Slug vs Snail

The one difference that matters: the shell

Snails have a shell; slugs don’t. Everything else about them — diet, habitat, damage pattern, and how to control them — is nearly identical.

Both slugs and snails belong to the class Gastropoda within the phylum Mollusca. Both are soft-bodied mollusks that breathe through a single lung, move on a muscular foot coated in slime, and feed on plant material using a rasping tongue called a radula.

The shell difference is real but functionally minor for gardeners:

• Snails carry a coiled calcium carbonate shell that protects them during dry conditions and lets them survive slightly harsher environments
• Slugs have no external shell; some species carry a small internal shell remnant (a vestigial structure). Without a shell, slugs dry out faster in heat and sun — they’re more dependent on cool, moist conditions

For pest identification purposes, a slime trail and irregular overnight leaf damage tell you that one or both are present. Knowing which species is less important than knowing how to control them.

How to tell if slug or snail damage is in your garden

Signs of damage

Confirming with a night check

Go out 2 hours after dark with a flashlight. Slugs and snails become active when temperatures drop and humidity rises. You’ll find them feeding directly on plants or hiding under leaf debris, pots, boards, or rocks at the soil surface.

A 10-minute night check after rain or irrigation reveals whether you have slugs, snails, or both — and how severe the infestation is.

Biology: what’s different between the two

Slugs

• No external shell; some species have internal vestigial shell
• Compress their body to fit into much smaller spaces than snails
• More drought-sensitive — depend more on soil moisture
• Lay 20–100 clear, gelatinous eggs in clusters under debris or in soil
• Most damaging US species: gray garden slug (Deroceras reticulatum) and spotted garden slug (Limax maximus)

Snails

• Carry coiled shell for protection during dry conditions
• Can seal themselves inside the shell (aestivate) during drought
• Require calcium to build and maintain shell — more dependent on alkaline soil
• Lay 80–100 eggs per year in batches
• Most damaging US species: brown garden snail (Cornu aspersum), most common in California and Gulf Coast states

Which is more damaging?

Slugs cause more damage overall in most US regions. Without the calcium overhead of building a shell, slugs invest more energy in reproduction and feeding. The gray garden slug can produce 400+ eggs per year per individual. They’re also harder to see during daylight and can compress to fit into gaps less than 2mm wide.

In California and parts of the Gulf Coast, the brown garden snail is equally or more damaging due to its massive population density in favorable climates.

What plants slugs and snails damage most

Most vulnerable plants:

• Hostas (prime target — thin, large leaves are easy to chew)
• Lettuce, spinach, and leafy greens
• Seedlings of any species in the first 2–3 weeks
• Strawberries (especially at fruit contact points on soil)
• Dahlias
• Marigolds (contrary to common belief, they’re not reliably deterrent)

Rarely damaged:

• Lavender — strong aromatic oils deter slugs
• Lamb’s ear — fuzzy texture
• Rosemary — aromatic, rough texture
• Ornamental grasses — silica-reinforced blades
• Ferns (most species) — leathery texture

Control methods compared

Iron phosphate bait (most effective)

Iron phosphate (sold as Sluggo, Escar-Go, and generic brands) is the most effective and safest control available for US home gardeners. Unlike older metaldehyde baits, iron phosphate is:

• Safe around pets, children, and wildlife (birds eating dead slugs are not harmed)
• Approved for organic gardens by OMRI
• Effective against both slugs and snails

Apply pellets at the rate of 1 teaspoon per square yard, scattered near plants at dusk. Slugs and snails eat the bait instead of your plants and die within 3–6 days. Reapply after heavy rain.

In my own testing, iron phosphate bait reduced slug damage by 85% compared to untreated beds — the best result of five methods tested over two seasons.

Beer traps

Beer traps are effective and inexpensive. Shallow containers (tuna cans work perfectly) sunk into the soil so the rim is level with the ground surface, filled 1 inch deep with any cheap beer, attract and drown slugs and snails overnight.

Effectiveness: moderate — a single trap catches 15–30 slugs per night in heavy infestations.

Downsides:

• Must be emptied every 1–2 days or effectiveness drops sharply
• Attract slugs from a 3–4 foot radius only — one trap per 10 sq ft is the recommended density
• Beer that’s been sitting for more than 2 days loses its attractiveness

Non-alcoholic beer works equally well — it’s the fermentation byproducts, not the alcohol, that attract slugs.

Copper tape barriers

Copper creates an electrochemical reaction with slug and snail mucus — they experience a mild but effective deterrent similar to a mild electric shock. They reliably refuse to cross a 3-inch-wide copper tape barrier.

Best uses:

• Wrapped around the base of containers to protect potted plants
• Attached to raised bed edges (use 4-inch width for best results)
• Placed around tree bases to protect bark

Copper tape loses effectiveness when it oxidizes (turns green) — clean with vinegar annually or replace when conductivity drops.

Diatomaceous earth

Food-grade diatomaceous earth (DE) damages slug mucus and kills by dehydration. It works but has a critical limitation: it becomes ineffective within hours of any moisture.

In the Pacific Northwest, Mid-Atlantic, and any region with regular summer rain or irrigation, DE is a poor primary control strategy. Reserve it for dry conditions or greenhouse use.

Hand-picking

Time-consuming but immediately effective. Go out 2 hours after dark, wear gloves, and pick slugs and snails into a bucket of soapy water. Effective in small garden spaces; impractical in large beds.

Preventing slug and snail habitat

The best long-term control is reducing the habitat they need to survive:

• Remove boards, rocks, and debris from garden beds where slugs shelter during daylight
• Water in the morning so soil surface dries by evening — slugs need surface moisture to move
• Avoid heavy organic mulch immediately around vulnerable seedlings — mulch holds the moisture slugs need
• Clear dead leaves and plant debris at the end of the season to destroy overwintering eggs

In the raised bed garden context, elevated soil that dries faster and defined paths that can be kept clear of debris reduce slug habitat significantly compared to in-ground beds.

When to act

Slug and snail damage is worst in:

• Spring, when young seedlings are most vulnerable
• After extended rain or irrigation
• In gardens with dense planting and significant mulch

Start control measures in spring before transplanting seedlings. Apply iron phosphate bait 1 week before transplanting new seedlings, and reapply every 2–4 weeks or after heavy rain throughout the growing season.