Jeanine W. Tessmer
The importance of entomology to legal investigations has been known for several hundred years, but it has been recognized as a separate specialty only for the last 20 years or so. Forensic entomology applies to any aspect of insect study that may aid in resolving a situation that goes through the legal system. This may range from insect parts found in food products to determining the time of death of a crime victim who goes undiscovered for several days.
With humans there are various methods of determining the time of death, such as rigor mortis and body temperature. But after 24 to 36 hours, these methods and others no longer give valid results. It is then that the services of the forensic entomologist become valuable.
Certain insects are highly attracted to dead and decomposing bodies, and their life cycles allow experts to determine the time of death. The insects most beneficial in this process are flies, specifically blowflies and flesh flies.
Familiarity with the biology and geographic distribution of these flies and the ability to identify specimens from all stages of the life cycle are what the forensic entomologist can bring to the investigation process. The time of death is established based on the known length of time for the flies to develop to that stage under a given set of conditions. Environmental factors (temperature, rainfall, kind of habitat and length of daylight hours) affect egg deposition and length of development.
Murderers frequently go to extreme lengths to cover up their crime and lead investigators in the wrong direction. Victims have been discovered submerged in water, burned in automobiles and wrapped in various kinds of materials to conceal them. They often are found in wooded areas, ditches and overgrown vacant lots. Research at LSU has been conducted to provide as much information as possible to help law enforcement personnel with their investigations.
Because of the similarities of swine tissue to that of humans, pigs have been used most frequently for field tests. Data have been collected from tests carried out in pastures, ditches, riverbanks, pine forests, hardwood forests, car trunks and burned vehicles. Field tests have been carried out in all four seasons of the year and at the time of both the new moon and full moon.
Since it is not always possible for an entomologist to go to the crime scene, it is necessary to educate and train others to collect and preserve entomological evidence and to record information on habitat and ambient conditions. The training of law enforcement personnel and crime scene investigators is an important part of the LSU AgCenter’s outreach educational program.
Jeanine W. Tessmer, Adjunct Instructor, Department of Entomology, LSU AgCenter, Baton Rouge, La.
(This article appeared in the spring 2001 issue of Louisiana Agriculture.)
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