Social Life in the Insect World Part 19

The Balaninus has antic.i.p.ated them all. The mother confided her eggs to the acorns while yet they were green. These have now fallen to earth, brown before their time, and pierced by a round hole through which the larva has escaped after devouring the contents. Under one single oak a basket might easily be filled with these ruined sh.e.l.ls. More than the jay, more than the field-mouse, the elephant-beetle has contributed to reduce the superfluity of acorns.

Presently man arrives, busied in the interest of his pig. In my village it is quite an important event when the munic.i.p.al h.o.a.rdings announce the day for opening the munic.i.p.al woods for the gathering of acorns. The more zealous visit the woods the day before and select the best places.

Next day, at daybreak, the whole family is there. The father beats the upper branches with a pole; the mother, wearing a heavy hempen ap.r.o.n which enables her to force her way through the stubborn undergrowth, gathers those within reach of the hand, while the children collect those scattered upon the ground. First the small baskets are filled, then the big _corbeilles_, and then the sacks.

After the field-mouse, the jay, the weevil, and so many others have taken toll comes man, calculating how many pounds of bacon-fat his harvest will be worth. One regret mingles with the cheer of the occasion; it is to see so many acorns scattered on the ground which are pierced, spoiled, good for nothing. And man curses the author of this destruction; to hear him you would think the forest is meant for him alone, and that the oaks bear acorns only for the sake of his pig.

My friend, I would say to him, the forest guard cannot take legal proceedings against the offender, and it is just as well, for our egoism, which is inclined to see in the acorn only a garland of sausages, would have annoying results. The oak calls the whole world to enjoy its fruits. We take the larger part because we are the stronger.

That is our only right.

More important than our rights is the equitable division of the fruits of the earth between the various consumers, great and little, all of whom play their part in this world. If it is good that the blackbird should flute and rejoice in the burgeoning of the spring, then it is no bad thing that acorns should be worm-eaten. In the acorn the dessert of the blackbird is prepared; the Balaninus, the tasty mouthful that puts flesh upon his flanks and music into his throat.

Let the blackbird sing, and let us return to the eggs of the Curculionidae. We know where the egg is--at the base of the acorn, because the tenderest and most juicy tissues of the fruit are there. But how did it get there, so far from the point of entry? A very trifling question, it is true; puerile even, if you will. Do not let us disdain to ask it; science is made of these puerilities.

The first man to rub a piece of amber on his sleeve and to find that it thereupon attracted fragments of chaff had certainly no vision of the electric marvels of our days. He was amusing himself in a childlike manner. Repeated, tested, and probed in every imaginable way, the child's experiment has become one of the forces of the world.

The observer must neglect nothing; for he never knows what may develop out of the humblest fact. So again we will ask: by what process did the egg of the elephant-beetle reach a point so far from the orifice in the acorn?

To one who was not already aware of the position of the egg, but knew that the grub attacked the base of the acorn first, the solution of that fact would be as follows: the egg is laid at the entrance of the tunnel, at the surface, and the grub, crawling down the gallery sunk by the mother, gains of its own accord this distant point where its infant diet is to be found.

Before I had sufficient data this was my own belief; but the mistake was soon exposed. I plucked an acorn just as the mother withdrew, after having for a moment applied the tip of the abdomen to the orifice of the pa.s.sage just opened by her rostrum. The egg, so it seemed, must be there, at the entrance of the pa.s.sage.... But no, it was not! It was at the other extremity of the pa.s.sage! If I dared, I would say it had dropped like a stone into a well.

That idea we must abandon at once; the pa.s.sage is extremely narrow and enc.u.mbered with shavings, so that such a thing would be impossible.

Moreover, according to the direction of the stem, accordingly as it pointed upwards or downwards, the egg would have to fall downwards in one acorn and upwards in another.

