Blowfly eggs and larvae can carry crucial evidence, like sperm, which could help in sexual assault investigations, a new study from the University of Portsmouth has found.
The findings demonstrate that blowflies can inadvertently collect and retain DNA evidence from sexual assault crime scenes, making them a potentially powerful tool for forensic investigations.
Forensic entomology is already well-established for its ability to estimate time of death and other details by studying insect activity. But this new study examines whether insects can carry DNA evidence to identify a sexual offences suspect.
Dr Katherine Brown viewing Calliphora vicina blowfly under a microscope
This discovery could prove invaluable in solving complex cases where conventional evidence is scarce or unavailable.
Alexine Clarke, from the University's School of Criminology and Criminal Justice , said: "I wanted to question whether eggs being laid on a body with semen present could act as a vessel for DNA, which would theoretically allow us to link an offender to the crime.
"Although forensic entomology can be used in death investigations to estimate time since death, recovering male offender DNA, attributed to sperm cells, from the gut content of blowflies is relatively new, and this is the first time research in England has looked specifically at sperm cells."
This research builds on existing knowledge of host DNA detection in blowfly and other insect larvae, with the important distinction that we can attribute the DNA to the cell-of-origin; sperm. Not only does this indicate the source of the DNA, but also potential activity, contributing significantly to serious crime and tackling violence against women and girls.
Dr Katherine Brown, Principal Lecturer in Forensic Science
Researchers designed an experiment to mimic real-world forensic scenarios. A small amount of boar semen was applied to the skin of pigs to simulate evidence sometimes found at serious and complex crime scenes. Blowflies were attracted to the decomposing remains and lay hundreds of eggs and larvae.
The scientists processed some of the blowfly eggs and younger larvae by washing and freezing them after collection. Other larvae were left to grow larger and their gut content was examined just before they pupate.
They used a specialist technique called differential extraction to separate the sperm from piglet skin cells. The samples were then analysed under a microscope to detect the presence of intact sperm.
Alexine Clarke separating sperm and skin cells using centrifugation
Mrs Clarke added: "In at least 50 per cent of the samples, sperm cells were present. This is an exciting finding because it shows that the blowfly eggs and larvae can retain evidence such as sperm, potentially linking perpetrators to crime scenes."
Dr Katherine Brown , Principal Lecturer in Forensic Science, said: "This research builds on existing knowledge of host DNA detection in blowfly and other insect larvae, with the important distinction that we can attribute the DNA to the cell-of-origin; sperm. Not only does this indicate the source of the DNA, but also potential activity, contributing significantly to serious crime and tackling violence against women and girls".
This paper was very much a scoping study and Mrs Clarke has plans to develop the research further. She is now working on a PhD at the University of Portsmouth, which is exploring whether you can get a full DNA profile from the samples.
Further research is also necessary to explore how environmental factors and time affect the preservation of such evidence on and within blowflies.
Dr Brown added: "As we expect samples to rapidly degrade, this project is interlinked with our Single-Cell DNA Identification ( SCAnDI ) work to maximise chances of obtaining a full DNA profile."
The paper is published in the Journal of Forensic Entomology .
