Last nite my son and I did slug watching in our backyard. Even though it was dry, there were many slugs out. Among those we saw were a Limax maximus and a Deroceras reticulatum (and several ants) eating a dead earthworm. When we first arrived at the scene, a large Arion subfuscus was also approaching. After I moved some grass blades out of the way, L. maximus and D. reticulatum got disturbed and left. But A. subfuscus stayed and started eating the worm ignoring the ants and us. Actually, the ants didn't seem to be bothering the slug.
A. subfuscus, Limax maximus and a Deroceras reticulatum are all European slugs introduced into the U.S. Although they are generally known to be plant-eaters, they won't pass an opportunity to eat dead worms, insects and even larger animals.