THE NEST-BUILDING ODYNERUS

The Mason-Wasps by Jean-Henri Fabre, is part of the HackerNoon Books Series. You can jump to any chapter in this book here. THE NEST-BUILDING ODYNERUS

CHAPTER VIII. THE NEST-BUILDING ODYNERUS

If further proofs than those submitted elsewhere were needful, to demonstrate that the organ does not imply the function, that the implement does not determine the work,1 the Odynerus group would furnish us with very remarkable evidence. With a close similarity of organization, not only in the details but also in the aggregate, a similarity which makes these insects one of the most natural genera in respect of structure, they possess a great variety of industries, bearing no relation one to the other, though carried on with the same equipment. Apart from the likeness in form, one single characteristic unites this group, whose habits are so unlike: all the Odyneri are game-hunters; they victual their families with grubs paralysed with the sting, with little caterpillars and small Beetle-larvæ.

But to achieve this common end, the larder furnished with its egg and stuffed [177]with game, how many several methods of construction! If we were better-acquainted with the biology of the genus, we should perhaps find architects of almost as many different schools as there are species. My investigations, which were dependent on opportunity, have as yet borne upon only three of the Odyneri; and these three, with the same implement, the curved, toothed pincers of their mandibles, apply themselves to the most dissimilar industries.

One of them, O. reniformis, whose work I have described in an earlier chapter, digs a deep gallery in a hard soil and with the rubbish constructs, at the mouth of her well, a sort of curved chimney, with a guilloche pattern, the materials of which are afterwards again employed to close the abode. Formerly, when I made her acquaintance in front of a steep loamy bank baked by the sun, I whiled away the long hours of waiting by conversing, turn and turn about, with the Hoopoe, who taught me how to pronounce Latin, and with my Dog, who, lying in the shade of a leafy thicket, cooling his belly in the moist sand, taught me how to practise patience. The Wasp was rare and by no means prodigal of her returns to the nest where I was watching her skilful tactics. [178]Nowadays, every spring, I have a populous colony of her before my eyes in one of the paths of my enclosure. When the period for the works arrives, I surround the hamlet with stakes to mark the site, lest heedless footsteps should destroy the pretty chimneys built of grains of earth.

The second, O. alpestris, Sauss., is by trade a resin-worker. Possessing the same tool as her colleague the miner, but not the same skill, she does not dig herself a dwelling; she prefers to settle down in borrowed lodgings provided by an empty Snail-shell. The shells of Helix nemoralis, of H. aspersa,2 when very incompletely developed, and of Bulimulus radiatus are the only dwellings that I have known her to occupy and also the only ones that would serve her turn under the stone-heaps where, in company with Anthidium bellicosum, she performs her labours in July and August.

Saved by the Snail from the hard task of excavation, she specializes in mosaic and produces a work of art which is superior in elegance to the miner’s temporary guilloche. Her materials are, on the one hand, resin; on the other, little bits of gravel. Her method is very unlike that of the two resin-workers [179]who find a lodging in the shell of the Edible Snail. These two swamp with gum, on the outer surface of the lid, their coarse, angular bricks, which are unequal in size, variable in nature and often of a half-earthy character, so that the unevenness of the work, in which the pieces are laid side by side at random, is hidden under a coat of resin. On the inner surface the gum does not fill the gaps and the cemented fragments appear with all their irregular projections and their clumsy arrangement. Remember also that the bits of gravel are kept exclusively for the operculum, or lid, the final covering; the partitions which mark off the cells are made entirely of resin, without any mineral particles.

The Alpine Odynerus works on a different plan: she saves pitch by making better use of stone. A number of round, flinty atoms are set in a bed of still sticky cement, on the outer surface. They fit one against the other, are almost all of the same size, that of a pin’s head, and are selected singly by the artist amid the miscellaneous rubbish that litters the ground. When it is well-executed, as is frequently the case, the result suggests a piece of embroidery worked with roughly-fashioned beads of [180]quartz. The Anthidia of the Snail-shell, rude labourers that they are, accept all that falls to their mandibles: angular splinters of limestone, morsels of flint, bits of shell, hard particles of earth; the daintier Odynerus as a rule inlays with beads of flint only. Can this taste for gems be due to the brilliancy, the translucency, the polish of the grain? Can it be that the insect takes pleasure in its casket of precious stones? The answer will be the same as in the case of the ornamental rose-window, the tiny shell sometimes inserted in the centre of the lid by the two resin-gatherers who inhabit the shell of the Edible Snail: why not?

Be this as it may, the gem-collector is so pleased with her pretty pebbles that she puts them everywhere. The partitions that subdivide the shell into chambers are reproductions of the lid: each has a carefully-finished mosaic of translucent flints on the front surface. In this manner three or four cells are contrived in the shell of the Edible Snail; in that of the Bulimulus, two at most. The cells are small but correctly shaped and strongly protected.

