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.

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.

• large, often pointed tubercles
• clear mucus
• pale, sometimes green tinted sole
• usually dark head and tentacles
• sole almost round when contracted

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.

All year but harder to find in the warmer months.

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

Uncommon in Leicestershire and Rutland but thought to be expanding.