(Shutterstock)Investigators have used the consistency of insect growth on human remains for more than a century to assist them in determining time of death. Flies are by far the most commonly used bugs for the purpose, since they leave eggs, maggots and other traces on, in, and around a corpse.

But mites that hitch a ride to the decomposing remains might be an overlooked indicator to pin down postmortem interval after months or even years, according to a study in the Journal of Medical Entomology today.

“Development of arthropods, particularly blow flies, associated with decomposing human remains currently represents one of the more reliable methods for estimating the… time of death of an individual,” write the researchers. “Little attention has been paid to the utility of mites despite the fact that they may represent the first and/or final ecological seres (waves) association with carrion decomposition due to the success associated with blow fly biology in (time of death) estimation.”

"They're very small and hard to notice," said Meaghan Pimsler, the lead author of the study, formerly of Texas A&M and now with the University of Alabama, in an interview with Forensic Magazine. "As with anything, the smaller it is, the harder it is to work with."

The mite, known as Myianoetus muscarum, essentially hitches a ride on flies to get its carrion meal, according to the study. The study analyzed three different case histories of the mite on advanced-decomposition indoors, all in Texas.

Two of the bodies were found in closed-off rooms in apartments in Harris County in February 2015. The third was found with a window open, in Hayes County, in April 2011. 
The scientists found mites on all three bodies, in conjunction with the growth of flies maggots and larva on the remains, they found. They also tracked the weather conditions, and the ambient temperature in the residences where the deceased were found. 

The entomologists made no dates of death conclusions based solely on the mite populations – but they found enough variation based on the circumstances to recommend a full look into the new bugs. 

The mite growth could be a parallel track that would supplement the fly work – and make postmortem interval more accurate, they found. 

Houseflies are the primary indoor insect of use for timing deaths, according to the textbook Practical Homicide Investigation by Vernon Geberth, former NYPD investigator. The blow fly, greenbottles and sheep maggot flies are other species that entomologists currently analyze for their inquiries. Other insects that have come into play are carrion beetles, ants and even worms, depending on the location of the body, Geberth writes. 

Mites had previously played a pivotal role in three well-known murder cases, they added. The skeletal remains of an infant boy found in 1991 in Hawaii produced mites which yielded a death estimate that matched the confession of the murderer. A child pulled from a plastic bag in a German residence in 2004 was killed between a year and a year and a half earlier, based on the mite evidence. And a thick coating of the mite leavings on a mummified newborn in Paris was documented in 1894 – as one of the earliest examples of forensic entomology ever applied to a criminal case.

“The presence of mites on a resource may have important implication to the forensic entomologist, as the mites can arrive early in decomposition and potentially prey on eggs and larvae of primary colonizers,” concluded the team in the latest study. “The coevolution of mites and their insect hosts has led to a dual succession: as insect species replace each other temporally throughout decomposition, mite species associate with those insects also change over time.”

Pimsler, who currently works with bees at the University of Alabama, told Forensic Magazine the mites could be a valuable forensic resource - but a whole scientific framework needs to be established.

"If this is a tool we want to use, we'd want to establish a framework with controlled experiments," Pimsler said. "As with all forensics, it's a puzzle with many different pieces."