The protection, for that matter, is not restricted to these multiple paved hangings: [181]if you hold the Snail-shell to your ear and shake it, you hear a rattle of stones. The Odynerus, in fact, is as familiar as the Anthidia with the art of fortification by means of barricades. I make a breach in the side of the Snail-shell and pour out the heap of loose gravel that blocks the vestibule between the last partition and the lid. One detail should be noted: the materials which I collect are not homogeneous. Small polished pebbles predominate, but they are mixed with fragments of coarse limestone, bits of shell and particles of earth. The Odynerus, so fastidious in choosing the flint for her mosaics, employs for her filling the first rubbish that comes to hand. Even so do the two resin-gatherers act when barricading their Snail-shells. As a conscientious historian, I will add that the incoherent heap of rubbish is not always there: another point of resemblance with the practice of the Anthidia.

To my great regret, I can carry the biography of the Alpine Odynerus no farther. The insect appears to me to be very rare. I come upon its nest at long intervals in winter, the only season propitious to laborious searches in the stone-heaps. With the dwelling and its inhabitant, hatched in my [182]specimen-jars, I am familiar; but the egg, the larva and the provisions I do not know.

In compensation, I possess all the details that could be desired about the third species, O. nidulator, Sauss. This insect, like the just mentioned, is ignorant of the art of laying the foundations of its abode and demands a ready-made lodging. Like the Osmiæ, the Megachiles and the cotton-spinning Anthidia, it wants a cylindrical gallery, either natural or excavated by miners. Its art consists in partitioning a tunnel and subdividing it into chambers: plasterer’s art, in short.

Here then, in three species, the only ones whose habits I have had the opportunity of learning, we see three very different trades: the miner’s, the resin-worker’s and the plasterer’s. In these three guilds I find exactly the same equipment of tools; and I defy the most meticulous magnifying-glass to tell us what organic modification suggests to the one insect the pavement of pebbles upon a bed of resin, to the second the mine-shaft with its guilloched chimney, to the third the alien cylinder, partitioned with mud. No and again no: the organ does not constitute the function, the tool does not make the workman. With similar implements, [183]the Odynerus group executes the most dissimilar tasks, because each species has its predetermined skill, its art that governs the tool and is not governed by it. How plainly this conclusion would appear had I been privileged to review the entire Odynerus genus! How many industries remain for us to see, with the tool undergoing no modification! I suggest investigations on these lines to whomsoever it may concern, were it only in order to shed a little light upon this numerous and difficult group, of which the future will, I trust, give us a lucid classification based upon its industrial guilds.

Let us leave these generalities and pass to the detailed story of the Nest-building Odynerus. There are few Wasps with whose private life I am better acquainted; and I owe this abundant information to circumstances which, for me, impart a double value to the facts, because of the pleasant memories evoked. I had often extracted the Nest-building Odynerus’ series of cells from the old galleries of the Anthophoræ; I knew that the insect occupies dwellings not dug with its own mandibles and that its labours are confined to the partitions; I knew its yellow larva and its slender, amber-hued [184]cocoon. I knew nothing of all the rest, when I received from my daughter Claire a bundle of reed-cuttings which filled me with exultation.

Brought up in a zoological house, the dear child has retained a vivid memory of our evening talks, in which the insect so often cropped up; and her discerning eye is able quickly to distinguish, amid her casual discoveries, anything that may assist me in my studies of instinct. Her country home, in the neighbourhood of Orange, boasts a rustic poultry-house constructed partly of reeds laid in horizontal stages. In the middle of June last year (1889), she noticed, when visiting her Hens, certain Wasps making their way in large and busy numbers into the cut reeds, coming out again and soon returning laden with a load of earth or some malodorous little grub. Her attention once aroused, the rest did not take long: she had discovered a magnificent subject for me to study. That very evening I received a bundle of reeds, with a letter giving me circumstantial details.

The Wasp, as Claire called it and as Réaumur named it of old, when speaking of a species of the same genus but of very different habits, the Wasp, so the letter told [185]me, hoards in her nests a dumpy head of game, covered with black spots and smelling strongly of bitter almonds. I informed my daughter that this game was the larva of the Poplar Leaf-beetle (Chrysomela populi), a Beetle with red wing-cases reminding one, on a larger scale, of the Coccinella, or Common Ladybird. Insect and larva should be found together on the poplars of the neighbourhood, browsing promiscuously on the leaves. I added that a glorious opportunity had presented itself and that we must profit by it without delay. She therefore received instructions to keep a watch on this, that and the other and to furnish my insect laboratory with reed-stumps as and when they became colonized and with poplar-branches covered with Chrysomela-grubs. A collaboration was thus set up between Orange and Sérignan, the facts observed on both sides mutually completing and corroborating each other.

Let us come quickly to the bundle of reeds, the first examination of which gratifies my fondest hopes. It contains things that reawaken all the enthusiasm of my youth: cells converted into game-baskets, eggs on the point of hatching beside the victuals, new-born grubs biting into their first victim, [186]larvæ of fuller growth, weavers at work on their cocoons, in fact everything that one could wish for. Never, except with the Scoliæ in my heap of garden-mould,3 has fortune served me better. Let us make an orderly inventory of these rich documents.

