How Insects Aid Investigations

Forensic Entomology uses the established timetables of metamorphosis progression in certain species of insects found in or near the corpse to aid Forensic investigations. The insects feed on decaying remains and are found in a corpse at specific points in the decomposition process. This is known as "Insect Succession," and it is a predictable pattern based on the specific species and the weather at the time. Forensic Entomologists can examine the insects present in the body to approximate the time since death, known as the Post-Mortem Interval. Temperature is a very important factor in insect colonization. It has a strong impact on the time period needed for insect development because insects are ectothermic, or "cold-blooded". Their development is based on environmental temperatures; if the environment is too cold and a temperature threshold is not met, the insect will not develop until that temperature threshold is met.

Forensic Entomologists use Accumulated Degree Days, or ADD, to predict how long the insect has been present in the corpse. ADD is the thermal input needed for an insect to grow and develop. It can also be measured in hours rather than days; this is known as Accumulated Degree Hours, or ADH. ADD and ADH take into consideration not only the stage that the insect is currently in, but also the external temperatures of the environment to predict the stage of development the insect should be in based upon those temperatures. Discrepancies in these two times are investigated and can help approximate not only how long the person may have been dead, but also if the body may have been moved after death. This is a fairly accurate method because insects tend to colonize the corpse from minutes to mere hours after death.

Assessing insects based on size and stage of development while considering the environmental temperature generally produces a reliable estimation of time since death. Essentially, the size of the larva, or "maggot", indicates the age; this generally means that the larger the larva is, the older it is. Beetles are usually found at the later stages of decomposition, such as in the active and advanced decay phases. Beetles generally are involved in breaking down of various body structures such as hair and skin, but they can also be found preying upon any fly larvae that may still be present in the body. Beetles from the Dermestid family are also known as "skin beetles" because of their tendency to feed on skin remains. Dermestid larvae are often used in museums to clean tissues from bones for this reason! Beetles from the Staphylind (Rove Beetles) and Silphid (Carrion Beetles) families feed on the maggots of many fly species found within corpses.

image of Dermestid Beetle Larvae on otter skull and Rove Beetles

In addition to Post-Mortem Interval approximations, insects can also help identify other pertinent information in a death investigation. Insects can help narrow down the location a death occurred if there is suspicion that the body has been moved. Sometimes insects are found in very specific niche habitats; if that insect is found outside of its established typical habitat, it may warrant additional investigation. For example, a body found in a corn field with maggots typically only found in urban areas might suggest that the person was killed elsewhere and dumped in the corn field cornfield at a later date. While there is variation, some insect species have definite preferences for when and where they will lay eggs. For example, some species will only lay eggs in shaded or indoor areas. If a body is found with this type of egg or larva out in a sunny location with no shade, it raises the suspicion that perhaps the person died in a different location and the body was moved at a later date. If no insects are found in a corpse at all, it can generally be assumed that the body was stored in such a way as to prevent insect colonization. Some examples of this include freezing, tightly sealing the body in a container or burying the body very deeply in the ground. In cases where neglect or abuse prior to death is suspected, insects also prove useful. Typically, Forensic Entomologists look for key species found in cases of neglect and abuse such as the Green Bottle Fly, False Stable Fly and Lesser House Fly, which are all attracted to urine and feces. This is an indicator because those three species are more highly attracted to urine and feces rather than the decomposition odors of a corpse that attracts other insects. Urine and feces are typically found in soiled underclothes, diapers or soiled bed linens, which may indicate some level of neglect or abuse. Finding these insects in a corpse can signal prolonged neglect or abuse that contributed to death and is generally regarded as suspicious. DNA can be taken from any blood found in the insects' digestive tracts and tested to possibly establish a link between both the victim and the suspect.

image of Green BottleFly, False Stable Fly, Lesser Housefly

Finally, insects can also be used to determine if toxins or drugs are present in the corpse; this specialty of Forensic Entomology is known as Entomotoxicology. Entomotoxicology can provide crucial toxicology evidence when the body is in advanced stages of decomposition that would otherwise be unattainable due to the absence of body fluids used in standard toxicology testing. Entomotoxicologists take samples of the insects found in the corpse and compare their size and stage in development to known standards to determine any obvious discrepancies. Certain toxins, such as cocaine, accelerate the growth process of the larva stage, whereas other toxins, such as methamphetamine, cause a decrease in the average size of the pupae. Entomotoxicologists also examine the feces of the insects or obtain samples directly from the insects and test for toxins using methods, such as gas chromatography. In addition to toxins, Entomotoxicologists can also identify unique environmental factors or traits about the deceased such as abnormally low levels of common contaminants such as Mercury. An abnormally low level of mercury is often linked to a specific geographical anomaly or location and can help identify where an individual is from if it is unknown at the time of the investigation.

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