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Focus on Forensic Entomology
James Clery, Dept of Zoology and Entomology, Rhodes
University, South Africa
Forensic entomology (FE) is the use of insects in matters of the law. FE can be broken down into various areas of application. FE can be used to help investigate where the fault lies in stored products to determine if insects infesting a shipment of say coffee were brought in with the shipment from the country of production, or infested later, during storage. Often a lot of financial interest is involved with such legal actions.
A suspect's movements can be identified through an analysis of insects found on certain objects. The most commonly used is from car bumpers, windshields and grills. It is possible to determine, from the insects recovered, whether that car had been recently driven through certain areas. This may be important if a suspect had not driven through such an area where a body had been found. It creates a situation where the suspect is unable to explain their actions. The origin of cannabis production can be determined through an analysis of the insects that are often caught in with the plant material that is later shipped. Insects that are only found in certain areas of South America due to restricted distribution can allow for a targeted search for production sites. Stored cannabis can also become infested with insects, mainly beetles, after harvesting and prior to shipment. The same applies as before due to geographical specificity of the insects concerned.
Insects may be involved with cases of sudden due to anaphylactic shock and other types of allergic responses to insect bites or stings. Similarly, traffic accidents may be attributed to insects. It is a common reaction to become agitated and cause an accident if an insect flies into an open window. A specific case of an airplane crash was due to a bees nest in one of the engines which caused a blockage in the air intake valve. Medico-legal entomology, or medico-criminal entomology, involves the use of insects to obtain information regarding cases of unnatural death. The human body, like other animal remains, will pass through a series of decompositional stages. This is a continual process but can be divided into specific stages for clarity. The number of stages determined depends on the size of the cadaver, and the time of year in which the body is exposed. The following stages are found: Fresh, bloated, decay and lastly remains. The fresh stage lasts up until bloating from anaerobic bacteria occurs. This is dependent on the conditions in which the body is present.
Usually Bloat starts at greater than 48 hours after death. Autolysis, or cell breakdown, accompanies this bloating stage. Decay is the putrefactive stage, involving anaerobic bacteria, and can be subdivided into early, mid and advanced. Flies will lay eggs into the body openings and at wound sites if they are exposed and environmental conditions are suitable for fly activity. Maggots will consume the flesh and disseminate bacteria throughout the body. After the majority of the flesh is removed, the dry remains stage begins. The remaining dried flesh, skin and tendons will be removed by certain families of beetles and moths. The entire process of decay will depend on the environment, and may not occur at all if flies are excluded from the body. In this case mummification and adipocere, a waxy substance created from the fat layer in the body, formation may occur. Each stage of decomposition will have certain insects involved. This will be from flies through to beetles and finally moths. The blowflies are the first to find the body and lay eggs. Then come the houseflies and flesh flies. Flesh flies lay larvae directly onto the body, the eggs hatching inside the adult female fly.
Beetles now come into the picture, where they feed both on the maggots feeding on the body and the body itself. Dermestidae, and other beetles consuming dried materials, will finish off the remains along with the Tineid moths. Flies are holometabolous and therefore have a complete metamorphosis, the maggot stage being completely different in habitat and mode of life to the adult. The adult will lay eggs on carrion, and maggots will emerge. The maggots will feed and pass through three stages of development. After consuming adequate food for development to adult, the maggots will enter a pre-pupal stage where they wander from the body looking for a sheltered area for pupation. There they will pupate and start to develop into adult flies. The adults emerge from the pupal cases. After emergence the adults are unable to fly and may be mistaken for spiders in an indoor death scene. After as little as thirty minutes they will be fully able to fly and the life cycle is brought full circle. Knowledge of the processes of decomposition can be used in the following ways in medico-criminal entomology. Season of death can be determined because certain species of insects are only active at certain times of the year.
