Forensic entomology

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Meat fly on rotting meat

The forensic entomology is a branch of forensic science , in which the entomology for the elucidation of legal cases, mainly homicides , is used. Among other things, due to the sequence of the larval stages and the colonization by different types of insects, indications of the time the corpse was laid , the cause of death and the circumstances of death can be collected. Even with living organisms, food and buildings, insects can offer conclusions about certain circumstances.

General

The term Entomology comes from the Greek and means " Entomology " (éntomos = cut, notched, logos = Customer, teaching). The word forensics comes from the Latin word forum (= marketplace, forum, court hearing) and is used in the sense of judicial .

Forensic entomology is most commonly used in connection with investigations into a found corpse. The post-mortem decomposition process of an organic body takes place, among other things, by bacteria , fungi and insects. The insects are mostly juvenile stages of necrophagous insects such as the maggots of blowflies , cheese flies or meat flies . Various beetles are also involved, such as the carrion beetle (including the gravedigger and the bacon beetle ) as well as other species that are attracted by the (fragrance) substances produced during decay or that in turn feed on necrophagic insects.

The infestation of living bodies with insects, especially maggots, also allows certain conclusions to be drawn. This condition is known as " myiasis " (maggot disease). It is often an indication of a lack of hygiene and care or - indirectly - of a weakened general condition. Open wounds, in which maggots eat necrotic tissue , are thus cleaned by their excretions. In medicine, maggots are therefore also used specifically to support wound healing ( maggot therapy ).

Another area of ​​forensic entomology is the investigation of insect infestation in food (e.g. in the storage of food).

The investigation of insect infestation in buildings is also a branch of forensic entomology.

history

There have been several approaches to use and experiments with forensic entomology throughout history. The concept of forensic entomology dates back to the 13th century. Even in works of art from the 15th and 16th centuries there are representations of connections between insects and dead bodies. In modern forensic medicine in Europe, maggots were discovered as an aid from the end of the 18th century. However, it is only in the last 30 years that forensic entomology has been systematically researched as a helpful source of evidence in criminal investigations. With their own experiments and interest in entomology and death, many people helped lay the foundations for today's modern forensic entomology. These people include, in particular, Song Ci , Francesco Redi , Bergeret d'Arbois , Jean Pierre Mégnin and the German doctor Hermann Reinhard .

Song Ci

Song Ci (also known as Sung Tz'u) was a lawyer and investigator into deaths. He lived in China in the late 13th century. In 1247 Song Ci wrote a book called '洗冤 集 錄' (English book title: “Washing Away of Wrongs”). In this book, Song Ci describes various cases in which he made notes about human deaths and the possible causes of death. He describes in detail how a corpse is examined before and after the burial. He also explained the procedure to determine a likely cause of death. The purpose of the book was to serve as a guide to other investigators so that they could better investigate and evaluate crime scenes. His wealth of detail in explaining his observations laid the foundations for modern forensic entomologists. In addition, his notes are considered to be the first records of a person who used forensic entomology for judicial purposes. This book was very popular and marks the first time the general public became aware that insects could be used in investigative proceedings.

The book remained an isolated case; the next Chinese work on forensic entomology was not published until 750 years later.

Francesco Redi

The Italian doctor Francesco Redi refuted the theory of spontaneous generation in 1668 . According to Redi's theory, maggots develop on rotting meat in a very short time. In one experiment, he used rotting meat that was completely, only partially or not exposed to the air and therefore freely accessible. Redi showed that the rotting meat, which was completely and only partially exposed to the air, maggots from flies developed. On the other hand, no maggots developed on the rotting meat that was not exposed to the air. This discovery completely changed the previously held view of the decomposition of organisms and led to further studies of the life cycles of insects and entomology in general.

Bergeret d'Arbois

Dr. Louis François Etienne Bergeret (1814-1893) was a French hospital doctor and the first known to use forensic entomology in a specific case. In a case report published in 1855, he presented the general life cycle of insects and made many hypotheses about their mating behavior. Using these assumptions, he first applied forensic entomology to estimate the time elapsed since death. His report used forensic entomology as a tool to substantiate his hypothesis of how and when the person died.

Hermann Reinhard

The first systematic study of forensic entomology was carried out in 1881 by the German doctor Hermann Reinhard , who played an important role in the history of forensic entomology. He dug up many corpses and showed that the buried corpses show the development of many different insect species. Reinhard conducted his first study in East Germany and collected many humpback flies ( Phoridae ) from this first study. But he also came to the conclusion that not all insects or their development were related to the buried corpse. For example, he found 15-year-old beetles that had little direct contact with the buried corpses. Reinhard's work and studies have been used extensively in other forensic entomology studies.