Already various Bees that favour borrowed houses have shown us the insect discriminating between one dwelling and another and selecting the best to make their homes in. We now have a predatory Wasp who, following the example of the Osmiæ, the Leaf-cutters and the Cotton-bees, leaves the ancestral cabin for the cylinder of the reed, to which man’s pruning-knife has prepared the access. The natural shelter, of indifferent quality, is succeeded by the artificial and more convenient refuge. The Odynerus’ primitive lodging is the abandoned corridor of the Anthophora, or any other burrow dug in the earth by no matter what miner. The wooden tube, free from damp and bathed in sunshine, is recognized as preferable; and the insect hastens to adopt it when the opportunity occurs. The tunnel of the reed must be recognized as an excellent habitation, [187]superior to all others, for never outside any abode of Anthophoræ have I seen a colony of Odyneri so populous as that of the Orange poultry-house.

The reeds invaded are laid horizontally, a condition on which the Bees likewise insist, if only to shelter from the rain the house-door, plugged with pervious materials, such as mud, cotton, or round, leafy disks. Their inner diameter attains an average of two-fifths of an inch. The length occupied by the cells varies greatly. Sometimes the Odynerus takes possession only of that fragment of the interval between two knots which the stroke of the pruning-knife has left free, a fragment longer or shorter according to the chances of the cutting. In that case, a small number of cells is enough to fill the available space. But generally, if the stump be too short and not worth the trouble of working, the insect bores through the partition at the end and thus adds a complete internode to the vestibule with the open entrance. In a lodging of this kind, some eight inches long, the number of chambers will amount to fourteen or fifteen.

In thus enlarging the house by removing a floor, the Odynerus displays two separate talents, the plasterer’s and the carpenter’s. [188]Her knack for wood-working, moreover, is extremely useful in another circumstance, as we shall see. The Three-horned Osmia, also an enthusiastic partitioner of reeds, does not employ this means of obtaining a spacious lodging at small cost. I find that she always leaves the first party-wall intact, building the row of cells against it, however short the section may be. To make an opening in a slight barrier is not one of her methods. She could do it if she wished; for to gnaw through the ceiling of the cell on hatching and then through the general door of the nest is a more difficult job. She possesses in her mandibles a tool powerful enough for the purpose; but she is not aware that a splendid gallery lies beyond the obstacle. How did the Odynerus learn, if she did not know from the beginning, what the Osmia, with her greater experience of the reed, does not know?

Apart from the ingenious device of breaking down the party-wall in order to enlarge the premises, the Odynerus is the Osmia’s equal as a plasterer and partition-builder. The results of the two industries resemble each other so closely that we should easily confuse them if we merely examined the structure. We find in both [189]cases, at irregular intervals, the same partitions, the same round disks of fine earth, of mud gathered wet on the brink of an irrigation-ditch or stream. Judging from the appearance of the materials, I imagine that the Odynerus has fetched her clay from the banks of the neighbouring torrent, the Aygues.

Identity of construction is maintained even in details which I had at first regarded as a feat peculiar to the Osmia. Let us recall her compartment-building secret. If the reed be of middling diameter, the cell is first stocked with provisions and next bounded in front with a partition run up then and there, without any pause in its construction. If the reed, without being excessively wide, be of a certain thickness, the Osmia, before stowing away the victuals, gets to work on the front partition, providing it with an opening at the side, a sort of service-hatch, through which the honey is more easily discharged and the egg more easily placed in position. Well, this secret of the service-hatch, which was revealed to me by the glass tube, is as well-known to the Odynerus as to the Osmia. She, too, in the bigger reeds, finds it to her advantage to close the larder in front before [190]bringing the game; she shuts the cell with a door provided with a sort of wicket, through which the victualling and the laying are done. When everything is finished inside, a plug of mortar closes the hatch.

I did not of course see the Odynerus working at her partition with its wicket-door, as I saw the Osmia performing in my glass tubes; but the work itself speaks quite plainly of the method followed. In the centre of the partitions in the medium reeds there is nothing in particular to be seen; in the centre of the partitions in the larger reeds there is a circular aperture, afterwards filled with a plug, which always differs from the rest of the partition by projecting inwards and sometimes differs in colour. The thing is obvious: the small partitions are made in one spell, whereas the work on the larger ones is interrupted and then resumed.

As we see, it would be pretty difficult to distinguish the Odynerus’ nest from the Osmia’s, if our enquiries were confined to the cells. One characteristic, however, and not the least curious enables an attentive eye to tell the owner without opening the reed. The Osmia closes her dwelling with a thick plug of earth similar in nature to that employed [191]for the partitions. The Odynerus, it goes without saying, does not neglect this means of defence: she, too, makes a solid stopper; but to the unsophisticated method of the Osmia she adds the resources of a more highly-finished art. Over her earthen stopper, a thing liable to be spoilt by frost and damp, she spreads, on the outside, a good thick layer of a composition of clay and chopped-up woody fibres. It matches the red wax with which we seal the corks of our bottles.

These fibres, which resemble the remains of a coarse tow retted by long exposure to the air, I should be inclined to look upon as taken from reeds spoilt by the rain and bleached by the sun. The Odynerus planes them off in shavings, which she afterwards crumbles by chewing them. This is how the Common Wasps and the Polistes work on soft dead wood, when gathering the raw material for their brown paper. But the reed-dweller, who has no intention of employing her scrapings for paper-making, does not cut up these fibrous particles anything like so finely. She contents herself with breaking them up and unravelling them a little. Mixed with thick mud, the same as that of the partitions and the final plug, [192]they make an excellent loam, which is far less liable to go to pieces than unmixed clay would be. The efficacy of this ingenious stucco is evident. After some months of exposure to the inclemencies of the weather, the Osmia’s door, made of earth only, is very much dilapidated, whereas the Odynerus’ door, covered on the outside with a layer of fibrous composition, remains intact. Let us credit the Odynerus with inventing and patenting the loam covering and proceed.

