In short, no, they don't. They do however eat decaying plant matter. Sometimes it appears as if snails may be eating your plant, but they are only eating the decaying areas on the plant. Ramshorn and Malaysian Trumpet snails are excellent tank cleaners. Some larger snails keep the same diet. All that I've kept (those that are normally available at the LFS) have not eaten plants. I'm not sure if there is any one species in particular that will eat plants. I've never known one that would eat live plant matter. Maybe someone else can chime in?