Body colonization and degradation in a freshwater system: the role of the crayfish Procambarus clarkii

The study of decay in freshwater systems is important for the estimation of the mPMI, the PMSI and the manner of death. In previous experiments, the importance of Procambarus clarkii in the consumption of dead bodies in freshwater was assessed. The present study aimed at characterizing the role of P. clarkii in the decomposition of carcasses by studying the population dynamics in relation to the decomposition stage and the wounds caused by the crayfish's feeding activity. The study was conducted in Nonantola, Northern Italy, and consisted in two experiments, one in July, and one in August-September. Five pig carcasses enclosed in lobster pots were placed inside a freshwater dew pond. The number of P.clarkii detected on each carcass was recorded following a fixed sampling protocol, together with the type and outline of the wounds caused by the crayfish's feeding activity, and meteorological data. Results show that 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. The initial day corresponded with the first peak in P. clarkii population with up to 100 specimens detected in each lobster pot. In the following days, the crayfishes continued their activity, increasing the percentage of damaged skin, until the full laceration of the dermal layer. The second peak in crayfish's population occurred at end of the floating decay stage, with the carcass lying on the pond's bottom. From that moment, the feeding activity continued in the internal part of the carcass, until the flesh was completely consumed. This study shows that the feeding activity of P.clarkii is crucial in the dismemberment of bodies in freshwater, and the importance in the forensic field is on two main points. First, by detecting differences in the colonization in relation to the position in the water column, these results are useful for the estimation of the mPMI interval; second, it emerged that the typical shape of the wounds made by the Crustaceans could be confused for sharp force injuries which could lead to a wrong report on the causes of death