A human cadaver is an attractive breeding habitat for necrophagous insects and for those species that are predators of necrophages. One of the important tasks of forensic entomologists is to provide a reliable list of species associated with decomposing bodies both in the adult and larval stages. We present here a case of a human cadaver discovered in Central Sweden and the insect fauna associated with it. This is the first report of Hydrotaea similis larvae developing in a dead human body. The larvae of H. similis have only recently been studied and, therefore, even if previously they had been collected during forensic casework or experiments, the larvae could not have been properly identified, except if reared to the adult stage. To facilitate future studies and casework, detailed descriptions are provided here of the morphology of third instar larvae of both H. dentipes and H. similis using combined SEM and light microscopy techniques. We describe characters that allow for easy species identification and discrimination of these two forensically important and closely related species.