Can Insects Talk? At Crimes Scenes They Can Speak Volumes
Forensic entomology had its beginnings way back in the 1300s, but during the last few decades it has been given a more serious look by criminal investigators. It is the study of insects that provides a relationship to the acts of criminals. Forensic entomology is basically involved with death investigations, but in recent cases it has been used for the detection of drugs and toxic substances and in some case to pinpoint the actual location where the crime was committed.
Pathologists and crime scene investigators alike attempt to determine the approximate time of death, as this knowledge can either substantiate or disprove a subject’s alibi.
The insects found on or around a cadaver can provide an estimate as to how long ago death occurred. The outcome of such an investigation will provide a range of time. This estimate may be a few hours to days or months to bodies that died several years ago.
The science involved here is to use insects to give a minimum Post Mortem Interval (PMI), which is based on the rate that certain insects mature. Once they hatch from eggs, some insects have an immature stage—better known as the “maggot stage.” Movement during the maggot stage is very limited, but as adults these animals become more mobile than most animals on this planet. These same insects have developed the ability to hatch from eggs, pass through the maggot stage and become mature adults while reaching maturity on dead creatures including humans.
The most common insects that are often first to appear at a death scene are the various species of blow flies.
According to NC State University, depending on the ambient temperature … maggots usually complete development in 4 to 10 days, and then their larvae burrow in the soil and pupate for up to a week. Adult flies emerge from puparia and make their way to the surface of the soil. About a week later, females begin to deposit eggs and the life cycle is repeated.
The entomologist seeks to recover these insects at every stage of their development, as they are a valuable tool used in a toxicological investigation. A mass of maggots can quickly skeletonize a cadaver in a brief period of time. As a body begins to decay, body fluids like blood and urine and soft tissue quickly disappear. When only a greatly desiccated corpse is discovered, the only toxicological evidence remaining will be inside the insects themselves.
So time is of the essence and the entomologist must busy himself collecting as many samples as possible at various stages of their development. Because many insects will assimilate drugs and poisons that build up in human tissue prior to death, a toxicological evaluation can recover them.
Another valuable clue is that DNA evidence can be extracted from the digestive tracts of insects. And if physical violence occurred between the deceased and the perpetrator, DNA from that subject may also be recovered—proving a link between the suspect and the body.
An entomological investigation of a death scene is conducted using the following steps:
1. Observe the general area and location of the body. Describe the location based on surrounding vegetation, proximity to roads or paths. Make a meteorological investigation to determine temperatures on various parts of the corpse, and general weather conditions over a period of time.
2. Observe the infestations of insects on the body and what stages of development are observed: eggs, larvae, pupae and/or adults. It is also important to become aware of other insects such as ants and beetles.
3. Collect samples of live and dead insects for analysis as well as digging into the soil around the body to locate and collect pupae.
A. Make notes of whether doors and windows are open or closed. Ascertain the room temperature. Determine if the initial responders to the scene may have been responsible for opening or closing them
B. Repeat Steps 2 and 3 above.
Before responding to a dead body investigation, the entomologist should check his equipment and supplies, being certain to have sufficient numbers of evidence containers to be used to collect insect samples.
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