Ash-black Slug

Fast Facts

Latin name: Limax cinereoniger

Notable feature: the UK’s largest slug, Ash-black Slugs can grow to 25cm long! They have a keel down their back, and a white stripe down the middle of their foot.

Conservation Status: Least Concern

Where in the UK: widespread, but only found locally on ancient woodland sites, thought to be declining.

Ash-black slug (Limax cinereoniger) © Duncan Sivell


The Ash-black Slug (Limax cinereoniger) is the UK’s largest native slug, and is in fact the largest land slug in the world; growing up to 25cm in length!  Most Ash-black Slugs are between 10 and 20cm long, but larger ones have been recorded.

Ash-black Slugs are one of the keeled slugs – they have a ridge or keel running along their back. The keel is pale in comparison to the dark grey body colour.  The mantle always lacks spots or markings but these may be present on the body and tail. with some Ash-black Slugs have thick black and grey stripes along their bodies.  If you turn an adult Ash-black Slug over you will see that the underside of the foot is dark grey with a white stripe down the middle, and the mucus is clear.

Juveniles are often different in appearance, appearing toffee-brown in colour with an all-white sole.

This nocturnal slug is only found in ancient or long-established woodlands.  On damp nights the slugs emerge to feed on fungi, lichens and algae and can be found on the woodland floor, on stumps or up trees.  During the day they hide under large pieces of dead wood.

Slugs and snails belong to a class of invertebrates call the gastropods – meaning belly-foot.  The BBC One series Wild Isles featured the Ash-black Slug in their Woodland episode in March 2023.

  • Size:  Up to 25cm
  • Life span: Up to 5 years (maturing after approximately 2 years)
  • Diet:  The Ash-black Slug feeds on fungi, lichens and algae
  • Reproduction:  The Ash-black Slug, being an hermaphrodite, can self-fertilise, but will usually mate with another slug.  Mating occurs in autumn or spring and egg-laying occurs shortly after.
  • When to see: Adult Ash-black slugs can be found all year round.
  • Population Trend: Thought to be declining.  It is common in much of its range, but mostly rare or absent in southern-most Europe.
  • Threats:  Loss of ancient woodland habitat.  Air pollution leading to loss of lichens on which it grazes.  Impacts of light pollution are no known 
  • Fun Fact: Ash-black Slugs mate suspended from vegetation and their genitalia is as long as their body!
  • Bonus Fun Fact: In the past, slugs were sometimes used as a cure for warts.  An artifact in the Pitt Rivers Museum in Oxford consists of a glass jar containing a slug impaled on a thorn, the label on the jar gives the following instructions: “Charm for Warts, Oxfordshire. Go out alone & find a large black slug. Secretly rub the underside on the warts and impale the slug on the thorn. As the slug dies the warts will go.”

How you can help: 

Buglife is working to increase awareness of invertebrates and the Ash-black Slug through specific projects and campaigns including Back from the Brink project Ancients of the Future but we need your help!

Join a recording scheme and log your finds (ie. through the Conchological Society of Great Britain & Ireland) or download the iRecord app and get recording!

If you’d like to know more about slugs and snails visit the Conchological Society website.

Do remember that we rely on donations to continue our work.  If you have searched, found and learnt about our incredible invertebrates on our website, please do consider Making a Donation, Becoming a Member or maybe even making a purchase in our shop.  For more ideas on how to support our work find out how to Get Involved.  Thank you 🕷