Part 4

Such is the conclusion arrived at by Léon Dufour before this incomprehensible marvel of the dead Buprestis untouched by corruption. An antiseptic fluid, incomparably superior to anything that human science could produce, would explain the mystery. He, the Master, skilful of the skilful, thoroughly used to most delicate anatomy; he who with magnifying glass and scalpel has scrutinised the whole circuit of entomology, leaving no corner unexplored; he, in short, for whom the organisation of insects has no secrets,—can advance no better conjecture than an antiseptic liquid to give at least a kind of explanation of a fact which leaves him confounded. Let me insist on this comparison between the instinct of the animal and the reason of the sage in order the better to demonstrate in due time the overwhelming superiority of the former.

I will add but a few words to the history of the C. bupresticida. This Hymenopteron, common in the Landes, as we have heard, seems to be rare in the department of Vaucluse. It is only at long intervals that I have met with it, in autumn, and always isolated specimens, on the spiny heads of Eryngium campestre, in the environs of Avignon or round Orange and Carpentras. In the latter spot, so favourable to burrowing hymenoptera, from its sandy soil of Mollasse, I had the good fortune, not indeed of being present at the exhumation of such entomological riches as Léon Dufour describes, but of finding some old nests which I feel certain belonged to Cerceris bupresticida, from the shape of the cocoons, the kind of provender stored up, and the existence of the Hymenopteron in the neighbourhood. These nests, hollowed in a very friable sandstone, called safre in those parts, were filled with remains of beetles, easily recognised, and consisting of detached wing-cases, empty corslets, and whole feet. Now these remains of the larva’s feast all belonged to one species, and this was a Buprestis, Sphænoptera geminata. Thus from the west to the east of France, from the department of the Landes to Vaucluse, the Cerceris remains faithful to its favourite prey; longitude does not affect its predilections, a hunter of Buprestids among the maritime pines of the ocean sand-hills, it is equally so amid the evergreen oaks and olives of Provence. The species is changed according to place, climate, and vegetation—causes influencing greatly the insect population, but the Cerceris keeps to its chosen genus, the Buprestis. For what strange reason? That is what I shall try to demonstrate.

CERCERIS TUBERCULATA

With my mind full of the great deeds of the Buprestis hunter, I watched for an opportunity of observing in my turn the labours of the Cerceris, and I watched so closely that finally I got my chance. True, it was not the Hymenopteron celebrated by Dufour, with such sumptuous provisions that when dug up they made one think of the powder from a nugget broken by the miner’s pickaxe in some gold field: it was a closely related species, a giant brigand which contents itself with more modest prey—in short, Cerceris tuberculata or C. major, the largest and strongest of the genus.

The last fortnight in September is the time when our Hymenopteron makes its burrows, and buries in the depths the prey destined for its brood. The position of the domicile, always sagaciously chosen, is governed by those mysterious laws varying with the species, but unchangeable for any one of them. The Cerceris of Léon Dufour requires a horizontal, beaten, compact soil, like that of a path, to avoid landslips and changes which would ruin its gallery with the first rain. Ours, on the contrary, selects vertical ground. By this slight architectural modification she avoids most of the dangers which might threaten her tunnel; therefore she is not particular as to the nature of the soil, and hollows her gallery either in friable earth with a little clay, or in the crumbling soil of the Mollasse, which makes the labour of excavation much easier. The only indispensable condition seems to be that the soil should be dry, and exposed to the sun for the greater part of the day. It is therefore in the steep bank along a road, and in the sides of hollows made by rain in the sandy Mollasse, that our Hymenopteron makes its abode. Such conditions are frequent near Carpentras in what is known as the hollow way, and it is there that I have found C. tuberculata in the greatest abundance, and have collected most of the facts relating to its history.

It is not enough to choose this vertical situation; other precautions are taken to guard against the already advanced season. If some bit of hard sandstone project like a shelf, or if a hole the size of one’s fist should have been hollowed naturally in the ground, it will be under this shelter or in this cavity that the gallery is made, a natural vestibule being thus added by the Cerceris to its own edifice. Although there is no kind of community among them, these insects like to associate in small parties, and I have always found their nests in groups of about ten, with orifices, though usually far apart, sometimes touching.

