Forensic footwear evidence
Questioned document examination
Forensic materials engineering
Forensic polymer engineering
Vehicular accident reconstruction
|Auguste Ambroise Tardieu
William M. Bass
Use of DNA in forensic entomology
Forensic entomology is the application and study of insect and other arthropod biology to criminal matters. Forensic entomology is primarily associated with death investigations; however, it may also be used to detect drugs and poisons, determine the location of an incident, detect the length of a period of neglect in the elderly or children, and find the presence and time of the infliction of wounds. Forensic entomology can be divided into three subfields: urban, stored-product and medico-legal/medico-criminal entomology.
Historically there have been several accounts of vague applications for and experimentation with forensic entomology. The concept of forensic entomology dates back to at least the 1300s. However, only in the last 30 years has forensic entomology been systematically explored as a feasible source for evidence in criminal investigations. Through their own experiments and own interest in arthropods and death many people have helped to lay the foundations for today's modern forensic entomology, these include Song Ci, Francesco Redi, Bergeret d’Arbois, Jean Pierre Mégnin and the German doctor Hermann Reinhard.
Song Ci (also known as Sung Tz’u), was a lawyer and death investigator who lived in China in the late 13th century. In 1247 A.D. Song Ci wrote a book entitled 洗冤集錄 (commonly translated to “Washing Away of Wrongs”). In this book Song Ci depicts several cases in which he took notes on how a person died and elaborates on probable causes. He goes into detail on how to examine a corpse both before and after burial. He also explains the process of how to determine a probable cause of death. The purpose of this book was to be used as a guide for other investigators so they could assess the scene of the crime effectively. His level of detail in explaining what he observed in all his cases laid down the fundamentals for modern forensic entomologists and is the first recorded account in history of someone using forensic entomology for judicial means. This book was immensely popular and represented the first time that the general public became aware that insects could be used in criminal investigations.
In 1668, Italian physician Francesco Redi disproved the theory of "spontaneous generation", or abiogenesis. The accepted theory of Redi's day claimed that maggots developed spontaneously from rotting meat. In an experiment, he used samples of rotting meat that were either fully exposed to the air, partially exposed to the air, or not exposed to air at all. Redi showed that both fully and partially exposed rotting meat developed fly maggots, whereas rotting meat that was not exposed to air did not develop maggots. This discovery completely changed the way people viewed the decomposition of organisms and prompted further investigations into insect life cycles and into entomology in general.
Dr Louis François Etienne Bergeret (1814–1893) was a French hospital physician, and was the first to apply forensic entomology to a case. In a case report published in 1855 he stated a general life cycle for insects and made many assumptions about their mating habits. Nevertheless these assumptions led him to the first application of forensic entomology in an estimation of postmortem interval (PMI). His report used forensic entomology as tool to prove his hypothesis on how and when the person had died.
The first systematic study in forensic entomology was conducted in 1881 by Hermann Reinhard, a German medical doctor who played a vital role in the history of forensic entomology. He exhumed many bodies and demonstrated that the development of many different types of insect species could 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 the development of 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.
Jean Pierre Mégnin, an army veterinarian, 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 theory of predictable waves, or successions of insects onto corpses. By counting numbers of live and dead mites that developed every 15 days, and comparing this with his initial count on the infant, he was able to estimate how long that infant was dead.
In this book he asserted that exposed corpses were subject to eight successional waves whereas buried corpses were subject only to two waves. Mégnin made many great discoveries that helped shed new light on many of 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 helped to establish the scientific discipline of forensic entomology.
Urban forensic entomology typically concerns pest infestations in buildings or gardens that may be the basis of litigation between private parties and service providers such as landlords or exterminators. Urban forensic entomology studies may also indicate the appropriateness of certain pesticide treatments and may also be used in stored products cases where it can help to determine chain of custody, when all points of possible infestation are examined in order to determine who is at fault.
Stored-product forensic entomology is often used in litigation over infestation or contamination of commercially distributed foods by insects.
