Forensic entomology is the study of insects in criminal investigations. Think you know something about the field because you’ve seen Gil Grissom on CSI or Jack Hodgins of Bones working on cases? Read on.
1. ONE OF THE FIRST DOCUMENTED CASES OF FORENSIC ENTOMOLOGY TOOK PLACE IN 13TH-CENTURY CHINA.
It’s likely people have been trying to hide evidence of wrongdoing for as long as there have been people. Judging by the title of his 1247 book The Washing Away of Wrongs [PDF], the pioneering forensic investigator Sun Tz'u certainly thought so. In his account of Song Dynasty forensic medicine, he describes the case of a murdered farmer in which the suspects were told to lay their sickles on the ground. No blood was visible on the tools, but blow flies swarmed one of the sickles, revealing the identity of the murderer.
2. FLIES ARE THE HEROES OF THE FIELD.
Many insect species practice necrophagy, including the aptly named carrion beetles (family Siphidae), skin beetles (Dermestidae), and bone beetles (Cleridae). One recent study even found a caterpillar munching on human skin. But flies are the most avid flesh-eaters—especially those in the Sarcophagidae and Calliphoridae families. With more than a thousand species, the Calliphoridae family of flies goes by a lot of names, including blow flies, carrion flies, bluebottles, greenbottles, and cluster flies. (Think of the swarms you’ve seen hovering above roadkill.)
All of them share something in common: an ability to sniff out death soon after it occurs, often in minutes. They’re attracted by volatile molecules called apeneumones that are released by bacterial activity as a body starts to decompose. Predacious insects also come to feed on these bugs, which can offer a secondary set of clues.
3. THEY CAN USE INSECTS TO INFER TIME OF DEATH, AMONG OTHER THINGS.
Blow flies are often the first insects to appear on the scene. They lay eggs on rotting flesh so that when larvae hatch, they have a ready food supply. After feeding, the maggots crawl off to find a place to pupate underground. They hatch about 10 days later.
This lifecycle is illuminating for forensic entomologists, who collect insect samples from a body. Gail Anderson, co-director of the Centre for Forensic Research at Simon Fraser University in Burnaby, British Columbia, says that of the insect samples she collects, “half of them I will keep preserved so they can be produced in court years later, and the rest I will raise through to adulthood to identify them. This takes quite some time.” If the insect samples are eggs, it could take as long as a month. This gives her an estimate of how long the insects have been on the body, which she submits in a report to the police. “So if I say the insects have been on the body for at least seven days, that indicates the person has been dead for at least seven days.” This is called the postmortem interval—the time since death has occurred.
Jeffery Tomberlin, director of the Forensic Laboratory for Investigative Entomological Science (a.k.a. F.L.I.E.S.) at Texas A&M University, prefers to talk about time of colonization rather than time of death. “What that means is: What would be the circumstances that would lead an insect to be attracted to colonize the body? That could be death, it also could be neglect or abuse, it could be colonization before death. All of that can take place.” He says the investigators use this “circumstantial information” to draw conclusions about “what happened to that person to cause death.” They may also be able to tell if a body was moved or disturbed based on the insects present. A bug that doesn’t belong in the local environment likely came from somewhere else.
4. THEY RARELY GO TO CRIME SCENES.
Despite what you may have seen on CSI or Bones, virtually all forensic entomologists are academic researchers employed by universities, not police departments. They're civilians with Ph.Ds, not cops with badges. How often they consult on cases varies—anywhere from five to 20 times a year, and sometimes more. Tomberlin estimates that of the more than 100 cases he’s worked on, he’s only been to a crime scene once or twice, and he mostly handles insect samples gathered by investigators. His involvement usually starts with a phone call from investigators, during which he’ll ask questions: What’s the stage of decomposition? What kind of insect activity did they see?