When the sun shines it is wonderful to see the ways of these hard-working miners. Some patiently extract bits of gravel from the bottom of a hole with their mandibles, and push out the heavy mass; others scratch the walls of their tunnel with the sharp rakes of their tarsi, forming a heap of rubbish which they sweep out backward, and send sliding down the steep incline in long dusty streams. It was these periodical sand waves thrown out of galleries in process of construction which betrayed my first Cerceris, and led to the discovery of the nests. Others, either weary, or having completed their hard task, rested and polished their antennæ and wings under the natural caves which usually protect their dwelling, or else sat motionless at the mouth of their holes, only displaying their wide, square faces, barred with yellow and black. Others again were flying with a deep hum on the bushes near the cochineal oak, where the males, always on the watch near the burrows in process of construction, speedily join them. Couples form, often troubled by the arrival of a second male, which tries to supplant the happy possessor. The humming grows menacing, quarrels begin, and often both males roll in the dust until one acknowledges the superiority of his rival. Not far off the female waits with indifference the upshot of the struggle, accepting finally the male bestowed on her by the chances of the fight, and the pair fly out of sight to seek peace in some distant thicket. Here the part of the male ends. One half smaller than the females, they prowl about the burrows but never enter, and never take any part in the hard work of excavation, or that perhaps yet harder of provisioning the cells.

In a few days the galleries are ready, especially as after some repairs those of the preceding year are used again. Other Cerceris, as far as I know, have no fixed home, transmitted from one generation to another. True Bohemians, they establish themselves wherever the chances of their vagabond life may lead them, so long as the soil suits them. But C. tuberculata is faithful to her penates. The projecting shelf of sandstone used by its predecessors is used again; it hollows out the same layer of sand hollowed by its forbears, and, adding its own labour to theirs, obtains deep-seated retreats sometimes only visited with difficulty. The diameter of the galleries would admit a thumb, and the insect can move about easily, even when laden with the prey which we shall see it capture. Their direction is horizontal, from four to eight inches, then makes a sudden turn downward more or less obliquely, now in one direction, now in another. Except the horizontal part, and the angle of the tunnel, the direction seems to depend on the difficulties of the ground, as is proved by the windings and changes in the farthest part of this kind of canal, which is half a yard in length. At the far end are the cells, not numerous, and provisioned with five or six dead beetles. But let us leave the details of how a Cerceris builds, and turn to more wonderful facts.

The victim chosen to feed the larvæ is a large weevil (Cleonus ophthalmicus). One sees the captor arrive, carrying the victim between its feet, body to body, head to head. It alights heavily some way from the hole to complete the journey without the aid of wings, and drags the prey laboriously with its jaws, on ground if not vertical, at least very steeply inclined, which often results in sending captor and captive headlong to the bottom, but the indefatigable mother finally darts into her burrow, covered with dust, but with the prey of which she has never let go. If she does not find walking with such a burden easy, it is otherwise with her flight, which is surprisingly powerful, if one considers that the strong little creature is carrying a prey nearly as large as and heavier than herself. I have had the curiosity to weigh the Cerceris and her prey separately, and the first weighed 150 milligrammes, and the second about 250, almost double.

These weights speak eloquently for the vigorous huntress, and I never wearied of watching how swiftly and easily she resumed her flight, and rose out of sight with the game between her feet when approached too closely. But she did not always fly away, and then, though it was difficult to do so, and yet avoid hurting her, I would make her drop the prey by worrying and upsetting her with a straw. Then I would take possession of the victim, and the Cerceris, thus despoiled, would hunt about, go into her hole for a moment, come out, and resume the chase. In less than ten minutes the sharp-sighted insect would find a new victim, murder it and carry it off, not seldom to my profit. Eight times running have I stolen from the same individual; eight times did the indefatigable Cerceris resume her fruitless journey. Her perseverance tired out mine, and I let her keep the ninth capture.

