the leopard slug is a species of slug in the family Limacidae, the keeled slugs. It is one of the largest keeled slugs, Limax cinereoniger being the largest. the scientific name, Limax maximus, means biggest slug, although it is not the biggest. The leopard slug 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 branch.