Durham Slug - Arion flagellus


60-100mm. Often greenish but can range from yellow to black. Usually larger than the similar A. subfuscus, it is also distinguished by its colourless mucous (orange in A. subfuscus) and the large tubercles on its back (only 6-9 rows between the dark bands behind the mantle). The crests of the tubercles are often pointed and may also be highlighted yellow. The sole is nearly always paler than the body and generally has a greenish tint. The foot fringe doesn't contrast with the body colour and the lineations don't extend very far across the sole.

Similar Species

Juveniles look similar to the Dusky Slug, Arion subfuscus, but can be distinguished by the coarse tubercles and dark head and tubercles. The Dusky Slug has particularly fine tubercles.

Identification difficulty
ID guidance
  • large, often pointed tubercles
  • clear mucus
  • pale, sometimes green tinted sole
  • usually dark head and tentacles
Recording advice

Unless identified by a recognised expert, a photo is required. If the photo doesn't show the key ID features then in the comments box describe the size and identifying characters you have observed.


Disturbed habitats, wasteground, roadsides and gardens.

UK Status

Widespread but patchily distributed and probably under-recorded, most records coming from the western half of Britain.

VC55 Status

Uncommon in Leicestershire and Rutland.

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Leicestershire & Rutland Map


Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015

UK Map