Science
Forensic Entomology: What Can Flies on the Wall Tell Us About Murder?
Flies, beetles, mites, and parasites follow crime wherever it leads
Forensic entomology is the study of insects (especially flies and beetles) and arthropods in criminal investigations. Bugs share a lot of information. Let’s dig in!
**TW: This article will discuss death, decay, and all matter of detail to better illustrate the field of forensic entomology and how inspecting bugs solves crimes. If you’d rather not learn about those topics, consider another article!**
The scene was normal — or as normal as a dead body sacked out in the middle of the woods ever could be. The investigator had driven twenty miles up the winding road to the clearing where the woman’s body lay, slowly sinking into the damp morning grass. They’d gotten the call about an hour earlier. She’d been missing for about a week, so the investigator was expecting the regular (if gruesome) ordeal.
Except upon investigation, the body was still cold to the touch.
The maggots hadn’t even had enough time to set in.
What is forensic entomology?
Forensic entomology is the study of insects (especially flies and beetles) and arthropods in criminal investigations. Bugs at the scene of a crime share a lot of information. Using fly larvae alone, forensic entomologists can learn:
- How long a body has been dead
- If the body was moved
- If the body contains toxins or drugs
- Distinguish between suicide and murder
- Link a suspect to a murder
- The DNA of a body that has already decomposed past recognition
The first written record of forensic entomology used to solve a murder case took place in 13th-century China. In The Washing Away of Wrongs, Sun Tzu describes an impromptu murder trial. After a farmer was found murdered in his field, all suspects placed their tools on the ground. The tools all looked clean, and their sharp blades glistened in the sun. But only one sickle had untraceable amounts of blood staining the blade, and that tool attracted blowflies. Only one sickle had been used for murder.
Today, forensic entomology helps criminal investigations when a body is found more than 72 hours old. Up until the three-day mark, other methods are more accurate than any insect evidence. But when the body begins to decompose, bugs tell their side of the story.
When the body is still fresh, entomologists use maggots to determine how long the corpse has been lying in its habitat. Young maggots cannot bite through human flesh, but rather use preexisting wounds to crawl under the skin, eating soft tissue found within.¹
Older maggots show their age through instars or periods between molting where the creatures have distinctive features that can pinpoint the number of days since these eggs hatched. And as they eat, fly larvae gather valuable information: the DNA of their meal or any illicit substances running through their tissues.²
This information is useful to forensic entomologists, who must preserve some fly larvae for accurate dating and keep another sample alive for further study.
If a body has been in its environment long enough to dry out, the maggots will probably have done their worst, grown up, and flown away. At this stage, beetles are more likely to scavenge the remains. Scientists then use whatever information they have about the successive waves of scavengers to determine the post-mortem interval or estimated time since death.²
Researchers stress that this is an estimated time of death because many factors such as temperature, treatment, or the condition of the body alter when insects first appear and how fast they develop. Someone who met their end from a potent poison will have fewer insects colonizing their body because, well, poison kills bugs too. A body coursing with cocaine will have accelerated decomposition. And although we try not to imagine it, a living person subject to devastating neglect or abuse can also harbor fly larvae and parasites, and that might skew the post-mortem intervals quite a bit.²
Of course, investigators have other ways of observing how long a corpse has been around. Well before forensic entomologists, or any of the forensic ‘ologists are busy in their labs, an investigator assesses the crime scene and records as much information as possible.
They get to see the whole ordeal up close and personal.
How long has this corpse been dead, anyway?
Bodies follow more or less the same progression of decomposition, barring extreme environmental preservation. Early postmortem changes are as follows:
- Liver Mortis- About one hour following death, the blood pools to the back of the body.
- Rigor Mortis- Chemical pathways momentarily freeze the muscles
- Algor Mortis- The body becomes cold
- Tache Noir- Eyeballs dry and discolor
- Greenish Discoloration, Marbling, and Skin Slippage affect the body
- Mummification, Saponification, or Putrifaction ensues.
- Post-Decay
- Skeletonization
Investigators use many of these benchmarks to determine how long it has been since a corpse has left this mortal coil, but forensic entomology helps confirm established post-mortem intervals or PMIs.²
Fly larvae are the most well-studied insects used for forensic entomology, but they are only present during initial corpse breakdown. Many flies buzz off when the body begins to dry out, and new colonizers enter the scene. A variety of beetles and mites may nibble on corpses that have begun to dry.
But how exactly do scientists use these critters to learn more about crime scenes? What information needs to be available for forensic entomologists to glean information from these creepy crawlies?
Flies, beetles, and mites — oh my!
One way that entomologists age larvae — especially maggots — to determine the PMI is by using instars, or the developmental stage in between molts before an insect becomes an adult. Maggot instars are easy to identify using the number of spiracles or breathing holes present in fly larvae.²
Popular flies include the blowfly or bottle fly, which lay their eggs on dead animals. Another species of fly that seems particularly eager to find corpses is the coffin fly, which may dig over two meters of dirt to lay its eggs in lean tissue.
