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Understanding Environmental Effects on Blowflies Permits Fine-Tuning of Evidence Revealed From Fly Colonization of Decomposing Bodies

by Douglas Ankney

Forensic investigators have long used the well-known stages of blowfly development found on bodies post mortem to determine the amount of time that has elapsed since death. However, that standard of measurement is misleading when the temperatures around the body are outside the moderate range.

For example, in a recent case from Las Vegas, a body was found on a sidewalk in July. Since no blowflies were detected, investigators assumed the body had not been there long enough for the flies to locate and colonize it. But entomologist Aaron Tarone proposed an alternative explanation: “[The] temperature of the concrete surrounding the body, or the temperature of the body itself, was above the thermal tolerance of blowflies.” That is, it was simply too hot for the blowflies to be active on or around the body.

Researchers from Texas A&M University, with the support of the National Institute of Justice, used two blowfly species and measured aspects of their behavior at differing temperatures to determine “when and where blowflies can be active based on environmental temperature.” The researchers noted after testing blowflies at their four larval stages that the flies experienced “knockdown” (defined as “an inability to walk or locomote”) at various high and low temperatures.

By allowing for temperature changes and corresponding “knockdown” throughout a given day, the research will help investigators avoid overestimating or underestimating the amount of time elapsed since death. Additionally, the measurements from the research could provide evidence that a body was transported after death, e.g., from a colder high elevation to a warmer low elevation and vice versa.

Tarone said the research also provides “information as to how suboptimal environmental conditions, such as heat waves or cold snaps, affect adult colonization and larval development” and will help “to better understand basic aspects of blowfly thermal biology in order to improve our use of blowflies as evidence in death investigations.” 


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