Snails are usually active in the summer, but if it gets too warm or too dry for them, they enter a period of inactivity known as estivation. They find a safe place—such as a tree trunk, the underside of a leaf, or a stone wall—and suction themselves onto the surface as they retreat into their shell. Thus protected, they wait until the weather becomes more suitable. Occasionally, snails will go into estivation on the ground. There, they go into their shell and a mucous membrane dries over the opening of their shell, leaving just enough space for air to get inside allowing the snail to breath.
In late fall when temperatures drop, snails go into hibernation. They dig a small hole in the ground or find a warm patch, buried in a pile of leaf litter. It is important that a snail finds a suitably protected place to sleep to ensure its survival through the long cold months of winter. They retreat into their shell and seal its opening with a thin layer of white chalk. During hibernation, the snail lives on the fat reserves in its body, built up from a summer of eating vegetation. When spring comes (and with it rain and warmth), the snail wakes and pushes the chalk seal to open the shell once again. If you look closely in spring, you may find a chalky white disc on the forest floor, left behind by a snail that has recently come out of hibernation.