Carabidae
Ground beetles- Kind
- Wild — attract it
- Best for
- Night-time predation at ground level; give them cover
Pest
Slugs
Deroceras reticulatum and other species
The short answer
Slugs eat irregular holes in leaves, flowers and low-hanging fruit, and can destroy seedlings overnight. They feed in the dark and in damp weather, then hide, so the silvery slime trail is often the only sign by morning. The grey field slug is among the commonest culprits. No single method works on its own. Hand-pick by torchlight, trap under boards or in beer traps, and remove daytime hiding places. If you use a bait, use iron phosphate: metaldehyde poisons dogs and cats, and it has been illegal to use outdoors in Great Britain since 2022.
Control it with
hero macro · grey field slug on a lettuce leaf at night
Deroceras reticulatum feeding on a lettuce leaf after dark, with a fresh slime trail. Photo: pending.
Identification
The grey field slug (Deroceras reticulatum), also called the netted field slug or grey garden slug, grows to 35–50 mm long. Its slime is colourless until the slug is disturbed, when it turns milky white. The RHS names it, the brown soil slug and the common garden snail as the species most likely to eat garden plants. Keeled slugs live mostly underground and tunnel into potato tubers.
Many slugs in a garden do no harm. The UK has more than 44 slug species, and the RHS says only very few feed on living plants. Many eat decaying matter such as dead leaves, dung and even dead slugs and snails. In US gardens, UC IPM also lists the banded slug, the three-band garden slug, the tawny slug and the greenhouse slug (Milax gagates). Slugs range from about 1/4 in to 2 in (6 mm–5 cm) or more (University of Minnesota). Size is not a reliable way to tell a pest from a harmless species. What you catch on damaged plants at night is the better guide.
Easily confused with
- EarwigsAlso a pestEarwig feeding makes the same ragged holes, but only slugs leave slime trails. A torch check after dark shows which one is feeding.
Damage symptoms
Slugs rasp at plant tissue with file-like mouthparts. UC IPM describes the holes as irregular with smooth edges, and the RHS calls them ragged. The RHS notes that slugs feed at night, so the damage appears overnight. Seedlings and soft young growth suffer most. The University of Minnesota notes that severe feeding can injure plants, and seedlings above all. UC IPM's check is the shiny slime trail, which confirms a slug or snail.
- Irregular holes in leaves and flowers
- Shiny, silvery slime trails on leaves, soil and paths
- Seedlings and young transplants grazed to the stem or gone overnight
- Holes in ripening fruit close to the ground, such as strawberries and tomatoes
- Hosta, lettuce and delphinium leaves riddled with holes
- Narrow tunnels in potato tubers, made by keeled slugs underground
Lifecycle & degree days
Slugs lay their eggs in damp, sheltered places in the soil, under debris, mulch and boards, and the eggs are what usually survive the winter. The figures below are for the grey field slug unless stated. They come from Oregon State University's work in the Pacific Northwest, where there are two generations a year, with mating in autumn and again from spring into early summer. Activity follows moisture rather than the calendar: slugs feed at night and on cloudy or foggy days, and shelter through cold weather and hot, dry spells.
- Eggs
- Clusters of about 40 (slugs in general: 3–40); 500+ per lifetime
- Hatch
- 2 weeks to a month; up to 5 months if laid in late winter
- Maturity
- 5–6 months over winter (slugs in general: 3–6 months)
- Lifespan
- 6–12 months, a few up to 18
- Generations / yr
- Two possible (Pacific Northwest)
- Overwinters
- Mostly as eggs in soil and debris
J
F
M
A
M
J
J
A
S
O
N
D
Host crops
Lettuce & leafy greensCabbage & brassicasHostasStrawberryPotatoBeansBasil & herbsBedding plantsTomato (ripening fruit)CitrusLawn seedlings
Slugs attack almost any soft growth. The plants UC IPM names include basil, beans, cabbage, dahlia, delphinium, hosta, lettuce, marigolds and strawberries, and it lists citrus as especially susceptible. It also calls slugs serious pests of turfgrass seedlings and of ripening fruit close to the ground. The RHS singles out seedlings, hostas, soft young shoots on herbaceous plants and maincrop potatoes.
Monitoring & action thresholds
Action threshold
No garden threshold
AHDB says no slug threshold has been set for horticultural crops. Its arable thresholds are one slug per refuge trap for potatoes and oilseed rape, and four per trap for winter cereals. In a garden, what matters is timing: seedlings and new transplants are the plants at risk, so protect them first, especially in damp weather.
