Where snails go in winter

In a mild winter a garden snail may stay active whenever the night is above freezing and the ground is wet. In a hard winter it hibernates. The preparation looks like estivation: a retreat into the shell, an epiphragm, a sheltered crevice. The site is often deeper. Snails work into leaf litter, under stacks of tiles, into loose soil at the foot of a wall, and sometimes into the hollow of a log. A cluster may share one pocket, each animal sealed on its own.

Cold is a water problem as well as a temperature problem. Ice forming inside tissue punctures it. Some snails supercool, keeping their fluids liquid below freezing, and some tolerate a limited amount of ice. Which strategy a species uses depends on the winters it evolved with. A Mediterranean garden snail in a northern bed is nearer the edge of its physiology than a local woodland species. A sudden frost after a warm, wet night catches animals that have not yet sealed, and those are the ones you find dead on the open soil.

Snow can help. A layer of snow insulates the surface of the ground. The dangerous places are open, windswept, and bare. Compost heaps, the bottoms of hedges, and the north side of a shed are ordinary refuges, not because the snail understands buildings, but because those places stay damp and lose heat more slowly than a raked bed.

Leave the refuges alone until spring if you can. Cutting a border back to bare soil in November, and again in a February tidy, throws the winter population into the open. If a pile of pots or timber has to be moved, shift it in one piece rather than spreading it across a frozen path. The snails inside have already done the difficult part, which was choosing.