Jean Pierre Mégnin

The military veterinarian Jean Pierre Mégnin published numerous articles and books on various subjects, including the books 'Faune des Tombeaux' and 'La Faune des Cadavres', which are considered to be two of the most important books of forensic entomology in history. With his second book he created a revolutionary work on the life cycles and reproduction of insects on corpses. In particular, Mégnin discovered that the cycles of colonization by insects are predictable, especially with exposed corpses. By counting the number of live and dead mites that developed every 15 days and comparing it to the original number on a child's body, he could estimate how long the child had been dead.

In this book, he claimed that up to eight consecutive life cycles of insects occur on exposed corpses, while only two cycles can be observed on buried corpses at the same time. Mégnin made many discoveries that helped shed new light on many common features of decaying flora and fauna. Mégnin's work and study of the larvae and adult forms of insect species found in corpses sparked the interest of future entomologists. They encouraged more research on the link between arthropods and the deceased. He also contributed to creating the scientific discipline of forensic entomology.

Areas of application

Determination of the time of death

Gravedigger ( Nicrophorus vespilloides )

The main field of forensic entomology is the determination of the time of death or lying time of a corpse. By means of a forensic entomological examination, conclusions can be drawn about the lying time of a corpse based on the age, number and type of insects found. Even relatively short periods of time can be determined in this way, since dead bodies are naturally populated by insects very quickly.

Insects use a corpse as a source of food and breeding ground. Corresponding references to the time of death of the person or the lying time of the corpse can be derived from the presence of certain insect species or their stages of development (eggs, larvae) on the corpse. For an exact determination, however, it is necessary to soak the found insects in alcohol at a known time as quickly as possible, to freeze them or to photograph them with a high-resolution camera. Otherwise, the animals continue to develop, so that an exact determination becomes more and more difficult as time goes on.

A corpse is colonized by different insects depending on the state of putrefaction and degree of moisture. Blowflies deposit either eggs or already hatched tiny maggots on fresh corpses within a very short time . Blowflies larvae can also be found on older, already distended corpses . Depending on the humidity , there are also carrion beetles , rump beetles and beetles . On bodies in dry or pulpy state, in particular of maggots are cheese fly and fur beetles , ham beetle , skin beetles , carpet beetle and Burying Beetles encountered. Woodlice , centipedes , mites , moths and arachnids first settle on mummified or skeletonized corpses.

Tiny white maggots hatch from the eggs in a short time. The exact determination of the time of death depends on the individual circumstances. The development of the maggots in particular depends to a large extent on the temperature and humidity. But the time interval from egg-laying to hatching of the first generation of maggots can vary considerably and varies from a few hours to a day. The period of time that a maggot needs up to a certain development phase depending on defined environmental factors (body length measured in mm) has been determined and specified species-specifically in so-called isomegale diagrams .

If the temperature is too high or too low, the brightness is too high, the wind is strong or the drought is too great, few or no insects will settle on a corpse. Another influencing factor is the accessibility of a corpse for insects. For this reason, for the work of forensic entomology, precise analyzes of the location of the corpse must also be included in the examination process.

While the examination of maggots is helpful in determining shorter time intervals, (only) statements about longer time intervals can be made using beetles. The number of insect generations - recognizable by the simultaneous occurrence of maggots and empty pupa shells in the vicinity of the corpse - is also important for limiting the time period.

When comparing the methods, the observation of the body temperature that has fallen allows statements to be made over rather short periods of time. Chemical analyzes of the body allow conclusions to be drawn in medium-long periods of time, insect infestation in even longer periods.

Location determination

Places where a corpse was found that deviate from the final location can also be determined with the help of insects. The insects found, including stages of development, are used for the analysis. Species-specific feeding traces can also be used to determine the insect species. Many insect species only inhabit certain habitats (so-called "habitats"). If there are insects on a corpse that are atypical for the environment at the place where the corpse was found, it can be concluded that the corpse has previously been moved away from another location. Correspondingly, the typical environmental conditions for them can also be determined on the basis of the insects found.

Detection of substances

Furthermore, insects can be used to find out whether certain drugs or poisons were present in the corpse . This is particularly helpful if the corpse has already decomposed too much for appropriate examinations. When the insects eat parts of tissue, they also take in their ingredients. The toxicological analysis of the insects found can thus provide information about drugs or toxins present in the corpse. This area of ​​work is also known as entomotoxicology. Gas chromatography and HPLC in combination with mass spectrometry as highly sensitive and specific methods come into question as analytical methods . These analytical working methods were used for the reliable detection of methamphetamine and its metabolites , as well as methylphenidate and phenobarbital . For the benefit of the forensic examinations described, there are also critical statements that recommend restraint in interpreting the analysis results obtained. The phenotypic development of insects can also be changed by the ingestion of certain active substances.

Influencing factors

Flies lay eggs on the carcass of a bird.

