A TRUFFLE-HUNTER: THE BOLBOCERAS GALLICUS

Social Life in the Insect World by Jean-Henri Fabre, is part of the HackerNoon Books Series. You can jump to any chapter in this book here. A TRUFFLE-HUNTER: THE BOLBOCERAS GALLICUS

CHAPTER XVI. A TRUFFLE-HUNTER: THE BOLBOCERAS GALLICUS

In the matter of physics we hear of nothing to-day but the Röntgen rays, which penetrate opaque bodies and photograph the invisible. A splendid discovery; but nothing very remarkable as compared with the surprises reserved for us by the future, when, better instructed as to the why and wherefore of things than now, and supplementing our feeble senses by means of science, we shall succeed in rivalling, however imperfectly, the sensorial acuteness of the lower animals.

How enviable, in how many cases, is the superiority of the beasts! It makes us realise the insufficiency of our impressions, and the very indifferent efficacy of our sense-organs; it proclaims realities which amaze us, so far are they beyond our own attributes.

A miserable caterpillar, the Processional caterpillar, found on the pine-tree, has its back covered with meteorological spiracles which sense the coming weather and foretell the storm; the bird of prey, that incomparable watchman, sees the fallen mule from the heights of the clouds; the blind bats guided their flight without collision through the inextricable labyrinth of threads devised by Spallanzani; the carrier pigeon, at a hundred leagues from home, infallibly regains its loft across immensities which it has never known; and within the limits of its more modest powers a bee, the Chalicodoma, also adventures into the unknown, accomplishing its long journey and returning to its group of cells.

Those who have never seen a dog seeking truffles have missed one of the finest achievements of the olfactory sense. Absorbed in his duties, the animal goes forward, scenting the wind, at a moderate pace. He stops, questions the soil with his nostrils, and, without excitement, scratches the earth a few times with one paw. "There it is, master!" his eyes seem to say: "there it is! On the faith of a dog, there are truffles here!"

He says truly. The master digs at the point indicated. If the spade goes astray the dog corrects the digger, sniffing at the bottom of the hole. Have no fear that stones and roots will confuse him; in spite of depth and obstacles, the truffle will be found. A dog's nose cannot lie.

I have referred to the dog's speciality as a subtle sense of smell. That is certainly what I mean, if you will understand by that that the nasal passages of the animal are the seat of the perceptive organ; but is the thing perceived always a simple smell in the vulgar acceptation of the term—an effluvium such as our own senses perceive? I have certain reasons for doubting this, which I will proceed to relate.

On various occasions I have had the good fortune to accompany a truffle-dog of first-class capacities on his rounds. Certainly there was not much outside show about him, this artist that I so desired to see at work; a dog of doubtful breed, placid and meditative; uncouth, ungroomed, and quite inadmissible to the intimacies of the hearthrug. Talent and poverty are often mated.

His master, a celebrated rabassier[5] of the village, being convinced that my object was not to steal his professional secrets, and so sooner or later to set up in business as a competitor, admitted me of his company, a favour of which he was not prodigal. From the moment of his regarding me not as an apprentice, but merely as a curious spectator, who drew and wrote about subterranean vegetable affairs, but had no wish to carry to market my bagful of these glories of the Christmas goose, the excellent man lent himself generously to my designs.

It was agreed between us that the dog should act according to his own instincts, receiving the customary reward, after each discovery, no matter what its size, of a crust of bread the size of a finger-nail. Every spot scratched by his paw should be excavated, and the object indicated was to be extracted without reference to its marketable value. In no case was the experience of the master to intervene in order to divert the dog from a spot where the general aspect of things indicated that no commercial results need be expected, for I was more concerned with the miserable specimens unfit for the market than with the choice specimens, though of course the latter were welcomed.

Thus conducted, this subterranean botanising was extremely fruitful. With that perspicacious nose of his the dog obtained for me both large and small, fresh and putrid, odorous and inodorous, fragrant and offensive. I was amazed at my collection, which comprised the greater number of the hypogenous fungi of the neighbourhood.

What a variety of structure, and above all of odour, the primordial quality in this question of scent! There were some that had no appreciable scent beyond a vague fungoid flavour, more or less common to all. Others smelt of turnips, of sour cabbage; some were fetid, sufficiently so to make the house of the collector noisome. Only the true truffle possessed the aroma dear to epicures. If odour, as we understand it, is the dog's only guide, how does he manage to follow that guide amidst all these totally different odours? Is he warned of the contents of the subsoil by a general emanation, by that fungoid effluvium common to all the species? Thus a somewhat embarrassing question arises.

