Seems like dermestid larvae (the adults are tiny beetles) like chocolate. I guess this chocolate bar was part of a long-forgotten bag of Halloween treats. Dermestids are scavengers, they'll feed on any dry plant or animal material; grain, flour or even skin. (*warning* Don't click previous link if you have a weak stomach.) I knew that some Beatles liked chocolate (i.e., Savoy truffle); however, I didn't know that beetles do too.