Discovery could give investigators a new tool in death investigations

A discovery by FIU researchers could help forensic investigators close the gap on estimating time of death.

Often, death investigations rely on maggots — the larvae of blow flies that are among the first insects to colonize a body after death — to estimate how long a person has been dead. The presence of eggs or the sizes of the maggots are indicators of time since death. Yet, there is a stage in development during which the maggot’s physical form changes very little, which limits the precision of time-of-death estimates. While changes may not be visible on a maggot’s outside, its genes can still tell a story.

Rather than relying on the physical appearance of maggots, FIU biologists Matthew DeGennaro, a leading insect researcher, and Jeffrey Wells, whose insect research is tied to forensics, have identified a technique that focuses on a maggot’s gene expression and metabolic changes to more accurately estimate how long someone has been dead. In doing so, they have created a molecular “clock” that could revolutionize death investigations worldwide. The findings were published inPLOS Genetics.

“Studying insects can reveal insights that benefit our lives” DeGennaro said. “Estimating the time of death is a surprising example.”

The traditional process of estimating time since death using insects involves collecting data on the maggots' developmental stages. Because insects are cold-blooded, both temperature and time must be considered. In the past, the time since death was determined by looking at size, weight and appearance. The older the maggot, the longer the person has likely been dead.

However, there is one problem with that process: As the maggots get older (specifically late-stage larvae), they don’t change much in size or shape, which makes it difficult for medical examiners to pinpoint their age. This time period could last from hours to days, depending on the temperature. Weight and behavior are unreliable indicators during this time, which creates a large gap in accuracy for estimating time of death.

The researchers successfully pinpointed nine specific genes that act as reliable molecular markers for age. Ph.D. student Sheng-Hao Lin was able to detect changes in gene expression that happened during the late-stage larval timeframe. This allowed the researchers to create a molecular clock that works even when maggots aren't physically changing and, as a result, the team was able to reliably determine the age of the late-stage maggots.

Now that the foundational research is complete, the next step is testing the molecular clock in real-world conditions.