March 2013. Can anyone help me with an identification for these common beetles (this group are recently emerged), I think they belong to the family Lucanidae.

A member wrote, they should belong to the family of Passalidae (Bess Beetles), Scarabaeoidea, a sort of social living beetles. They live in decaying wood. The freshly emerged imagines are red-brown in colour, later becoming dark – just as your picture shows.