Discover: December 2007 Archives

A Maggot for the Prosecution

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Copyright Jessica Snyder Sachs, as first appeared in Discover magazine

Insects can help solve murders but their testimony is being attacked in the courts. Pigs in stockings may help make the bugs respectable.

In the cow town of Stroud, Oklahoma, no one thinks twice about a junk pile alongside a neighbor's driveway. But people paid attention to the pile by Aureliano Cisneros's house, thanks to the thick swarm of shiny, fat flies and a ripening stench. On August 8, 1994, police discovered within that junk pile the decaying, maggot-packed body of Cisneros himself. Apparently, after being stabbed in the chest and neck, he had collapsed in front of his house; a short drag mark in the lawn suggested that someone then tried to move the 220-pound corpse before hiding it beneath the heap of dresser drawers, suitcases, and blankets.


Suspicion quickly fell on Cisneros's wife, Linda Howell. The previous Thursday night, August 4, witnesses saw the couple storm out of a local bar, with Howell saying, "You son of a bitch, I'm gonna kill you!" When investigators came to Howell's door, though, she said she'd been wondering where Cisneros was. Yes, they'd argued Thursday night, she acknowledged, but they'd made up before morning. She hadn't seen her husband for two days, since the evening of Saturday, August 6, when he left home to join some buddies.

The police didn't buy her story and arrested her for the murder of her husband. Yet when Jackie Johnson, a deputy inspector at the Oklahoma State Bureau of Investigation, looked over the forensic evidence, she wasn't very confident about the case. None of the reports gave her anything to refute Howell's claim that Cisneros was still alive two days after their public brawl.

Ironically, it was Howell's defense attorney, Frank Muret, who led Johnson to the evidence she needed. When she was handing over the forensic reports to Muret, he asked if they had looked at the maggots on the corpse. If they had, he was entitled to know what they'd found. As soon as Muret walked out the door, Johnson picked up her phone. Two calls later, she had located Neal Haskell, one of North America's most unusual private investigators. Haskell is a forensic entomologist--a scientist trained in gleaning criminal information from insects. He is, in fact, the world's only full-time forensic entomologist, though he counts as his colleagues a dozen or so other researchers who pursue forensics as a sideline. Haskell earned his Ph.D. from Purdue back in 1993. Now he crisscrosses the continent in a dusty white van with the Indiana license plate MAGGOT, consulting with the police in homicide cases and conducting research of his own.

Johnson asked Haskell if he could testify about Cisneros's time of death based on photographs, case reports, and a few vials of maggots--that is, fly larvae--collected from the body. "No problem," Haskell replied.

Haskell identified the larvae as belonging to two common flies: the black blowfly and the secondary screwworm. He then determined that these maggots were in their third developmental stage, or instar, the last before they would crawl away from the corpse to pupate and mature into adult flies. Since temperature influences the pace at which flies develop, he consulted the temperature records from the nearest weather stations, then calculated that the maggots had come from eggs laid on the body 72 to 96 hours before discovery. In other words, Cisneros could have died no later than the morning of August 5--a day earlier than Howell claimed she had last seen her husband alive.


Howell's lawyer did not exactly cave in when faced with the scientific evidence. Instead he tried to have it suppressed. During the pretrial hearings, Muret pointed out that much of the research on how blowflies develop has been conducted not on human cadavers but on dead pigs or cows' livers, and that, he argued, makes the findings inapplicable to homicides. Haskell replied that, as a matter of fact, he was preparing to publish some of his own research on human corpses, done in Tennessee. The results were consistent with nonhuman experiments.

Next Muret objected to Haskell's reliance on research done outside Oklahoma. He questioned whether developmental charts created in Tennessee are accurate enough for flies in, say, Oklahoma. This leap of faith--that blowflies in different regions grow at the same rate--is generally accepted by entomologists but remains unproved. "I've collected maggots at hundreds of workshops from one end of this country to the other," Haskell countered gruffly. "I've never seen significant variation in their growth rates outside of that determined by temperature."

Which led Muret to his next and final objection. Haskell had relied on weather readings that had been recorded miles away from Cisneros's house. Since temperature is a powerful influence on how quickly larvae grow, police should have recorded the temperature at the scene of the crime. Pulling out a field manual that Haskell himself had published, the defense attorney pounced on a passage detailing the proper procedure for determining temperature at the scene of a murder. "Did the police at the scene take ambient air temperature readings at one-foot and four-foot heights in close proximity to the body?" he asked, repeating Haskell's own instructions. "Did they take ground surface temperatures, body surface temperatures, and maggot-mass temperatures?"

