The Natural History of Selborne

Birds eat ivy-berries, which now begin to ripen: they are of great service to the winged race at this season, since most other berries ripen in the autumn.  The shell-less snails, called slugs, are in motion all the winter in mild weather, & commit great depredations on garden-plants, & much injure the green wheat, the loss of which is imputed to earth-worms; while the shelled snail, does not come forth at all ’til about April the tenth; and not only lays itself up pretty early in the autumn, in places secure from frost; but also throws-out round the mouth of it’s shell a thick operculum formed from it’s own saliva; so that it is perfectly secured, & corked-up as it were, from all inclemencies.  Why the naked slug should be so much more able to endure cold than it’s housed congener, I cannot pretend to say.