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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.
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.
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.
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.
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.
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.
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.
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