What animal hibernates the longest?

Although you might not think of snails as animals that hibernate, some do. Snails hibernate inside their shells, sealing the opening with mucus to retain moisture inside and prevent drying out. They also defend themselves from hot weather, albeit this is known as aestivation, not simply in cold weather. They can sleep for up to three years at a stretch, which seems like a very long time. Once more, this is their natural instinct for survival. If the situation is not ideal, they will sleep until conditions are safe to emerge.