Forensic entomology, a specialised branch of forensic science, uses insects present on corpses to aid in criminal investigations. This field involves analysing different species of insects typically found on cadavers, understanding their life cycles, examining their occurrence across various environments and observing how insect populations evolve throughout the decomposition process.
The earliest recorded instance of forensic entomology dates to the 13th Century documented by a Chinese lawyer and death investigator Sung Tzu in a medico-legal textbook ‘His Yuan Chilu’ (One possible translation: The washing away of wrongs). He recounts an incident of a stabbing near a rice field. The day after the murder, the investigator instructed all workers to place their sickles on the ground. Blow flies attracted by unseen trace of bloods, swarmed to one particular sickle revealing the murder weapon. The beginning of this science may be traced back to the 13th century; nonetheless, it has developed gradually throughout time and advanced with cutting-edge research.
Forensic Entomologists
Forensic Entomologists utilise their knowledge of insect bionomics to analyse insects found on cadavers and the acquired information to determine the ‘elapsed time’ since the death of a person. This involves a few crucial steps. The first is to acquire evidence. When a body is found, entomologists or crime scene investigators collect the insects found at the scene. This covers both adults and the immature phases of their life cycle, such as eggs, larvae and pupae. Samples are taken from various regions of the body as well as the surrounding environment. Additionally, it is a must to gather environmental data around the scene.
Therefore, entomologists take into account environmental factors such as temperature, humidity and weather as these influence insect growth rates. For instance, warmer temperatures speed up insect development, while cooler conditions slow it down. By considering these factors, the PMI estimation becomes more accurate.
The next step is to identify the species and their life stages. The insects found on the cadavers are identified using taxonomic keys and compared to known specimens. Different species come to a rotting body at distinct phases, making identification critical to calculate the time since the person has died.
The final stage is to analyse the collected data and to draw conclusions to determine the ‘Postmortem Interval’ or PMI. Insects have specific developmental timelines, especially in their larval stages. For example, blowflies are often among the first to colonise a body, and their larvae go through multiple instars (growth stages) before reaching maturity. By analysing the size and development stage of the larvae, entomologists can estimate how long the insects have been feeding on the body. Thereby estimations are drawn to determine the PMI.
Legal investigations
Forensic entomology can be used in a variety of ways in legal investigations other than determining the PMI, which is the most common application. This can help narrow down timeframes in criminal cases, potentially aligning with other evidence like witness testimonies or missing person reports. Interestingly, one could determine the location of death and whether a corpse has been transported. Insects are often specific to environments thus by identifying the colonising insect species, the forensic entomologist can conclude where the corpse has been. For example, some species may thrive in a forest but not in urban settings while some areas have distinct insect biota. If a body is moved after death, the presence of insect species from the original location can help investigators determine where the death has likely occurred. This can be critical in homicide cases where perpetrators try to conceal the crime.
Stage of infestation
Forensic entomology may aid in detecting neglect or abuse in certain cases. In some cases, living victims such as neglected children or elderly individuals may suffer from untreated wounds that become infested with insects. By examining the stage of infestation, entomologists can provide timelines that indicate how long a person has been neglected or abused.
Toxicological analysis
Moreover, forensic entomology can be applied on toxicological analysis. In advanced cases, forensic entomologists can analyse the contents of insect bodies for traces of drugs or toxins. This is especially useful when a body is too decomposed for traditional toxicology tests.
Insects feeding on the remains can accumulate chemicals, offering clues about whether the deceased had been exposed to certain substances before death,
While forensic entomology provides valuable information, it is not without challenges. Environmental factors such as weather, temperature and the microclimate where a body is found can significantly impact insect activity and development. Additionally, different species of insects may appear at varying times in different geographical locations, requiring entomologists to have localised knowledge of insect behaviour.
Another challenge lies in the interpretation of insect evidence. While insects can offer a time frame, the exact timing of death can be difficult to pinpoint due to variability in insect life cycles. Entomologists must use their expertise to consider multiple variables and offer estimates that can be used alongside other forensic evidence.
Forensic Entomology is a unique and invaluable tool in Forensic Science. It allows investigators to harness the natural behaviour of insects to gather crucial information about the time and circumstance of death. Though, it may seem unlikely that something as small as a blowfly could aid in solving a murder, Forensic Entomologists have demonstrated time and again the power of these tiny witnesses. As the field continues to advance, it will undoubtedly remain a key component of modern forensic investigations, helping to provide justice through the intricate study of life and death.
