The concept of forensic entomology goes back several hundred years. But it has only been over the last few decades that scientists haves made a systematic study of the science to determine if it actually is a feasible discipline for use at crime scenes.
According to ” Insects in Legal Investigations:” 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.
Forensic entomology is identified as the use and study of insects as their appearance at a crime scene relates to the commission of a crime. It is a study primarily relating to death investigations, but it may also reveal the presence of narcotics, drugs and poisonous substances in a corpse. A trained forensic entomologist may also be able to pinpoint the exact location where death occurred and the approximate time the victim died.
A forensic entomologist can estimate the time of death based on his examination of the growth stages of certain insects—in particular he is looking for evidence of blow flies. A female blow fly will deposit a mass of eggs in the vicinity of any open body orifices or wounds. Over time (8-24 hours) these eggs will begin to hatch into an immature larvae stage (maggots). Maggots have very limited mobility so their feeding range is large enough infestation can result in the quick disappearance of soft body tissue and bodily fluids. These maggots can skeletonize a corpse in a matter of days, removing any tissue or fluids that would permit laboratory analysis.
At and around the crime scene, evidence of the insect infestation is collected. This includes fly eggs, maggots, pupa stage and adult flies. During the pupa stage, the larvae leave the body and burrow into the surrounding soil. After a short time the pupa emerges from the soil and completes the metamorphosis—becoming an adult blow fly. Each can be important in their relation to the corpse. Maggots, pupa, and flies can contain toxins and foreign matters present in the body tissues they consumed. The presence of specific stages of the cycle can help determine the time of death, which will be discussed later. And the type of bugs and flies can determine location of the body. Many times entomologists have identified non-resident species of bugs that indicate the corpse had been moved from one location to the place of discovery post-mortem. It is important for the investigator to collect all forms of entomological evidence to complete the story.
Once samples from the scene arrive at the lab, the various growth stages are examined and recorded. From these data the Post Mortem Interval (PMI) is determined. The PMI indicates the period from the time of death to the time evidence is collected and examined. Many times this can place the time of death within a day or two of the victim’s actual death. Other factors are important to note, such as temperature of the soil, air temperature, and surrounding soil and vegetation, as these can all affect the gestation cycle.
If the reader is interested in learning more on this subject matter, you may download a free technical bulletin that describes the step-by step evidence collection procedure as well as the tools and supplies needed by the forensic entomologist at the crime scene. Entomology Manual
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