The subterranean fungi occur only at certain points, often in groups. Now the Beetle [[316]]has been this way; with his delicate scent he has recognized the site as good, for the burrows are numerous hereabouts. We will therefore dig near the holes. The clue is accurate. In a few hours, thanks to the tracks left by the Bolboceras, I possess a handful of hydnocystes. It is the first time that I have gathered this particular fungus. Let us now catch the insect. That presents no difficulties: we have only to dig up the burrows.
I make my experiments the same evening, filling a large earthen pan with fresh, sifted sand. With a stick as thick as my finger, I make six vertical tunnels in the sand, two decimetres[9] deep and placed at a suitable distance apart. A hydnocystis is lowered to the bottom of each; and I insert a fine straw, to show me the exact position later. Lastly, I fill up the six cavities with caked sand. When this surface has been carefully smoothed, so that the level is everywhere the same, except for the six straws, landmarks that mean nothing to the Bolboceras, I let loose my captives, covering them with a wire-gauze cage. There are eight of them.
At first there is nothing to see save the inevitable [[317]]uneasiness due to the incidents of their exhumation, transport and confinement in an unknown place. My exiles from home try to escape, climb up the wire, burrow right at the edge of the enclosure. Night falls and things grow calmer. Two hours later, I come to take a last look at them. Three are still buried under a thin layer of sand. The five others have each dug a perpendicular shaft at the very foot of the straws which tell me where the fungi lie. Next morning, the sixth straw has its well like the others.
This is the moment to see what is happening underground. I remove the sand methodically in vertical slices. At the bottom of each burrow is a Bolboceras eating his truffle, the hydnocystis.
Let us repeat the experiment with the partly-consumed victuals. The result is the same. At one brief, nocturnal spell of work, the dainty is discovered underground and reached by means of a gallery which runs plumb to the spot where the morsel lies. There is no hesitation, no trial excavation guided by guesswork. This is proved by the surface of the soil, which everywhere is just as I left it when I smoothed it down. The [[318]]insect could not have made straighter for the coveted object had it been guided by sight; it always digs at the foot of the straws, my sign-posts. The Dog, nosing the ground for truffles, hardly achieves this degree of precision.
Has the hydnocystis then a very pungent smell, able to give such positive information to its consumer’s scent? Not at all. To our nostrils it is a neutral object, devoid of any appreciable olfactory character. A tiny pebble taken out of the ground would impress us just as much with its faint aroma of fresh earth. As a revealer of underground fungous products, the Bolboceras here rivals the Dog. He would even rise superior to the Dog, were he able to generalize. But he is a rigorous specialist: he knows only the hydnocystis. Nothing else, so far as I am aware, tempts him to dig.[10]
Both of them search the subsoil very closely, at the level of the ground; and the object which they seek is not far down. Were they farther away, neither the Dog nor the insect [[319]]would notice effluvia so subtle, not even the smell of a truffle. To make an impression at a great distance, powerful odours are needed, capable of perception by our olfactory sense. Then the exploiters of the odorous thing come hastening up on all sides from afar.
When, for the purpose of my studies, I require insects that dissect corpses, I expose a dead Mole in the sun, in a distant corner of the enclosure. As soon as the animal swells, distended by the gases of putrefaction, and the skin begins to turn green and the fur to fall from it, up come numbers of Silphæ[11] and Dermestes,[12] Necrophori[13] and other Burying-beetles, of whom one would find not a single specimen in the garden, or even in the neighbourhood, without this bait.
They have been informed by their sense of smell, at a great distance all around, whereas I myself can avoid the stench by taking a few steps back. Compared with their scent, mine is contemptible; but still, in their [[320]]case as well as mine, there is really here what our language calls a smell.
I can do better still with the flower of the dragon arum (Arum dracunculus), so remarkable for its shape and for its unequalled stench. Imagine a wide, lanceolate blade, of a clarety purple, half a yard long and rolled below into an ovoid pouch the size of a hen’s egg. Through the opening of this wallet rises a central column springing from the bottom, a long, bright-green club, encircled at its base by two bracelets, one of ovaries, the other of stamens. Such, briefly described, is the flower, or rather the inflorescence, of the dragon arum.