Hidden in the shadows of the UK’s ancient woodlands lives one of the most extraordinary members of our native fauna. The ash-black slug (Limax cinereoniger) is not only Britain’s largest slug, but also one of the biggest land slugs in the world.
This nocturnal gastropod can reach an impressive 30cm in length, yet remains largely unseen due to its secretive habits and forest-floor camouflage.
How big is the ash-black slug?
Most adult ash-black slugs measure between 10cm and 20cm, though some have been recorded reaching up to 30cm – making them one of the biggest land slugs in the world.
What do ash-black slugs look like?
Juvenile ash-black slugs are typically a warm toffee-brown, gradually darkening as they mature into their characteristic black or charcoal-grey colouring. A distinct white or yellowish ridge, called a keel, runs down at least half the length of the adult’s back. They also feature spotted grey tentacles and a pale stripe along the foot, making them easier to identify – if you’re lucky enough to spot one.
Where can ash-black slugs be found?
These slugs are distributed across parts of the UK but are restricted to ancient woodland habitats, where they live among leaf litter and decaying logs. Unfortunately, such environments are increasingly threatened, and so sightings of ash-black slugs are becoming rarer. Air pollution is also a concern, as it affects the lichens they often rely on for food.
What do they eat?
Ash-black slugs feed on a mix of lichens, fungi and algae, foraging across the forest floor at night.
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How do ash-black slugs reproduce?
Ash-black slugs are hermaphrodites, meaning each individual possesses both male and female reproductive organs. While they are capable of self-fertilisation, they usually seek out a partner to exchange sperm.
Mating is a spectacle in itself: the slugs ascend trees and dangle from a mucus thread, entwining corkscrew-shaped penises – as long as their bodies – to exchange sperm. The process of these slugs having sex is one of the most elaborate and unusual mating rituals in the animal kingdom.
Breeding takes place in spring or autumn, with eggs laid in moist soil or under leaf litter. Juveniles typically emerge between October and May.
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Top image credit: Getty Images