Estivation: If the weather becomes too warm or too dry for a terrestrial snail (namely in the summer months), they enter a stage of inactivity known as estivation.  The snaill will find a safe place, like: a tree trunk, in inconspicuous leaf, or a stone wall.  It will then suction itself onto the chosen surface as it retreat into its shell.  The snail is then safe until the weather returns to a habitable condition. Sometimes, a snail will go into estivation on the ground.  In this case, it goes into its shell and a mucus membrane dries over the opening of theshell, leaving just enough space for air to get inside and allowing the snail to breathe.

Hibernation: Snails go into hibernation in the late fall when temperatures drop.  They will dig a small hole in the ground, or find a warm patch buried in a pile of leaf litter.  They pull back into their shell and seal the opening with a thin layer of white chalk.  During hibernation, the snail lives on reserves in its body, built up from eating all summer.  When spring brings more favorable conditions, the snail wakes and pushes the chalk seal to open the shell.