Every fan of Grissom on CSI knows that the insects present around a dead body provide clues about the time of death and location of the crime scene, especially if the body was moved. That’s because insects and other decomposers show up in a very strict succession. Blowflies, for example, can hone in on a corpse and lay eggs within minutes, and by examining the developmental stages of larvae and pupae, forensic entomologists can build a timeline. While their presence is key, the physical marks they leave behind on the cadavers are just as important to the investigation, influencing the interpretation of events related to the person’s death. In two studies published this month in the Journal of Medical Entomology, researchers studying decomposition ecology describe rare and never-before-seen interactions between cadavers and naturally-occurring arthropods.
At the Forensic Anthropology Center at Texas State, Jennifer Pechal of Michigan State and colleagues stumbled on two unusual post-mortem activities: A katydid (Pediodectes haldemani, also known as a bush cricket) and a pill bug (Armadillidium cf. vulgare, also known a roly poly or woodlouse) feeding on the remains of a 153-kilogram Caucasian male who was placed nude and supine in the field on May 22, 2012. The gravid female katydid (possibly looking for an extra source of protein) was found feeding on the right forearm on May 24, leaving behind an opening that was later exploited by fire ants. The roly poly was found on the left forearm on May 25. Human cadaver-eating has never been documented for these two critters before (though this roly poly species has been found feeding on rat carcasses).
Because tissue injuries could be interpreted as trauma from before or around the time of death, the small marks created by the two critters post-mortem could be misinterpreted as drug abuse, defense wounds, or even torture, Science explains.
During a yearlong survey at the Southeast Texas Applied Forensic Science facility, another team led by Natalie Lindgren from Sam Houston State University observed four insect-cadaver interactions that were either never or poorly documented until now. They found Eristalis arbustorum rattail maggots on a 76-year-old male placed face down under 60 centimeters of soil near a stream. This is the first record of the species colonizing human remains. After the cadaver was removed from the shallow, water-filled grave, eight moth flies (Psychoda alternate) were found mating and laying eggs in it. Though rare, their presence in decomposition studies have been documented before, and they typically indicate that the body was either buried or deposited in an aquatic or wet habitat.
They also found scorpionflies (Panorpa nuptialis) on the cadaver of a 77-year-old male (pictured above). Not only have they never been observed on human cadavers before (they're predators of bugs thought to be harmless to humans, Washington Post explains), they were also the first to arrive, within just 20 minutes. Discovering new early-arrivers is important for entomologists relying on insect succession to determine portions of the postmortem interval.
Finally, in perhaps the most graphic of the case studies, the team saw a noctuid caterpillar (Spodoptera latifascia) chewing and ingesting dried skin near the toenail of a 66-year-old male (pictured below). “Roaches, ants, crayfish, starfish, bees, and wasps all leave characteristic markings as a result of their scavenging behavior,” North American Forensic Entomology Association’s Jason Byrd explains in a news release. “Knowledge that a noctuid is an opportunistic scavenger will be beneficial to entomologists because the pattern of scavenging is likely different than that of other insects, and it should not be accidentally attributed to a pattern injury from a human perpetrator."
Images: Entomological Society of America