After the nest, the victuals. One sort of game alone is served to the Odynerus’ family: this is the larva of the Poplar Leaf-beetle (Chrysomela populi, Lina p.), a larva which, in company with the adult insect, ravages the poplar-leaves at the end of spring. Consulted merely by our taste, the Odynerus’ game is anything but enticing in shape and still less in smell. It is a plump, thickset grub, with a bare, flesh-white skin covered with several lines of glossy black dots. The abdomen, in particular, has thirteen rows of these black spots, namely, four on the top, three on each side and three underneath. The four dorsal rows vary in structure: the two in the middle consist of plain black specks; those [193]on either side consist of little pimples, each shaped like a truncated cone with a minute opening at the top. One of these cones rises on the right and left of each abdominal segment, except the last two; there is also one on the right and one on the left of the metathorax and mesothorax. These two are larger than the others. There are nine pairs of perforated pimples in all.

If we tease the creature, we see welling up from the bottom of these several little craters an opalescent liquid, which runs and spreads all over the larva. It has a strong smell of bitter almonds, or rather of nitrobenzene, commonly known as essence of mirbane, a powerful and most repulsive smell. The discharge of this substance is a means of defence. We have only to tickle the insect with a straw or to grip one of its legs with the tweezers and the eighteen scent-bottles at once begin to work. Whoso handles the grub will find his fingers stink and will throw away the noisome perfumer in disgust. If the Chrysomela-larva’s object in placing nine pairs of nitrobenzene-stills on its back was to repel man, it has, I admit, thoroughly succeeded.

But man is the least of its enemies. Far more formidable is the Odynerus, who [194]seizes the scented creature by the skin of the neck and, despite its sprays of perfume, dispatches it with a few stings. This was the bandit against whom, above all, it should have defended itself; and the poor grub has not been happily inspired in this respect. Considering the huntress’ exclusive taste for this sort of game, we must presume that the Chrysomela’s drug-shop possesses a delicious aroma in the Odynerus’ opinion. The defensive secretion becomes a deadly bait. Even so with other means of protection: each advantage invariably has some corresponding disadvantage.

I have read, I forget where, the story of certain South-American Butterflies, some of whom tasted bitter, others not. The first were respected by the birds because of their bitterness; the second were eagerly swallowed. What did the persecuted insects do? Unable to acquire the disagreeable flavour of the bitter ones, they at least imitated their shape and their costume. And the birds were taken in by the fraud.

This was put forward as a striking proof of evolution in view of the struggle for life. I am repeating the story more or less correctly, as it lingers vaguely in my memory, for I have never attached more importance [195]than they deserve to pretty inventions of this kind. Is it really certain that the pungent Butterflies escaped destruction because of their taste? Might there not be, among the birds, a few passionate lovers of bitters, to whom the defensive flavour was, on the contrary, an added lure? My two acres of pebbles tell me nothing of things Brazilian; nevertheless I learn within their four walls that a grub of detestable flavour, of the most repulsive aroma, has, like the others, its appointed consumers and very zealous consumers at that. If the struggle for life made it acquire its scent-bottles, then the struggle for life is a fool: it should have left the creature without them. In this way the enemy most to be feared, the Odynerus, who is attracted by the smell, would have been avoided.

The non-pungent Butterflies teach us something more. In order to protect themselves from the birds, they have imitated the pungent ones’ costume. Pray, then, let some one tell us why, among so many naked larvæ on which the little birds feast, not one has thought of assuming the Chrysomela’s black-buttoned overall. Unable to provide themselves with stinking retorts, they should at least possess a colourable [196]imitation, in order to put their persecutors off. The simple creatures! It never entered their heads to protect themselves by mimesis! We will not blame them; it is not their fault. They are what they are; and no bird’s beak will make them change their costume.

The Chrysomela’s defensive fluid has a look of essential oil: it discolours paper with a semitransparent stain which disappears by evaporation. Its colour is opalescent; its flavour is horrible; its odour is excessively strong and may be compared with that of the nitrobenzene of our laboratories. Were it not that I lack the leisure and the apparatus, I would gladly undertake a little research-work into this singular product of animal chemistry, which, I think, is quite as worthy of exploration by our tests as the milky exudations of the Salamander or the Toad. Meanwhile I commend the problem to the chemists.

In addition to the eighteen flasks of essential oil, the grub possesses yet another protective device, which is at once defensive and locomotory. The end of the intestine expands, at the insect’s pleasure, into a large amber-coloured pimple, whence oozes a colourless or very pale-yellow liquid. I [197]find it difficult to distinguish the odour of this liquid, because the strip of paper on which I collect it is always infected by the creature’s mere touch. Nevertheless I seem to recognize, in a fainter degree, the smell of nitrobenzene. Can there be any connection between the product of the dorsal flask and that of the intestinal pimple? There very well may be. I suspect, also, that it possesses special virtues, for the Odynerus, who is a fine judge in such matters, will tell us presently how greatly she appreciates this liquid.

