Blowflies are often the first to arrive to the scene of a crime, lured by body fluids and gasses emitted from a corpse within 10 minutes of a murder occurring.
For that reason, forensic scientists have long used blowflies to help establish time of time. And while the fly’s lifespan does play a central role—for example, it takes five days to go from egg to maggot, so a maggot-covered corpse would most likely have been dead for five days—it’s much more complicated than that.
“[Species] identification is the most critical step,” says Jonathan Parrott, assistant professor of forensic science at Arizona State University. “If you identify the species wrong, you are going to be applying incorrect data to your estimated time of death.”
But this data doesn’t exist—or at least didn’t until Parrott began developing one of Arizona’s first databases of forensically important blowflies two years ago. Today, he’s two-thirds through the project that will ultimately help investigators determine more accurate and robust time-of-death estimations from insect evidence.
“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.”
Both data sets are important as blowflies respond differently to external conditions. Factors such as temperature, humidity and changing seasons can affect the lifecycle of a blowfly species. For example, a blowfly species found on an abandoned body during summer in Chandler, Arizona may have a different lifecycle than a blowfly in the winter just 30 miles north.
“By analyzing species from different areas, especially at the genetic level, we can answer questions about species migration, possible invasive species and learn how climate change and human disturbances are affecting species migration,” said Parrott.
Collection and analysis
Parrott’s team collects anywhere from 10 to 100s of blowflies each week. That means, at any given time, there are about 3,000 blowflies in the ASU lab.
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The researchers use a simple plastic trap baited with chicken liver—a blowfly favorite. The traps are placed in an enclosed location just outside of the lab, where they can be undisturbed. Others are put in specific locations around Chandler and Avondale.
Once collected and returned to the laboratory, the insects are separated into different species—nine in total. Some are placed in vials with an ethanol-water solution and studied under a microscope both morphologically and for DNA and RNA. Others are placed in boxes covered with nets and placed in an incubator, which ensures temperature and humidity control. Still others are mounted and classified in display boxes.
Data logged from the collected blowflies includes species, locations, dates, seasons, temperature, humidity and other conditions.
“We are using the DNA data to build standard operating procedures, which are absent in forensic entomology,” said Parrott. “Since some species of blowflies are very closely related, DNA sequences can separate one species from another.”
In addition to determining species in the Phoenix area, Parrott’s lab is expanding to surrounding states, particularly to areas where data is missing and disturbances are limited, such as national parks and monuments.
“This project is important in the field of forensic entomology as it also aids in identifying blowfly populations and their tendencies to stay in particular climates and locations,” said undergraduate researcher Kathryn Melancon, who is majoring in forensic science. “This survey can also be used to monitor the rise and fall of populations.”
The electronic database will be released in increments for use by the public starting later this year.
