Some snail species can enter a state of dormancy that can last for years, which is similar to sleep but more accurately described as hibernation or estivation. The desert snail Eremina desertorum has been documented to survive dormancy for up to 6 years. During dormancy, Snails create a hard mucus layer over their shell opening to prevent water loss and they will dramatically reduce their metabolic rate. Snails can "wake up" when conditions become favorable again, usually due to moisture.
