Social Life in the Insect World

by Jean-Henri Fabre

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.