Postmortem injuries caused by the freshwater crayfish Procambarus clarkii

The feeding activity of animals can affect the decomposition of human cadavers because of tissue laceration and consumption. Nonetheless postmortem animals' activity may cause considerable damage to the body, producing perimortem wounds' modification that could lead to an incorrect assessment of the PMI or a wrong cause of death. Moreover, evaluation of aquatic arthropods activity can be useful in estimating the PMSI (Post Mortem Submersion Interval). Procambarus clarkii (Girard, 1852) is a freshwater crayfish native of south-eastern USA, present in Europe with invasive populations, that are found also in Northern Italy. Previous experiments assessed the influence of the crayfish in the decomposition of animal carcasses in a freshwater system. The aim of this study was to investigate the role of P. clarkii as a carrion-feeder, studying the type and outline of the wounds caused by the crayfish's feeding activity on the carcasses. Two experiments were performed in Nonantola (MO), Northern Italy (both during summer, one in July and one in August). Five pig carcasses (Sus scrofa) enclosed in lobster pots were placed inside an artificial freshwater dew pond. For each carcass the number of feeding P. clarkii, together with the type and size of lesion was carefully recorded following a fixed sampling protocol, together with water level and meteorological data. Results show that in both the experiments, the Crustaceans attacked the carcasses a few hours after their positioning, starting to damage the external epidermal layer with lacerations up to 4cm, generally ascribable to round shape wounds. In the following days, the crayfishes continued their activity, increasing the percentage of damaged skin until the full laceration of the dermal layer. From that moment, the feeding activity continued mostly in the internal part of the carcass, with the attack of the internal organs, until the flesh was completely eaten and only bones remained. The study of post mortem injuries could be very important in real cases of dead bodies recovered in freshwater systems, because the typical shape of the wounds caused by the Crustaceans could be confused for sharp force injuries and lead to a wrong report on the causes of death