Haskell granted that they had not. In making his calculations, he had used a composite of temperatures taken at weather stations miles from Stroud. Muret objected, calling the calculations guesswork, and urged the judge to rule Haskell's testimony inadmissible.

"Fortunately," recalls Haskell, "that judge was also a rancher, a no-nonsense kind of guy. When he finally made his ruling, he basically said, `When it's hot in Oklahoma City, it's hot in Stroud.'"

The judge admitted Haskell's testimony. Soon afterward Howell accepted a plea bargain.

Disputes like these over the courtroom legitimacy of entomological evidence are becoming more frequent and more pointed. In the coming years, says forensic anthropologist Bill Bass, of the University of Tennessee, such challenges will largely determine whether forensic entomology can take its place alongside such established practices as DNA fingerprinting, fiber analysis, and ballistics. Even his own science, says Bass, the identification of victims from recovered bones, "is ten years or so ahead of entomology in terms of acceptance in the courtroom."

Some forensic entomologists welcome this trial by fire. It's worth the struggle, they say, because their science offers the most reliable way of determining the time of death at a crime scene, short of an eyewitness. "Medical examiners have never been comfortable determining time of death," admits Amy Fantaskey, a pathologist with the University of Hawaii Medical School. In the first 72 hours, pathologists can make crude estimates based on rigor mortis, blood-pooling patterns, and body temperature. "But these are iffy determinations, more art than science," says Fantaskey. And beyond 72 hours, as the body cools, blood-pooling patterns fade, and rigor mortis melts away, these methods become useless.

This is exactly why some judges have been so receptive to forensic entomology. Insects populate the human corpse--or any carcass--in predictable waves over the course of weeks. The first to arrive are the husky bombardiers known as blowflies, or bottle flies, distinguished by their metallic sheen. Though cold weather and closed doors can delay their arrival, in warm weather they materialize within minutes of a body hitting open ground. "Just leave a steak uncovered by the barbecue," notes entomologist Gail Anderson of Simon Fraser University in Burnaby, British Columbia. "You'll see how fast they pull in."

Entomologists suspect that the first blowflies to find a corpse lay down chemical signals that draw kin from miles around. Within hours, the body crawls with flies. The females pack their eggs, like a paste of Parmesan cheese, around wounds and orifices such as eyes, nose, and mouth. Eggs typically hatch 12 to 72 hours later, depending on the temperature and the species of blowfly. The squirming maggots begin life the size of a pen nib. As they feed, they secrete enzymes that enable them to slice through soft tissue like butter. As their numbers swell into the tens of thousands, they move through the corpse in roiling, crackling packs, all of them growing quickly through their instars in a matter of days or weeks.

After reaching a fat third instar, the satiated larvae--about half an inch long--crawl away from the corpse and bury themselves in soil or debris. If they are in a house, they will seek dark crevices such as the folds of bedsheets. Their larval skins shrink and harden into pupa cases. The adults emerge 6 to 14 days later. Unable to fly for several hours, they skitter around the corpse like hyperactive spiders, waiting for their wings to expand.

The development of various species of blowflies has been so well documented that blowflies have become the most reliable postmortem insect clock. Once these flies depart, it becomes harder to determine time of death with precision. An entomologist must then knit together the arrival and departure of several other kinds of insects that visit the body in a more or less orderly succession.

Hawaii entomologist Lee Goff has made good use of this puzzle-piece approach. In 1996 he handled a particularly grisly case in which the decomposed corpse of a Marine--with an execution-style bullet wound--was found in a rain forest just off the Old Pali Highway on Oahu. By the time Goff arrived (in his usual mariner, aboard a Harley-Davidson, with his collecting bottles and a collapsible butterfly net tucked into a side pouch), most of the blowflies had already come and gone, but a host of other insects were still busy with the corpse. "We had clerid beetles and hide beetles, both of which like their bodies slightly dried. I also found larvae of a rove beetle--it arrives early, but you don't see its larvae until a couple weeks into decomposition. Then I had hairy maggot blowfly; this was neat because it takes at least 17 days to emerge, and all I had were empty puparia." Goff also found cheese skippers, flies that arrive no later than a week after death. "The trick to cheese skippers," says Goff, "is that after a month, they pop off the corpse to pupate in the soil. So the fact that I find larvae means we're under 34 days." Finally Goff found soldier flies. "This one's pretty definitive for my time estimate because they let the body age for about 20 days before coming in. And the ones I collected were fifth instars, between 9 and 11 days old."

