Limax maximus

Limax maximus (literally, "biggest slug"), known by the common names great grey slug and leopard slug, is a species of slug in the family Limacidae, the keeled slugs. It is among the largest keeled slugs, Limax cinereoniger being the largest. Limax maximus is the type species of the genus Limax. The adult slug measures 10 C20 cm (3.9 C7.9 in) in length and is generally a light grey or grey-brown with darker spots and blotches, although the coloration and exact patterning of the body of this slug species is quite variable. This species has a very unusual and distinctive mating method, where the pair of slugs use a thick thread of mucus to hang suspended in the air from a tree branch or other structure. Although native to Europe, this species has been accidentally introduced to many other parts of the world. It was first discovered outside its native range in Philadelphia, USA in 1867.

from Wikipedia