Where the Bugs Are: Forensic Entomology

To watch the X-Files' Dana Scully probe corpses, you'd think that every physician and scientist is expert in reading clues in maggot patterns. Not so. The American Board of Forensic Entomology (ABFE) lists just eight members; a total of 63 professionals practice this science worldwide. Forensic entomology is the study of arthropods, used to solve matters of legal interest, most often of a criminal nature. "It's mostly a repeated tale of human tragedy combined with some remarkable insect ecology,

Sep 3, 2001
Ricki Lewis
To watch the X-Files' Dana Scully probe corpses, you'd think that every physician and scientist is expert in reading clues in maggot patterns. Not so. The American Board of Forensic Entomology (ABFE) lists just eight members; a total of 63 professionals practice this science worldwide. Forensic entomology is the study of arthropods, used to solve matters of legal interest, most often of a criminal nature. "It's mostly a repeated tale of human tragedy combined with some remarkable insect ecology," says Jeffrey Wells, assistant professor, department of justice sciences, University of Alabama at Birmingham.

Use of forensic entomology is spotty, compared to routine procedures such as ballistics or blood spatter, hair, and fiber analyses. "It depends on the area and the police force. Here in British Columbia it is pretty routine," explains Gail S. Anderson, an associate professor, school of criminology, at Simon Fraser University, Burnaby, B.C. "If the police are used to using an entomologist, we just become part of the investigation, usually in cases in which time of death is in question."

Interest in the field is rising, but positions are still scarce. And police are learning to do part of the forensic entomologist's job. "I regularly train police all over Canada and other countries, as do all my colleagues," adds Anderson. Jeff Tomberlin, a postdoctoral researcher at the Coastal Plain Experiment Station in Tifton, Ga., agrees. "I rarely go to crime scenes, but I often give presentations to police on how to collect evidence."

William Rodriguez, chief deputy medical officer for special investigations, Office of the Armed Forces Medical Examiner, Washington, D.C., says forensic entomology has "come into its own.... As a science, [it] has developed into a field that is widely recognized in the courts and in other areas of forensic science."

Rodriguez says that law enforcement agents are routinely taught to collect insect specimens at a crime scene. "Insects are the most accurate way to estimate the time since death. [They] are one of the first things collected at the scene and at the morgue."

Use of forensic entomology is recorded as early as the mid-1300s, during a murder investigation in China. In 1855, a French physician named Bergeret determined that the insects in and around a baby's corpse, found behind the plaster mantle in a house, placed the time of death back several years, thus implicating the former, and not current, homeowners.1

Requirements: A PhD and a Strong Stomach

Training for forensic entomology is eclectic. "Certification requires a doctorate in medical entomology with research and case investigation experience in forensics," says attorney Robert Hall, an ABFE diplomat and associate vice provost, University of Missouri, Columbia. Solid backgrounds in insect taxonomy and natural history, as well as comprehension of accepted standards of crime scene investigation and evidence handling, are important too, says Wells. Training in ecology is crucial, as a rotting corpse is in essence an ecosystem, with the diners' comings and goings a classic example of succession.

Other requirements are harder to define. "Forensic entomology is a field that is for the strong of stomach and weak of nose. It takes time to get used to it," says Tomberlin.

Usually, the road leading to a forensic entomology career arises from a scientist's dual interest in insects and cadavers. For Richard W. Merritt, an entomology professor, Michigan State University, East Lansing, this meant taking entomology courses as an undergraduate while driving an ambulance at night. "In 1968 I had a case in which an elderly woman's legs had ulcerated, and fly larvae infested her extremities. I collected and identified the flies at the scene and at the suggestion of my professor, published an article on the situation. I went on to work on cases with the police during graduate school for entomology." For Tomberlin, a favorite course in entomology coincided with working at a funeral home. His first week on the job, in 1992, a call came to pick up a body that had been in the woods a few days. "This was Georgia in May, so it was hot. I volunteered to go with the funeral director to collect the body. There wasn't much left of him, but it really fascinated me. And so the seed was planted," he recalls.

Neal Haskell, a professor of forensic science and biology at St. Joseph's College in Rensselaer, Ind., credits his career to boyhood experiences down on the farm in northwest Indiana. "My first memory of becoming interested in maggots on dead things was when I was 5 years old. I have a vivid recollection of a calf that had died at the end of May. It was one huge, writhing mass of maggots, going snap, crackle, and pop." After college, he joined the Marines, where he learned about guns, and continued that interest in the late 1960s as a firearms instructor at a local county sheriff's department. In 1981, local detectives familiar with his interest in insects asked him to examine an infested, bloated body blackened from decay. It was Haskell's first autopsy, and he was hooked.

Haskell honed his skills on dead pigs and visits to the "Body Farm," otherwise known as the University of Tennessee Forensic Anthropology Facility in Knoxville, where 40 or so corpses in various conditions provide a laboratory for forensic scientists. Returning to school, he earned the first Ph.D. in forensic entomology in the country, from Purdue University in 1991.

Soon, cases began arriving from the medical examiner's office in Indianapolis. Haskell's advice to would-be forensic entomologists: "To be the best basketball player, you shoot a lot of baskets. To be the best forensic entomologist, you dissect a lot of pigs--I did 1,250. But, I had to be a top-notch entomologist first." A pig's organs are about the same size as a human's, hence porkers have long been a staple in physiology research. They also make good practice models in forensics.

