Forensic entomology is the science and study of insects and other arthropods related to legal investigations. It can be divided in three subfields: urban, stored-product and medicolegal/medicocriminal.
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. Such questions may include the appropriateness of certain pesticide treatments. Stored-product forensic entomology is often used in litigation over infestation or contamination of commercially distributed foods by insects.
Medicolegal forensic entomology includes arthropod involvement in events such as murder, suicide, rape, physical abuse and contraband trafficking. In murder investigations it deals with what insects lay eggs when and where, and in what order they appear in dead bodies. This can be helpful in determining the time or post mortem interval (PMI) and location of the 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; )
There are many types of insects that can be involved in forensic entomology, but the ones listed here are mostly necrophagous (corpse-eating) and related to medicolegal entomology (directly related to the crime and found on the corpse). This is not a full list; there are many variations due to climate, and many other insects that are necrophagous. This is outlined by Mostovski and Mansell. The order in which the insects feed on the corpse is called the faunal succession.
Insects of forensic importance
Flies (Order Diptera)
Flies are often first on the scene. They prefer a moist corpse for the maggots to feed on, as such a corpse is easier for them to chew. The most important families are:
Beetles (Order Coleoptera)
Many mites feed on a corpse. Macrocheles mites are 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 feeds 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 estimate. Nicrophorus beetles find the ammonia excretions of blowfly maggots toxic, and the Poecilochirusmites, by keeping the maggot population low, allow Nicrophorus to occupy the corpse.
Moths (Order Lepidoptera)
Clothes-moths - Family Tineidae - feed on mammalian hair during their larval stages and may forage on any hair that remains. They are amongst the final animals contributing to the decomposition of a corpse.
Wasps, ants, and bees (Order Hymenoptera)
The insects in this group, 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.
Books on forensic entomology
A brief history of forensic entomology is presented by Mark Benecke
Please note - these sites may contain strong graphic images and descriptions.
What is Forensic Entomology?
Forensic Entomology is the use of the insects, and their arthropod relatives that inhabit decomposing remains to aid legal investigations. The broad field of forensic entomology is commonly broken down into three general areas: medicolegal, urban, and stored product pests. The medicolegal section focuses on the criminal component of the legal system and deals with the necrophagous (or carrion) feeding insects that typically infest human remains. The urban aspect deals with the insects that affect man and his immediate environment. This area has both criminal and civil components as urban pests may feed on both the living and the dead. The damage caused by their mandibles (or mouthparts) as they feed can produce markings and wounds on the skin that may be misinterpreted as prior abuse. Urban pests are of great economic importance and the forensic entomologist may become involved in civil proceedings over monetary damages. Lastly, stored product insects are commonly found in foodstuffs and the forensic entomologist may serve as an expert witness during both criminal and civil proceedings involving food contamination.
Here are a few examples: The diverse applications of
forensic entomology include the detection of abuse in children and
neglect of the elderly. Published cases exist that detail
parents intentionally using wasps and bees to sting their children
as a form of punishment. Additionally, entomological evidence
has been used to prove neglect and lack of proper care for wounds
existing on the elderly under both private and institutional care.
What information can a forensic
entomologist provide at the death scene?
The forensic entomologist can use a number of different techniques including species succession, larval weight, larval length, and a more technical method known as the accumulated degree hour technique which can be very precise if the necessary data is available. A qualified forensic entomologist can also make inferences as to possible postmortem movement of a corpse. Some flies prefer specific habitats such as a distinct preference for laying their eggs in an outdoor or indoor environment. Flies can also exhibit preferences for carcasses in shade or sunlit conditions of the outdoor environment. Therefore, a corpse that is recovered indoors with the eggs or larvae of flies that typically inhabit sunny outdoor locations would indicate that someone returned to the scene of the crime to move and attempt to conceal the body.
Similarly, freezing or wrapping of the body may be indicated by an altered species succession of insects on the body. Anything that may have prevented the insects from laying eggs in their normal time frame will alter both the sequence of species and their typical colonization time. This alteration of the normal insect succession and fauna should be noticeable to the forensic entomologists if they are familiar with what would normally be recovered from a body in a particular environmental habitat or geographical location. The complete absence of insects would suggest clues as to the sequence of postmortem events as the body was probably either frozen, sealed in a tightly closed container, or buried very deeply.
