History of forensic entomology

The concept of forensic entomology dates back to at least the 1300s but only in the last 30 years has it been systematically explored as a feasible source for evidence in criminal investigations. Many new techniques have been discovered and used in order to more accurately gather evidence, or possibly introduce an entire new way to look at old information. Over the years it has become more popular as case studies open doors to new ideas and techniques once though defunct, but now have proved to be invaluable in some courtroom battles. Forensic entomology not only uses arthropod biology, but it pulls from other sciences introducing fields like chemistry and genetics, exploiting their inherent synergy through the use of DNA in forensic entomology.

Notable forensic entomologists

Forensic entomology is defined as the interaction of arthropods and the judicial system. Until only recently forensic entomology has started to play more crucial roles in cases concerning murder and homicide. In history there have been several accounts of vague applications and experimentation of this science. There were many people who help lay the foundation of today’s forensic entomology. Sung Tz’u, Bergeret, Megnin and Reinhard were some of the biggest contributors to this science through there experiments and own interest about arthropods and death.

Sung Tz’u was a lawyer and death investigator in the late 13th century. He wrote a guide commonly translated the “Washing Away of Wrongs” (洗冤集錄) in 1235 A.D. This book was to be used as a guide for other investigators so they could assess the scene of the crime efficiently. In this book he depicts several cases in which he took notes on how the person died and probable causes. He goes over in detail on how to examine a corpse both before and after burial. He also explains the process of how to determine the cause of death from murder to suffocation. His detail in explaining what he saw in all his cases laid down the fundamentals for forensic entomologists. This is the first recorded account of someone in history using this science for judicial means.

Dr Bergeret d’Arbois was a hospital physician who was the first to apply forensic entomology in a case report that included an estimation of postmortem interval (PMI) in 1855. The report stated a general life cycle for insects and many assumptions about their mating habits. Yet he was the first to apply the new technique of PMI which gave the starting point to how this process is done. His main focus was not that of forensic entomology but rather using this subject more like a tool to prove his hypothesis of how the person and when the person died.

The first systematic study in forensic entomology was conducted in 1881 by Reinhard, a German medical doctor who played a vital role in the history of forensic entomology. He exhumed many bodies and progressed the knowledge of what types of species can be tied to buried bodies. Reinhard conducted his first study in east Germany, and collected many Phorid flies from this initial study. He also concluded that not all the insects living with corpses underground were associated with them, since there were 15-year-old beetles who had little direct contact with them. Reinhard's works and studies were used extensively in further forensic entomology studies.

Another important figure is Pierre Mégnin, an army veterinarian who published many articles and books on various subjects including the books Faune des Tombeaux and La Faune des Cadavres, which are considered to be among the most important forensic entomology books in history. In his second book he did revolutionary work on the the theory of predictable waves, or succession of insects on corpses. By counting how many live and dead mites were developed each 15 days, and comparing this with his initial count on the baby, he was able to estimate how long that baby was dead. In this book he asserted that exposed corpses were subject to eight successional waves whereas buried corpses were only subject to two waves. He had many great discoveries that helped shed light on the general characteristics of decaying flora and fauna. Mégnin's work and study of the larval and adult forms of insect families found in cadavers sparked the interest of future entomologists and encouraged more research in the link between arthropods and the deceased, and thereby helping create the discipline of forensic entomology.

Case studies

Case 1: The body of a female was found on June 4 alongside a road. She was partially clothed and later identified as a fourteen-year-old prostitute whose brother had reported her missing four days earlier. The cause of death was neck and head wounds. She was last seen alive with a thirty-year-old army sergeant on the morning of May 31. The accurate time of death was needed to make a substantial case against the sergeant. Estimates were made based mainly on the physical appearance of the body, but none with any scientific methodology. Samples of different insects were collected from the area around the wounds. Among these samples were maggots and adult flies. Some of the maggots were taken alive and reared into adults while others were preserved. The crime scene photographs included pictures of the surrounding area and pictures of insects on the body at the time of discovery. Many reports were looked at, including autopsy and the condition of the body when found. The climatological data was also collected from a government weather station close by. This showed what kind of weather the body was subjected to. After putting all of the evidence together, entomologists found that the first insect colonization of the body was on May 31. This showed a PMI of four days and also that the sergeant was with the victim on the day she died. He was charged with first degree murder. He later admitted to killing her with a hatchet around noon on May 31. He was sentenced to life in prison without parole. This case illustrated insects and how they affect human decomposition.

Case 2: On a small farm in south-central Indiana, a body had been thrown down a well and then completely covered with debris. The investigators did not know where this well was located but were able to find it when they observed thousands of flies hovering over a pile of tires. The decomposing remains were found at the very bottom of the well. No flies were able to get to them due to the debris, but the smell still attracted them. This case illustrates the importance of blow flies.

