The Curious Case of ForensicsJul 05, 2012
“So what? Who cares?”
The questions came two decades ago from the back of the room — a senior, tall with black hair and glasses. Two dozen bored faces that only moments ago had been watching the clock were now fixed on Eric Benbow, a junior transfer student completing his first year as a biology major at Univ. of Dayton. He stood alone at the front of the classroom.
Twenty minutes earlier, he had dimmed the lights and flipped on the overhead projector. The illuminated screen showed an aquatic insect that filters water through fans on its head in search of bacteria to eat. With chalk in hand, Benbow had filled the blackboard with crude drawings, formulas and key points, hypothesizing how water flow might affect the insect’s life cycle. Then came the questions.
“I said something, but it wasn’t very good,” said Benbow ’94, now an assistant professor in UD’s biology department. “Probably to the effect of, ‘Understanding stream flow characteristics and the insect’s responses to changes in flow could lead to the ability to control their population.’ I forget exactly.”
But he hasn’t forgotten the questions. They have followed him through life — in Ohio woodlands, through Ghanaian streams, into labs and classrooms — and directed his mission as a researcher and an educator answering his own questions and sparking new ones in the minds of the next generation of scientists.
I spy a fly
Benbow and two students hunched over a pig carcass, not believing what they were seeing.
It was late May 2011, unseasonably cold, and the sky had been dumping rain all night. Their lanterns looked thin in the blackness. Three-inch thorns on honey locust trees stretched to shred their yellow ponchos. Slippery mud sent them sprawling. Low-hanging limbs slapped their wet faces.
Roughly four hours earlier, they had placed six fresh pig carcasses in woods outside of Dayton. They were returning now, just before midnight, to study the progress of their decomposition. The trio was studying how bacteria and insects, particularly blow flies, interact in decomposition and how that information can be used to improve estimates of how long an organism — be it a pig in a science experiment or a murder victim dumped in the woods — has been dead.
“Flies don’t fly in the dark, though we don’t fully understand why,” Benbow said. “Because of this, it’s generally accepted among forensic entomologists that flies don’t lay eggs at night, or in cold weather or the rain. If you find a maggot on a carcass in the morning, it is assumed eggs were laid that morning or before nightfall the day before.”
The waterlogged team expected to confirm this. Instead, they witnessed a female blow fly walk out of the pig’s nostril, scamper a few feet and then disappear. Shining a flashlight into the nose, the three scientists saw what looked like 30 to 50 small grains of white rice, arranged in a pea-sized clump: blow fly eggs.
“Write this down,” Benbow told his students. “What you just saw isn’t supposed to happen.”
So what? Just a month before their nocturnal discovery, a criminal case was decided based in part on evidence of blow fly larvae on a dead body. A forensic entomologist testified about time of death. What were the chances, he was asked, of flies laying eggs on the victim’s body in the middle of the night under dry, warm conditions?
“He said it was incredibly unlikely or would never happen,” Benbow said. “But there we were, under the harshest conditions. We saw it. If a criminal investigator assumes eggs were laid in the morning when they were actually laid the night before, the post-mortem interval would be off by 12 hours.”
Who cares? Senior biology major Maureen Berg ’12, who was with Benbow that night. She followed up on the unusual incident with a research project of her own. Returning to the same woods at nightfall, she set out several baits — some on the ground and some suspended 3 feet off the ground — under high light, low light and no light conditions. The experiment tested which conditions were most favorable for a blow fly to lay eggs at night.
Berg observed no nocturnal egg laying, even under high light; however, the baits on the ground and with the most light were consistently the first to have eggs deposited in the morning. She is working the results into a paper she plans to submit for publication. Benbow encourages his students to explore new ideas and pursue work of professional quality.
“There are times students see something in the field that I’ve taken for granted, but they see something because their eyes are fresh,” he said. “I always make sure they get credit.”
Pebble in a stream
As a boy, Benbow spent summer days wading and digging in the streams of State Farm Park in northeast Kettering, Ohio. He’d bring crayfish, minnows, leeches and other creek creatures home, where his mother allowed him to keep them.
Years later, when he once described his fieldwork to his mother, he said, “You know when I used to go out to the creek to hunt for crayfish and catch minnows? I’m doing that now but with a $10,000 piece of equipment instead of a Styrofoam cup.”
He still visits those streams with students and also with his 4-year-old daughter, Arielle, whose favorite activity with Daddy is putting on flip-flops to wade in the water and dig up critters.
“At a recent parent-teacher conference at Arielle’s preschool, I learned that she is always digging up worms and bugs to show to the other kids,” he said with a proud smile. “And she does it in heels and a dress.”
Both of his daughters — Alia is 1 — will be entomologists, he said, only half joking. “I at least want them to appreciate insects, not to be afraid.”
So far, so good. Arielle confidently picks up millipedes, but she avoids centipedes (she knows they bite). And when Benbow’s wife, Melissa Fortman Benbow ’04, finds a spider crawling in a corner, it’s Arielle who runs to her rescue.
