Identification
Slugs and shelled snails that feed at night and after rain. Symptoms: irregular holes in the leaves and young seedlings eaten off completely, silvery slime trails on leaves and soil. The greatest damage occurs in damp, shaded spots — particularly on lettuce, strawberries and hostas. The most damaging in gardens are the slugs (which lack an external shell): the Spanish slug (Arion vulgaris, formerly described as A. lusitanicus) and the grey field slug (Deroceras reticulatum). The leopard slug (Limax maximus) can be morphologically similar to them, but it feeds mainly on decaying organic matter and fungi and may even prey on other slugs, so it is of little importance as a pest of living plants. Shelled forms — grove snails (Cepaea) or the protected Roman snail (Helix pomatia) — usually cause less damage. The body is soft, elongated and permanently covered in slime; on the head there are two pairs of retractable tentacles — the longer upper pair bears the eyes, the shorter lower pair serves a tactile and olfactory function. Slugs and snails are hermaphrodites: they lay spherical, transparent or pearly eggs in clusters, hidden in damp soil, under stones and in leaf litter. A single Spanish slug can lay several hundred eggs; both eggs and young slugs overwinter, and feeding lasts from spring to late autumn, intensifying on warm, damp nights. The damage has smooth edges and often appears in the middle of the leaf blade, not only from the margin; seedlings and transplants are sometimes eaten down to bare soil, and on strawberries and ripening vegetables the slugs gnaw hollows into the fruit. The decisive diagnostic sign is the dried, silvery glistening slime trail — no insect leaves one.
Treatment
Hand-picking at dusk, traps (boards, beer), barriers of sharp materials (shells, ash, gravel), preparations based on iron phosphate (safe for animals). Reduce damp hiding places and water in the morning rather than the evening. Effective control combines several methods at once. The foundation is systematic hand-picking after dusk and after rain — ideally with a torch — and laying out damp boards, tiles or sheets, under which the slugs shelter during the day and from which they can easily be removed in the morning. Containers of beer sunk into the bed attract and drown some individuals, but they act locally and are treated as a supporting method, not a standalone solution. Loose barriers (sharp shells, gravel, wood ash) and copper strips hinder the slugs' passage, but hygroscopic materials lose their effectiveness once wetted and need renewing after every rain — so they are only a shield, not full protection. It is worth supporting the natural enemies of slugs: hedgehogs, toads, birds, ground beetles and predatory glow-worm larvae. A biological method with real effect on slugs is watering the soil with a suspension of the parasitic slug nematode Phasmarhabditis hermaphrodita — it parasitises the slugs, but works only in damp and sufficiently warm soil. Among chemical products, granular molluscicides based on iron (III) phosphate are used, relatively safe for pets and beneficial fauna, breaking down into natural soil components. The historically common metaldehyde is being ever more strongly restricted and withdrawn from garden use (including a ban on outdoor use in the United Kingdom) and is being replaced precisely by iron phosphate. Preventive measures — removing mulch and weeds near the beds, thinning dense plantings for better airflow and watering in the morning — reduce damp hiding places and genuinely lower slug pressure.
How to tell it apart from look-alikes
| Feature | Slugs and snails | Caterpillars of butterflies and moths (e.g. cabbage moth) |
|---|---|---|
| Slime trail | Silvery, dried slime streaks on leaves and soil | No slime; dark pellets of droppings present |
| Culprit during the day | Hidden under boards, stones or in leaf litter — absent from the plant | Caterpillar usually on the plant, in the head or bud |
| Shape of damage | Smooth-edged holes, also in the middle of the blade; seedlings eaten down to the soil | Chewing from the margin and eating out the mesophyll, sometimes webbing |
| Additional traces | No droppings or cast skins | Dark droppings, cast skins, sometimes webbing |
Control — organic and chemical methods
Organic and biological methods
| Method | How it works | When to use |
|---|---|---|
| Hand-picking and shelter traps | Evening and post-rain collection with a torch; boards, tiles and damp sheets as daytime shelters to be cleared in the morning. | From spring to autumn, especially after rain |
| Beer traps | Containers of beer sunk into the bed attract and drown slugs; a local effect, a purely supporting method. | Growing season |
| Barriers and habitat modification | Sharp loose materials and copper strips hinder passage, but loose barriers weaken after rain; removing mulch and watering in the morning reduces damp hiding places. | — |
| Supporting natural enemies | Hedgehogs, toads, birds, ground beetles and glow-worm larvae reduce the population; a preventive, not an interventional, method. | — |
| Phasmarhabditis hermaphrodita nematodes | Watering the soil with a suspension of parasitic slug nematodes; effective against slugs in damp, warm soil. | Damp soil, temperature above about 5 degrees C |
Chemical methods
| Method | How it works | When to use |
|---|---|---|
| Iron (III) phosphate molluscicide | Granules relatively safe for animals, breaking down in the soil; replaces the phased-out metaldehyde. | Under high pressure, following the label |
We give active-ingredient groups and modes of action, not brand names — specific products and their approval vary by country and are sometimes withdrawn. Always check and follow the current label.
Sources
- Plant protection in the garden