By this means, and by breaking open cells already filled with provisions, I got nearly a hundred weevils, and in spite of what I had a right to expect from what Léon Dufour has told us of the habits of the Cerceris bupresticida, I could not repress my astonishment at the sight of the singular collection which I had made. His Cerceris, though it limits itself to one genus, yet takes any species within that limit, but the more exclusive C. tuberculata preys exclusively on Cleonus ophthalmicus. On looking through my booty I met with but one single exception, and that belonged to a closely allied species, C. alternans—one which I never met with again in my frequent visits to the Cerceris. Later researches furnished me with a second exception, Bothynoderes albidus, and these are all. Can a specially succulent and savoury prey explain this predilection for a single species? Do the larvæ find in this unvaried diet juices which suit them peculiarly, and which they would not find elsewhere? I do not think so, and if Léon Dufour’s Cerceris hunted all the kinds of Buprestids, no doubt it was because they all have the same nutritive properties. But this must generally be the case with all the Curculionidæ; their alimentary properties must be identical, and in that case this amazing choice can only be one of size, and therefore of economy of labour and time. Our Cerceris, the giant of its race, chooses C. ophthalmicus as the largest in our district, and perhaps the commonest. But if this favourite prey fail, it must fall back upon other species, even if smaller, as is proved by the two exceptions above mentioned.

Moreover, it is by no means the only one to hunt the long-nosed class of weevils. Many other Cerceris, according to their size, strength, and the chances of the chase, capture Curculionidæ most various in genus, species, shape, and size. It has long been known that Cerceris arenaria feeds her young with similar food. I myself have found in its burrows Sitona lineata, S. tibialis, Cneorhinus hispidus, Brachyderes gracilis, Geonemus flabellipes, Otiorhynchus maleficus. Cerceris aurita is known to prey on Otiorhynchus raucus and Phytonomus punctatus. In the larder of Cerceris ferreri I saw Phytonomus murinus, P. punctatus, Sitona lineata, Cneorhinus hispidus, Rhynchites betuleti. This weevil, which rolls up vine leaves into the shape of cigars, is sometimes of a superb metallic blue, but more usually of a splendid golden copper. I have found as many as seven of these brilliant insects laid up in one cell, and the gorgeous colours of the little heap might almost bear comparison with the jewels buried by the huntress of the Buprestids. Other species, especially the weaker, hunt smaller game, the lesser size being compensated by numbers. Thus, Cerceris quadricincta heaps in each cell some thirty Apion gravidum, but does not disdain on occasion bigger weevils, such as Sitona lineata, Phytonomus murinus. Cerceris labiata also lays up small species. Finally, the smallest Cerceris in my part of France, C. julii, hunts the least weevils, Apion gravidum and Bruchus granarius, game proportioned to its own size. To end this list of provender, let us add that some Cerceris follow other gastronomic laws, and bring up their families on Hymenoptera. Such is C. ornata. These tastes being alien to our subject, let us pass on.

We see that out of eight species of Cerceris which lay up Coleoptera as food, seven hunt weevils and one Buprestids. What singular reason confines the chase of these Hymenoptera within such narrow limits? What are the motives of such an exclusive selection? What internal likeness is there between the Buprestids and the weevils, outwardly quite dissimilar, that both should become food for carnivorous and nearly related larvæ? No doubt between such and such a victim there are differences as to taste and nutritive qualities which the larvæ thoroughly appreciate, but there must be a far graver reason than these gastronomic considerations to explain these strange predilections.

After all that has been so admirably said by Léon Dufour on the long and marvellous preservation of the insects destined as food for the carnivorous larvæ, it is needless to say that the weevils which I dug up, as well as those taken from between the feet of their murderer, were perfectly fresh, though permanently motionless. Freshness of colour, suppleness of the membranes and smallest articulations, normal condition of the viscera, all combine to make one doubt whether the inert body under one’s eyes can really be a corpse, all the more that even under the magnifying glass it is impossible to perceive the smallest wound; and in spite of one’s self one expects every moment to see the insect move and walk. Yet more, in weather so hot that insects which had died naturally would in a few hours have become dried up and crumbly, or again in damp weather which would with equal rapidity have made them decay and grow mouldy. I have kept specimens in glass tubes or cones of paper over a month with no precautions, and wonderful to say, after all this length of time, the intestines were as fresh as ever, and I found dissection as easy as if the creatures were alive. No, in presence of such facts one cannot talk of an antiseptic, and believe in real death; life is still there—life latent and passive—vegetative life. It alone, struggling successfully for a time against the destructive invasion of chemical forces, can thus preserve the organism from decomposition. Life is still there, but without motion, and we have under our eyes such a marvel as chloroform or ether might produce—a marvel caused by the mysterious laws of the nervous system.

