Snails need moisture to survive. That’s why they live in damp and moist places. Moisture is necessary to produce the mucus they use to slide over surfaces.
Fun fact: This mucus is so thick that snails can slide over sharp edges such as blades, knives, and rough surfaces without being scratched.
As such, snails go into a deep sleep, when the right levels of moisture are missing. This sleep could last as long as 3 years.
This also explains why they avoid sunlight and hide most of the day. Heat dries out their bodies, which can kill them. Snails love the humid and cool conditions of the night. This is when they are most active.
Hibernation and Estivation
Conditions that drive snails to sleep for 3 years include winter and high temperatures such as summer.
During winter, snails go into hibernation. They withdraw into their shells and form a mucous membrane around their shells to insulate themselves.
During summer or in drought and desert conditions, they aestivate. Aestivation is the process of going dormant during hot and dry periods.
Snails roll into their shells and bury themselves underground to escape such weather, sleeping for up to 3 years or more. Sometimes even unto their own deaths.