I paid special attention to the ordinary toadstools and mushrooms, which announced their near advent by cracking the surface of the soil. Now these points, where my eyes divined the cryptogam pushing back the soil with its button-like heads, these points, where the ordinary fungoid odour was certainly very pronounced, were never selected by the dog. He passed them disdainfully, without a sniff, without a stroke of the paw. Yet the fungi were underground, and their odour was similar to that I have already referred to.

I came back from my outings with the conviction that the truffle-finding nose has some better guide than odour such as we with our sense-organs conceive it. It must perceive effluvia of another order as well; entirely mysterious to us, and therefore not utilised. Light has its dark rays—rays without effect upon our retinas, but not apparently on all. Why should not the domain of smell have its secret emanations, unknown to our senses and perceptible to a different sense-organ?

If the scent of the dog leaves us perplexed in the sense that we cannot possibly say precisely, cannot even suspect what it is that the dog perceives, at least it is clear that it would be erroneous to refer everything to human standards. The world of sensations is far larger than the limits of our own sensibility. What numbers of facts relating to the interplay of natural forces must escape us for want of sufficiently sensitive organs!

The unknown—that inexhaustible field in which the men of the future will try their strength—has harvests in store for us beside which our present knowledge would show as no more than a wretched gleaning. Under the sickle of science will one day fall the sheaves whose grain would appear to-day as senseless paradoxes. Scientific dreams? No, if you please, but undeniable positive realities, affirmed by the brute creation, which in certain respects has so great an advantage over us.

Despite his long practice of his calling, despite the scent of the object he was seeking, the rabassier could not divine the presence of the truffle, which ripens in winter under the soil, at a depth of a foot or two; he must have the help of a dog or a pig, whose scent is able to discover the secrets of the soil. These secrets are known to various insects even better than to our two auxiliaries. They have in exceptional perfection the power of discovering the tubers on which their larvæ are nourished.

From truffles dug up in a spoiled condition, peopled with vermin, and placed in that condition, with a bed of fresh sand, in a glass jar, I have in the past obtained a small red beetle, known as the truffle-beetle (Anisotoma cinnamomea, Panz.), and various Diptera, among which is a Sapromyzon which, by its sluggish flight and its fragile form, recalls the Scatophaga scybalaria, the yellow velvety fly which is found in human excrement in the autumn. The latter finds its refuge on the surface of the soil, at the foot of a wall or hedge or under a bush; but how does the former know just where the truffle lies under the soil, or at what depth? To penetrate to that depth, or to seek in the subsoil, is impossible. Its fragile limbs, barely able to move a grain of sand, its extended wings, which would bar all progress in a narrow passage, and its costume of bristling silken pile, which would prevent it from slipping through crevices, all make such a task impossible. The Sapromyzon is forced to lay its eggs on the surface of the soil, but it does so on the precise spot which overlies the truffle, for the grubs would perish if they had to wander at random in search of their provender, the truffle being always thinly sown.

The truffle fly is informed by the sense of smell of the points favourable to its maternal plans; it has the talents of the truffle-dog, and doubtless in a higher degree, for it knows naturally, without having been taught, what its rival only acquires through an artificial education.

It would be not uninteresting to follow the Sapromyzon in its search in the open woods. Such a feat did not strike me as particularly possible; the insect is rare, flies off quickly when alarmed, and is lost to view. To observe it closely under such conditions would mean a loss of time and an assiduity of which I do not feel capable. Another truffle-hunter will show us what we could hardly learn from the fly.

This is a pretty little black beetle, with a pale, velvety abdomen; a spherical insect, as large as a biggish cherry-stone. Its official title is Bolboceras gallicus, Muls. By rubbing the end of the abdomen against the edge of the wing-cases it produces a gentle chirping sound like the cheeping of nestlings when the mother-bird returns to the nest with food. The male wears a graceful horn on his head; a duplicate, in little, of that of the Copris hispanus.

Deceived by this horn, I at first took the insect for a member of the corporation of dung-beetles, and as such I reared it in captivity. I offered it the kind of diet most appreciated by its supposed relatives, but never, never would it touch such food. For whom did I take it? Fie upon me! To offer ordure to an epicure! It required, if not precisely the truffle known to our chefs and gourmets, at least its equivalent.