Medicolegal forensic entomology covers evidence that may be gathered through arthropod studies at events such as murder, suicide, rape, physical abuse and contraband trafficking. In murder investigations it deals with which insects lay eggs when and where, and in what order they appear in dead bodies. This can be helpful in determining a post mortem interval (PMI) and location of a death in question. Since many insects exhibit a degree of endemism (occurring only in certain places), or have a well-defined phenology (active only at a certain season, or time of day), their presence in association with other evidence can demonstrate potential links to times and locations where other events may have occurred (e.g., an Ohio man who claimed to have been in Ohio on the date his wife and children were murdered in California was found to have grasshoppers and other nocturnal insects from the west on his car grille, indicating that the car had been driven at night to the western US, and he was subsequently convicted.). Another area covered by medicolegal forensic entomology is the relatively new field of entomotoxicology. This particular branch involves the utilization of entomological specimens found at a scene in order to test for different drugs that may have possibly played a role in the death of the victim.
There are many different types of insect studied in forensic entomology. The insects listed below are mostly necrophagous (corpse-eating) and are particularly relevant to medicolegal entomological investigations. This is not a full list as there are many variations due to climate (see Mostovski and Mansell). The order in which insects feed on a corpse is known as faunal succession.
Many mites (class acari) feed on corpses with Macrocheles mites common in the early stages of decomposition, while Tyroglyphidae and Oribatidae mites such as Rostrozetes feed on dry skin in the later stages of decomposition.
Nicrophorus beetles often carry on their bodies the mite Poecilochirus which feed on fly eggs. If they arrive at the corpse before any fly-eggs hatch into maggots, the first eggs are eaten and maggot development is delayed. This may lead to incorrect PMI estimates. Nicrophorus beetles find the ammonia excretions of blowfly maggots toxic, and the Poecilochirus mites, by keeping the maggot population low, allow Nicrophorus to occupy the corpse.
Moths (order lepidoptera) specifically Clothes-moths – Family Tineidae – Is closely related to the butterfly. Most species of moth are nocturnal, but there are crepuscular and diurnal species. Moths feed on mammalian hair during their larval stages and may forage on any hair that remains on a body. They are amongst the final animals contributing to the decomposition of a corpse.
Wasps, ants, and bees (order hymenoptera) are not necessarily necrophagous. While some feed on the body, some are also predatory, and eat the insects feeding on the body. Bees and wasps have been seen feeding on the body during the early stages. This may cause problems for murder cases in which larval flies are used to estimate the post mortem interval since eggs and larvae on the body may have been consumed prior to the arrival on scene of investigators.
Forensic entomologists have been used in several cases where parents have used bees to sting their children as a form of discipline. Also entomologists have been called on to determine whether or not bees or wasps have been the cause of an accident. Whether through their presence or by stinging it has be speculated that these insects have been the cause of numerous automobile accidents.
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.
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 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 (SEM) 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 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 the species from which the egg originated, so it may not be useful in a field study or to quickly identify a particular egg. The SEM method is good if you have ample time and resources to determine the species of the particular fly egg. 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.
Sometimes scanning electron microscopy is not available and a quicker and lower cost technique can be found in potassium permanganate staining. This process involves a few basic steps. Once the eggs 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 are 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.
In 2001, a method was devised by Jeffrey 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 using 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.
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.
This environment had a daily average maximum temperature of 19.4 degrees Celsius and a daily minimum temperature of 11.1 degrees Celsius. The average rainfall for the first 3 weeks in this environment was 3.0 mm/day. Around days 17–45, the body began to start active decay. During this stage, the insect successions started with Calliphora stygia, which lasted until day 27. The larvae of Chrysomya rufifacies were present between the day 13 and day 47. The H. rostrata, larvae of Lucilia sericata, Psychodidae family, and sylvicola were found to occur relatively late in the bodies decay.
This environment had an average daily maximum temperature of 21.4 degrees Celsius and minimum of 13.5 degrees Celsius. The daily average rainfall was recorded as 1.4 mm/day for the first 3 weeks in this environment. The post-decay time interval, beginning at day 6 after death and ending around day 15 after death, is greatly reduced from the average post-decay time, due to the high average temperature of this environment. Insects obtained late in the post-active stage include the Callihora quadrimaculat, adult Phaeroceridae, Psychodidae and Piophilidae (no larvae from this family were obtained in recovery).