They’ll send him reports and photographs, which he'll evaluate. If he thinks he can be of use, he’ll ask for insect samples—if they’re available. “The main question is: Are insects relevant to the case? That doesn’t mean they’re present,” he notes. “You can have cases where insects are excluded, and that can be just as informative as their being present.” If there are no insects around, that means a body may have been frozen, buried, or wrapped.
5. THEIR TOOL KITS AND LABS ARE PRETTY LOW-TECH.
To collect samples in the field, Anderson takes what looks like a toolbox filled with vials, forceps, notebooks, preserving alcohol, water, and paper towels. “It’s not very high-tech. People try to make a lot of money by selling these kits to people, but realistically, you can make it up yourself,” she says.
The standard lab equipment forensic entomologists use is equally basic, says Tomberlin. “We have incubators for growing insects and microscopes for identifying insects. Nothing really complex.” On occasion, they send samples out for genetics testing, however, which does involve more sophisticated tools.
6. THEY’RE OFTEN ASKED TO WEIGH IN BEFORE INVESTIGATORS HAVE DETERMINED IF A DEATH IS NATURAL OR CRIMINAL.
The sooner a body is sampled for insects, the better. That means it may be too early for investigators to know whether foul play is involved. In Tomberlin’s experience, most of the time, it is—even though he tries to avoid knowing what the investigators' initial conclusions are. "I try to steer clear of information like that. And there's a reason for that: I don't want to get mixed up in bias," he says. But most of the time, the police have given him enough context and background information that he knows what they're thinking. He estimates that 90 percent of the cases he’s worked have involved criminal intent.
7. FLY LARVAE CAN REVEAL THE PRESENCE OF DRUGS ...
If a body is too decomposed for a forensic toxicologist to perform an analysis to see if drugs or poison are present, larval specimens can be analyzed instead. When larvae feed, their bodies accumulate and store drugs, which can be sampled. Drugs also alter insect growth. “If they’re on something that’s sort of a downer, it will slow down their development. If they’re on something that’s more of an upper, it will speed up their development,” Anderson says.
8. ... AND CAN ALSO RETAIN HUMAN DNA.
Our bodies break down what we eat much faster than blow fly larval bodies do, says Anderson. “They have a large storage organ, and they fill that storage organ with their host food, and that stays there for quite some time. So we’ve got a much greater window of detecting the human body in the maggot than we have the steak in your gut.”
This is especially helpful in cases where a body isn’t present but the maggots that fed on it are. Imagine this scenario: “Say somebody murdered somebody and left her in the basement, and then he heard somebody was coming to find her,” Anderson says. “So he picks up the body and dumps her out in the bush, and we go to the scene and we find a lot of maggots. And [the murderer] says, ‘Oh, well, that’s just from some dog food.’ Well, you could analyze those maggots and get the DNA out and say, ‘No, they’re not from dog food, they are in fact human, and they are from your wife, Dolores.’”
9. THE FIRST SIGHTING OF A BODY OFTEN WEEDS OUT PEOPLE WHO AREN’T SUITED TO THE WORK.
It usually happens in graduate school. Students are prepped beforehand, but the sight of a dead body—especially one in a decomposed state—can still be too unsettling. For Tomberlin, that weeding-out process happened earlier. As an undergraduate, he took an elective about the applications of entomology in the world; forensics was one of them. At the same time, he got a job in a funeral home helping with funerals and receiving human remains. "While taking that class and working at the funeral home, we actually had a case of a decomposed body, and I got to see it in action," he says. He was one of three students working there. "You learn real quick the psychology of death. When we picked up the first set of remains, one person quit on the spot—said, 'I can't do this.' The second person said, 'I'll work here, but I don't want to see it.' And I was the only one who said, 'I can handle it.'"
10. CHALLENGING CASES OFTEN LEAD TO NEW KNOWLEDGE.
Eight-year-old Mindy Tran disappeared in Kelowna, British Columbia, in August 1994. After a massive manhunt, her body was found weeks later in a shallow grave. Anderson was present for her exhumation and autopsy—difficult and disturbing work, but necessary for her analysis. However, that analysis was stymied because there was little data about insect activity in buried bodies. “I was asked to give some answers, and I said, ‘but I don’t have any answers, because I don’t have any data from buried bodies—nowhere in Canada.’” The nearest case she could find had taken place in Tennessee. Frustrated, she told her then-graduate student Sherah VanLaerhoven, “There’s not a damned thing we can do about it, because we don’t have the data.”
