The slugs are hermaphroditic and have a full set of organs of both genders. They have relatively large penises which, during mating, wrap around each other in a tight spiral. They sometimes have difficulty separating afterwards. When separating seems impossible, one slug gnaws off either its own, or its partner's penis, so that separation is then possible. No replacement penis grows, and the apophallated slug adopts a purely female function from that point onward.