Goff thus placed time of death at 29 to 31 days before the body's discovery. Military police confronted two Marines seen with the victim 30 days earlier, and they confessed.

Part of what makes the method work so well for Goff, though, is Hawaii's isolation and its relatively limited number of insect species. Experts on the mainland find it harder to make such definitive analyses. They often encounter dozens of different cadaver-loving insects, only the most common of which have been studied adequately. "It's not unusual to find ourselves estimating the developmental time of a lesser-known insect based on that of a close relative that's been better studied," admits forensic entomologist Robert Hall of the University of Missouri. This kind of deduction is an easy target for legal attack. "On cross-examination, a good lawyer will say, `So, Dr. Hall, what you're telling us is you're guessing.'"

For forensic entomologists to answer such challenges requires thousands of hours of more research and legions of graduate students, but these are hard to come by in their underfunded field. A noticeable exception has been a program set up by Gail Anderson of Simon Fraser University, largely funded by the Canadian Police Research Center. Anderson's students camp out across the rugged landscape of British Columbia year-round, each baby-sitting the carcasses of several dozen pigs. To simulate real-life homicides, some of the victims lie buried in soil or partially submerged in streams or lakes.

In 1995, Anderson's students began clothing some of their pigs. "In Canada, at least, most of our murder victims are dressed," she explains. "We needed to document whether this altered insect behavior." The research raised eyebrows across North America when a school newspaper intercepted a grad student's e-mail request for used panties and bras.

Wire services quickly spread the story:


"I was sure I was going to get kicked out of the program for that one," recalls Leigh Dillon, now a coroner. "But certain things you can't find at Goodwill." In fact, by studying pigs in underwear, the entomologists learned some important things--that clothing, for instance, helps conserve moisture in a corpse, so that it will remain attractive to blowflies longer than if it is naked, and that maggots tend to eat the skin when a body is clothed but not if it is unclothed.

Then there are greater barriers between a fly and its host, which pose an even greater puzzle for forensic entomologists. It's one thing to say that blowflies will find an exposed corpse within minutes. But what if the body lies indoors, in a car mink, or wrapped in garbage bags? Because of such uncertainties, entomologists are only willing to offer estimates of the minimum time elapsed since a death, leaving open the possibility that the flies were delayed in reaching the body. Haskell will add 48 to 72 hours to death estimates for bodies found in closed spaces. "If a fly hasn't found the body by then, it's not going to," he says.

A better approach is to replicate the murder, says Goff, who recently did just that by wrapping a pig carcass in blankets and dropping it in his backyard. His impromptu experiment gave the court a convincing postmortem interval for a woman found in similar circumstances. "But things got a little twitchy with my neighbors," he admits.

Forensic entomologists also know that their science will be reliable only if police and medical examiners recognize the value of the bugs they encounter. Lamar Meek of Louisiana State University grumbles about one case in which the only specimen he was given was a photograph of a mass of eggs on a victim's ear. Since the body was indoors and had been found in the late morning, he testified that for the blowflies to have had enough time to find the corpse, the murder must have happened at least a day earlier--and possibly a day and a half earlier, on the evening the suspect admitted burglarizing the home. In response, the defense made their own estimate from the photograph of how old the eggs were, which they claimed pointed to the murder's taking place the following night. Meek knew their reasoning was poor but couldn't categorically refute it because he didn't have the actual eggs to analyze. "I couldn't disprove it with a picture."

Researchers like Meek wish that a forensic entomologist could be part of every crime-scene investigation, but with so few experts in the country, the next-best approach is for homicide investigators to be trained to do the necessary fieldwork. Some police departments are beginning to send their officers to "police entomology" courses held at universities around the country. Among them is the annual spring workshop directed by K. C. Kim at Penn State. This year found Kim, Haskell, and grad student David Skipper leading a line of detectives, pathologists, and coroners through the woods behind the Penn State campus.

"In the seventies or eighties, my superiors would have laughed at this," said Pennsylvania state trooper Jim Shubzda as he traipsed through the forest. "Maggots were just something we pushed aside to look at other Stuff."

As the group approached a forested area, the breeze grew perfumed with a sweet, skunklike smell. The more jaded in the group grinned at the familiar scent. "We've got some stinkers," someone cracked. Pushing aside branches, the group followed a deer trail leading to Joe Pig 1, 2, and 3. Spaced about 100 feet from each other, the victims lay in three different stages of maggot-infested decay. (The pigs had been killed by injection before being brought to the forest.)

