Animal Diversity Web, University of Michigan: "Arion subfuscus is native to the Paleartic and has been introduced to northeastern North America, where it ranges from eastern Canada to South Carolina, and as far west as Indiana." In Europe it is represented by two subspecies that are difficult to distinguish, so it is best treated as a complex subfuscus/fuscus. Found on false nettle Boehmeria cylindrica. In Europe it feeds on anything organic, mostly on soil surface, but has been also observed on tree trunks as high as 6 ft from ground.