The functions of this vegetative life are slackened and troubled no doubt, but still they are feebly exercised. I have the proof of this in that action of the viscera which takes place normally and at intervals in the weevils during the first week of that deep slumber, which will never be broken, and yet which is not death. It only ceases when the intestine is empty, as is shown by autopsy. But the faint rays of life which the creature manifests do not stop there; and though sensation appears annihilated for ever, I have succeeded in reawakening some vestige of them. Having placed weevils, recently exhumed and absolutely motionless, in a bottle with sawdust moistened with benzine, I was not a little surprised to see a quarter of an hour later moving antennæ and feet. For a moment I thought I could recall them to life. Vain hope! these movements, last trace of a sensitiveness about to cease, soon stopped, and could not be excited a second time. I have repeated this experiment from some hours to several days after the murder, and always with the same success; only movement is tardy in appearing in proportion as the date of the victim’s death is distant. The movements are always from the forepart backward. First, the antennæ move, then the front tarsi tremble and share in the oscillations; next, the second pair do the same; and finally, the third. Once movement is excited, all these members oscillate without any order until all become again motionless, as they do sooner or later. Unless death has been quite recent, movement does not go beyond the tarsi, and the legs remain motionless.

Ten days after the murder I could not obtain the least sign of irritability by the proceeding described, and I had recourse to the Voltaic battery. This is more effective, and provokes muscular contractions where the vapour of benzine fails. One or two elements of Bunsen suffice, which are armed with the rheophores of slender needles. Plunging the point of the one under the furthest ring of the abdomen, and the point of the other under the neck, you obtain each time that the current is established, not only the quivering of the tarsi, but a strong flexion of the feet, which fold themselves under the body, and relax when the current is interrupted. These movements, very energetic during the first days, gradually lose intensity, and after a certain time appear no more. On the tenth day I have still been able to obtain visible motions, but on the fifteenth the pile was unable to provoke them, notwithstanding the suppleness of the limbs and freshness of the viscera. I have submitted also to the action of the pile Coleoptera really dead, Blaps, Saperda, Lamia, asphyxiated by benzine or sulphureous gas, and two hours later it was impossible to provoke the movements obtained so easily from weevils lying already for several days in the singular state, intermediate between life and death, into which their redoubtable enemy plunges them.

All these facts contradict the supposition of an animal completely dead, and the hypothesis of a real corpse rendered incorruptible by some antiseptic liquid. One can only explain them by admitting that the animal is struck in the principle of its movements, and that sensitiveness, suddenly benumbed, dies slowly out, while the more tenacious, vegetative functions die yet more slowly and preserve the intestines during the time necessary for the larva.

The most important detail to show was how the murder is committed. Evidently, the chief part must be played by the poisoned dart of the Cerceris. But where and how does it penetrate the body of the weevil, covered with a hard cuirass, with pieces so closely joined? Even under the magnifying glass nothing told where the sting entered. Direct examination, therefore, was required to discover the murderous ways of the Cerceris—a problem before whose difficulties Léon Dufour had already recoiled, and the solution of which seemed to me for a time impossible. I tried, however, and had the satisfaction of succeeding, though not without some groping about.

