Snail vs slug damage and behavior

Snails and slugs are mollusks -- not insects -- and are among the few garden pests that operate primarily at night and in wet conditions. Their damage is distinctive once you know the sign, and their management involves habitat manipulation as much as any.

Snails and slugs are mollusks — not insects — and are among the few garden pests that operate primarily at night and in wet conditions. Their damage is distinctive once you know the sign, and their management involves habitat manipulation as much as any pesticide.

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Identifying snails vs. slugs

Snails: Mollusks with a spiral shell on their back. Withdraw into the shell when disturbed. Common garden snail in the US: brown garden snail (Cornu aspersum, formerly Helix aspersa). Per UC IPM, the brown garden snail is the primary snail pest in California and the western United States; it was introduced from Europe as a food source in the 1850s. Up to 1.5 inch shell diameter.

Slugs: Snails without a shell (or with a very reduced internal plate). Slugs cannot withdraw and dry out faster than shelled snails. Common species: gray garden slug (Deroceras reticulatum), spotted garden slug (Limax maximus, which can reach 4–5 inches), and black slug (Arion ater). Per Penn State Extension, gray garden slug is the most common vegetable garden slug in the northeastern United States.

Both leave a dried, silvery mucus trail. Per UC IPM, the slime trail dries to a glistening, silver line on leaf surfaces, the soil, and surfaces under boards or debris.