Before taking the evidence of the huntress, let us note that the grub employs its anal pimple to move along with. Too short in the legs, it is a sort of cripple using its inflated stern as a lever. Another fact, whose interest will appear at the proper time, is that, at the moment of the metamorphosis, the larva fastens itself by the anus to a poplar-leaf. The larval skin is pushed back while it remains clinging; and the nymph appears half-sheathed in this slough. The nymph in its turn splits; the perfect insect releases itself; and the two cast-off suits of clothes, one partly enclosed within the other, retain their place on the leaf, fastened to it by the anal extremity. [198]The nymphosis takes about twelve days in all. It would be irrelevant to linger any longer over the larva of the Chrysomela; the little which it is expedient to say must not exceed the limits of my subject, which is the story of the Odynerus.

We know the game grazing on its poplar-leaf in the sun; let us see it stowed away in the larder. I count the number of head in a reed-stump occupied by seventeen cells, with their stores of food complete, or nearly so, some still containing the egg, the others a young larva attacking its first morsel. In the best-provisioned cells ten grubs are packed together; in those least well-supplied there are only three. I perceive, moreover, that, generally speaking, the abundance of provisions diminishes in the upper and increases in the lower stories, though the order of progression is not always very exact. The varying ration of the two sexes is probably responsible: the males, which are smaller and more forward, are given the upper chambers, with a frugal bill of fare; the females, which are larger and more backward, are given the lower chambers, with a plentiful table. Another reason, I think, contributes to these variations in number, namely, the size of the [199]game, which is more or less young, more or less plump.

Whether big or small, all the head of game are absolutely motionless. Armed with a magnifying-glass, I watch in vain for any oscillation of the palpi, any quivering of the tarsi, any pulsation of the abdomen, symptoms of life so frequently observed in the victims of the predatory Wasps. There is nothing, ever. Can the larvæ stabbed by the Odynerus be really dead? Can the provisions consist of actual corpses? By no means: their profound inertia does not preclude a remnant of life. The proofs are striking.

To begin with, inspected cell by cell, my bundle of reeds tells me that the big larvæ, those which have acquired their full development, very often adhere by their hinder part to the walls of the cell. The meaning of this detail is evident. Captured when the metamorphosis was at hand, the grub, despite the blows of the stiletto, has made its usual preparations: it has hung itself firmly to the adjoining support, the earthen partition or the tube of the reed, just as it fastens itself to the poplar-leaf. The creature is so fresh in appearance and its anal adhesion is so accurate that I actually [200]hope to see the victim’s skin split and the nymph appear. My hope is not at all exaggerated; it is based on facts no less curious which I shall describe later. Events did not respond to the probabilities on which I all but relied. When removed from the charnel-house with their point of support and put in a safe place, none of the larvæ settled for the nymphosis went beyond the preparatory action. This action in itself, however, is eloquent enough: it tells us that a remnant of life faintly animates the grub, since it retains power to make the necessary arrangements for the transformation.

That the grub is no corpse is revealed in another manner. I place in glass tubes, with a plug of cotton, twelve larvæ removed from the Odynerus’ larders. The sign of latent life is the creature’s freshness and its hue, a soft pinky white; the sign of death and corruption is a brown colouring. Well, eighteen days later one of the grubs begins to turn brown. A second is seen to be dead in thirty-one days. In forty-four days, six are still fresh and full. Finally, the last continues in good condition for two months, from the 16th of June to the 15th of August. It goes without saying that, [201]under the same conditions, larvæ which are really dead and unbruised, larvæ asphyxiated with bisulphide of carbon, turn brown in a few days.

As I should have expected, the laying-peculiarities of the Nest-building Odynerus are precisely identical with those of O. reniformis, the object of my earlier observations. I again witness, with the satisfaction that results from verifying an interesting fact, the curious arrangements already described. The egg is laid first, right at the back of the cell. Next comes the stacking of the provisions in the order of capture. In this way the eating proceeds from the oldest to the most recent.

I was above all anxious to ascertain whether the egg was pendulous, that is to say, whether it hung by a thread at one point of the cell, in accordance with what I had learnt from the Eumenes and from O. reniformis. A kinswoman of the latter must, I felt certain beforehand, conform to the method of the suspension-cord; but there was reason to fear that the journey from Orange and the jolting of the cart might have broken the delicate pendulum. I recalled my anxieties, my minute precautions, during the removal of the cells with [202]the egg of O. reniformis swinging from the ceiling. The cart, ignorant of its precious burden, might have undone everything.

But no, to my great surprise. In most of the cells which were sufficiently recent I find the egg in place, slung sometimes from the arched roof of the reed, sometimes from the upper edge of the partition, by a thread which is just visible and about one twenty-fifth of an inch long. The egg is itself cylindrical and measures about an eighth of an inch. The reeds, opened wide and placed in glass tubes, enable me to witness the hatching, which takes place three days after the closing of the cell and probably four days after the laying.

