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Arizona Blowfly Database Develops Empirical Support for Time of Death Estimation

by Anthony W. Accurso

A research project in Arizona seeks to develop support for a method of determining time of death by cataloging information about blowfly species.

The gases emitted by a corpse can attract nearby blowflies to colonize and help break down a body. While blowflies will get to a body within minutes, the life cycle of the flies will vary depending on the specific species, making the process of determining the time of death imprecise.

“Species identification is the most critical step,” said Jonathan Parrott, an assistant professor of forensic science at Arizona State University. “If you identify the species wrong, you’re going to be applying incorrect data to your estimated time of death.”

According to Forensic Magazine, “a blowfly species found on an abandoned body during summer in Chandler, Arizona, may have a different life cycle than a blowfly in the winter just 30 miles north.”

Parrott’s project has been using DNA to identify distinct blowfly species, then subjecting each to specific temperature and humidity environments to obtain information about how these affect the timing of a fly’s life cycle.

“What makes our research unique is that there has not been any developmental or DNA data available prior to our project,” said Parrott. “We are cataloging both morphological and genetic data.”

Knowing that certain environmental conditions can alter biological periods – like how long it takes eggs to hatch into maggots – can make the difference between suspicion and exoneration if a suspect can establish an alibi for the actual time of death instead of an inaccurate one based on rough estimates which fail to account for species differences.

Parrott’s work will contribute to standard operating procedures for law enforcement investigations in Arizona. Eventually, this work will need to be done elsewhere to bolster this method of time-of-death analysis in other states.  




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