A second explanation suggests itself, not less perilous. It might be said: "The cuckoo lays her egg on the gra.s.s, no matter where; she lifts it in her beak and places it in the nearest appropriate nest." Might not the Balaninus follow an a.n.a.logous method? Does she employ the rostrum to place the egg in its position at the base of the acorn? I cannot see that the insect has any other implement capable of reaching this remote hiding-place.

Nevertheless, we must hastily reject such an absurd explanation as a last, desperate resort. The elephant-beetle certainly does not lay its egg in the open and seize it in its beak. If it did so the delicate ovum would certainly be destroyed, crushed in the attempt to thrust it down a narrow pa.s.sage half choked with debris.

This is very perplexing. My embarra.s.sment will be shared by all readers who are acquainted with the structure of the elephant-beetle. The gra.s.shopper has a sabre, an oviscapt which plunges into the earth and sows the eggs at the desired depth; the Leuscopis has a probe which finds its way through the masonry of the mason-bee and lays the egg in the coc.o.o.n of the great somnolent larva; but the Balaninus has none of these swords, daggers, or pikes; she has nothing but the tip of her abdomen. Yet she has only to apply that abdominal extremity to the opening of the pa.s.sage, and the egg is immediately lodged at the very bottom.

Anatomy will give us the answer to the riddle, which is otherwise indecipherable. I open the body of a gravid female. There, before my eyes, is something that takes my breath away. There, occupying the whole length of the body, is an extraordinary device; a red, h.o.r.n.y, rigid rod; I had almost said a rostrum, so greatly does it resemble the implement which the insect carries on his head. It is a tube, fine as a horsehair, slightly enlarged at the free extremity, like an old-fashioned blunderbuss, and expanding to form an egg-shaped capsule at the point of origin.

This is the oviduct, and its dimensions are the same as those of the rostrum. As far as the perforating beak can plunge, so far the oviscapt, the interior rostrum, will reach. When working upon her acorn the female chooses the point of attack so that the two complementary instruments can each of them reach the desired point at the base of the acorn.

The matter now explains itself. The work of drilling completed, the gallery ready, the mother turns and places the tip of the abdomen against the orifice. She extrudes the internal mechanism, which easily pa.s.ses through the loose debris of the boring. No sign of the probe appears, so quickly and discreetly does it work; nor is any trace of it to be seen when, the egg having been properly deposited, the implement ascends and returns to the abdomen. It is over, and the mother departs, and we have not caught a glimpse of her internal mechanism.

Was I not right to insist? An apparently insignificant fact has led to the authentic proof of a fact that the Larinidae had already made me suspect. The long-beaked weevils have an internal probe, an abdominal rostrum, which nothing in their external appearance betrays; they possess, among the hidden organs of the abdomen, the counterpart of the gra.s.shopper's sabre and the ichneumon's dagger.

CHAPTER XVIII

THE PEA-WEEVIL--_BRUCHUS PISI_

Peas are held in high esteem by mankind. From remote ages man has endeavoured, by careful culture, to produce larger, tenderer, and sweeter varieties. Of an adaptable character, under careful treatment the plant has evolved in a docile fashion, and has ended by giving us what the ambition of the gardener desired. To-day we have gone far beyond the yield of the Varrons and Columelles, and further still beyond the original pea; from the wild seeds confided to the soil by the first man who thought to scratch up the surface of the earth, perhaps with the half-jaw of a cave-bear, whose powerful canine tooth would serve him as a ploughshare!

Where is it, this original pea, in the world of spontaneous vegetation?

Our own country has nothing resembling it. Is it to be found elsewhere?

On this point botany is silent, or replies only with vague probabilities.

We find the same ignorance elsewhere on the subject of the majority of our alimentary vegetables. Whence comes wheat, the blessed grain which gives us bread? No one knows. You will not find it here, except in the care of man; nor will you find it abroad. In the East, the birthplace of agriculture, no botanist has ever encountered the sacred ear growing of itself on unbroken soil.