This determination can be made from insect remains or empty pupal cases. A different assemblage of insects will be found during the different seasons. Geographic origin can be determined because many insects are localized within certain boundaries due to their ability to withstand cold and other climatic conditions. Competition with other species may also limit dispersal. A certain region may be pinpointed from the insect species found, and movement of the body from one area to another suggested. Certain species of flies will only be found in urban or rural environments. Thus it is possible to determine whether a cadaver had been moved from an urban to rural environment following death based upon fly species present on the body. A break in the decomposition process may suggest movement or storage of the remains. The process of decomposition will be altered if the body is wrapped or stored following death and no fly access has been gained. The body will decompose through bacterial action and no longer be appealing for the first wave of blowflies to lay eggs if it is later dumped. The 'missing' blowfly species would indicate a missing link in the chain of events. The microclimate of the cadaver at the time of death can be determined via the species found on the body. Certain flies will only lay eggs in the dark and others only in the light.
From identification it may be possible to determine that the person had been killed indoors and later dumped outside.
Calliphora, the bluebottle flies, prefer to lay eggs in darker places,
and Lucilia, the greenbottle flies, prefer to lay eggs
in well-lit environments." Trauma can be determined if the maggot infestation occurs preferentially in a non-orifice site. This can be determined by the age of the maggots in certain areas of the body. If the maggots collected from the genitals of a female victim are as old, or older, than the ones from a natural site then it is suggestive of sexual trauma to the genital area. Similarly infestation in the hands is very suggestive of ante-mortem defense wounds. At least a closer inspection should be made to try and determine if any damage to the bones can be determined such as caused by sharp instruments. It is very common for the hands to be very well preserved even in well-decomposed bodies because the hands become mummified and unattractive for maggot consumption. Neglect can be determined from the age of the maggots in a wound in nursing home patients. The minimum time since the changing of a dressing can be made. Similarly, neglect of infants can be determined from the aging of maggots infesting unchanged diapers. Infestation of the genitals often occurs, with subsequent invasion of living tissues. This infestation of living tissue is termed myiasis. The presence of drugs in a well-decomposed cadaver can be determined by a toxicological analysis of the insects recovered from the body.
Post Mortem Interval (PMI) is the primary aim of any investigation involving insects. This may be obtained by two major methods. 1) Maggot age and development 2) Succession based. The first case is used in cases where a full fly life cycle has not been completed. As soon as the pupae have hatched and the adult flies emerged, the second succession based approach must be employed. As temperature regulates the fly life cycle a higher temperature will result in a faster developmental rate. The time from oviposition until the stage of the larvae recovered from the body can be determined and the PMI estimate made. The succession based approach uses the assemblage of insects found on the body at the time of discovery. Different fly and beetle species prefer different stages of decomposition, from fresh to skeletonization. As the body progresses through the various stages, different species will find the body attractive and lay eggs or larvae. This assemblage will be specific for the duration of decomposition, season, habitat and geographic region.
After death the human body proceeds through a series of decompositional stages, with characteristic insect species being associated with each. Flies will locate a body soon after death, where they feed upon exudates, and oviposit eggs into the natural body openings and at wound sites. Maggots hatch from these eggs and pass through three stages of development whilst consuming the soft tissue. The maggots eventually develop into pupae, whereupon the adults emerge, thus completing the cycle. Forensic Entomology exploits this natural process of decomposition in order to obtain information regarding manner of death, possible corpse movement after death, identify drug use in heavily decomposed bodies, how long a child or patient had been neglected, link suspects to crime scenes, determine the immediate conditions at the time of death, and most commonly, estimate the Post Mortem Interval (PMI). When forensic entomology is to be employed in a case, recognition, collection and preservation of the entomological evidence is required. At crime scenes insects may be found far from the body, and a through search under and between objects should be made. At autopsy, a more detailed search may be made on the body itself. Prompt packaging, and delivery, to the entomologist is vital to safeguard the survival of the living evidence, and ensure the best PMI estimate is obtained.
James Clery has worked as a forensic entomologist in New York, London and is
now studying with a leading group in this field in South Africa.
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