A new project being run by researchers at Bournemouth University aims to create a more reliable measure of time of death in criminal cases by creating the first ever industry standard protocol on which forensic entomologists can base their calculations.
Protocol on blowfly development
will standardise estimations of
when someone died
In the hours following death, pathology-based techniques are usually the most reliable in establishing the amount of time that has passed but, after a few days, insect-based evidence is often the only reliable means of making a determination.
Scientists have long used the lifecycle of blowflies and other insects to establish the time of death by estimating the amount of time that has passed since eggs were laid on the corpse, a calculation known as the minimum post-mortem interval. However, though such techniques have been used in hundreds of court cases, the basis for such calculations can vary widely from one forensic scientist to another.
"At the moment, everyone is using a different procedure and different conditions, which leads to very different results,” says Dr Andrew Whittington, Senior Lecturer in Forensic Science at Bournemouth University.
"As an example, a type of blowfly common to Britain might not be cold tolerant in Dorset, but if the same species was found in Edinburgh, it's likely to be cold tolerant, which means it can lay its eggs and they will develop at a lower temperature. This needs to be taken into account, when calculating a post-mortem interval. At present, the data used doesn't reflect these kinds of variables."
Blowflies, along with many other species of fly, undergo a specific development cycle that is relatively predictable. They are attracted by volatile compounds given off by the body and will usually arrive at the scene of a death within minutes.
The fly will then proceed to lay hundreds of eggs in batches around the natural bodily orifices such as the nostrils, mouth and ears, as well as any open wounds. These eggs will often hatch within approximately 24 hours to release a larva or maggot. Larvae then undergo three stages of development known as the first, second and third instar.
After this point the maggot’s skin contracts to form a hardened capsule known as the puparium, which is designed to protect the insect through metamorphosis until it becomes an adult. By determining which stage of instar development is present on a corpse, scientists can work backwards to establish how long ago the first insects arrived.
Dr Whittington began to establish a benchmark for the lifecycle of blowflies through collecting samples from non-suspicious deaths. In these cases, the time of death was known, which enabled the team to pinpoint different stages of the lifecycle.
“The idea behind creating a standardised industry protocol to be used in the laboratory which can establish the lifecycle of a particular species of blowfly, is that we would then have comparative conditions that can be used anywhere in the world.”
Having been awarded Higher Education Innovation Funding, Dr Whittington plans to expand this by creating lab based experiments using blood agar as a rearing medium for blowfly maggots to study their growth under a variety of conditions.
"If we know that blowflies reach a certain stage of development under certain temperature conditions, we can then apply this data to a post-mortem situation, which will help forensic experts to build up a much more accurate picture of the time of death."