Arion fasciatus lives in large part of Europe in open anthropic habitats such as gardens. It is quite easily distinguishable, because it has a yellow band bellow a dark band on each side.
I have collected this slug and placed it in the terrarium (a glass) with a piece of bark. After 24 hours this slug has taken this position as is on the photo instead of trying to hide in some crevice of the bark. It was “sleeping” like this and it did not move during the the photographing, that have taken 5 minutes. That is ideal cooperation.
I do not know the length of this contracted specimen, but the extended body of this specimen is 36 mm. While this species can reach the body length up to 50 mm.