So they decided to create the data. They devised a series of experiments to study buried pig carcasses, which often stand in for human remains in forensic studies [PDF]. The experiments took more than a year and their analysis even longer, but thanks to the data generated by the experiments, Anderson was able to pinpoint the girl’s death to the day after her disappearance, and she presented it in both preliminary and Supreme Court. (Tran’s accused killer was acquitted in 2000; the case remains unsolved.)
Another gap in the forensic knowledge is how human bodies behave in water, so soon after, Anderson began submerging pigs, first in fresh water and later in the sea off Vancouver Island. This 2012 video shows one of the experiments, conducted in a low-oxygen environment some 900 feet down.
Tomberlin and his students also study pig remains, to learn about the variation of insect colonization. "You see remains where colonization is immediate and in other remains it's delayed, so a lot of the work we do is trying to understand why we see this variation," he says. His Ph.D students leave the lab too, doing open-field studies on swine carcasses. They've seen that much of the variability is due to environmental factors—temperature, time of day, moisture, season—and biological factors such as whether a fly is pregnant or not, or male or female.
11. THEY CAN IDENTIFY WOUND PATTERNS THAT MIGHT NOT BE VISIBLE TO THE NAKED EYE.
Insects are attracted to a wound site first. Eggs are fragile and dry out easily, as do newly hatched larvae, and they’re too tiny to eat dried-out human skin. That’s why the fly mother lays her eggs where larvae will be able to get liquid protein right away. From the perspective of a newborn maggot, “a wound is gorgeous, because it’s filled with blood,” says Anderson. In the absence of a wound, flies lay eggs in natural orifices (often on the face because the others are usually covered with clothing).
By determining the colonization pattern on the body, forensic entomologists can tell if the insects first colonized a region that is not an orifice. If the oldest insects are in those regions, it strongly suggests the presence of a wound. The palms of the hands, for instance, have some of the toughest skin on the body. If colonization happened at the palms first, that’s likely evidence of defense wounds. Ultimately, the forensic pathologist determines whether a wound is present, but it’s the entomologist’s job to point out unusual insect activity that can help guide the investigation.
12. THEY ALSO CONSULT ON ANIMAL CASES.
Forensic entomology can help determine whether abuse or neglect is present in farm or domestic animals, and it can play a role in wildlife poaching as well. “We do quite a lot of work with the SPCA,” Anderson says.
13. THE CSI EFFECT IS REAL—AND PROBLEMATIC.
One of the biggest misconceptions is that there is such a thing as a “forensic scientist.” There isn’t. Scientists who work in forensics have a specialty they study, train, and work in for years, whether that’s pathology, toxicology, anthropology, or some other subset. “There isn’t one career,” Anderson says. “There are 50 careers.” They’re also not police investigators, which would require many additional years of training. “I think I once calculated that Grissom in CSI was about 143 before he actually started his job,” Anderson says.
"The CSI effect is very real," Tomberlin says. "What people see on TV is what they think is real in terms of how we apply science and what we can determine. I think too many people have seen Silence of the Lambs. We're not sitting around playing chess with insects."
TV is just entertainment, of course, and it's good that the popularity of such shows has brought more science into people's homes, Anderson says. But for people like forensic entomologists, tasked with finding evidence that can help solve crimes and be presented in court, the problem is that these misleading TV depictions—analyses that happen in minutes when in real life they would take a year, observations with the naked eye leading to conclusions that would in fact require many lab tests—can have a very real effect on judges and juries. “Your average viewer is also a jury member," Anderson points out. "And that is very dangerous.”
All photos via iStock.
Editor's note: This post has been updated.