Page:Natural History, Mollusca.djvu/53

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41
MOLLUSCA.

line or circle, than night after night they are gnawed away, until nothing remains but the brown earth, and the label which tells where the seed had been. But to the farmer the consequences are often much more important. In wet seasons the slugs increase with such rapidity in the fields, that a wheat-crop after one of clover, tares, or beans, is very uncertain, and may be said generally to fail. The damage annually done to corn, clover, and turnips, by these apparently insignificant creatures, is very great. In France and the South of Europe, the vineyards are subject to similar attacks from the vine snail (Helix pomatia). The buds and opening leaves of the vine are gnawed off by them as they appear, and the hopes of the autumnal vintage are often blasted.

But much more lamentable than any of these are the injuries inflicted upon shipping, and the piers and defences of maritime towns, by the ship-worm (Teredo navalis). Ranging over extensive seas from the tropics to the shores of Northern Europe, this boring worm, or rather Mollusk with a worm-like form, is incessantly engaged in devouring and destroying all kinds of woodwork that is immersed in the sea. Linnæus long ago styled it the calamity of ships, and there is no maritime nation which has not confessed the formidable power of this subtle enemy. In the years 1731 and 1732, the United Provinces were under a dreadful alarm; for it was discovered that these mollusks had made such depredations on the piles which support the banks of Zealand and Freisland, as to threaten them with total destruction, reclaiming from man what he had with unexampled labour wrested from the ocean. A few