Nancy,

Your snails will do well on any left over greens you don't give to your
turtle.  Also keep some egg shell or crushed oyster shell in the tank to
help with shell building.  Mist daily or provide a shallow dish of water.
By the way, I introduced garden snails (Helix aspersa) into the fenced off
garden area where my box turtles live just to give them an added treat.
Believe me (and Paul and Amy), no matter that your turtle is well fed on
prepared foods -- he or she will make short work of the snails.  Of course
the snails do not respect the wall around the turtle area and my roses have
to bear the brunt of the more adventerous snails.  To close, lots of folks
in the UK keep snails, including the huge African varieties.

Tom Eichhorst in New Mexico, USA