British distribution: Widespread but rather local.
A large slug, reaching 10 to 20 cm when extended, with distinctive black spots on the mantle, and black spots or stripes running the length of the body. It is a limacid slug (i.e. member of the family Limacidae), with a small calcareous shell enclosed by the mantle. The posterior end of the body has a pronounced dorsal keel.
The mating ritual in this species is reportedly quite remarkable, with coupling taking place while the two intertwined individuals are hanging by a mucus string from a branch or other aerial structure.
Photograph: the author's garden, Paisley, Renfrewshire, 1983.