In many parts of the world, snails and slugs are the most damaging of garden pests. Snails and slugs are almost the same, with slug just being snails without a shell. Both cause damage simply by eating the leaves and plant tissue with mouths that are under their bodies. They hide during the day, and eat at night - though they may come out on damp, gray days as well.
It's almost impossible to eradicate snails and slugs since they can come in from neighboring land, on new plants, or even as eggs in the soil of new plants. The eggs looks like clusters of pearls, about 1/8 inch in size. They're often found under boards, rocks and pots and should be destroyed.
Chemical controls
Physical controls
Biological controls
Ducks love to eat snails and slugs.
Decollate snails feed on the brown garden snail. They will also feed on succulent leaves or berries near ground-level. They are sold in some areas, and are illegal in some areas.