This characteristic I grasped only after patient investigation. At the southern foot of the hills of Sérignan, not far from the village, is a wood of maritime pines alternating with rows of cypress. There, towards Toussaint, after the autumnal rains, you may find an abundance of the mushrooms or "toadstools" that affect the conifers; especially the delicious Lactaris, which turns green if the points are rubbed and drips blood if broken. In the warm days of autumn this is the favourite promenade of the members of my household, being distant enough to exercise their young legs, but near enough not to fatigue them.

There one finds and sees all manner of things: old magpies' nests, great bundles of twigs; jays, wrangling after filling their crops with the acorns of the neighbouring oaks; rabbits, whose little white upturned scuts go bobbing away through the rosemary bushes; dung-beetles, which are storing food for the winter and throwing up their rubbish on the threshold of their burrows. And then the fine sand, soft to the touch, easily tunnelled, easily excavated or built into tiny huts which we thatch with moss and surmount with the end of a reed for a chimney; and the delicious meal of apples, and the sound of the æolian harps which softly whisper among the boughs of the pines!

For the children it is a real paradise, where they can receive the reward of well-learned lessons. The grown-ups also can share in the enjoyment. As for myself, for long years I have watched two insects which are found there without getting to the bottom of their domestic secrets. One is the Minotaurus typhæus, whose male carries on his corselet three spines which point forward. The old writers called him the Phalangist, on account of his armour, which is comparable to the three ranks of lances of the Macedonian phalanx.

This is a robust creature, heedless of the winter. All during the cold season, whenever the weather relents a little, it issues discreetly from its lodging, at nightfall, and gathers, in the immediate neighbourhood of its dwelling, a few fragments of sheep-dung and ancient olives which the summer suns have dried. It stacks them in a row at the end of its burrow, closes the door, and consumes them. When the food is broken up and exhausted of its meagre juices it returns to the surface and renews its store. Thus the winter passes, famine being unknown unless the weather is exceptionally hard.

The second insect which I have observed for so long among the pines is the Bolboceras. Its burrows, scattered here and there, higgledy-piggledy with those of the Minotaur, are easy to recognise. The burrow of the Phalangist is surmounted by a voluminous rubbish-dump, the materials of which are piled in the form of a cylinder as long as the finger. Each of these dumps is a load of refuse and rubbish pushed outward by the little sapper, which shoulders it up from below. The orifice is closed whenever the insect is at home, enlarging its tunnel or peacefully enjoying the contents of its larder.

The lodging of the Bolboceras is open and surrounded simply by a mound of sand. Its depth is not great; a foot or hardly more. It descends vertically in an easily shifted soil. It is therefore easy to inspect it, if we take care first of all to dig a trench so that the wall of the burrow may be afterwards cut away, slice by slice, with the blade of a knife. The burrow is thus laid bare along its whole extent, from the surface to the bottom, until nothing remains of it but a demi-cylindrical groove.

Often the violated dwelling is empty. The insect has departed in the night, having finished its business there. It is a nomad, a night-walker, which leaves its dwelling without regret and easily acquires another. Often, on the other hand, the insect will be found at the bottom of the burrow; sometimes a male, sometimes a female, but always alone. The two sexes, equally zealous in excavating their burrows, work apart without collaboration. This is no family mansion for the rearing of offspring; it is a temporary dwelling, made by each insect for its own benefit.

Sometimes the burrow contains nothing but the well-sinker surprised at its work: sometimes—and not rarely—the hermit will be found embracing a small subterranean fungus, entire or partly consumed. It presses it convulsively to its bosom and will not be parted from it. This is the insect's booty: its worldly wealth. Scattered crumbs inform us that we have surprised the beetle at a feast.

Let us deprive the insect of its booty. We find a sort of irregular, rugged, purse-like object, varying in size from the largeness of a pea to that of a cherry. The exterior is reddish, covered with fine warts, having an appearance not unlike shagreen; the interior, which has no communication with the exterior, is smooth and white. The pores, ovoidal and diaphanous, are contained, in groups of eight, in long capsules. From these characteristics we recognise an underground cryptogam, known to the botanists as Hydnocystis arenaria, and a relation of the truffle.

This discovery begins to throw a light on the habits of the Bolboceras and the cause of its burrows, so frequently renewed. In the calm of the twilight the little truffle-hunter goes abroad, chirping softly to encourage itself. It explores the soil, and interrogates it as to its contents, exactly as does the truffle-gatherer's dog. The sense of smell warns it that the desired object is beneath it, covered by a few inches of sand. Certain of the precise point where the treasure lies, it sinks a well vertically downwards, and infallibly reaches it. So long as there is food left it does not again leave the burrow. It feasts happily at the bottom of its well, heedless of the open or imperfectly closed burrow.

