How often does a snail change shells?
Snails don't change their shells. Unlike crustaceans, molluscs
like snails keep the same shell throughout their lifetime. The
shell is formed from secretions from the snails mantle, the flesh
under the shell, and some snails (such as the giant African snails
kept as pets) can be seen running their mouths along the edge of
their shells, to build up another layer on the shells lip.
The stripes that make up the pattern of a snails shell are the
result of different compositions of shell material at different
times.