The development of insects is influenced by several factors. Both the weather and the location have a decisive influence. When it comes to the weather, exposure to sunlight, humidity and temperatures are decisive. In addition, the location of a corpse, for example, in water, in or outside of buildings, in rural or urban areas, outdoors or in vehicles or hung on trees can have different consequences for colonization by insects. The condition of the corpse is also decisive, so that, for example, cremated corpses are colonized by insects in a different way.

temperature

Insects are cold-blooded animals, so their development time and freedom of movement are highly dependent on the ambient temperatures. At higher temperatures a faster development is made possible, at lower temperatures a correspondingly slower development.

If the ambient temperature drops below a certain range, the development time of insects is even extended due to their natural instincts so that they can hatch in a time with a better climate, thereby increasing their chances of survival and reproduction.

In addition, the order of colonization of a corpse by insects can be influenced by the temperature. Basically, a corpse is first colonized by flies and only later by beetles. However, beetles are less sensitive to temperature than flies, so that earlier or only colonization by beetles is possible at lower temperatures.

humidity

The species diversity and development time of the insects is also influenced by humidity and precipitation.

In the case of most insect species, their development is indirectly slowed down during heavy rainfall, as this lowers the ambient temperature and as a result slows down the development of the insects. A very humid environment (e.g. from light rain), on the other hand, acts as an insulator, creating a higher core temperature in a mass of maggots, which in turn enables the insects to develop more quickly.

Precipitation can also affect the order in which a corpse is settled. Basically, flies of the blowfly family are one of the first insects on a corpse, followed by flies of the meat fly family . However, in contrast to blowflies, meat flies are also able to fly in the rain, so that, under appropriate circumstances, meat flies exceptionally reach the corpse before blowflies. As a result, there is a different distribution of the respective numbers of maggots on the corpse.

With high humidity (and corresponding temperatures), a greater variety of insects develops. In addition, different types of insects develop differently depending on the existing humidity, so that this influences the composition and size of the population. In extreme drought, the population and biodiversity of insects can be severely decimated.

Exposure to sunlight

A corpse that is exposed to strong sunlight becomes more warm during the day. As a result, it offers insects a warmer environment, which significantly shortens their development time.

In an experiment carried out by Bernard Greenberg and John C. Kunich with the help of rabbit carcasses, it was found that the development time of maggots was significantly reduced at temperatures from mid-70 ° C to well above 80 ° C.

In contrast, corpses have lower temperatures in shady areas. As a result, insects naturally need a longer development time.

geography

Most of the insects that play an entomological role in the colonization of a corpse are distributed almost worldwide. However, some species of insects are endemic. As a result, endemic insect species can be used to determine whether the corpse has been moved from another location.

Male fly of the species Chrysomya rufifacies

For the area of ​​the USA it is known that, for example, the flies of the species Chrysomya rufifacies, which belong to the family of the blowflies (Calliphoridae), the most important insect species for entomological forensics , are not found in the regions of southern California, Arizona, New Mexico, Louisiana, Florida or Illinois can be found. Corresponding findings are all the more important because flies of the blowfly insect species are one of the first insects on a corpse.

Beetles offer the greatest diversity of species among insects with over 350,000 described species. In addition, beetles are very adaptable and therefore distributed almost worldwide, with the exception of the Antarctic and in higher mountain regions. The greatest diversity of beetles is found in the tropics. As a result, the beetle species found on the corpse and their area of ​​distribution can also be used to determine the location (s).

Suspended bodies

Suspended bodies have a specific number and variety of insects, especially flies. Above all, the quantity of flies on a suspended body differs from the number on a body lying on the ground.

In addition, a suspended body dries out faster, which means that there is less potential food source for maggots.

When a suspended body begins to decompose, body fluids naturally run out onto the floor below. As a result, most of the insects, particularly the rhinoceros and other non-flying insects, are found in this area. Fly maggots that were initially on the suspended body can later be found on the floor underneath.

Isolation on waters

Female of the fly species Chrysomya megacephala

According to a case study by entomologist M. Lee Goff of a body found on a boat half a mile from shore, it was found that only maggots of one species of fly were present on the body. From this he concluded that bodies of water represent a natural barrier for insects, so that in such cases only a few species of insect can be found on a corpse. In this respect, stronger attractants are needed to create an incentive for insects to cross longer stretches of water.

Another finding by entomologist Goff from his studies is that fly maggots that have been exposed to salt water for more than 30 minutes have a delay of 24 hours in their development. However, sufficient studies are lacking for specific temporal relationships between the exposure time to salt water and the resulting delay in development.

Settlement of buildings

The settlement of buildings by insects is significantly influenced by the weather.

Insects enter buildings in search of food, water, warmth and shelter. Particularly in a dry outdoor climate, the removal of moisture drives insects into buildings in search of water. The temperatures in the open air and in buildings are also decisive for whether insects move into buildings or outside.

In addition, the settlement of buildings is significantly influenced by the available food supply.

Forensic entomologists

Well-known forensic entomologists from Germany are Mark Benecke from Cologne and Jens Amendt from the Institute for Forensic Medicine at the University of Frankfurt am Main .

References

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