Case 4: Around some junk cars near Spokane, Washington, the body of a young female was found in August. The cause of death was multiple stab wounds to the neck and chest area. Blow flies were found around the wound so the eggs were collected from the wound. They showed no embryonic development in later analysis which means the eggs were probably laid less than eight hours before they were collected. The last time the victim had been seen alive was two days earlier, but if she had been killed then there would have been maggots on the wound instead of the eggs. This suggested that she had probably been murdered the night before her remains were found. An investigation later proved this fact. This case shows the importance of blow fly eggs.

Case 8: In the middle of November, police went to a house to investigate reports of a foul smell. The house was located in the southeastern U.S. The police discovered the body of a young woman in the basement in a shallow grave. The cause of death was a gunshot wound to the head. Two species of fly larvae were collected from the scene, Calliphora vicina and Synthesiomyia nudiseta. Using information known about these two species and the data collected about the climate, entomologists were able to determine that there was a PMI of 28 days from the time of discovery. With this information, investigators were able to find a suspect who later confessed to killing the young woman 28 days before her body was found. The insects proved to be the only scientifically reliable way of determining the PMI in this case. This is an example of the importance of blow fly maggots.

Case 14: In Maryland, the body of a young woman who had reportedly gone for a walk a few days earlier was discovered in a sparsely vegetated power line right of way. The body was found with partial decay and maggot masses on the chest, neck, and palms of the hands. No samples were taken and the cause of death was ruled a drug overdose. Later an entomologist reviewed the crime scene pictures and determined that there was probably some sort of wound under the maggot masses. The body was then exhumed and examined by forensic anthropologists who found evidence of stab wounds. The cause of death was then changed to a homicide. This also illustrates the importance of blow fly maggots.

Case 16: The badly decomposed body of a partially clad woman was found in a landfill in suburban Maryland. This area was vegetated with only short grass which gave the body no protection from the sun. The skeletized skull showed evidence of a blunt trauma. The neck and chest were also completely skeletized. Maggots were taken from the soil beneath the remains, which were later identified as Phormia regina, black blow flies. It was also later discovered that only Phaenicia sericata, green bottle flies, were usually found at this particular landfill. This led investigators to believe the body had begun decomposition in a shaded place, been colonized by the black blowflies, and then dumped at the landfill. Investigators later estimated that the woman had been murdered, put in a truck trailer for a few days, and then dumped when the smell got to be too much. This conclusion was reached because she was identified as a prostitute who usually did her business with truck drivers. This is one more case illustrating the importance of blow fly maggots.

Case 17: Unidentified skeletal remains were found by a highway in Indiana. It was mid-July and the person had been wearing many layers of clothing suggesting it was colder the last time that person was alive. It was determined that the decedent had died of natural causes but he still needed to be identified. To accomplish this, a search of the missing persons reports was started from the time period of March 15 – May 15. This time period was established due to the condition of the remains. This would have taken quite awhile, so an analysis was done of the insect and climatological data collected. The presence of Phormia regina puparia suggested that the body was not exposed for more than 35 days. The forensic entomologist concluded that the person had died 30 days before the remains were found after completing the analysis. The remains were finally identified as a hitchhiker that was last seen alive 31 days before the discovery. The entomological data provided a more accurate time which made identification easier. This is an example of the importance of blow fly puparia.

Case 21: In an oak and maple wooded area of the Cumberland Mountains, the skeletal remains of a young girl were discovered on January 29. A mostly empty wasp nest with about 100 cells was recovered from the cranial cavity. This nest showed that a colony of Polistes wasps had built and occupied the cranium during the previous summer. These wasps most likely were searching for possible nest sites in mid-April and they would need a protected, dry place for the nest. This means that the inside of the skull would have had to be cleaned out by early spring of the year before. One sphaerocerid, which usually invade during full bloat, puparial case was also found in the skull. This is a second wave fly which shows that normal faunal succession happened in the warm season. With all the entomological evidence it was concluded that the PMI was about 18 months. This PMI was supported by two other forensic methods as well. When the remains were identified it was also discovered that she had gone missing two years earlier in February. This illustrated the importance of other insects in forensic entomology.

Case 22: A few years ago, in Chicago, a woman was attacked and raped by a man in a ski mask. A suspect’s ski mask was seized and the cockleburs in it were analyzed. The suspect said he had not worn the mask since winter. The cockleburs contained small caterpillars which had a one year life cycle. The moths lay their eggs during early summer, the caterpillars then develop in the cocklebur, pupate during the winter and then become adults and break out the following summer. Due to the larvae still in the cockleburs, it was concluded that they had attached to the mask in the early to mid summer, around the same time as the rape. The suspect later confessed. This is another example of the importance of other insects.