Dermestid beetles and Common sexton beetles come for the corpse after it has dried out a little, but opportunist species like springtails and clothes moth caterpillars may also help break down the body after the flies have long departed. One problem with using beetles to solve crimes however is that data connecting beetle development with established PMIs are not as robust as studies on flies.²
But these challenges can also inspire further research. In 1994 British Columbia a missing victim was found in a shallow grave. Little forensic entomology research had been done in the area, and the closest study had been conducted in Tennessee. So researchers (mostly graduate students) got to work. They buried pigs and found the proper PMI for the body eight months later. The killer however was never found.
Scientists may also look to mites to understand crime scenes. Mites are tricky. Most of us would rather not recognize that we are covered in microscopic mites, but these arthropods can help pinpoint where something is a little off at a crime scene. For example, if you find human follicle mites Demodex folliculorium — which are typically found in eyelashes and the eyebrows — in the middle of a secluded wood, that’s weird.²
Mites can also hitchhike on bugs. They can hitchhike on other mites. Different rooms in a house can be more or less likely to host different numbers of mites. These arthropods can even tell you whether the victim has been around pets, or if the victim has been moved.²
You might not be able to see mites and bugs, but they see you. And they follow delicious crime wherever they can.
Forensic entomology in the news
Bugs have helped solve many cold cases. In 2003 one southern England a forensic entomologist was called into an investigation involving a partially decomposed body that had been left in a burning wood. Because no bugs were found on the body, the team concluded that the corpse must have been wrapped and chilled at a local refrigeration unit.
Mites have also helped investigators solve a murder in California. According to Amendt et al., “A police officer and another 20 members of a search team got bitten by the chiggers of the mite Eutrombicula belkini when investigating the body of a 24-year-old woman at a rural location.” Since the mite was restricted to a very limited area and the arthropod rarely bit humans, the team was able to locate similar characteristic bites on one of the suspects and further tie this person to the scene of the crime.²
Here are some more examples of how forensic entomology has helped investigators solve crime.
What we still don’t understand
While the number of forensic entomology publications is rising each year, the number of forensic entomologists remains stagnant. The American Board of Forensic Entomology only boasts eight members, and there are only 63 professionals worldwide.
This scarcity makes sense — forensic entomologists need a PhD in entomology, zoology or a related field and “three years of professional experience involving medico-legal forensic entomology casework” to join the Board, and can only expect to make a $60,000 average salary.
Many of these forensic entomologists are academics or state employees. There is little demand for private investigation companies to employ forensic entomologists, which might explain the low pay range for this extremely skilled job. But let’s not lose hope. ForensicsColleges.com suggests that “Between 2019 and 2029, the BLS projects that 2,400 fresh positions will be needed” and the site further breaks down growth statistics for forensic entomology and related careers in the US.
And yet there is still so much work to be done. While studies have slowly created baselines for under-investigated species and forensic entomology in colder climates, these baselines will inevitably shift with global climate change.²
Forensic entomology can also be used more widely in wildlife crimes or animal abuse cases. While there are a few examples of forensic entomology being used to solve crimes involving illegal poaching of bear cubs and rhinoceroses, there is still a lot of room for growth.
Additionally, most of the literature on this topic is published in the US, Canada, Australia and the UK.³ However there is lots of great research coming from other countries, which is an important development. Researchers will need to establish benchmark PMIs to apply this method to a variety of countries where forensic entomology might be useful.
Another understudied field is aquatic forensic entomology. Decomposition slows wayyyyy down in aquatic environments due to reduced insect activity and cooler temperatures. Aquatic insects like mayflies, caddisflies and even some true flies spend some or all of their life in water. What about studies on pond skimmers? And those nasty bugs that live in your pool? While studies on these aquatic insects and arthropods do exist (here and here) applications for criminal investigations remain few and far between.²
Which is just to say — there’s a lot more information about death that nature can provide. Good thing there’s a growing market for the discipline that lies at the intersection of insects and crime.
Great Decay
If you’ve made it this far, I don’t suppose I need to tell you that forensic creepy crawlies are an essential part of decomposition, a self-sufficient unit in the breakdown of living things.
“Although the details may be gruesome, insects that colonize corpses are performing the necessary breakdown of organic material that must occur postmortem. Only by this breakdown — by insects, fungi, and bacteria — can bodies be released to reenter the circle of life,” says entomologist and writer Emily Hartop.
Forensic entomology lies at the intersection of the natural world and the criminal sphere, and both realms are undeniably goth. These fields are unequivocally important. But for every science enthusiast eager for more information about how we are using insects to solve crimes, there is someone caught in the crossfires of criminal investigation.
So let this be a warning: insects and arthropods are always active, always watching.
[1] Roach, Mary. Stiff : the Curious Lives of Human Cadavers. 1st ed., W.W. Norton, 2003.
[2] Amendt, Jens., et al. Current Concepts in Forensic Entomology. Edited by Jens. Amendt et al., 1st ed. 2010., Springer Netherlands, 2010, https://doi.org/10.1007/978-1-4020-9684-6.
[3] Lei, Gang, et al. “A Bibliometric Analysis of Forensic Entomology Trends and Perspectives Worldwide over the Last Two Decades (1998–2017).” Forensic Science International, vol. 295, 2019, pp. 72–82, https://doi.org/10.1016/j.forsciint.2018.12.002.