This environment had recorded daily average maximum and minimum temperatures were 18.0 and 13.0 degrees Celsius, respectively. The average rainfall in this habitat was recorded at 0.4 mm/day. After the bloat stage, which lasted until day 7 after death, post active decay began around day 14. In this habitat, the H. rostrata, Phoridae adult, Sylvicola larvae and adult are the predominant species remaining on the body during the pre-skeletonization stages.
Throughout its history the study of forensic entomology has not remained an esoteric science reserved only for entomologists and forensic scientists. Early twentieth-century popular scientific literature began to pique a broader interest in entomology. The very popular ten-volume book series, Alfred Brehem’s Thierleben (Life of Animals, 1876–1879) expounded on many zoological topics, including arthropods. The accessible writing style of French entomologist Jean-Henri Fabre was also instrumental in the popularization of entomology. His collection of writings Souvenirs Entomologique, written during the last half of the 19th century, is especially useful because of the meticulous attention to detail to the observed insects’ behaviors and life cycles. 
The real impetus behind the modern cultural fascination with solving crime using entomological evidence can be traced back to the works Faune de Tombeaux (Fauna of the Tomb, 1887) and Les Faunes des Cadavres (Fauna of the Cadaver, 1894) by French veterinarian and entomologist Jean Pierre Mégnin. These works made the concept of the process of insect ecological succession on a corpse understandable and interesting to an ordinary reader in a way that no other previous scientific work had done. It was after the publication of Mégnin’s work that the studies of forensic science and entomology became an established part of Western popular culture, which in turn inspired other scientists to continue and expand upon his research.
The use of forensic science, including forensic entomology, became a popular part of fiction beginning with the stories of Edgar Allan Poe. He is noted for including graphic depictions of human decomposition in some of his works, including entomological references. The poem "The Conqueror Worm", published in 1843, features death symbolized through a "worm" feasting upon human remains. The worm is a reference to the maggots which are present on a corpse after death and aid in decomposition. In his short story "The Premature Burial," published in 1850, he discusses the Victorian Era’s fascination with being buried alive, including references to autopsy procedures of the day and the known pattern of human decomposition. Poe is also recognized as the inventor of the modern detective story. "The Murders in the Rue Morgue," published in 1841, follows detective C. Auguste Dupin as he attempts to solve the murder of two women. Dupin carefully assesses the crime scene, noting such forensically important evidence as location and conditions of the bodies, as well as physical evidence present at the scene. Although no specific entomological reference is present, the process of crime scene evaluation is similar to that which a forensic entomologist would undergo using a Death Scene Form. Poe’s character Dupin was the inspiration for countless other analytical crime-solvers, including Sir Arthur Conan Doyle’s detective Sherlock Holmes.
In the movie The Silence of the Lambs, a series of murders are committed in which the killer skins his victims, leading the investigators to dub the unidentified killer "Buffalo Bill." In a scene depicting an autopsy of one of the victims, the investigators notice something in the victim's throat. The pupa of a Death's-head Hawkmoth is removed with forceps. In another scene, entomologists in the film explain to investigators that the particular species discovered on the victim, identified as Acherontia styx, is not native to the United States and must have been imported by the killer. Because of the enormous popularity of the film The Silence of the Lambs, these scenes referencing the overlap between entomology and forensic science are what most people associate with the work of forensic entomologists.
In the 1991 movie My Girl, protagonist Thomas Jay dies due to anaphylaxis after being stung by bees, to which he was mortally allergic. Often with such cases death due to anaphylaxis, an immediate cause of death may not be apparent, requiring the expertise of a forensic entomologist.
In the television show CSI: Crime Scene Investigation, forensic entomologist Gil Grissom is famous for his knowledge of bugs. He is a valuable part of the CSI team with his ability to distinguish insect types and their significance at the crime scene.