Forensic entomology
Forensic entomology is a field of forensic science that uses insects found on corpses to help solve criminal cases. This includes the study of insect types commonly associated with cadavers, their respective life cycles, their ecological presences in a given environment, as well as the changes in insect assemblage with the progression of decomposition.[1] Insect succession patterns are identified based on the time a given species of insect spends in a given developmental stage, and how many generations have been produced since the insects introduction to a given food source.[2] Insect development alongside environmental data such as temperature and vapor density, can be used to estimate the time since death, due to the fact that flying insects are attracted to a body immediately after death, determine any possible movement of the body after death, and the determination of antemortem trauma. .[3] [4] The identification of postmortem interval to aid in death investigations is the primary scope of this scientific field. However, forensic entomology is not limited to homicides, it has also been used in cases of neglect and abuse, in toxicology contexts to detect the presence of drugs, and in dry shelf food contamination incidents. Equally, insect assemblages present on a body, can be used to approximate a given location, as certain insects may be unique to certain areas.[5] Therefore, forensic entomology can be divided into three subfields: urban, stored-product and medico-legal/medico-criminal entomology.
Forensic entomology subfields[edit]
Urban forensic entomology[edit]
Urban forensic entomology typically concerns pests infestations in buildings, gardens, or other urban environments, and may be the basis of litigation between private parties and service providers such as landlords or exterminators [13] For instance, urban forensic entomology can be used to evaluate the efficiency of pest control techniques, ascertain the size of the infestation, and identify the responsible party in situations involving pest infestations in rental homes. 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.[14] For example, urban forensic entomology can assist in determining responsibility when stored goods, like grains or packaged foods, are contaminated with insects. It can also help identify the infestation origin. Moreover, environnemental management and public health depend heavily on urban forensic entomology. Researchers can track the transmission of disease carried by insects by examining insect populations in urban settings. Furthermore, it can also guide conservation efforts by evaluating the environmental effects of urbanization on insect populations.
Stored-product forensic entomology[edit]
Stored-product forensic entomology is often used in litigation over insect infestation or contamination of commercially distributed foods. [13] [15] Insect infestations in stored goods, including grains, flour, and packaged meals, are the subject of this branch of forensic entomology, which also examines the legal ramifications of these findings. Stored-product forensic entomologists may be asked to identify the bug species involved, evaluate the amount of the infestation, and pinpoint the infestation's source in a legal proceeding. [16] In addition, they might offer expert testimony about the circumstances that gave rise to the infestation and suggest safeguards to stop it from happening again.
Forensic entomology on stored products not only helps with legal matters but also with food safety and quality assurance. Forensic entomologists work to guarantee that food products are safe for consumption by identifying insect species and tracking their presence in stored goods. Additionally, this sector contributes to the general enhancement of food business practices by researching and developing novel techniques for pest management and product preservation. [16]
The role of insects in the decomposition processes[edit]
When it comes to the breakdown of organic materials, including human bodies, insects are essentials. Chemical emitted during decomposition attract necrophilic insects, or insects that feed on dead creatures. These insects hasten the decomposition process by aiding in the breakdown of bodily tissues. [25]Among the first insects to reach a body, blow flies are regared as primary colonizers. Their oviposited eggs are laid in natural openings, wounds, or damp places, and decaying tissues are consumed by their maggot larvea. By feeding on the remnants, other insects like mites and beetles may also aid in the decomposition process.
Forenisc investigators can learn important details from insects' activites, including the length of time passed since death, the presence of medication or toxins in the body, and the movement or disturbance of the body following death.
Factors[edit]
Moisture levels[edit]
Both the decomposition and insect activity on a corpse are significantly influanced by humidity. Elevated humidity can hasten the decomposition process by fostering microbial proliferation, which facilitates the breakdown of tissues. Additionally the odors and gases produced by this microbial activity draw insects to the body. These smells are particularly attractive to insects like blowflies and flesh flies, which may quickly populate a body in humid conditions. [43]
Low humidity, on the other hand, can impede the breakdown process. Mummification rather that breakdown may result from the body losing moisture more quickly in arid settings. Given that many insects need damp atmosphere to survive, this may discourage their activity. Nonetheless, some insects, like dermestid beetles, can survive in dry environments and can still be found on a body. [44][45]
The existence of standing water next to a body can also affect the activity of insects. Aquatic insects, such as water beetles and some fly species, may be drawn to bodies near water sources. These insects can colonize the body and hasten its decomposition. Furthermore, because different insect species have distinct preference for habitats, the presence of water might influence the kinds of insects that inhabits the body.
All things considered, the rate and pattern of a corpse's decomposition and insect colonization are greatly influenced by its humidity. To estimate the postmortem period and reconstruct the circumstances around a death, forensic entomologists can benefit from an understanding of how humidity levels affect decomposition. [46]
Submerged corpses[edit]
M. Lee Goff, a noted and well respected forensic entomologist, was assigned to a case involving the discovery of a decomposing body found on a boat half a mile from shore. Upon collection of the maggot mass, only one insect, Chrysomya megacephala, was discovered. He concluded that the water barrier accounted for the scarcity of other flies. He also noted that flies will not attempt to trek across large bodies of water unless there is a substantially influential attractant.