M. Lee Goff, an entomology professor, University of Hawaii, Honolulu, recalls using a pig more experimentally. "A woman's body was found in a wooded area, wrapped in layers of blankets. I could account for 10 and one-half days of insect activity, but she had been missing for 13 days," he recalls. Could the tight wrappings have slowed insect activity? The defense attorney asked Goff to find out. "So I took a dead 50-pound pig. I duplicated the wrappings, and let it stay in my backyard. The neighbors weren't too happy. It took two and one-half days for the flies to penetrate; two and one-half plus 10 and one-half days put the suspect in the company of the victim."

Tools and Clues in Forensic Entomology

Only a few types of insects eat rotting human flesh. "A couple of dozen species are likely to colonize a corpse during the full decay, but at any one time, only half a dozen or so are likely to be present," explains Felix Sperling, associate professor of insect systematics, University of Alberta. The two main players are the carrion feeders or blowflies (Calliphoridae), and the flesh flies (Sarcophagidae). The occasional beetle participates too, and bloodsuckers such as mosquitoes and lice can carry evidence away.

Courtesy of M. Lee Goff

Culture of Sarcophagidae, or flesh flies, in the laboratory

One of the toughest challenges for forensic entomologists is to distinguish the three larval stages, or instars, of important species. Whereas blowfly larvae tend to look alike, beetle larvae are very diverse, ranging from white to brown, skinny to fat, and hairless to hairy. Investigators look to mouth parts, spiracles, and genitalia to identify species, but even the best forensic entomologist must sometimes rear a maggot to adulthood on beef liver to see what it is. The pupae, or cocoons, are valuable too, although police often ignore blowfly pupae, which look like rat excrement, according to Haskell.2

Forensic entomologists must be alert to the unusual. Merritt recalls a case in which a car containing a dead woman was found upside down at the bottom of the Muskegon River in western Michigan. The husband claimed that he hadn't seen his wife in weeks, but black fly larvae and pupae indicated otherwise. The cold water had delayed decay so that normal entomological analysis wasn't possible. Says Merritt: "Based on the identification of the cocoon and known life cycle of the black fly species on the windshield in late June, the car had to have gone into the river long before June, as the husband claimed. The man was convicted of murder, based in part on the life cycle of an aquatic insect."

By comparing species found on a body with those in the area, forensic entomologists can also determine if a body was moved. The lack of insects can tell a story too. In one case, the body of a dead woman lying on a bed near an open window was mysteriously insect-free. When a prosecutor pointed out this enigma, the accused boyfriend admitted to having killed her earlier and placing her near an open window to suggest entry of a stranger.

Ecology is part of crime scene analysis. Relates Merritt, "Factors that affect the rate of decomposition in water, for example, include temperature, bacterial content, salinity, and algal blooms. A corpse submerged in a highly eutrophic, shallow lake will decompose much more rapidly than a corpse in a cooler, deeper lake with a lower bacterial count."

Forensic entomologists use data to estimate the time elapsed since insect activity began--called the postmortem interval, or PMI--that could be the time of death. This is done in either of two ways. Says Wells: "The accumulated degree model, commonly used in agriculture, assumes that within a certain range, maggot development is a linear function of temperature, measured as the degrees above a critical temperature where development stops. Alternatively, some people chop the temperature/time curve thought to have occurred at the scene into short intervals, such as six hours. The average temperature during that time is then used to estimate the growth based on a lab model at a similar constant temperature."

DNA Fingerprinting of Maggot Gut Contents

As in other areas of forensic science, DNA fingerprinting is a powerful tool when used on insects. "DNA technology is used to help identify insect species, instead of using the general morphological characteristics, and to recover human blood meals from the gut contents of insects," explains Jason Byrd, an assistant professor of criminal justice and biology, Virginia Commonwealth University, Richmond.

Sperling's group established this subspecialty in 1994, using the mitochondrial gene for cytochrome oxidase.3,4 "MtDNA is particularly durable, even in dried and degraded material, and we wanted to use sequences that could help to understand the phylogeny of the flies," he says. "The rates of divergence are about right to give good differences between species, but not so much that homologies are uncertain between species." The researchers use phylogenetic analysis software to align DNA sequences to derive likely evolutionary relationships, adds Wells, who did postdoctoral work in Sperling's lab.

Forensic entomology can be the stuff of nightmares. Some forensic entomologists won't speak of the worst horrors; others will. One who did was Goff. "A 16-month-old child was found abandoned by the edge of a lake. She had feces in her diaper, and flies had been initially attracted to that. The eggs hatched, and when they'd consumed the feces, they moved on to the child. When we found her she was close to death, dehydrated, starving, and being eaten alive." From the stages of the maggots and the body temperature, Goff estimated that she had suffered for about 27 hours. The mother was convicted of attempted murder, and an aunt adopted the child, who recovered.

For those fascinated by arthropods and mystery solving, forensic entomology can be rewarding. "All death investigations are interesting to a degree, and all have unique characteristics," says Hall. "Probably the most satisfying aspect is to participate in finding out the truth regarding a particular death." Goff adds another limitation: "I'm rarely asked to be a dinner speaker."

Ricki Lewis (rickilewis@nasw.org) is a contributing editor for The Scientist
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References
1. web.missouri.edu/~agwww/entomology

2. www.forensic-entomology.com/info.htm

3. F.A.H. Sperling et al., "A DNA-based approach to the identification of insect species used for postmortem interval estimation," Journal of Forensic Sciences, 39: 418-27, 1994.

4. J.D. Wells, F.A.H. Sperling, "DNA-based identification of forensically important Chrysomyinae (Diptera: Calliphoridae), Forensic Science International, 3065:1-6, August 2001.