“You know, Mommy, this one won’t bite,” she’ll say as she scoops it up in her hand and releases it outside.
Still, there is a flyswatter in Benbow’s home: “Flies carry pathogens,” he said.
Death becomes him
Forensic science is under the microscope. In 2009, the National Research Council issued what Benbow characterized as a scathing report criticizing the forensic sciences for a lack of sound scientific research.
Benbow is among a team of researchers at the forefront of responding to this report with two articles published in 2011 on the future of forensic science research. That same year, he received a grant from the National Institute of Justice (in collaboration with Texas A&M Univ. and the USDA-Agricultural Research Service) to fund his research on the interaction of insects and microbes in body decomposition. The nearly half-million-dollar grant was UD’s first from the NIJ and its first for forensic research.
“DNA fingerprinting was the only one that escaped strong criticism from the NRC,” Benbow said. “But for the rest of the forensic sciences, too much evidence is anecdotal, and there is virtually no data on error rates. We don’t know how often these techniques are wrong.”
Meanwhile, thanks to popular TV shows like CSI: Crime Scene Investigation, the general public is fed the perception that forensics can pick out the tiniest of threads to unravel an entire case.
“It’s a glammed-up, fabricated portrayal of forensics, and this can hurt cases,” said Benbow, who has worked on several cases and testified in one. “Juries have an unrealistic expectation of evidence, that a scientist can simply go out to a crime scene, find all of the evidence and close the case. But it’s a lot of work, and the data aren’t always crisp and clean.”
In a recent experiment, Benbow and graduate student Andy Lewis ’08 — the third person with Benbow and Berg that night in the woods — found that for a person on trial, the difference between “guilty” and “not guilty” could be 85 feet.
Blow flies are often the first insects to lay eggs on decomposing remains, usually within hours or even minutes after death. The larvae hatch and develop through life stages — called instars — at a rate closely linked to temperature. The warmer the air and soil, the more quickly they grow.
From the time they hatch until they reach the third instar, they are simply growing bigger — about the size of a grain of rice at first instar to 10 times larger by third instar — feeding on the rapidly decomposing carcass. During the third instar, they stop feeding and crawl away in search of a dark, moist place to burrow, become pupae and begin the process of metamorphosis to become flies.
On average, in Ohio’s summer climate, the entire process — from first instar to pupae — takes five to seven days.
Combining the size of the oldest blow fly larvae with data on temperature and other environmental conditions, forensic entomologists can calculate the age of larvae and thus determine the time of initial colonization, biological data that then assists in establishing a time of death.
“It is, therefore, essential that investigators locate the oldest larvae at a crime scene, otherwise the interpretation of the insect data can be compromised and erroneous,” Benbow said.
When forensic entomologists arrive at a scene, they search for the oldest larvae, looking under leaf debris and digging up soil samples. They collect the larvae using forceps or common tablespoons and often kill them by dropping them in ethanol or boiling them in water to stop their growth. For this, some entomologists carry camp stoves into the field.
Most forensic entomologists recommend a search radius of 10 meters for the oldest larvae. Like with flies and egg laying, it’s conventional wisdom that larvae burrow into the ground to begin pupation within 2 to 10 meters of the carcass.
But in Benbow and Lewis’ study, the larvae from two of six pig carcasses moved farther, with one larval mass traveling 14 meters and the other 26 meters — about 85 feet.
“Our study suggests that in a forensic case with insect evidence, there would be a one-in-three chance that the oldest larvae would not be collected if the search stayed within the current recommendation of 10 meters,” Benbow said.
Missing the oldest larvae could affect a time-of-death estimate that might bolster or contradict an alibi.
Still, even with improved research, Benbow knows there will always be uncertainty. Expert testimony will always be expert opinion. But what he hopes he can offer is solid, objective data that can establish a degree of certainty.
“If we can go from making estimates with, for instance, a 50/50 probability to something like 85 percent based on research and data, then you can start giving juries something more concrete to consider, something more objective,” he said.
Forensic entomology has long been an isolated field of study, but Benbow and his colleagues are finding ways to link it to other disciplines. Benbow considers himself a forensic ecologist because of his research on the interactions between microbes and insects. How does the soil composition of where the body is laid affect insect behavior? How do bacteria interact with — even communicate with — insects? What if a body is dumped in the water?
This last question nagged at Jen Lang ’10, now a graduate student in Benbow’s lab. The research on decomposition in water is remarkably slim, and even fewer studies have focused on the role of bacteria. But as a microbiologist who “likes going outside,” Lang couldn’t resist pursuing an answer.
She studies biofilm — the slime on rocks — which is rich in biological diversity. “It’s like a rainforest on a smaller scale,” she said.