When no more food is left it removes in search of further booty, which becomes the occasion of another burrow, this too in its turn to be abandoned. So many truffles eaten necessitate so many burrows, which are mere dining-rooms or pilgrim's larders. Thus pass the autumn and the spring, the seasons of the Hydnocystis, in the pleasures of the table and removal from one house to another.

To study the insect rabassier in my own house I had to obtain a small store of its favourite food. To seek it myself, by digging at random, would have resulted merely in waste of time; the little cryptogam is not so common that I could hope to find it without a guide. The truffle-hunter must have his dog; my guide should be the Bolboceras itself. Behold me, then, a rabassier of a kind hitherto unknown. I have told my secret, although I fear my original teacher will laugh at me if he ever hears of my singular form of competition.

The subterranean fungi grow only at certain points, but they are often found in groups. Now, the beetle has passed this way; with its subtle sense of smell it has recognised the ground as favourable; for its burrows are numerous. Let us dig, then, in the neighbourhood of these holes. The sign is reliable; in a few hours, thanks to the signs of the Bolboceras, I obtain a handful of specimens of the Hydnocystis. It is the first time I have ever found this fungus in the ground. Let us now capture the insect—an easy matter, for we have only to excavate the burrows.

The same evening I begin my experiments. A wide earthen pan is filled with fresh sand which has been passed through a sieve. With the aid of a stick the thickness of a finger I make six vertical holes in the sand: they are conveniently far apart, and are eight inches in depth. A Hydnocystis is placed at the bottom of each; a fine straw is then inserted, to show me the precise position later. Finally the six holes are filled with sand which is beaten down so that all is firm. When the surface is perfectly level, and everywhere the same, except for the six straws, which mean nothing to the insect, I release my beetles, covering them with a wire-gauze cover. They are eight in number.

At first I see nothing but the inevitable fatigue due to the incidents of exhumation, transport, and confinement in a strange place. My exiles try to escape: they climb the wire walls, and finally all take to earth at the edge of their enclosure. Night comes, and all is quiet. Two hours later I pay my prisoners a last visit. Three are still buried under a thin layer of sand. The other five have sunk each a vertical well at the very foot of the straws which indicate the position of the buried fungi. Next morning the sixth straw has its burrow like the rest.

It is time to see what is happening underground. The sand is methodically removed in vertical slices. At the bottom of each burrow is a Bolboceras engaged in eating its truffle.

Let us repeat the experiment with the partly eaten fungi. The result is the same. In one short night the food is divined under its covering of sand and attained by means of a burrow which descends as straight as a plumb-line to the point where the fungus lies. There has been no hesitation, no trial excavations which have nearly discovered the object of search. This is proved by the surface of the soil, which is everywhere just as I left it when smoothing it down. The insect could not make more directly for the objective if guided by the sense of sight; it digs always at the foot of the straw, my private sign. The truffle-dog, sniffing the ground in search of truffles, hardly attains this degree of precision.

Does the Hydnocystis possess a very keen odour, such as we should expect to give an unmistakable warning to the senses of the consumer? By no means. To our own sense of smell it is a neutral sort of object, with no appreciable scent whatever. A little pebble taken from the soil would affect our senses quite as strongly with its vague savour of fresh earth. As a finder of underground fungi the Bolboceras is the rival of the dog. It would be the superior of the dog if it could generalise; it is, however, a rigid specialist, recognising nothing but the Hydnocystis. No other fungus, to my knowledge, either attracts it or induces it to dig.[6]

Both dog and beetle are very near the subsoil which they scrutinise; the object they seek is at no great depth. At a greater depth neither dog nor insect could perceive such subtle effluvia, nor even the odour of the truffle. To attract insect or animal at a great distance powerful odours are necessary, such as our grosser senses can perceive. Then the exploiters of the odorous substance hasten from afar off and from all directions.

If for purposes of study I require specimens of such insects as dissect dead bodies I expose a dead mole to the sunlight in a distant corner of my orchard. As soon as the creature is swollen with the gases of putrefaction, and the fur commences to fall from the greenish skin, a host of insects arrive—Silphidæ, Dermestes, Horn-beetles, and Necrophori—of which not a single specimen could ever be obtained in my garden or even in the neighbourhood without the use of such a bait.