When they fly from their holes to the chase, the Cerceris go here and there, sometimes on one side, sometimes on the other, and return from all directions, loaded with prey, so that they must seek it on all sides; but as they barely take ten minutes between going and returning, the space worked over could not be very great, especially considering the time necessary to discover the prey, to attack and render it an inert mass. I, therefore, set myself to examine all the adjacent ground with close attention, hoping to discover some Cerceris on the hunt. One afternoon devoted to this weary work convinced me of the uselessness of my researches, and of the little chance I had of surprising any of the few Cerceris, scattered here and there, and soon lost to view by their rapid flight; above all, in difficult ground, planted with olives, I gave up the attempt. But by carrying live weevils to the neighbourhood of the nests might I not tempt the Cerceris by a prey found without trouble, and so observe the drama? The notion seemed good, and the very next day I set out to find live Cleonus ophthalmicus. Vineyards, wheat-fields, and crops of lucerne, and heaps of stones did I visit and examine one and all, and after two days of close search I possessed—dare I own it?—three weevils! bare, dusty, maimed of antennæ or tarsi, shabby old creatures which, perhaps, the Cerceris would not touch! Since the day of that fevered search, when, for a weevil’s sake, I bathed myself in perspiration during my wild expedition, many a year has passed, and yet, in spite of almost daily entomological researches, I am still ignorant of the life and habits of this Cleonus, which I met here and there, straying on the edge of paths. Wonderful powers of instinct! in the same spots, and in a fraction of time, one Hymenopteron would have found hundreds of these insects which man cannot find, and found them fresh and shining, no doubt just emerged from the cocoon!

No matter; let us experiment with my wretched victim. A Cerceris has just gone into her gallery with her prey; before she comes out for a new expedition I place a weevil a few inches from her hole. The weevil moves about; when it strays too far I bring it back to its place. At last the Cerceris shows her wide face at the mouth of her hole; my heart beats fast. She walks for a few minutes near her dwelling, sees the weevil, brushes against it, turns, passes several times over its back, and flies off without even honouring my captive with a bite—my captive which cost me so much labour! I was confounded—knocked over. New attempts at other holes, new disappointments. Decidedly these dainty hunters will have none of the game which I offer them. Perhaps they find it too old, too tasteless; perhaps, in handling it, I communicated some smell to it which displeases them. Foreign contact disgusts these connoisseurs.

Should I be more fortunate if I obliged the Cerceris to defend herself? I enclosed one with a Cleonus in a bottle, irritating them by shaking it. The Hymenopteron, sensitive by nature, was more impressed than the other prisoner, with its dull, heavy organisation; she thought of escape, not attack. Their parts were exchanged; the weevil became the aggressor, sometimes seizing with the end of its trunk a foot of its mortal foe, who made no attempt at defence, so terrified was she. I could devise nothing more; my desire to be present at the dénoûment had only added to former difficulties. Well, let us try again.

A luminous idea flashed upon me, bringing hope, so naturally did it touch the very heart of the question. Of course, it was the right thing and must succeed. My disdained game must be offered to the Cerceris in the heat of the chase—then, absorbed and preoccupied, she will not discover its imperfections. I have already said that on returning from the chase the Cerceris alights at the foot of the incline at some distance from the hole, whither she laboriously drags the prey. What I then had to do was to deprive her of her victim, drawing it away by one foot with pincers, and instantly throwing her the living weevil in exchange. This manœuvre succeeded perfectly. As soon as the Cerceris felt the prey slip under her body and escape her, she stamped with impatience, turned round, and perceiving the weevil which had replaced hers, flung herself upon it and clasped it in order to carry it away. But she promptly perceived that this prey was alive, and then the drama began and ended with inconceivable rapidity. The Cerceris faced her victim, seized its proboscis with her powerful jaws and grasped it vigorously, and while the weevil reared itself up, pressed her forefeet hard on its back as if to force open some ventral articulation. Then the tail of the murderess slid under the Cleonus, curved and darted its poisoned lancet swiftly two or three times at the joining of the prothorax, between the first and second pair of feet. In a twinkling all was over. Without one convulsive movement, with no motion of the limbs such as accompany the death of an animal, the victim fell motionless for ever, as if annihilated. It was at once wonderful and terrible in its rapidity. Then the assassin turned the Weevil on its back, placing herself body to body with it, her legs on either side of it, and flew off. Three times I renewed the experiment with my three Weevils, and the same scene was always enacted.

