The pupa of Piophila casei, the cheese skipper.  This life stage is the intermediate stage between the active larva (maggot) and the adult fly.   In many instances, investigators overlook this stage as they mistake it as roach eggs or rat droppings.  This is actually the dried, hardened, outer skin of the third instar larva.  After the developing adult fly emerges from within, the empty shell will remain in the environment for extended periods of time.  These cases have been recovered in Egyptian mummies, Mexican tomb shafts, and in the skulls of ancient Bison.   The presence of pupa at a death scene is valuable evidence that should not be overlooked.