Under Benbow, whom she describes as a mentor, she has linked her biofilm research and aquatic insect behavior to estimates of post-mortem interval, or time after death. This new approach caught the attention of the American Society of Forensic Sciences, which awarded Lang, Benbow and collaborators a small grant this summer to explore interactions of aquatic insects and biofilm formation on decomposing pig carcasses.
Lang is also organizing a session on aquatic entomology at the Entomological Society of America’s annual meeting in November. She enjoys dabbling in multiple disciplines, likening her work to quiltmaking: “I’m looking at data and research from different disciplines, synthesizing that information and using it to explain new ideas.”
Her approach is essential to good science, Benbow insists, and he urges all his students to think beyond a narrow focus.
“Don’t get me wrong. I still believe in becoming highly specialized, knowing how to do your part really well,” he said, “but you need to know how to connect that with what others are doing. Not everyone can do that, but that’s what I teach my students.”
Even with the National Research Council report, Benbow and his colleagues have met some resistance toward their novel, collaborative approach, often from fellow scientists asking pointed, emotional questions at conferences. But he welcomes it.
“No one has ever tried to look at the interactions between microbes and flies, so I get some scrutiny, but that’s good for the science. That’s the whole point of the NRC criticism, that forensic science had gone unchallenged for so long. We’re just advocating for better science.”
For the living
Benbow received his doctorate from UD in 1999. Soon after, his phone rang. On the other end of the line was Richard Merritt, a Michigan State University professor who at the time was one of just six scientists certified by the American Board of Forensic Entomologists.
Merritt had just received a grant to study the effect of road salt on aquatic insects, and he had been discussing the topic with UD biology professor Al Burky, Benbow’s doctoral adviser. Within days, Merritt hired Benbow to do postdoctoral work in his lab.
Benbow quickly saw the connection between such research and forensic entomology. “It was just a different group of insects in a different environment,” he said.
A few years later, Benbow and Merritt applied the same set of knowledge to a different problem: Buruli ulcer, a disfiguring tropical skin disease thought to be transmitted by a biting water bug.
“I knew nothing of disease ecology, but I was interested in this case,” Benbow said. “I approached it as a microbe/insect question.”
Victims of Buruli ulcer suffer raw, gaping wounds that can overtake an entire limb and force amputation. Children younger than 15 in sub-Saharan Africa and the elderly in Australia are its primary victims. The social stigma can be profound, with permanent disfigurement making it difficult to find a spouse or a job in developing countries of Africa. Scientists have long recognized a connection between the disease and bodies of water such as slowly flowing rivers, ponds, swamps and lakes, but the exact mode of transmission is unknown.
In Ghana, Benbow was part of a team of researchers to run tests in the field. Until then, all of the experiments that implicated the biting water bug had been done in the lab. Wearing waders to protect against infection, Benbow spent hours in ponds and streams collecting bugs and water samples. It got so hot, Benbow recalled, that he often wondered whether his waders were leaking as they filled with sweat up to his calves.
His research produced no strong evidence to support the water bug hypothesis. The disease remains a mystery, but Benbow is today among the top researchers in the world studying the transmission of Buruli ulcer into human populations, acting as a consultant for the World Health Organization, which labels Buruli ulcer as one of the most neglected but treatable tropical diseases. More than 50,000 people in 30 countries have contracted the disease, though it often goes unreported.
“The interaction between bacteria and insects affects all kinds of systems,” he said. “The more we understand these interactions, the better we can apply it to forensics, disease prevention, the health of our water systems; the possibilities go on and on.”
In a Science Center classroom full of first-year biology students, Benbow put up a slide of an aquatic insect with the filtering fan on its head — the same one he put up decades ago in the room right across the hall.
He told his students the story of his junior-year presentation. He told them about the questions: “So what? Who cares?”
Then he pointed to the insect and asked them, “Do you know what this is? It’s a black fly larva.”
It carries disease to hundreds of thousands of people all over Africa, he told them: river blindness. It uses the fans on its head to filter water and feed on the bacteria. Could this natural process be used against it? If an insecticide were developed that could be dropped into streams, would the larvae feed on the particles the way they naturally do? Would that kill them? If so, thousands of people could be spared from disease.
Then he told them about mosquitoes, which lay eggs in aquatic habitats and whose larvae feed on algae and bacteria. What if you could disrupt their feeding through a better understanding of how the microbial communities interact with early larval development, he asked them. Would that reduce the spread of malaria?
“So what? Who cares?”
Nearly 20 years after he stumbled through a response to that simple challenge, after 20 years of research in aquatic habitats, disease ecology and forensics, Benbow has a list of ready answers: Buruli ulcer. Disease transmission. Scientific inquiry. Crime victims’ loved ones. Students asking big questions.
“A lot of scientists are in it just for the data, they’re not interested in how their data can be useful. Yes, the science is interesting, but once you’ve testified in court, once you’ve visited victims of Buruli ulcer, once you’ve seen how your data can have an impact on people’s lives, that’s what keeps pushing you forward. That’s why it matters.”
Source: Univ. of Dayton, Cameron Fullam