They have been warned by the sense of smell, although far away in all directions, while I myself can escape from the stench by recoiling a few paces. In comparison with their sense of smell mine is miserable; but in this case, both for me and for them, there is really what our language calls an odour.

I can do still better with the flower of the Serpent Arum (Arum dracunculus), so noteworthy both for its form and its incomparable stench. Imagine a wide lanceolated blade of a vinous purple, some twenty inches in length, which is twisted at the base into an ovoid purse about the size of a hen's egg. Through the opening of this capsule rises the central column, a long club of a livid green, surrounded at the base by two rings, one of ovaries and the other of stamens. Such, briefly, is the flower or rather the inflorescence of the Serpent Arum.

For two days it exhales a horrible stench of putrid flesh; a dead dog could not produce such a terrible odour. Set free by the sun and the wind, it is odious, intolerable. Let us brave the infected atmosphere and approach; we shall witness a curious spectacle.

Warned by the stench, which travels far and wide, a host of insects are flying hither; such insects as dissect the corpses of frogs, adders, lizards, hedgehogs, moles and field-mice—creatures that the peasant finds beneath his spade and throws disembowelled on the path. They fall upon the great leaf, whose livid purple gives it the appearance of a strip of putrid flesh; they dance with impatience, intoxicated by the corpse-like odour which to them is so delicious; they roll down its steep face and are engulfed in the capsule. After a few hours of hot sunlight the receptacle is full.

Let us look into the capsule through the narrow opening. Nowhere else could you see such a mob of insects. It is a delirious mixture of backs and bellies, wing-covers and legs, which swarms and rolls upon itself, rising and falling, seething and boiling, shaken by continual convulsions, clicking and squeaking with a sound of entangled articulations. It is a bacchanal, a general access of delirium tremens.

A few, but only a few, emerge from the mass. By the central mast or the walls of the purse they climb to the opening. Do they wish to take flight and escape? By no means. On the threshold of the cavity, while already almost at liberty, they allow themselves to fall into the whirlpool, retaken by their madness. The lure is irresistible. None will break free from the swarm until the evening, or perhaps the next day, when the heady fumes will have evaporated. Then the units of the swarm disengage themselves from their mutual embraces, and slowly, as though regretfully, take flight and depart. At the bottom of this devil's purse remains a heap of the dead and dying, of severed limbs and wing-covers torn off; the inevitable sequels of the frantic orgy. Soon the woodlice, earwigs, and ants will appear to prey upon the injured.

What are these insects doing? Were they the prisoners of the flower, converted into a trap which allowed them to enter but prevented their escape by means of a palisade of converging hairs? No, they were not prisoners; they had full liberty to escape, as is proved by the final exodus, which is in no way impeded. Deceived by a fallacious odour, were they endeavouring to lay and establish their eggs as they would have done under the shelter of a corpse? No; there is no trace of eggs in the purse of the Arum. They came convoked by the odour of a decaying body, their supreme delight; an intoxication seized them, and they rushed into the eddying swarm to take part in a festival of carrion-eaters.

I was anxious to count the number of those attracted. At the height of the bacchanal I emptied the purse into a bottle. Intoxicated as they were, many would escape my census, and I wished to ensure its accuracy. A few drops of carbon bisulphide quieted the swarm. The census proved that there were more than four hundred insects in the purse of the Arum. The collection consisted entirely of two species—Dermestes and Saprinidæ—both eager prospectors of carrion and animal detritus during the spring.

My friend Bull, an honest dog all his lifetime if ever there was one, amongst other eccentricities had the following: finding in the dust of the road the shrivelled body of a mole, flattened by the feet of pedestrians, mummified by the heat of the sun, he would slide himself over it, from the tip of his nose to the root of his tail, he would rub himself against it deliciously over and over again, shaken with nervous spasms, and roll upon it first in one direction, then in the other.

It was his sachet of musk, his flask of eau-de-Cologne. Perfumed to his liking, he would rise, shake himself, and proceed on his way, delighted with his toilet. Do not let us scold him, and above all do not let us discuss the matter. There are all kinds of tastes in a world.

Why should there not be insects with similar habits among the amateurs of corpse-like savours? We see Dermestes and Saprinidæ hastening to the arum-flower. All day long they writhe and wriggle in a swarm, although perfectly free to escape; numbers perish in the tumultuous orgy. They are not retained by the desire of food, for the arum provides them with nothing eatable; they do not come to breed, for they take care not to establish their grubs in that place of famine. What are these frenzied creatures doing? Apparently they are intoxicated with fetidity, as was Bull when he rolled on the putrid body of a mole.

