Bull ant, Myrmecia sp. Credit: Fir0002/Flagstaffotos
Forensic entomology is primarily focused on using blow flies and beetles to estimate the time since death. And while that information is always helpful, forensic entomologist Paola Magni is urging forensic professionals to consider the activity of other insects as well—specifically ants.
“Ants are often overlooked as a mere incidental presence on a cadaver, and their importance can be missed by an untrained eye,” said Magni, a professor at Murdoch University (Australia) and one of the world’s leading forensic entomologists. “Understanding ant activity on bodies can help us reconstruct the events that occurred at the time of death and during early post-mortem periods.”
Magni is the lead author of a new study published in Forensic Sciences that looks at 10 real cases of ant activity on cadavers during the early post-mortem period. The research—a first of its kind— proposes a classification system to aid in identifying bloodstain patterns caused by ant activity. The proposed classifications could aid in identifying and describing ant-produced external hemorrhages, determining the body’s original position and potential movement, and providing clues about the cause of death.
The cases described in the study occurred between 2015–2021 in the Andaman and Nicobar Islands, Union Territory (India). All cadavers were analyzed in the fresh stage of decomposition, with an estimated post-mortem interval between 4 hours and 1 day.
In the past, ant activity has been mostly reported as abrasions on decomposing bodies. With their sharp mandibles versus soft human tissue, ants can produce alterations that mimic active or recent hemorrhages, which can be misleading during investigations. However, this study found and classified ant-induced blood pattern analysis into four separate groups: droplet, stripe, pool and mixed.
Droplet pattern
According to the study, blood droplets can result from the abrasions of ant mandibles on the skin or mucosal surfaces of a cadaver. For droplets to maintain their shape, they need to form on a flat surface parallel to the ground and exposed to the air. Therefore, the presence of droplets suggests that the body position has remained undisturbed since the insect activity, providing a stable flat surface for the formation and maintenance of such patterns.
In this case, Magni and team found droplets on the protruded tongue of a cadaver that was found hanging (fully suspended). The protrusion of the tongue is a common occurrence in cases of asphyxiation by hanging or strangulation, as it is caused by the pressure applied to the neck’s soft tissues and blood vessels. The soft and exposed tissues of the protruded tongue may attract ants, and the pressure on the surrounding tissues and blood vessels could result in external hemorrhages.
However, the team also found droplets on cadavers that were partially hanging, with feet touching the ground. They observed droplets on the feet and stomach area, as well as the scrotum. The researchers found that the presence of body hair can help maintain the droplets’ shape and prevent dripping.
Stripe pattern
Stripe patterns are also common in hanging cadavers, and can be found with a mixed pattern of droplets. The position of the body, as well as the initial location of ant bites can influence the shape and the distribution of the stripe pattern, according to the researchers. Additionally, clothing or other items in contact with the body can affect the stripe pattern, as some blood may be absorbed, resulting in saturation stains.
Pool pattern
When ants are active in a confined area of the body, they may produce a large number of blood droplets that merge into small pools or large blood stains. Depending on the posture of the body and the area overtaken by ants, the blood pool can be found on the body surface, under the body, or associated with clothing.
Analyses of the pool pattern considers multiple factors, such as the shape, diameter, and depth of the blood pool, as well as the texture and the porosity of the surface on which it has formed. The research team says this information can provide valuable insights into the nature and timing of the hemorrhage.
Mixed pattern
Finally, a mixed pattern exhibits the characteristics of two or more of the other bloodstain patterns, and can occur when the crime/death scene was highly dynamic—such as a struggle or altercation—or the body was moved early post-mortem, for example by first responders. In this study, mixed patterns were often observed developing as a consequence of natural events and on the posterior body regions of bodies due to non-standard recovery procedures.
“Ultimately, these new classifications could improve the accuracy of reconstructing the events that occurred during the early post-mortem period, as well as the circumstances surrounding death,” Magni said.
The study authors consider this area of research ongoing due to the changing nature of ants and insects as invasive species continue to make their impact across the world.
“We continue to learn more about the impact of blowflies, beetles and ants in the post-mortem period—but ants in Australia are changing, so what does that mean for long term criminal investigations?,” Magni said. “We are now looking into how these changes in species will have a different impact on cadavers as there will be ongoing implications in the forensic space.”