How to Identify the Bad Slugs

Britain is home to around 30 species of slug, and the good news is that only four are troublesome in the garden. The bad news is that those four are the most prolific! Knowing your enemy and its habits is vital when formulating your attack and defence plans.

Garden Slug  (Arion hortensis Agg.)

The Garden Slug

Garden Slug  (Arion hortensis)

The Garden Slug is the smallest of our nuisance slugs, typically reaching no more than 3cm (1¼”) in length. However, it makes up for its small size by its voracious appetite. It’s a small blackish creature with a pale side stripe and, like all Arion species, is characterised by its rounded cross section. The sole is yellow or orange, as is the mucus.

This slug attacks from all angles. At ground level it chomps its way through the stems of tender young plants and devours the leaves of vegetables such as lettuce. It climbs to munch the higher leaves, and also the hearts of cauliflowers. Still not content, it burrows deep beneath the soil, attacking root crops such as the potato, carrot and beetroot, and even flowering bulbs.

Field Slug  (Derocereas reticulatum)

The Field Slug

Field Slug  (Derocereas reticulatum)

The Field Slug is another small slug, growing up to 4cm (1½”) in length. It’s lighter coloured than the Garden Slug, usually grey or fawn with dark speckles. It has a whitish sole and a short ‘keel’, or ridge, on the back of the tail end.

The Field Slug only feeds on the surface but will virulently munch its way through most vegetation, and is often found nestling among the leaves of lettuces and cabbages.

Of all the common garden slugs, the Field Slug probably causes most damage.

Keel Slug  (Tandonia budapestensis)

The Keel Slug

Keel Slug (Tandonia budapestensis)

The Keel Slug, as its name suggests, has a keel, with a yellow or orange stripe along the ridge. This is a larger slug, up to 6cm (2½”) long and dark grey or olive in colour. When contracted, the Keel Slug often curls into a ‘sickle’ shape.

This species is less commonly seen, but that’s only because it’s a burrowing specialist. Spending much of its time underground, the Keel Slug attacks most root crops, with potatoes being a particular favourite. Other root tubers and flowering bulbs are also on the menu.

Ever wondered what happened to all those tulip bulbs?

Black Slug  (Arion ater)

The Black Slug

Black Slug  (Arion ater)

The Black Slug is the ‘grand-daddy’ of garden slugs, reaching lengths of 20cm (8”), although up to 13cm (5”) is more typical. The skin is coarse and granular and the sole is pale, often fringed with orange.

Due to its huge size the Black Slug often accepts the blame for most garden carnage, but actually its three smaller cousins wreak the most havoc.

The Black Slug prefers a diet of rotting vegetation, fungi, manure, and even the odd decomposing dead animal. Only during springtime when these aren’t so abundant, and tender young seedlings are, does it cause most damage in the garden.

So remember the old saying:
  If it’s black, put it back.
  If it’s grey, keep it at bay.

When disturbed, the Black Slug contracts itself into a slimy hemispherical hump, making itself difficult to be pecked up by a hungry bird. It sometimes rocks from side to side; thought to be an attempt to confuse its predator.

Red Slug  (Arion rufus)

The Red Slug

Red Slug  (Arion rufus)

Despite the name, black slugs come in varying colours ranging from red and orange to brown, grey, and even white. The lighter colours are most common in the south, possibly being more efficient at reflecting the heat of the sun. The brown forms are often the younger slugs, becoming darker with maturity.

The orange and red forms have been considered a separate species – the Red Slug – but this classification is debatable.

The Little Book of Slugs

The Little Book of Slugs: book cover

The Little Book of Slugs

Want to learn more about the slugs in your garden?

Then I think you’ll like The Little Book of Slugs by Allan Shepherd & Suzanne Galant, with its mix of zany humour and sound practical advice.

  • Know your enemy; even the slug has its Achilles Heel.
  • Tired of fighting? Grow plants that slugs won’t eat.
  • Over 70 ways to combat slugs without using chemical pellets.

The Little Book of Slugs
Find out more

More books about slugs

What do you want to do now

  • So many slugs
    Why Britain is the slug capital of the world.
  • Banishing slugs
    Banishing slugs involves one of three basic approaches.
  • Nematodes
    Learn about these naturally occurring slug parasites.

Did you

Research has shown that the average UK garden has a population of over 20,000 slugs and snails

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