I see the new-born grub enclosed almost wholly, head downwards, in the sheath provided by the pellicle of the egg. Very slowly it slides forward in this scabbard and the suspension-cord stretches to the same extent. It is extremely fine in the part consisting of the original thread, but very much thicker in the portion resulting from the slough of the egg. The grub’s head reaches the nearest piece of game at one point or another; and the fragile creature takes its first mouthful. If anything startles it, if I tap the reed, it lets go and [203]withdraws a little way into the sheath of the egg; then, reassured, it once more glides forward and resumes the point attacked. At other times a jerk leaves it indifferent. This suspension-stage of the new-born larva continues for about twenty-four hours, after which the grub, now somewhat fortified, lets itself drop and eats in the ordinary manner. The victuals last it for twelve days. Immediately afterwards comes the working of the cocoon, in which the insect remains, a yellow larva, until next May. It would be tedious to follow the Odynerus in its career of eating and weaving. The consumption of dishes highly spiced with nitrobenzene and the spinning of the cocoon, of a fine amber-coloured fabric, involve nothing so remarkable as to deserve special mention.

Before leaving this subject, I will state a problem which the pendulous egg sets to the embryogenist. Every insect’s egg, if cylindrical in form, has two poles, the front and back, the cephalic and the anal pole. By which of the two does the insect see the light?

By the hinder pole, the Eumenes and the Odyneri tell us. The end of the egg fastened to the wall of the cell was evidently the first to issue from the oviduct, in view [204]of the mother’s absolute need first to glue the suspension-thread somewhere, before abandoning her egg to space. In the ovarian tubes and in the oviduct, which are too narrow to allow of an inversion, the anal pole therefore passes first. Pointing in the same direction as the egg, the new-born grub will thus hang head downwards, with its hinder end uppermost, at the end of its thread.

By the front pole, the Scoliæ, the Spheges and the Ammophilæ in their turn reply, as do all the Hunting Wasps that fix the egg to some portion of the victim. It is, indeed, always by the cephalic end that the egg adheres to the prey, at a definite point selected by the mother’s prudence; for the safety of the nurseling and the preservation of the victuals demand that the first bites shall be taken here and here only. For the same reasons as above, the extremity fastened to the game has emerged into the light of day before the other.

Both these opposite testimonies are equally truthful. According as its destiny is to be glued to the wall of the cell or to be kept away from it on another support, the egg takes its plunge into life by the front pole or the rear pole, which requires [205]an inverse direction in the ovaries and the oviduct. In this manner the new-born grub always has its food under its mandibles; and its utter lack of experience does not expose it to the danger of death from inanition in front of a heap of provisions which its mouth would not yet be able to seek and find. There is the problem. I beg and entreat the embryogenists to solve it, without reference to preordination, with the sole aid of protoplastic energy.

To know the Odynerus in the privacy of her home was not enough: the thing was to see her also at work as a huntress. How does she capture her game? How does she operate on it, in order to keep it fresh while deprived of life and movement? What is her surgical method? As, for the moment, I knew of no smallest colony of the Chrysomela’s persecutor in my neighborhood, I put the matter to Claire. She was on the spot, in daily contact with the Hen-house where the memorable events that form the subject of this essay occurred; and—a most important circumstance—I knew her to be both quick-witted and willing. She accepted the burdensome task with enthusiasm. I, on my side, was, if possible, to attempt certain observations with the captive [206]insect. So as not to influence each other in our appreciation of facts which, by their rapidity, might leave room for doubt, we each agreed to keep our results secret until we were both certain of our data.

Fully instructed as to what to do, Claire begins. She soon discovers on the banks of the Aygues some poplars covered with Chrysomela-larvæ. From time to time an Odynerus arrives, alights upon a leaf and goes off again with her capture in her legs. But things are happening too high up; detailed inspection of the struggle between the huntress and the victim is impracticable. Moreover, the appearances of the Odynerus on the tree which was being watched among so many others, all equally propitious to the chase, occur at long intervals, which try the patience beyond all bounds. Tenacious in her desire to see, to learn and to be useful to me, my zealous collaborator bethinks herself of an ingenious expedient. A young poplar, with a wealth of Chrysomelæ, is pulled up, together with the lump of earth clinging to it. Lavish precautions are taken to avoid the shocks which, during the uprooting and the removal, might cause the herd of larvæ to drop off. The business is so successfully done that the tree [207]arrives without a hitch at its destination, in front of the Hen-house. It is put back in the earth immediately facing the reeds wherein the Odynerus makes her dwelling. No matter whether it takes root again or not, provided that the little tree keep fresh for a few days with abundant watering: that is all that is wanted.

After installing her observatory, Claire proceeds to lie in wait, hiding behind some branches beside the poplar, whose foliage is in full view. She watches in the morning; she watches when the heat of the day has come; she watches in the afternoon. Next day, she begins again; on the day after that, she is still at it; and so she continues until at last fortune smiles upon her. O blessed patience, of what are you not capable! The swarm of Odyneri, out in search of larvæ, were, on their return, warned by the smell of nitrobenzene of the presence of the transplanted and game-laden poplar. Why make distant expeditions when the quarry abounds outside one’s door? The little tree was extensively exploited. Under such conditions the huntress was not long in revealing the secret of her tactics. Over and over again Claire witnessed the act of murder by the dagger. But she paid dearly for satisfying [208]our common curiosity; she had to keep her room for several days as a result of sunstroke. For that matter, she was prepared for the misadventure, well knowing, from my own example, that this is the assured reward of observations made beneath an implacable sun. May the eulogies of science repay her for a little headache! The results of her watches agreed at all points with those of my own. I shall explain them by telling what I saw myself.

