During the greater part of the year, the Aygues is a broad expanse of white pebbles; of the torrent naught remains but the bed, a furrow of enormous width, comparable with that of its mighty neighbour, the Rhone. Let the rain fall persistently, [[143]]let the snows melt on the slopes of the Alps; and the thirsty furrow fills for a few days: roaring, it overflows to a great distance and turbulently shifts its shoals of pebbles. Return a week later. The roar of the flood is succeeded by silence. The terrible waters have disappeared, leaving on the banks, as the trace of their brief passage, wretched muddy puddles soon absorbed by the sun.
These sudden freshets bring a thousand live gleanings swept off the flanks of the mountains. The dry bed of the Aygues is a most interesting botanical garden. There you may gather many vegetable species brought down from the higher levels, some temporary, disappearing without offspring in a single season, others persisting and adapting themselves to the new climate. They come from far away, from the heights, these exiles; to pluck this one or that in its true environment you would have to climb Mont Ventoux, pass beyond the zone of the beeches and reach the altitude where trees cannot grow.
Alien zoology in its turn is represented in the osier-beds, whose calm is disturbed only during unusually prolonged floods. My attention is attracted especially by the land-mollusc, that champion stay-at-home. In stormy weather, when the thunder growls—lou tambour di cacalauso, as the Provençal calls it—the most that the Snail permits himself in the matter of moving about is to issue from his stronghold, some crevice in the rocks, [[144]]and to browse before his door upon the grasses, mosses and lichens made tender by the flood. It takes a cataclysm to make that one travel!
The wild freshets of the Aygues succeed in doing so. They bring into my part of the world and deposit in the osier-thickets the largest of our Snails, Helix pomatia, the glory of Burgundy.[1] Rolled down the grassy mountain-slopes by the showers, the exile defies immersion within the water-tight cover of his chalky operculum; he endures the jolting, thanks to his strong shell. He travels by stages, from one osier-bed to another. He descends as far even as the Rhone and colonizes the Île des Rats and the Île du Colombier opposite the mouth of the Aygues.
Whence does he come, this enforced emigrant, whom one would vainly seek elsewhere in the land of the olive? He loves a moderate temperature, green turf, cool shades. His place of origin is certainly not here, but far away on the rounded heights of the lower, outermost Alps. The highlander’s exile none the less seems pleasant. The big Snail does quite well in the marshy scrub on the banks of the torrent.
Neither is the Apoderus a native. She is a castaway, hailing from the hazel-clad heights. She has made the voyage in a little boat, that is to say, in the leafy cockle-shell in which the grub is born. The vessel was tightly closed, which [[145]]made the passage possible. Running ashore at some point on the bank in the height of summer, the insect perforated its cell and, not finding its favourite tree, established itself upon the alder. There it founded a family, remaining faithful to the same tree for the three years during which I had to do with it. It is probable, for that matter, that the origin of the settlement dates farther back.
The history of this stranger interests me. The primordial conditions of her life—climate and food—are changed. Her ancestors lived under a temperate sky; they grazed on the leaf of the hazel-bush; they manufactured cylinders out of piece-goods made familiar by the constant practice of past generations. But the wanderer is living under a torrid sky; she grazes on the alder-leaf, whose flavour and nutritive properties must differ from those of the family diet; she works at an unknown piece, though it is not unlike the normal piece in shape and size. What changes has this disturbance of its diet and climate effected in the insect’s characteristics?
Absolutely none. In vain I pass the magnifying-glass over the exploiter of the alder and over the exploiter of the hazel-bush, of whom the latter has reached me from the heart of the Corrèze by post. I see not the least difference between the two, even in the smallest details. Can the method of industry have been modified? Without seeing [[146]]the work done with a hazel-leaf, I boldly assert that it is similar to that obtained with an alder-leaf.
Change the food and the climate, change the materials to be worked: if it can adapt itself to the new conditions imposed upon it, the insect persists, immutable in its craft, habits and organization; if it cannot, it dies. To be as one was or not to be: that is what the castaway of the torrent, like so many others, tells us.
Let us watch her at work on the alder and we shall know how she labours on the hazel-bush. The Apoderus does not know the method of the Rhynchites, who, to kill the elasticity of the leaf to be rolled, makes a deep puncture in the stalk. The red leaf-roller has a special modus operandi, in no way related to that of the puncture.