The role of aquatic insects in criminal investigations

Medicocriminal forensic entomology deals with arthropod involvement in events surrounding felonies, usually violent crimes such as murder, suicide and rape. Key elements in these investigations are determining the time between death and corpse discovery, which is generally referred to as the postmortem interval or PMI. Decomposition of a body submerged in an aquatic environment occurs at a rate roughly half that of decomposition in air, due to cooler temperatures and the inhibition of insect activity. Although most PMI's involve the use of terrestrial insects that colonize the body, such as Diptera and Coleoptera (e.g., blow flies, flesh flies, histerid and carrion beetles), aquatic cases may involve different groups of invertebrates, such as midges, caddisflies, crayfish, amphipods, and isopods. Generally aquatic insects are not known to be necrophagous (specifically finding and then feeding on dead tissue), as are terrestrial species. However, some aquatic insects will use submerged or floating corpses as a solid surface for attachment to facilitate feeding, whether it be filtering, feeding on periphyton, or hiding from predators. Other aquatic arthropods (e.g., crayfish) will feed extensively on human tissue. We present several case histories in which aquatic invertebrates have been used to help determine the PMI.