Forensic Entomology and the Death Scene
The dead can no longer speak for themselves. It is the job of the crime scene investigator to identify, document, collect, and preserve evidence of crimes that speak for the crime victim. In many cases, nature provides that evidence for investigators. Upon death, the body of the deceased immediately experiences physiological changes and begins the decomposition process. As the body decomposes, a common and predictable sequence of insects inhabit the body; this process is known as insect succession. Insects such as flies, wasps, beetles, and ants quickly attack the body if the deceased is not in a secure environment. Forensic entomologists identify insects from the crime scene, using accumulated degree hours (ADH) to estimate an approximate time of death. The ADH information allows forensic entomologists to estimate the time involved in developing the current stages of insect succession, in accordance with local conditions. It is the predictable pattern of insect succession occurring on the body that reveals the time of the first colonization of insects on the body.
The approximate time of death, or postmortem interval (PMI), can be critical to crime scene investigations in corroborating and refuting alibis of suspects and persons of interest, and to assist investigators in reconstructing the crime. These PMIs are the time between when the body was discovered and the time of death. PMI's can be used to identify locations of crimes or link suspects to crimes or crime scenes. Insects can reveal injury sites on victims, whether the victim was moved from one place to another, and whether victims were under the influence of drugs or other toxins. The most common insects involved in postmortem interval decision-making are Blow Flies or Necrophagous Flies (Diptera: Calliphoridae).
Within minutes of death, these blow flies can detect odors emitted from the body a mile away from the deceased. Gases released from the body, such as putrescine and cadaverine, alert these insects to a suitable location to lay their eggs. Eggs are deposited in clusters in moist and open areas of the body, such as eyes, ears, mouth, nose, private areas, and areas where wounds are present. The presence of flies, eggs, and larvae brings other carrion insects to the corpse in the succession process. The fly eggs then develop onto larvae, with various stages of larval development occurring until the larvae become flies. Fly larvae progress through three instar stages of growth, before entering the pupating stage, where the larvae appears enclosed in a cocoon-type structure. The fly later emerges from this pupa shell, completing the process of egg to fly. This progression for Blow Fly evidence and other carrion insect activity is what forensic entomologists use to make PMI determinations. In turn, the PMI determinations help investigators reconstruct the crime. Collecting flies, larvae in various stages, pupa casings, and other carrion insects provide a timeframe for forensic entomologists. This is a basic explanation of the entire process.
I once received a call from an acquaintance describing a problem he was experiencing with maggots around a dumpster. He advised of millions of maggots in the dumpster and a trail of maggots leading away from the dumpster. I asked him what the contents of the container were. He advised there were many packages of meat disposed of due to the product being outdated or having compromised packaging. My explanation was simple. The meat products were disposed of on a hot summer day. The blow flies identified the meat as a source for the deposit of eggs. The meat sources would be beneficial for the development and nourishment of fly larvae. The following day, these eggs became larvae and progressed through the three instar stages, before leaving the feeding source. In this stage, larvae will make their way to a safe area to pupate, and eventually emerge as flies. In the case example, the maggots leaving the dumpster area simply sought refuge for the pupating stage.
Another personal experience involved an actual death scene. A law enforcement agency employee who once approached me about a scene he had just processed possessed no real understanding of the importance of entomological evidence. He was filling in for a crime scene investigator off on vacation. The person advised me of a death scene he processed involving a severely decomposed body. He informed me of a large amount of flies, fly larvae, and other insects inhabiting the body of the deceased in describing the scene. I asked him what entomological evidence he collected during scene processing, and he advised none. I reminded him that every death scene should be treated as a homicide until evidence dictates otherwise. I also advised him that my philosophy on evidence was that I would rather have evidence and not need it, than need it and not have it; there is only one opportunity to collect evidence.
He not only failed to collect this important entomological evidence that may have been needed later in the investigation to determine PMI, but also didn't have a forensic entomology kit on his crime scene vehicle. This was a clear example of nature providing critical evidence associated with a possible crime, and that evidence not being recognized and collected. This employee was not a qualified CSI, and had no formal education and specialized training in crime scene investigations and forensics, but was allowed to process crime scenes. Nature often provides evidence, CSIs must have the knowledge and expertise to take advantage of this opportunity.
Forensic entomology has been widely accepted in recent years. Research supporting forensic entomology as a science between 2001 and 2021 grew significantly, as publications increased from less than 100 to nearly 1,400 (Charabidze & Martín-Vega, 2021). Dr. Edmond Locard, director of the world's first forensic laboratory in Lyon, France, revealed how every contact leaves a trace. Meaning that as people come into contact with other people and crime scenes, there is a transfer of materials. These materials are considered evidence, and it is critical that all evidence be identified and collected. In many cases, it is unknown at the scene how significant a specific item of evidence will be later in the investigation. It is imperative that all evidence is identified and collected. Often times evidence associated with crimes comes from nature, and this evidence can play an important role in informing investigations. This entomological evidence provided by nature often speaks for the dead.
Dr. Richard English
Sources:
Charabidze, D., & Martín-Vega, D. (2021). Looking back to move forward: How review articles could boost forensic entomology. Insects, 12(7), 648.
Saferstein, R. (2007). Criminalistics: An introduction to forensic science. (9th ed.). Pearson Prentice Hall.
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