same vigour as though nothing had yet happened. And this is repeated three or four times during the making of a single cigar, so much so that one asks one’s self whether the depositing of each germ does not demand the direct cooperation of the insatiable suitor.

According to entomological rules, once the fun is over, everything should relapse into calmness and each mother should to work at those cigars without further disturbance. In this case, the general law relents. I have never seen a scroll shaped without a male lurking in the neighbourhood; and, when I have had the patience to wait, I have always witnessed manifold pairings. These weddings repeated for each germ puzzle me. Where, relying on the books, I expected uniformity, I find uncertainty.

This is not an isolated case. I will mention a second and one that is even more striking. It is supplied by the Capricorn (Cerambyx Heros). I bring up a few couples in the volery, with sliced pears for food and oak billets wherein to lay the eggs. Pairing-time lasts during nearly the whole of July. For four weeks, the great horned one does nothing but mount his companion, who, gripped by her rider, wanders at will and, with the tip of her oviduct, selects the fissures in the bark best-suited to receive the eggs.

At long intervals, the Cerambyx alights and goes to refresh himself with a piece of pear. Then, suddenly, he stamps his feet as though he had gone mad; he returns with a frantic rush, clambers into the saddle and resumes his position, of which he makes free use at all hours of the night and day.

At the moment when an egg is being deposited, he keeps quiet: with his hairy tongue, he polishes the back of the egg-layer, which is a Capricorn’s way of caressing; [195]but, the instant after, he renews his attempts, which are usually crowned with success. There is no end to it!

The pairing continues in this manner for a month: it does not cease until the ovaries are exhausted. Then, mutually worn out, having nothing more to do on the trunk of the oak, husband and wife separate, languish for a few days and die.

What conclusion are we to draw from this extraordinary persistency in the Cerambyx, the Rhynchites and many others? Simply this: our truths are but provisional; assailed by the truths of to-morrow, they become entangled with so many contradictory facts that the last word of knowledge is doubt.

In the spring, while the leaves of the poplar are being worked into scrolls, another Rhynchites, she also gorgeously attired, makes cigars of the leaves of the vine. She is a little stouter, of a metallic gold-green turning to blue. Were she but larger, the splendid Vine Weevil would occupy a very respectable place among the gems of entomology.

To attract our eyes, she has something better than the brilliancy of her appearance: she has her industry, which makes her hated by the vine-grower, so jealous of his property. The peasant knows her; he even speaks of her by a special name, an honour rarely bestowed in the world of the smaller animals.

The rural vocabulary is rich where plants, but very poor where insects are concerned. A couple of dozen words, inextricably confused owing to their general character, represent the whole of entomological nomenclature in the Provençal idiom, which becomes so expressive and so fertile the moment it has to do with any sort of vegetation, sometimes even with a poor blade of [196]grass which one would believe known to the botanist alone.

The man of the soil is interested first and foremost in the plant, the great foster-mother; the rest leaves him indifferent. Magnificent adornment, curious habits, marvels of instinct: all these say nothing to him. But to touch his vine, to eat grass that doesn’t belong to one: what a heinous crime! Quick, give the malefactor a nickname, to serve as a penal collar!

This time, the Provençal peasant has gone out of his way to invent a special word: he calls the cigar-roller the Bécaru. Here the scientific expression and the rural expression agree fully. Rhynchites and Bécaru are exact equivalents: each refers to the insect’s long beak.

The Vine Weevil adopts the same method in her work as her cousin of the poplar. The leaf is first pricked with the rostrum at a spot in the stalk, which provokes a stoppage of the sap and flexibility in the withered blade. The rolling begins at the corner of one of the lower lobes, with the smooth, green upper surface within and the cottony strongly-veined lower surface without.

But the great width of the leaf and its deep indentations hardly ever allow of regular work from one end to the other. Abrupt folds occur instead and repeatedly alter the direction of the rolling, leaving now the green and now the cottony surface on the outside, without any appreciable order or arrangement, as though by chance. The poplar-leaf, with its simple form and its moderate size, gives a neat scroll; the vine-leaf, with its cumbersome girth and its complicated outline, produces a shapeless cigar, an untidy parcel.

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