24 May 2022

Kildare's Wildlife Watch: Spotting the foul-tasting Great Black Slug

With the Irish Peatland Conservation Council

Kildare's Wildlife Watch: Spotting the foul-tasting Great Black Slug

The Great Black Slug

While reviewing the articles I have written over the past number of years, I was surprised to discover I don’t seem to have ever written about the Great Black Slug (Slug Mór Dubh as Gaeilge).

Although I cannot be sure, it is the size of this slug, that can reach 18cm at maturity, is possibly where it gets its name from!

As its name also suggests, this slug is black and is mostly nocturnal, sheltering during the day to avoid drying out.

It can be found in a variety of habitats, but I have mostly recorded in on boglands. Interestingly, you will never find a snail on a bog. Snails make their protective outer hard shell from calcium but as bogs are extremely nutrient poor, there are no nutrients available for snails to build their shells. Nutrients are missing on bogs because the agents of decay, bacteria and fungi, cannot live in the waterlogged conditions, as there is no oxygen present.

The Great Black Slug is an omnivore, feeding on both carrion (the flesh of dead animals) and fresh and rotting vegetation.

With no legs, this slug moves using the contraction and extension of one muscular foot. The body is covered in mucus which supports them in slowly moving across surfaces.

It is said that the mucus on the body of the Great Black Slug is particularly foul to the taste, and therefore it can be considered a defensive mechanism to deter predators. However, on boglands foxes will happily feed on the Great Black Slug as will hedgehogs and frogs in our gardens.

The Great Black Slug is hermaphrodite, meaning they can self-fertilise. Once the white eggs hatch, the young slug varies in colour from brown, black and even orange. The Great Black Slug can be seen from spring through to autumn, and as it is most active in wet weather, you may find this species in your community this week.

Get in touch

Don’t forget, if you come across a wildlife species that you would like help identifying I would be happy to help. Contact me at

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