Barley, oats, and rye, the turnip and the beet, the beetroot, the carrot, the pumpkin, and so many other vegetable products, leave us in the same perplexity; their point of departure is unknown to us, or at most suspected behind the impenetrable cloud of the centuries. Nature delivered them to us in the full vigour of the thing untamed, when their value as food was indifferent, as to-day she offers us the sloe, the bullace, the blackberry, the crab; she gave them to us in the state of imperfect sketches, for us to fill out and complete; it was for our skill and our labour patiently to induce the nourishing pulp which was the earliest form of capital, whose interest is always increasing in the primordial bank of the tiller of the soil.

As storehouses of food the cereal and the vegetable are, for the greater part, the work of man. The fundamental species, a poor resource in their original state, we borrowed as they were from the natural treasury of the vegetable world; the perfected race, rich in alimentary materials, is the result of our art.

If wheat, peas, and all the rest are indispensable to us, our care, by a just return, is absolutely necessary to them. Such as our needs have made them, incapable of resistance in the bitter struggle for survival, these vegetables, left to themselves without culture, would rapidly disappear, despite the numerical abundance of their seeds, as the foolish sheep would disappear were there no more sheep-folds.

They are our work, but not always our exclusive property. Wherever food is ama.s.sed, the consumers collect from the four corners of the sky; they invite themselves to the feast of abundance, and the richer the food the greater their numbers. Man, who alone is capable of inducing agrarian abundance, is by that very fact the giver of an immense banquet at which legions of feasters take their place. By creating more juicy and more generous fruits he calls to his enclosures, despite himself, thousands and thousands of hungry creatures, against whose appet.i.tes his prohibitions are helpless. The more he produces, the larger is the tribute demanded of him. Wholesale agriculture and vegetable abundance favour our rival the insect.

This is the immanent law. Nature, with an equal zeal, offers her mighty breast to all her nurslings alike; to those who live by the goods of others no less than to the producers. For us, who plough, sow, and reap, and weary ourselves with labour, she ripens the wheat; she ripens it also for the little Calender-beetle, which, although exempted from the labour of the fields, enters our granaries none the less, and there, with its pointed beak, nibbles our wheat, grain by grain, to the husk.

For us, who dig, weed, and water, bent with fatigue and burned by the sun, she swells the pods of the pea; she swells them also for the weevil, which does no gardener's work, yet takes its share of the harvest at its own hour, when the earth is joyful with the new life of spring.

Let us follow the manoeuvres of this insect which takes its t.i.the of the green pea. I, a benevolent ratepayer, will allow it to take its dues; it is precisely to benefit it that I have sown a few rows of the beloved plant in a corner of my garden. Without other invitation on my part than this modest expenditure of seed-peas it arrives punctually during the month of May. It has learned that this stony soil, rebellious to the culture of the kitchen-gardener, is bearing peas for the first time. In all haste therefore it has hurried, an agent of the entomological revenue system, to demand its dues.

Whence does it come? It is impossible to say precisely. It has come from some shelter, somewhere, in which it has pa.s.sed the winter in a state of torpor. The plane-tree, which sheds its rind during the heats of the summer, furnishes an excellent refuge for homeless insects under its partly detached sheets of bark.

I have often found our weevil in such a winter refuge. Sheltered under the dead covering of the plane, or otherwise protected while the winter lasts, it awakens from its torpor at the first touch of a kindly sun.

The almanack of the instincts has aroused it; it knows as well as the gardener when the pea-vines are in flower, and seeks its favourite plant, journeying thither from every side, running with quick, short steps, or nimbly flying.

A small head, a fine snout, a costume of ashen grey sprinkled with brown, flattened wing-covers, a dumpy, compact body, with two large black dots on the rear segment--such is the summary portrait of my visitor. The middle of May approaches, and with it the van of the invasion.

They settle on the flowers, which are not unlike white-winged b.u.t.terflies. I see them at the base of the blossom or inside the cavity of the "keel" of the flower, but the majority explore the petals and take possession of them. The time for laying the eggs has not yet arrived. The morning is mild; the sun is warm without being oppressive.

