The European slug Arion subfuscus comes in different shades of brown, yellow and sometimes even red.
Pilsbry1 gives the location of the first U.S. record of A. subfuscus as Boston and the date as “Before December, 1841”. In gardens, abandoned fields and along the edges of second-growth forests in the northeast U.S., it is now one of the most common introduced slugs, along with Limax maximus, Deroceras reticulatum and Arion intermedius. Unlike Limax and Deroceras, however, both A. subfuscus and A. intermedius penetrate deeper into the woods.
These slugs constitute a part of what is called the “naturalized” fauna of the U.S. Unfortunately, they are here to stay.
1. Pilsbry, H.A. 1948. Land Mollusca of North America (north of Mexico ). Volume 2, part 2, p. 670. Academy of Natural Sciences, Philadelphia.