The Spanish slug, Arion vulgaris, has spread across most of Europe since the 1960s and is the slug that does the most damage in gardens. An adult lays around 400 eggs, so control is as much about timing as about method. Here you will learn how to tell it from slugs that do good, what ferric phosphate, nematodes and a slug edge can do, and when an evening's picking pays off most.
Spanish slug or a slug that does good
Four species are common in gardens, and only two of them need controlling.
Spanish slug (Arion vulgaris): 6-14 cm, usually a uniform reddish brown but can be orange, brown or almost black. Tough, sticky slime. Eats living plants, dead material and other slugs. This is the one you pick.
Grey field slug (Deroceras reticulatum): 4-6 cm, greyish beige with a netted pattern, and the slime turns milky white when you touch it. Takes seedlings and lettuce, and manages two generations a year.
Large black slug (Arion ater): native, 10-15 cm, jet black as an adult. Lives mostly in woodland and rarely reaches the densities of the Spanish slug.
Leopard slug (Limax maximus): 10-20 cm, grey with black spots. Lives mainly on dead plant material and fungi. It is often said to hunt Spanish slugs, but the evidence is thin. Leave it alone.
Colour alone is not enough for a safe identification, as brown forms of the large black slug look like the Spanish one. If the slug is reddish brown, over 6 cm and present in numbers, treat it as a Spanish slug.
The slug's year, month by month
The Spanish slug lives for one year. The adults die in October, and what survives the winter is eggs and young slugs buried up to 10 cm down in the soil or in the compost. Neither eggs nor slugs survive cold below minus 3 degrees without shelter, so a winter with bare frost and little snow cuts the population.
| Period | What happens | What you do |
|---|---|---|
| March to April | The soil warms up. Overwintered eggs hatch and the young slugs dig their way up. | Water in nematodes once the soil has passed 5 degrees. |
| May to June | The slugs grow fast, just as you are planting out young plants. | Pick at dusk. Every slug you take now is up to 400 fewer eggs in autumn. |
| July to August | Mating starts in July and the first eggs are laid in late summer. | Pick adults after rain, before they get to lay. |
| September to October | Eggs are laid in clutches of 20-30, in cracks in the soil and under anything lying on the ground. The adults die. | Turn over boards, pots and mulch and remove the eggs. |
| November to February | Eggs and young slugs rest buried in the soil. | Turn the compost on a cold day and leave the soil nearest the beds bare. |
When an evening's picking pays off most
The Spanish slug moves at night and in rain and hides in the soil on dry days. Go out at dusk or an hour after rain, with a head torch. A slug travels several metres in a night, so lay a board or an upturned pot in the bed. The next morning the slugs are sitting underneath it.
In May and June you take animals that have not yet laid eggs, and then 3 evenings in a row do more than a week in August. Cut the slug behind the head with secateurs. Salt is cruel and stays in the soil. Dead slugs attract living ones, so bury them.
What works and what does not
Ferric phosphate: the active ingredient in the slug pellets sold to home gardeners. The slug eats the pellets, withdraws and dies buried, so you rarely see it. Scatter thinly around what you want to protect and top up after rain. It kills but does not keep slugs out.
Nematodes: the roundworm Phasmarhabditis hermaphrodita is watered into moist soil in the evening, enters the slug and kills it within 1-3 weeks. It has been sold to gardeners in Britain since 1994. The limitation is size: slugs over roughly 1 gram can resist it, and a full-grown Spanish slug weighs many times more. Nematodes are a spring tool against young slugs, not a way to get rid of the big ones in August.
Slug edge: a metal strip along the top of the raised bed with an angled lip the slug cannot get round. The method we trust most, with two conditions. No leaf may hang out over the edge and form a bridge, and slugs and eggs already in the soil must be removed first, because the edge also shuts them in.
Copper tape: is said to give the slug an unpleasant reaction on contact. The effect is disputed, and a narrow strip on a dirty pot rarely stops a full-grown Spanish slug. We use it on the odd pot, not for a whole bed.
Beer traps: the smell of yeast attracts them and the slugs drown. Let the rim stand 1-2 cm above the soil surface, otherwise ground beetles that eat slug eggs drown too. Empty every 2-3 days. Place it at the edge of the bed, as it draws slugs in.
Plants slugs leave alone and plants they love
Slugs choose soft, juicy leaves and avoid anything hairy, tough, scented or poisonous. Nothing holds at 50 slugs per square metre, but the table holds in an ordinary garden. A plant is most exposed in the first 3-4 weeks after planting out. Among the perennials, choose by the leaves, not by flower colour.
| Slugs leave alone | Why | Slugs love | When it is worst |
|---|---|---|---|
| Lavender, thyme, rosemary, sage | Essential oils in the leaves | Lettuce | From germination to harvest |
| Peony, bergenia, hellebore | Tough, leathery leaves | Dahlia | The shoots in the first 3-4 weeks |
| Lamb's ears, snow-in-summer | Hairy leaves | Marigolds, zinnia | As young plants in June |
| Sedum, houseleek | Thick, waxy leaves | Hosta, lupin, delphinium | The shoots in April and May |
| Japanese anemone, astrantia, aquilegia, ornamental grasses | Rough or narrow leaves | Courgette, beans, brassicas | As seedlings |
| Foxglove, monkshood | Poisonous leaves | Basil, strawberries | All season, the berries in July |
How we do it with dahlias and lettuce in a raised bed
Dahlias are most exposed from planting out in late May until the shoots are 20-30 cm tall, roughly 3-4 weeks. During that time we pick around the plants every evening it has rained and lay a thin ring of ferric phosphate 20 cm from the stem. Once knee high, they can take the odd bite. Tubers started indoors stand taller at planting out, see the article on growing dahlias from tubers and the varieties among our dahlia tubers.
Lettuce cannot be rescued afterwards, one night is enough for a whole sowing. We fit a slug edge to the raised bed before we sow, pick slugs in the bed three evenings in a row before the edge goes on, and lay no bark mulch inside it. If you sow lettuce in batches every third week, losing one batch matters less. More on the set-up in the article on growing in a raised bed.
Four mistakes that give you more slugs next year
Starting in August: by then the slugs have already mated. Next year's population is decided in May and June.
Mulching thickly right next to the bed: mulch holds the moisture the slug needs. Leave 30 cm of bare soil around the raised bed.
Planting them in: eggs come along in the root ball of bought plants. Keep new plants apart for 2-3 weeks and look for slugs in the pot.
Relying on one method: ferric phosphate kills but does not keep them out, the slug edge keeps them out but does not kill, nematodes only take the small ones. Combine two, and always pick.
What a home gardener may use
Which slug products a home gardener may use is decided country by country, and the rules are not the same across Europe. A plant protection product has to be authorised in the country where you use it, and the label states whether it is cleared for amateur or home garden use. In Great Britain that authorisation sits with HSE, and outdoor use of metaldehyde slug pellets has been banned there since 2022, which is why the pellets on the shelf are based on ferric phosphate. In EU countries the national authority decides under Regulation (EC) No 1107/2009. Nematodes are a living biological control rather than a pesticide and are sold to home gardeners in Britain and in much of Europe, but check what applies where you live. We do not single out products, approvals change and the label decides. You will find more pests in the article on pests and diseases.
Author: Emma Vogiatzi
Fact-checked by Erik Hoekstra
Last updated 2026-10-20