Snails are also soft-bodied animals. Snails have shells and can withdraw inside them. In harsh conditions, they can seal the shell and stay alive inside for several years. While they don’t pose any physical danger to people, snails and slugs are a nuisance when they come indoors. Outdoors they can cause considerable damage to plants in gardens and flowerbeds. Since snails have shells, they need calcium in their diet. If limestone is not plentiful, they will sometimes feed on painted surfaces.