This intoxication draws them from all parts of the neighbourhood, perhaps over considerable distances; how far we do not know. The Necrophori, in quest of a place where to establish their family, travel great distances to find the corpses of small animals, informed by such odours as offend our own senses at a considerable distance.

The Hydnocystis, the food of the Bolboceras, emits no such brutal emanations as these, which readily diffuse themselves through space; it is inodorous, at least to our senses. The insect which seeks it does not come from a distance; it inhabits the places wherein the cryptogam is found. Faint as are the effluvia of this subterranean fungus, the prospecting epicure, being specially equipped, perceives them with the greatest ease; but then he operates at close range, from the surface of the soil. The truffle-dog is in the same case; he searches with his nose to the ground. The true truffle, however, the essential object of his search, possesses a fairly vivid odour.

But what are we to say of the Great Peacock moth and the Oak Eggar, both of which find their captive female? They come from the confines of the horizon. What do they perceive at that distance? Is it really an odour such as we perceive and understand? I cannot bring myself to believe it.

The dog finds the truffle by smelling the earth quite close to the tuber; but he finds his master at great distances by following his footsteps, which he recognises by their scent. Yet can he find the truffle at a hundred yards? or his master, in the complete absence of a trail? No. With all his fineness of scent, the dog is incapable of such feats as are realised by the moth, which is embarrassed neither by distance nor the absence of a trail.

It is admitted that odour, such as affects our olfactory sense, consists of molecules emanating from the body whose odour is perceived. The odorous material becomes diffused through the air to which it communicates its agreeable or disagreeable aroma. Odour and taste are to a certain extent the same; in both there is contact between the material particles causing the impression and the sensitive papillæ affected by the impression.

That the Serpent Arum should elaborate a powerful essence which impregnates the atmosphere and makes it noisome is perfectly simple and comprehensible. Thus the Dermestes and Saprinidæ, those lovers of corpse-like odours, are warned by molecular diffusion. In the same way the putrid frog emits and disseminates around it atoms of putrescence which travel to a considerable distance and so attract and delight the Necrophorus, the carrion-beetle.

But in the case of the Great Peacock or the Oak Eggar, what molecules are actually disengaged? None, according to our sense of smell. And yet this lure, to which the males hasten so speedily, must saturate with its molecules an enormous hemisphere of air—a hemisphere some miles in diameter! What the atrocious fetor of the Arum cannot do the absence of odour accomplishes! However divisible matter may be, the mind refuses such conclusions. It would be to redden a lake with a grain of carmine; to fill space with a mere nothing.

Moreover, where my laboratory was previously saturated with powerful odours which should have overcome and annihilated any particularly delicate effluvium, the male moths arrived without the least indication of confusion or delay.

A loud noise stifles a feeble note and prevents it from being heard; a brilliant light eclipses a feeble glimmer. Heavy waves overcome and obliterate ripples. In the two cases cited we have waves of the same nature. But a clap of thunder does not diminish the feeblest jet of light; the dazzling glory of the sun will not muffle the slightest sound. Of different natures, light and sound do not mutually interact.

My experiment with spike-lavender, naphthaline, and other odours seems to prove that odour proceeds from two sources. For emission substitute undulation, and the problem of the Great Peacock moth is explained. Without any material emanation a luminous point shakes the ether with its vibrations and fills with light a sphere of indefinite magnitude. So, or in some such manner, must the warning effluvium of the mother Oak Eggar operate. The moth does not emit molecules; but something about it vibrates, causing waves capable of propagation to distances incompatible with an actual diffusion of matter.

From this point of view, smell would have two domains—that of particles dissolved in the air and that of etheric waves.[7] The former domain alone is known to us. It is also known to the insect. It is this that warns the Saprinidæ of the fetid arum, the Silphidæ and the Necrophori of the putrid mole.

The second category of odour, far superior in its action through space, escapes us completely, because we lack the essential sensory equipment. The Great Peacock moth and the Oak Eggar know it at the time of their nuptial festivities. Many others must share it in differing degrees, according to the exigencies of their way of life.

Like light, odour has its X-rays. Let science, instructed by the insect, one day give us a radiograph sensitive to odours, and this artificial nose will open a new world of marvels.

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