Of course, each time I gave the Cerceris back her first prey and withdrew my Cleonus to examine it at greater leisure. This examination only confirmed my opinion of the terrible skill of the assassin. It is impossible to find the slightest trace of a wound, or the smallest flow of vital liquids from the point which was struck. But the most striking thing is the rapid, complete annihilation of all movement. Vainly did I seek even immediately after the murder for any trace of sensibility in the three Weevils done to death under my eyes—neither pinching nor pricking provoked it; to do so required the artificial means already mentioned. Thus these robust Cleonus, which, pierced alive with a pin and fixed by a collector on his fatal sheet of cork, would have struggled for days, weeks, nay, whole months, instantly lose all power of motion from the effect of a little prick which inoculates them with a minute drop of poison. Chemistry knows none so active in so small a dose; scarcely could prussic acid produce such an effect, if, indeed, it could do so at all. It is not then to toxology, but to physiology and anatomy that we must turn to find the cause of such instantaneous catalepsy; it is not so much the great virulence of the poison injected, as the importance of the organ injured by it which we must consider in order to explain these marvels. What, then, is found at the point where the sting penetrates?

ONE SKILFUL TO SLAY

The Hymenopteron has partly revealed her secret by showing us where the sting strikes. But does that explain the question? Not yet, by any means. Let us retrace our steps, forget for a moment what the insect has taught us, and consider the problem set before the Cerceris. The problem is this: to lay up in an underground cell a certain number of heads of game which may suffice to nourish the larva hatched from the egg laid upon the heap of provender.

At first sight this storing of food appears simple enough, but reflexion soon discovers graver difficulties. Our own game is brought down by a shot and killed with horrible wounds. The Hymenopteron has refinements unknown to us; she chooses to have her prey intact, with all its elegance of form and colour. No broken limbs, no gaping wounds, no hideous disembowelment. Her prey has all the freshness of the living insect; she does not destroy an atom of the fine-coloured powder which the mere contact of our fingers deflowers. If the insect were really dead, really a corpse, how difficult it would be for us to obtain such a result! Any one can slay an insect by stamping brutally on it, but to kill it neatly leaving no sign is no easy operation, within every one’s power. How many of us would be at our wits’ end if we had to kill on the spot, without crushing it, a little creature so tenacious of life that even beheaded it still goes on struggling! One must have been a practical entomologist before thinking of asphyxiation, and here, again, success would be doubtful with the primitive methods of vapour of benzine or burnt sulphur. In this deleterious atmosphere the insect struggles too long, and tarnishes its brightness. One must have recourse to more heroic methods—for instance, to the terrible exhalations of prussic acid slowly disengaging themselves from strips of paper impregnated with cyanide of potassium, or better still, as being without danger to the collector, to the thunderbolt of vapour of bisulphide of carbon. It requires a real art, an art calling to its aid the redoubtable arsenal of chemistry, to kill an insect neatly; to do that is what the elegant method of the Cerceris brings about so quickly, if we admit the stupid supposition that her prey really becomes a dead body.

A dead body! But that is by no means the diet of the larvæ, little ogres greedy for fresh meat, to whom game ever so slightly tainted would inspire insurmountable disgust. They must have fresh meat with no high taste—that first sign of decay. Yet the prey cannot be laid up alive in the cell like animals destined to furnish fresh meat to the crew and passengers of a vessel. What would become of a delicate egg laid among living food? What would become of the feeble larva, a worm bruised by the slightest thing among vigorous Coleoptera moving their long spurred legs for whole weeks? It is absolutely necessary—and here we seem caught in a blind alley—to obtain deathly immobility with the freshness of life for the interior organs. Before such an alimentary problem the best instructed man of the world would stand helpless—even the practised entomologist would own himself at a loss. The larder of the Cerceris would defy their reasoning powers.

Let us then imagine an academy of entomologists and physiologists, a congress where the question should be discussed by Flourens, Majendies, Claude Bernards. To obtain at once complete immobility and long preservation of food, the first and most natural and simple idea would be that of preserved meats. One would invoke some antiseptic liquid, as the illustrious savant of the Landes did with regard to his Buprestids, and attribute such virtue to the poisonous fluid of the Cerceris, but this strange quality has yet to be proved. Gratuitous hypothesis replacing the unknown quantity of the preserving liquid may perhaps be the final verdict of the learned assembly, as it was that of the naturalist of the Landes.