The Red Slug (Arion rufus), also known as the large red slug, chocolate arion, and European red slug, is a species of land slug in the family Arionidae, the roundback slugs.
They are widespread in their native range throughout western Europe, but have recently been found in parts of North America where they are considered to be invasive pests. In certain parts of their native range, however, red slugs have declined dramatically over the last few decades due to replacement by the externally similar Spanish slug (Arion vulgaris).
Red slugs have a respiratory pore in the front part of the mantle that allows them to breathe air without having to soak up water. The body color is often reddish, but orange, yellowish, brown and grayish forms are also usual, and some individuals may be black. The foot fringe is vertically striped and is often a different color than the back. The head and tentacles are usually darker than the rest of the body.
It is familiar from gardens and parks as well as disturbed agricultural landscapes, but also from a diversity of natural habitats including woodland, meadows, margins of water bodies, coastal habitat, and moorland. When resting, red slugs will contract into a hemispherical shape. When disturbed, it performs a rocking motion, sometimes for several minutes. Although predominantly nocturnal, rain brings it out during daylight. Red slugs are omnivorous and will generally eat whatever kind of plant matter it comes across, but will also eat invertebrates smaller than itself including insects, worms, and other slugs.