Search with a torch on a mild, damp evening, when slugs come up to feed; the RHS and UC IPM both recommend hand-picking this way. By day, use refuge traps. Lay a board raised about 1 in (2.5 cm) off the ground (UC IPM), or a cover about 10 in (25 cm) across over a spoonful of layers' mash or grain, never slug pellets (AHDB). Check underneath early the next morning while the soil is still moist. AHDB advises trapping only when the soil is visibly moist and between 41 and 77 °F (5–25 °C). On dry days, slugs stay out of sight whether they are there or not.
Beneficial
Biological control
Slugs have many predators. The RHS lists birds, frogs, toads, hedgehogs, slowworms and ground beetles, and Minnesota adds snakes, turtles, shrews and ducks. Ground beetles are the best documented of these. A 2021 review found that large carabids, among them Carabus species, Abax parallelepipedus and Pterostichus melanarius, prey mostly on slugs, and that the larvae of some, such as P. melanarius, are significant slug predators too. UC IPM notes that adult ground beetles are mostly active at night, hunting on the soil surface, and hide by day under mulch, litter and objects on the soil. The nematode Phasmarhabditis hermaphrodita has been sold in Europe as Nemaslug. It is watered onto moist soil of at least 41 °F (5 °C), and a dose protects the treated area for about six weeks. Infected slugs stop feeding soon after infection and die within 7–21 days. It works best on the grey field slug; larger species are only vulnerable when young. The current Nemaslug 2.0 sold in England, Scotland and Wales has switched to a related species, P. californica. Products containing P. hermaphrodita or related nematodes are not permitted for sale in the United States, so US gardeners cannot buy them.
Cultural controls
No one method below is reliable on its own, so combine removing daytime shelter with hand-picking and trapping, and treat the evidence on barriers with caution. On baits the sources disagree. UC IPM calls iron phosphate safer to use around children, pets and wildlife. The RHS says all slug pellets, organic ones included, have been shown to harm garden wildlife, and it does not recommend them.
- Hand-pick by torchlight on mild, damp evenings, and repeat. UC IPM, the RHS and the University of Minnesota all recommend it
- Lay boards raised about 1 in (2.5 cm) off the soil and scrape off the slugs sheltering under them each morning
- Sink beer traps level with the soil, with deep sides so slugs cannot climb out, and refresh them every few days. UC IPM says they only draw slugs from a few feet away. In a 2018 Garden Organic trial, lager traps caught an average of 6.4 slugs over 3–4 days, against 0.1 for plain water, in a dry season with few slugs
- Remove daytime shelter near vulnerable plants: boards, stones, debris, weedy margins and dense ground cover such as ivy
- Water in the morning, not the evening, so the ground is dry by nightfall (UC IPM)
- Do not rely on copper tape, grit, eggshells, bark or wool pellets. An RHS trial on 108 lettuces found none of them reduced damage. UC IPM does recommend vertical copper barriers at least 2 in (5 cm) tall, with 1–2 in (2.5–5 cm) buried in the soil
- Diatomaceous earth is generally not an effective deterrent (University of Minnesota)
- If you bait, use iron (ferric) phosphate and apply it in the late afternoon or evening, when slugs are active. Slugs stop feeding and die within about 3–7 days. Rebait the same spots, because slugs return to the same food sources. Never use metaldehyde where pets roam: in dogs, signs such as severe tremors begin 30 minutes to 6 hours after eating it and can progress to seizures
Chemical, last resort
Metaldehyde poisons dogs and cats, and has been illegal to use outdoors in Great Britain since 2022Check any product before it goes on. Open the compatibility matrix →
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sources
UC IPM Pest Notes: Snails and Slugs, UC ANR Pub. 7427 (Wilen & Flint, updated 03/2018)
UC IPM Natural Enemies Gallery: Predaceous ground beetles
RHS Advice: Slugs and snails; RHS Science: How to stop slugs and snails (barrier trial)
University of Minnesota Extension, Slugs (Weisenhorn & Hahn, reviewed 2024)
Oregon State University Slug Portal: Biology and Life Cycle of the Gray Field Slug
AHDB: Chemical and biological control of slugs; How to monitor slug populations in field crops
Barua, Williams & Ross 2021, Biological and bio-rational control strategies for slugs, Insects 12: 541
Denver et al. 2024, P. hermaphrodita and Monadenia fidelis, PLoS ONE 19: e0298165
Merck Veterinary Manual: Metaldehyde Poisoning in Animals (Puschner, updated 2026)
Garden Organic, What is the best way of trapping slugs? (2018 trial)
Nemaslug (BASF) product site: coverage, soil temperature and storage (accessed Sept 2026)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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