Garden slugs

What is garden slugs?

Garden slugs are mollusks, closer kin to clams than to insects. They are basically snails without shells. Several species show up in gardens, including the gray garden slug; the University of Maryland also lists the tawny and spotted garden slugs. They leave silvery slime trails wherever they crawl, and Colorado State notes they are mostly water and dry out easily.

Slugs feed mostly at night and on overcast, rainy days, rasping holes in leaves, flowers and fruit with a tongue-like mouthpart. Shade plants like hosta, lungwort and bellflower, leafy vegetables, strawberries and young seedlings are favorites. Light feeding is mostly cosmetic, but slugs can wipe out seedlings and make it hard to get a crop started. Trees and shrubs are generally not damaged (UMN).

Because slugs need moisture, the best control starts with the site: fewer hiding places, less overhead watering in the evening, better drainage and airflow, and less thick, damp mulch. Traps, hand-picking, barriers and low-toxicity iron-based baits fill in the gaps.

Plants it attacks: hosta, dahlia, delphinium (larkspur), bellflower, daylily, lungwort, marigold, basil, lettuce, cabbage, beans, strawberries, tomato and pepper fruit, asparagus spears, beets and Swiss chard, Turfgrass and other seedlings.

People and pets: Metaldehyde slug baits are attractive and toxic to dogs and cats, so keep them out of reach and off areas pets use; iron phosphate baits are described as less toxic and safer around pets and children (UC IPM, UMN, Colorado State, University of Maryland). UMN notes copper strips can have sharp edges that are a hazard for young children, and UC IPM advises wearing gloves when hand-picking.

Signs and damage

• Ragged holes with smooth edges in leaves, often in the middle of the leaf rather than along the edge.
• Silvery, dried slime trails on leaves, soil, pavers and walls.
• Seedlings and tender shoots eaten off entirely, sometimes overnight.
• Holes or rasped patches in strawberries, tomatoes and peppers close to the ground.
• Slugs hiding under boards, pots, stones, mulch and dense ground covers during the day.

Garden slugs identification: what to look for

• Adult: Soft, legless, shell-less mollusk, from about 1/4 inch to 2 inches or more depending on species (UMN); Maryland lists adults of its common species at 1.5 to 5 inches. Body tapers at both ends; usually brown or gray, some species spotted or banded.
• Eggs: Translucent to white, oval to round, gelatinous, about BB-size, in batches of a few to about 40 under leaves, in soil cracks or about an inch deep in loose soil.
• Damage: Irregular holes with smooth edges in leaves, flowers and low fruit; seedlings eaten off; slime trails confirm slugs rather than caterpillars or earwigs.
• Signs: Silvery dried slime trails on plants, soil and hard surfaces.
• Timing: Present spring to fall, most active in cool, wet weather; egg laying mainly in wet spring and fall periods.

Life cycle

All slugs are hermaphrodites, but they still mate before laying eggs. Eggs are laid in small batches in damp soil, soil cracks or under debris, mostly during wet spring and fall weather; Maryland notes up to about 200 eggs per slug. Eggs hatch in about a month if the soil stays damp. Young slugs grow to full size in roughly 3 to 12 months depending on species, and some live several years. Slugs overwinter in the soil as eggs or other stages and are less active in hot, dry weather. Colorado's common species often have two generations a year, one in spring and one in fall (UC IPM, University of Maryland, UMN, Colorado State).

When to look: Check for slugs with a flashlight after dark or early in the morning from spring through fall, especially during cloudy, rainy stretches.

Garden slugs look-alikes

A few things get mixed up with it:

• Snails (Cornu aspersum (brown garden snail) and others): Same kind of damage and slime trails, but they carry a spiral shell.
• Earwigs and caterpillars: Also chew holes in leaves, but they leave no slime trails. UC IPM says silvery trails confirm slugs or snails.
• Asiatic garden beetle (Maladera castanea): Another night feeder that chews leaves in gardens; it leaves notched leaf edges and no slime, and the beetles can be found at night or at lights.

How to control garden slugs

Cultural control

• Remove hiding spots near susceptible plants: boards, stones, pots, debris, weeds and dense ground covers.
• Water in the morning so plants and soil dry by evening, and use drip or soaker hoses instead of overhead sprinklers.
• Go easy on thick organic mulches like straw, grass clippings and chopped leaves in slug-prone beds (UMN, Colorado State).
• Open up air flow and light: thin or divide crowded plants, stake or trim low leaves, keep rows narrow, and improve drainage with compost where soil stays wet (UMN).
• Choose plants slugs tend to avoid, such as lavender, rosemary, sage, ferns, hydrangea, lantana, yarrow and ornamental grasses (UC IPM, UMN).
• Hand-pick at night with a flashlight and gloves and drop slugs into soapy water; check daily at first, then weekly (UC IPM).
• Set boards, shingles or damp folded newspaper on the ground and clean out the slugs under them each morning.
• Sink beer traps (or a sugar-water and yeast mix) so the rim is level with the soil, keep them deep enough to drown slugs, and refill every few days. Traps only reach a few feet, so use several.
• Ring raised beds or containers with copper bands wide enough to cover a slug, or with borders of gravel or sand. Diatomaceous earth only works while dry, and UC IPM found crushed eggshells and coffee grounds have not been shown to work. Don't use salt, which harms soil and plants.

Biological control

• Ground beetles, rove beetles, fireflies, toads, snakes, turtles, shrews and birds eat slugs (UMN, UC IPM, University of Maryland).
• Penned ducks, geese or chickens can cut slug numbers, but seedlings need protection from the birds (UC IPM).
• Spot-treat or use baits only where needed so these predators survive (UMN).

Chemical control

Slug baits (molluscicides) work best alongside the habitat changes above and do not give lasting control by themselves (UC IPM). Iron phosphate baits are considered less toxic and safer around children, pets and wildlife, can be used in vegetable gardens, and some are approved for organic use; ferric sodium EDTA works similarly but faster. Metaldehyde baits are attractive and toxic to dogs and cats; keep them away from pets and children, and Colorado State notes they are not labeled for direct use among vegetables and edible crops. UC IPM advises avoiding metaldehyde baits that also contain carbaryl, which harms earthworms and ground beetles. Scatter baits thinly (never in piles) in late afternoon or evening near hiding spots, after a light watering. Use only products labeled for this use; the label is the law.

Use only products labeled for this pest and this site; the label is the law. For trees, work with an ISA Certified Arborist. If you hire someone to apply pesticides, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Prevention

• Keep beds tidy and free of boards, pots and debris near slug-favored plants.
• Switch to morning watering and drip irrigation.
• Place slug-prone plants in the sunniest spots you can, away from shady, damp hiding areas.
• Use row covers to protect seedlings (University of Maryland).

When to call a pro

Most slug problems can be handled with the steps above. If you need help choosing or applying a bait product on a large planting, work with a licensed pesticide applicator (see our pesticide applicator license guide).

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Questions about garden slugs

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