Entomological evidence can also help determine the circumstances of abuse and rape. Victims that are incapacitated (bound, drugged, or otherwise helpless) often have associated fecal and urine soaked clothes or bed dressings. Such material will attract certain species of flies that otherwise would not be recovered. Their presence can yield many clues to both antemortem and postmortem circumstances of the crime. Currently, it is now possible to use DNA technology not only to help determine insect species, but to recover and identify the blood meals taken by blood feeding insects. The DNA of human blood can be recovered from the digestive tract of an insect that has fed on an individual. The presence of their DNA within the insect can place suspects at a known location within a definable period of time and recovery of the victims' blood can also create a link between perpetrator and suspect.
The insects recovered from decomposing human remains can be a valuable tool for toxicological analysis. The voracious appetite of the insects on corpses can quickly skeletonize the remains. In a short period of time the fluids (blood and urine) and soft tissues needed for toxicological analysis disappear. However, it is possible to recover the insect larvae and run standard toxicological analyses on them as you would human tissue. Toxicological analysis can be successful on insect larvae because their tissues assimilate drugs and toxins that accumulated in human tissue prior to death.
Information about the development and appearance of some common forensically important insects.
Insects have existed on earth for about 250 million years; comparatively humans have existed for about 300,000 years. Such an enormous amount of time has allowed insects to attain a wide diversity in both form and development. There are currently about 700,000 described species and it is estimated that there may be more than 10 million species of insects yet to be described. Some insects have evolved a gradual or "paurometabolous" development in which there is an egg that hatches into an immature or "nymph", which resembles the adult form, but is smaller and lacks wings. In the forensically important insects, this is best represented by the cockroaches. However, most forensically important insects undergo a complete or "holometabolous" development. There is an egg stage (except for a few insects such as the flesh flies that deposit living larvae) which hatches into a larval form and undergoes a stepwise or incremental growth. This pattern is caused by the successive molts (shedding of the outer skin that has become too small) that the larva must undergo before it finally enters the inactive pupal stage. The pupa is simply the hardened outer skin of the last larval stage and the adult will develop inside of this protective skin.
In the insects that undergo complete development, the larval stages appear quite different from the adult form. The larvae of flies (order Diptera) that are commonly recovered from decomposing human remains lack functional legs, and the body of many species appears cream colored, soft-bodied, and quite "maggot-like". For a picture of some of the maggots commonly found on human cadavers click here. Once the larva or "maggot" is through feeding it will migrate away from the corpse in order to find a suitable site to form the pupal stage. The pupae of blow flies are often overlooked, as they closely resemble rat droppings or the egg case of cockroaches. The pupal stage is an extremely important stage to the forensic entomologist and a thorough search should be made for the presence of pupae at any death scene. If the adult insect has not emerged, the pupa will appear featureless and rounded on both ends. For a picture of a blow fly pupa click here. If the adult insect has emerged, one end will appear as if it has been cut off, and the hollow interior will be revealed. For a picture of an adult emerging from the puparium Click here. Most adult blow flies appear a metallic green or blue and are easily recognizable. For a picture of two common adult blow flies click here.
The beetles (order Coleoptera) are one of the largest groups of animals and they also undergo complete development. Because of their development the larvae appear very different from the adult form. Although the larvae or "maggots" of a large number of blow fly species may look almost identical; the larvae of beetles may look very different from one species to the next. Beetle larvae recovered from corpses can be easily differentiated from maggots as they have 3 pairs of legs and the maggots found on decomposing remains will not have any legs. Once a larva as been identified as that of a beetle, further field identification can be accomplished because of the wide diversity of larval forms. The bodies of beetle larvae may range from almost white, robust, and hairless to dark brown, slender, and quite hairy. Others may appear almost black and have armored plates on their back. For a picture of some of the most common beetle larvae click here. Although the number and appearance of adult beetles that can be found on human remains is much too diverse to show even a representative sample, two of the most common carrion beetles can be viewed by clicking here.
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