It is the moment of nuptial flights; the time of rejoicing in the splendour of the sunshine. Everywhere are creatures rejoicing to be alive. Couples come together, part, and re-form. When towards noon the heat becomes too great, the weevils retire into the shadow, taking refuge singly in the folds of the flowers whose secret corners they know so well. To-morrow will be another day of festival, and the next day also, until the pods, emerging from the shelter of the "keel" of the flower, are plainly visible, enlarging from day to day.

A few gravid females, more pressed for time than the others, confide their eggs to the growing pod, flat and meagre as it issues from its floral sheath. These hastily laid batches of eggs, expelled perhaps by the exigencies of an ovary incapable of further delay, seem to me in serious danger; for the seed in which the grub must establish itself is as yet no more than a tender speck of green, without firmness and without any farinaceous tissue. No larva could possible find sufficient nourishment there, unless it waited for the pea to mature.

But is the grub capable of fasting for any length of time when once hatched? It is doubtful. The little I have seen tells me that the new-born grub must establish itself in the midst of its food as quickly as possible, and that it perishes unless it can do so. I am therefore of opinion that such eggs as are deposited in immature pods are lost.

However, the race will hardly suffer by such a loss, so fertile is the little beetle. We shall see directly how prodigal the female is of her eggs, the majority of which are destined to perish.

The important part of the maternal task is completed by the end of May, when the sh.e.l.ls are swollen by the expanding peas, which have reached their final growth, or are but little short of it. I was anxious to see the female Bruchus at work in her quality of Curculionid, as our cla.s.sification declares her.[8] The other weevils are Rhyncophora, beaked insects, armed with a drill with which to prepare the hole in which the egg is laid. The Bruchus possesses only a short snout or muzzle, excellently adapted for eating soft tissues, but valueless as a drill.

The method of installing the family is consequently absolutely different. There are no industrious preparations as with the Balinidae, the Larinidae, and the Rhynchitides. Not being equipped with a long oviscapt, the mother sows her eggs in the open, with no protection against the heat of the sun and the variations of temperature. Nothing could be simpler, and nothing more perilous to the eggs, in the absence of special characteristics which would enable them to resist the alternate trials of heat and cold, moisture and drought.

In the caressing sunlight of ten o'clock in the morning the mother runs up and down the chosen pod, first on one side, then on the other, with a jerky, capricious, unmethodical gait. She repeatedly extrudes a short oviduct, which oscillates right and left as though to graze the skin of the pod. An egg follows, which is abandoned as soon as laid.

A hasty touch of the oviduct, first here, then there, on the green skin of the pea-pod, and that is all. The egg is left there, unprotected, in the full sunlight. No choice of position is made such as might a.s.sist the grub when it seeks to penetrate its larder. Some eggs are laid on the swellings created by the peas beneath; others in the barren valleys which separate them. The first are close to the peas, the second at some distance from them. In short, the eggs of the Bruchus are laid at random, as though on the wing.

We observe a still more serious vice: the number of eggs is out of all proportion to the number of peas in the pod. Let us note at the outset that each grub requires one pea; it is the necessary ration, and is largely sufficient to one larva, but is not enough for several, nor even for two. One pea to each grub, neither more nor less, is the unchangeable rule.

We should expect to find signs of a procreative economy which would impel the female to take into account the number of peas contained in the pod which she has just explored; we might expect her to set a numerical limit on her eggs in conformity with that of the peas available. But no such limit is observed. The rule of one pea to one grub is always contradicted by the multiplicity of consumers.

My observations are unanimous on this point. The number of eggs deposited on one pod always exceeds the number of peas available, and often to a scandalous degree. However meagre the contents of the pod there is a superabundance of consumers. Dividing the sum of the eggs upon such or such a pod by that of the peas contained therein, I find there are five to eight claimants for each pea; I have found ten, and there is no reason why this prodigality should not go still further.

Many are called, but few are chosen! What is to become of all these supernumeraries, perforce excluded from the banquet for want of s.p.a.ce?