Carrying Poecilochirus mites. The beetle is (at least according to Wikipedia) not a host, but rather a symbiote. The beetles carry the mites to carrion where they feed on fly eggs and larvae. In return, the mites may protect beetle larvae from flies either directly or by reducing competition from fly larvae.
Used this key: http://www.acadianes.ca/journal/papers/majka_jaes11-silphid.pdf to help with the determination. Would appreciate confirmation, especially since Nicrophorus vespilloides is quite similar.