Snails

 Snails can sleep for up to three years by entering a state of dormancy called estivation (to avoid heat and dryness) or hibernation (to prevent cold temperatures). During these prolonged rest periods, their metabolism slows to conserve moisture and energy. To protect itself, the snail secretes a thick layer of mucus that hardens into a barrier, sealing the opening of its shell. This natural shield helps prevent dehydration and keeps out predators. When favorable weather conditions return, the snail simply dissolves the barrier and reawakens.