The use of blowfly larvae for offender identification during death investigations with non-consensual sexual contact

Forensic entomology facilitates death investigations by providing evidence into the estimation of time since death and victim identity. However, the application of entomology to identify an offender remains an under-researched area. This study replicated the circumstances of a death with non-consensual sexual contact to explore whether spermatozoa can be visualized from the external surface and crop contents of forensically relevant blowfly eggs and larvae. A sample of each immature stage of blowflies, from three piglet cadavers with a 6 mL deposit of boar semen on their surface, was recovered. Each sample was either submerged in distilled water (dH2O) and frozen at -18°C or allowed to develop to the third instar before undergoing a crop extraction technique. The samples were all subjected to a differential extraction process, isolating any present spermatozoa from the cadaver’s epithelial cells, and stained with hematoxylin and eosin. The results demonstrated that fully intact spermatozoa can be recovered from the external surface of blowfly egg masses and first instar larvae following oviposition upon a location in which semen was directly deposited. Additionally, sperm heads (with no attached flagellum) were recovered from within the crop content of laboratory-reared and feeding third instar larvae from the same cadaver. These findings demonstrate the potential use of forensically relevant blowflies within the investigation of deaths with non-consensual sexual contact.