In addition, the amount of time a maggot mass has been exposed to salt water can affect its development. From the cases Goff observed he found that if subjected for more than 30 minutes, there was a 24‑hour developmental delay. Not many more studies have been conducted and thus a specific amount of delay time is difficult to estimate.[47]
The main focus of a study accomplished by Payne and King [48] using fetal pigs, was the insect succession regarding carcass decomposition in an aquatic setting. Their results concluded that in the early floating stages of the cadaver, eggs were laid by blowflies. Moreover, by the bloating stage, most of the exposed flesh was absent and maggots migrated from the body. Many of the latter were present below the water line and fed on the carcass; with only their Spiracle (arthropods) protruding the surface.
Sun exposure[edit]
"Because insects are cold-blooded animals, their rate of development is more or less dependent on ambient temperature."[49]
Bodies exposed to large amounts of sunlight will heat up, giving the insects a warmer area to develop, reducing their development time.
An experiment conducted by Bernard Greenberg and John Charles Kunich with the use of rabbit carcasses to study accumulation of degree days found that with temperature ranging in the mid 70s to high 80s the amount of developmental time for maggots was significantly reduced.[50]
In contrast, bodies found in shaded areas will be cooler, and insects will require longer growth periods. In addition, if temperatures reach extreme levels of cold, insects instinctively know to prolong their development time in order to hatch into a more accepting and viable climate in order to increase the chance of survival and reproduction.
Furthermore, insect activity and colonization patterns can also be influenced by the length and intensity of solar exposure. Because the increasing temperature speeds up their development, insects are more likely to be active and colonize a body more quickly in places exposed to direct and extended sunlight. In comparison to shaded locations, this may result in a quicker succession of insect life and disintegration stages. On the other hand, because of the lower temperatures, shaded areas might have slower rates of insect activity and decomposition, which would delay the processes of insect colonization and decomposition.[51]
Air exposure[edit]
Air exposure can have a significant impact on insects and the determination of postmortem interval (PMI). Hanged bodies can be expected to show their own quantity and variety of flies. Also, the amount of time flies will stay on a hanged body will vary in comparison to one found on the ground. A hanged body is more exposed to air and thus will dry out faster, leaving less food source for the maggots.
The presence and behavior of insects on haging bodies can vary. As the body begins to decompose, a compilation of fluids will leak to the ground. This area is where most of the expected fauna can be found. Also, it is more likely that rove beetles and other non-flying insects will be found here instead of directly on the body. Fly maggots, initially deposited on the body, may also be found below.[47]
Geography[edit]
According to Jean Pierre Mégnin's book La Faune des Cadavres there are eight distinct faunal successions attracted to a corpse. While most beetles and flies of forensic importance can be found worldwide, a portion of them are limited to a specific range of habitats. It is forensically important to know the geographical distribution of these insects in order to determine information such as post mortem interval or whether a body has been moved from its original place of death.
Calliphoridae is arguably the most important family concerning forensic entomology given that they are the first to arrive on the corpse. The family can be found worldwide. Chrysomya rufifaces, the hairy maggot blow fly, is a forensically important member of the family Calliphoridae and is widespread, however it is not prevalent in the Southern California, Arizona, New Mexico, Louisiana, Florida, or Illinois regions.[52]
Flesh flies fall under the family Sacrophagidae and generally arrive at a corpse following Calliphoridae. Unlike Calliphoridae, however, members of this family are able to fly in heavy rain. This key advantage enables them to occasionally reach a body before Calliphoridae, affecting the maggot mass that will be discovered. Flesh flies are globally distributed including habitats in the United States, Europe, Asia, and the Middle East.[53]
Beetles are representative of the order Coleoptera which accounts for the largest of the insect orders. Beetles are very adaptive and can be found in almost all environments with the exception of Antarctica and high mountainous regions. The most diverse beetle fauna can be found in the tropics. In addition, beetles are less submissive to temperatures. Thus, if a carcass has been found in cold temperatures, the beetle will be prevalent over Calliphoridae.
Weather[edit]
Various weather conditions in a given amount of time cause certain pests to invade human households. This is because the insects are in search of food, water, and shelter. Damp weather causes reproduction and growth enhancement in many insect types, especially when coupled with warm temperatures. Most pests concerned at this time are ants, spiders, crickets, cockroaches, ladybugs, yellowjackets, hornets, mice, and rats. When conditions are dry, the deprivation of moisture outside drives many pests inside searching for water. While the rainy weather increases the numbers of insects, this dry weather causes pest invasions to increase. The pests most commonly known during dry conditions are scorpions, ants, pillbugs, millipedes, crickets, and spiders. Extreme drought does kill many populations of insects, but also drives surviving insects to invade more often. Cold temperatures outside will cause invasions beginning in the late summer months and early fall. Box elder bugs, cluster flies, ladybugs, and silverfish are noticed some of the most common insects to seek the warm indoors.[54] In general, insects are poikilothermic animals; thus meaning their level of activity is substantially depended upon their surrounding environmental conditions. An increase in the temperature will result in an accelerated metabolism of the insect; hence resulting in an increased activity.[55]
In literature[edit]
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.[69][70]
The real impetus behind the modern cultural fascination with solving crime using entomological evidence can be traced back to the works Faune des Tombeaux (Fauna of the Tombs, 1887) and Les Faunes des Cadavres (Fauna of Corpses, 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.[71]