Snails produce slime, which is a kind of mucus, via a special gland on the front of the snail’s foot. Scientists initially thought that the purpose of the slime was to enable snails to move. Over the years, however, researchers have learned that snail slime is a special substance with unique properties and several purposes.
As they travel on the slime they produce, the slime helps them to stick to whatever surface they’re on while their muscles are at rest. As their muscles contract and push down to propel them forward, however, the slime becomes more liquid and makes movement easier.
In addition to helping them move, their slime helps to protect snails’ skin from environmental hazards, such as sharp objects, bacteria, and the Sun’s ultraviolet rays. In dry weather, snails can curl up in their shells and seal themselves inside using their slime. This helps them to stay moist and comfortable even when the weather threatens to dry them out.
Slimy
https://wonderopolis.org/wonder/why-do-snails-leave-slime-trails