Case 24: Some young children brought into a hospital for diaper rash, malnutrition, and general neglect also proved to have maggots around the anal and genital areas. Analysis of the maggots by a forensic entomologist proved that they had been on the children for 4-5 days. This data showed how long the children had been neglected and it was the only evidence that provided an accurate length of neglect in the case. The use of entomological data has been used in many neglect cases, like this one, and ones dealing with sick or elderly people. The data has proved to be extremely useful in these cases. This is an example of forensic entomology in cases of abuse and neglect.

Advances in forensic entomology

There are many techniques currently being developed to differentiate between the various species of forensically important insects. A study in 2007 demonstrates a technique that can use scanning electron microscopy to identify key morphological features of eggs and maggots. Some of the morphological differences that can help identify the different species are the presence/absence of anastomosis, the presence/absence of holes, and the shape and length of the median area. The ability to use these morphological differences gives forensic entomologists a powerful tool that can help with estimating a post mortem interval and with other relevant information.

In 2001, a method was devised by Jeffery Wells and Felix Sperling to use mitochondrial DNA to differentiate between different species of the subfamily Chrysomyinae. This is particularly useful when working on determining the identity of specimens that do not have distinctive morphological characteristics at certain life stages.

A valuable tool that is becoming very common in the training of forensic entomologists is the use of mock crime scenes with pig carcasses. The pig carcass represents a human body and can be used to illustrate various environmental effects on both arthropod succession and the estimate of the post mortem interval.

Usually fly larvae are used to aid in the determination of a PMI. However, sometimes the body may not contain maggots and only the eggs are present. In order for the data to be useful the eggs must be identified down to a species level to get an accurate estimate for the PMI. There is more than one way to identify a fly egg by visual means. One method is called the scanning electron microscopic method (SEM). The SEM method provides an array of morphological features for use in identifying fly eggs; but, this method does have some disadvantages. The main one is that it requires expensive equipment and can take time to identify so it may not be useful in a field study or to quickly identify a particular egg. This method is good if you have ample time and resources to determine the species of the particular fly egg. Sometimes that option is not viable, and a quicker and lower cost technique can be found in potassium permanganate staining. This process involves a few basic steps. Once the eggs intended to be stained are collected, they are rinsed with a normal saline solution and then moved to a glass petri dish. The eggs are then soaked in a 1% potassium permanganate solution for one minute. Then the eggs were dehydrated and mounted onto a slide for observation. These slides can be used with any light microscope with a calibrated eyepiece to compare various morphological features. The most important and useful features observed for identifying eggs are things like the size, length, and width of the plastron, as well as the morphology of the plastron in the area around the micropyle. The various measurements and observations are then compared to standards for forensically important species and used to determine the species of the egg.

Although physical characteristics and sizes at various instars have been used to estimate fly age, more recently a study has been conducted to determine the age of an egg based on the expression of particular genes. This is particularly useful in developmental stages that do not change in size, such as the egg or pupa, where only a general time interval can be estimated based on the duration of the particular developmental stage. This is done by breaking the stages down into smaller units separated by predictable changed in gene expression. Three genes were measured in an experiment with Drosophila melanogaster: bicoid (bcd), slalom (sll), and chitin synthase (cs). These three genes were used because they are likely to be in varied levels during different times of the egg development process. These genes all share a linear relationship in regards to age of the egg; that is, the older the egg is the more of the particular gene is expressed. However, all the genes are expressed in varying amounts. Different genes on different loci would need to be selected for another fly species. The genes expressions are mapped in a control sample to formulate a developmental chart of the gene expression at certain time intervals. This chart can then be compared to the measured values of gene expression to accurately predict the age of an egg to within two hours with a high confidence level. Even though this technique can be used to estimate the age of an egg, the feasibility and legal acceptance of this must be considered for it to be a widely utilized forensic technique. One benefit of this would be that it is like other DNA-based techniques so most labs would be equipped to conduct similar experiments without requiring new capital investment. This style of age determination is in the process of being used to more accurately find the age of the instars and pupa, however, it is much more complicated as there are more genes being expressed during these stages. The hope is that through this, and other techniques similar to it, a more accurate PMI can be obtained.

Conclusion

Forensic entomology is still relatively a young science, but its importance has appreciated with time. In large part due to research, an improved systematic approach, and improved techniques, Forensic entomology is now a powerful discipline that's used more widely to effectively measure postmortem interval. Forensic entomology, in many cases, proves useful when needed and many cases and research findings each year help improve our knowledge of this exciting field.