Now for my turn. When the bundle of reeds selected by the Odyneri reached me, I was occupied with a most interesting question, as will be proved by the details reserved for another chapter.4 I was endeavouring to make the various Hunting Wasps, the species of whose prey was known to me, operate under a wire cover in my insect laboratory. This would determine the precise spots into which the sting was driven. My captives, confronted with their ordinary game, for the most part refused to unsheathe their weapons; others, less intent upon outdoor hunting, accepted the offer and stabbed their victims under my magnifying-glass. Why should not the Nest-building Odynerus be among these bold ones?[209]

We will try. I have plenty of Chrysomela-grubs, received from Orange; I keep them under a wire-gauze dome, with an eye to their metamorphoses and their perfume-stills. The game is at hand; the huntress is lacking. Where shall I catch her? I have only to ask Claire, who will hasten to send her. This is a sure expedient, but I hesitate to employ it: I fear lest the insect should reach me demoralized by the jolting of the cart and the tedium of a long captivity. To this bored and wearied creature an encounter with the Chrysomela will almost surely be a matter of indifference. I must have something better: I want the insect captured that moment with its aptitudes in their prime.

In front of my door is a field of yellow fennel-flower, an ingredient of that ill-famed liquor, absinthe. From its umbels Wasps, Bees and Flies of all sorts drink their fill. Let us take the net and see. The banqueters are numerous. I inspect the rows of plants amid the drinking-songs, the buzzing and the shrilling of the insects. Praise the Lord, here is the Odynerus! I catch one, I catch two, I catch six of them and I hurry back to my workroom. Fate is favouring me beyond my desires: my [210]six captures belong to the Nest-building Odynerus and all the six are females. Any one passionately interested in a problem and suddenly discovering the data required for its solution will understand my emotion. The joy of the moment has its anxious side: who knows what turn things will take between the huntress and the quarry? I shift an Odynerus and a Chrysomela-larva into a bell-glass. To stimulate the assassin’s ardour, I set the glass cage in the sun. Here is the story of the drama, told in detail.

For a good quarter of an hour, the captive clambers up the sides of the bell-glass, crawls down again and up again, seeking an outlet whereby to escape, and seems to pay no attention to the game. I was already despairing of success when suddenly the huntress falls upon the larva, turns it over, belly upwards, clasps it and stings it thrice in succession in the thorax, particularly under the neck, in the median region, a point at which the sting is more insistent than elsewhere. The close-clasped larva does its utmost to protest, emptying its scent-bottles and oiling itself with petrol; but these defensive tactics have no effect. Indifferent to the heady perfume, the Odynerus performs [211]her operation, wielding her lancet with the same certainty as if the patient were scentless. Thrice the sting is driven in, to kill the motor nerves in the three ganglia of the thorax. I repeat the experiment with other subjects. Few refuse to attack the prey; and each time three stings are administered with marked insistence at the point under the neck. What I saw under artificial conditions Claire, on her side, saw under conditions of liberty, in the open air, on the leaves of the transplanted poplar. The two collaborators, she and I, arrived at precisely the same result.

The operation is rapidly performed. Then the Odynerus, while dragging her prey along, belly to belly, munches at its neck for a considerable time, but without causing any wound. This action may well be equivalent to the practice of the Languedocian Sphex and the Hairy Ammophila,5 when, without inflicting a bruise, the one nibbles at the neck of her Ephippiger and the other at that of her Grey Worm, in order to compress and paralyse the cervical ganglia. I of course take possession of the torpid larvæ. The victim is absolutely inert, [212]save for a slight quivering of the legs, which soon ceases. When laid upon its back, the larva no longer stirs. It is not dead, however; that I have been able to prove. Its dull vitality is affirmed in another manner. During the first few days of this lethargy which knows no awakening, droppings are ejected until the intestine is empty.

On renewing my experiments, I witness something so singular that I am at first baffled. This time the prey is seized by the anal extremity and the sting is driven several times into the last segments, underneath the abdomen. This is the usual operation reversed and performed upon the hinder segments, instead of those of the thorax. The surgeon and the patient, who are head to head in the normal method, are in the present instance head to tail. Can it be by inadvertence that the operator is confusing the two ends of the grub and stinging the tip of the abdomen under the impression that she is stinging the neck? I believe it for a moment, but am soon undeceived. Instinct does not make mistakes of this sort.

