Well I have no data on Deroceras reticulatum except the damages it causes in agriculture, but Deroceras laeve is a parent species which can be found in the same environments.
Cosmocercoides dukae is a nematod which is parasitic in the slug D. laeve when young, and in the salamander Ambystoma laterale as an adult.
A similar, but different, species can be found in some toads.