Blowflies have long been used in forensic science to estimate time of death as they are often the first insects to arrive at a body, sometimes within minutes. However, new research suggests they may also play a role in preserving crucial DNA evidence, particularly in sexual assault cases. A study published in the Journal of Forensic Entomology, led by Katherine Brown and Alexine Clarke, has shown that blowflies can inadvertently collect and retain sperm DNA, offering forensic scientists a potential new method for linking perpetrators to crime scenes.

Blowflies as DNA Carriers

“Forensic entomology has traditionally been used to determine postmortem intervals but our study examined whether blowflies that come into contact with semen could retain DNA in a way that assists investigations,” Clarke explained. “While DNA has previously been recovered from blowfly larvae this is the first study in England to specifically examine sperm cells.” To test this, researchers placed three piglet cadavers outdoors in temperatures between 5.5°C and 14°C and applied boar semen to three locations on each. These were behind the ears, between the rear legs, and across the trunk. Blowflies quickly arrived and laid eggs which were later collected at different developmental stages for analysis.

Key Findings

Using differential extraction techniques, the researchers found intact sperm cells or sperm heads in at least 50 percent of the blowfly samples. The first instar larvae had the highest concentration of sperm and the most intact spermatozoa. By the third instar stage, the samples contained mostly sperm heads with detached flagella.

“This is an exciting discovery because it demonstrates that blowfly eggs and larvae can retain sperm evidence, potentially linking individuals to crime scenes in cases where conventional DNA collection methods are difficult,” Clarke noted.

Potential Forensic Applications

Brown, a principal lecturer in forensic science at the University of Portsmouth, highlighted the importance of this research. “This builds on existing knowledge of how DNA is detected in insect larvae but what makes it significant is that we can now attribute the DNA to its specific source, sperm,” she said. “This could be a valuable tool for investigating serious crimes particularly those involving sexual violence.”

Next Steps in Research

Clarke intends to expand the study by working towards generating full DNA profiles from blowfly samples. Future research will also explore how environmental conditions and time affect DNA preservation in these insects.

While still in the early stages, this study suggests that blowflies which are typically associated with decomposition could become an unexpected tool in forensic investigations. This could be particularly useful in cases where traditional DNA collection methods are challenging.

Republished courtesy of the Journal of Forensic Entomology 

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