Species: Ariolimax columbianus 

Common name: Banana slug
Family: Ariolimacidae 

One of the largest slugs in the world, banana slugs are an iconic species for the Pacific Northwest. They come in a variety of colors: yellow, green, gray, reddish brown, and even white. All forms are found with and without spots. 
Origin: Pacific Northwest
Diet: Dead plant material and fungi.
Behavior: Known for gnawing their mate’s penis off after mating.
Where in Oregon: West side of the Cascades to the coast, and Umatilla county.
Similar exotics to look for: None