For now, having finished thrusting with her sting, the Odynerus clasps the creature [213]and begins slowly, with great bites of the mandibles, to munch the last three segments, on the dorsal surface. A manifest gluttony accompanies these bites; all the mouth-parts are brought into play, as though the insect were feasting on some exquisite dish. Meanwhile the grub, bitten to the quick, desperately works its short legs, whose activity is not at all diminished by the stings administered behind; it struggles violently, protesting with its head and mandibles. The other takes no notice and continues gnawing at the larva’s rump. This lasts for ten or fifteen minutes; then the bandit releases the sufferer and leaves it where it lies, without troubling about it any further, instead of carrying it with her as she would not fail to carry game intended for the nest. Soon afterwards, the Odynerus begins to lick her fingers, as though she had been consuming some toothsome dainty: time after time she passes her tarsi between her mandibles; she is washing her hands after rising from table. What has she been eating? I must once more watch the epicure squeeze the juice from the rump.

Ever obliging, provided that I practise a little patience, my six captives, one after the other, operate on the Chrysomela-larvæ, at [214]one time in front, as game for the family, at another behind, as a little addition to their own diet. The honey with which I serve them on spikes of lavender does not make them forget this horrible treat. The tactics employed in obtaining it, though the same in the general aspect, vary in detail. The larva is always seized by the hinder end and the stings are administered in succession from back to front, on the ventral surface. Sometimes the abdomen only is attacked, sometimes the thorax also, when the victim is deprived of all movement. Evidently the object of these stings is not the immobility of the larva, since the latter can move quite well, ambling along, wounded though it be, when the sting has not gone higher than the abdomen. Inertia is indispensable only in the case of victuals intended for the cells. If the Odynerus is working on her own behalf and not for her family, it matters little to her whether the grubs whose dainties she covets struggle or not; it is enough if all resistance in the part to be exploited is abolished by paralysis. This paralysis, moreover, is quite accessory; and each huntress neglects or practises it at will, bearing more or less forward, without any fixed rule. When the sated Odynerus releases [215]the grub whose rump she has been chewing, it is sometimes therefore inert, like those intended for the cells, and sometimes endowed with almost as much activity as the untouched grubs, from which it differs only by the absence of its anal pimple, its support which reminds us of a cripple sitting in a bowl.

I examine the helpless ones. The anal blister has disappeared, nor can I make it reappear by squeezing the tip of the abdomen with my fingers. For the rest, in the place of this blister my pocket-lens shows me torn, rugged tissues; the end of the intestine is in tatters. Every elsewhere all around are bruises and contusions, but no gaping wounds. It is with the contents of the blister then that the Odynerus so deliciously slakes her thirst. When she munches the last two or three segments, she is milking the grub after a fashion; by means of the pressure, which favours the paralysis of the abdomen, she makes the rectal humour flow into the pocket, which she then rips open in order to sip the contents.

What is this humour? Some special product, some mixture of nitrobenzene? I cannot say for certain. I know only that the insect employs it in self-defence. When [216]frightened, it exudes it to ward off the assailant. The anal reservoir begins to work when the first little drop appears from the scent-bottles. What shall we say of this protective device which becomes the cause of excruciating torture? Unsophisticated creatures, acquire the power of stinking, after this; distil benzene; become bitter if you were not bitter before: you will always find a devourer to scrunch you, an epicure to nibble your rump! South-American butterflies, pray take note!

I will not close the lamentable history of the Chrysomela-grub without telling what becomes of the creature after this horrible mutilation. The complete inertia produced by the thoracic injuries has nothing to teach us that we do not already know from the facts perceived in the larvæ destined for the cells. We will therefore consider the case in which the grub is stung three or four times at the tip of the abdomen only. I secure the creature when the Odynerus abandons it, after greedily munching the last three segments and scraping out the end of the intestine, whose defensive and locomotory pimple has disappeared. These three segments are bruised and of a sickly colour; but I cannot discover the least rent in the skin. The abdomen [217]is paralysed. The insect no longer uses its anal lever when walking. The legs are perfectly mobile and the grub employs them: it crawls, it drags itself along, progressing with a vigour which would be normal but for the obstruction of the hind-quarters. The head also moves; the mouth-parts snap as usual. Apart from the paralysis of the abdomen and the mutilation of the rectum, the victim is in every respect the same as the lusty larva, browsing peacefully on the poplar-leaf. We have here a magnificent demonstration of the principle before which certain peevish objections are bound to fall to the ground: the effect of the sting is not felt, at least not at first, except at the points attacked. The sting strikes the nerve-centres of the abdomen and the abdomen is paralysed; it spares the thorax and the legs and head both remain active.

Ten hours after the operation, I examine the grubs again. The hind-legs are tremulous and are no longer of use for locomotion. Paralysis is overtaking them. Next day, they are inert; so are the middle legs. The head and the fore-legs are still working. On the day after, the whole grub is motionless, except the head. Lastly, on the fourth day, the creature is dead, really [218]dead, for it shrivels, dries up and goes black, while the larvæ subjected to the thoracic operation with a view to being used for provisions remain full and fresh-coloured for weeks and months. Did the grub die of its stings in the abdomen? No, for the others, stung in the thorax, do not die. It is the Odynerus’ cruel tooth and not the sting that killed it. With the tip of the abdomen crushed under the mandibles and the intestinal capsule pulled out by the roots, life has ceased to be possible.

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This book is part of the public domain. Jean-Henri Fabre (2021). The Mason-WaspsT. Urbana, Illinois: Project Gutenberg. Retrieved October https://www.gutenberg.org/cache/epub/66854/pg66854-images.html

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