Pig 1 was especially ripe that morning. The group's arrival dispersed a thick cloud of chunky black flies. Not so easily disturbed was a swarm of plump maggots churning inside an open wound on its flank. Masses of smaller maggots packed themselves into the pig's mouth and nostrils. Dusty patches of empty egg cases still clung to the wiry hairs around the cavities.

"Listen," whispered Skipper. Bending close to the open flank wound, students could catch the crackling of feeding maggots. Then a cascade of maggots tumbled out, pouring onto the ground. "Periodically they have to come up for air to cool off," Skipper explained. "A big maggot mass can generate a lot of heat."

The class broke into three groups, each assigned to a pig whose time of death they had to determine based on the insect evidence. "I want a nice sample of maggots from each wound and orifice," Skipper told his students. "Then get me at least one of everything else you can find." He supplied everyone with alcohol vials for preserved specimens and "maggot motels" (icecream cups with beef liver) for rearing live ones.

"All these things we're teaching you are to keep us from getting beat up in court," added Haskell. He launched into a diatribe on botched collections. "Once all we had were some squished maggots on a bloody blouse. I mean, for Christ's sake, they'd been stuffed in a paper bag and left in an evidence locker for over a year!"

Haskell reached for a long-handled butterfly net and then waited for a half-dozen blowflies to settle on Joe Pig 1's rump. He skimmed the net gracefully over the carcass and then gave the net a twist to trap several flies. After transferring the specimens into a vial, he handed the net to a pathologist to catch some flies of her own. She whacked the pig on the rump and came away empty.

Meanwhile, a monarch butterfly drifted down from the trees to settle on the white hairs of a pink ear on Pig 3. A student reluctantly poised himself to capture it, but Skipper called out, "Not of forensic value."

Later, in the lab, the students examined their maggots under microscopes. "Identifying species is the entomologist's job, not yours," Kim said, "but we want you to see what we look for so you can appreciate the importance of proper collection."

Specifically, the entomologist distinguishes different species of blowfly maggots by features such as the arrangement of the hooks lining their mouth and structures around their anus known as spiracles. Resembling a pair of sand dollars, the spiracles serve as breathing organs when the maggots bury their heads in putrefying flesh. The spiracles also reveal a maggot's stage of development--it starts life with one slit on each spiracle, and with each instar it adds another slit.

As forensic entomologists struggle to make determining time of death court-proof, recent work has begun to push the science's powers in new directions. At the FBI's National Center for the Analysis of Violent Crime in Quantico, Virginia, entomologist Wayne Lord has figured out how to use maggots to help medical examiners detect drugs or poisons in their hosts' bodies. "We've taken the you-are-what-you-eat scenario to its limit," says Lord. Recently he was asked to help determine the cause of death of a nearly skeletonized male body that had been found by hikers in a wooded area of Connecticut. He plucked blowfly larvae from the clothing and body cavities, made a puree of them, and from it detected high levels of cocaine. Combining Lord's results with the victim's case history, the medical examiner concluded that the man had died of an overdose.

In another case, Lord was faced with even less evidence: the mummified remains of a middle-aged woman who had died in her New England home two and a half years earlier. (Her death had gone unnoticed until foreclosure agents entered her house.) Instead of actual maggots or beetles, Lord could collect only empty blowfly pupae and beetle droppings. But even with these scant materials, he was able to detect an antidepressant. The woman's death was ruled a fatal overdose.

Most remarkable of all, Lord is now perfecting a method for tracing DNA found in bloodsucking insects to the humans on which they have fed. "It's only a matter of time before we put this research to work in an actual case," Lord says. "Most likely it will involve a rape and murder, in which the suspect's blood is retrieved from crab lice left on the victim." At the moment, Lord is still determining the feasibility of this approach, but he is confident it will work. If he's right, then someday one more previously mute witness will speak for the dead.

JESSlCA SNYDER SACHS ("A Maggot for the Prosecution," page 102), former editor of, Science Digest, is a science writer from the Atlanta area. "During the course of this assignment I inadvertently sickened and completely alienated the film processor at our local photo shop," she says. "I had a roll of film that was half family vacation pies, half maggot-infested body pies. My husband, not knowing, took them in to be developed without warning her. Boy, did she tell him off when he picked them up!" Sachs is now the proud owner of a black T-shirt that reads ENTOMOLOGY AND DEATH.

Jessica Snyder Sachs, a regular contributor to National Wildlife magazine, is the author of Good Germs, Bad Germs: Health and Survival in a Bacterial World (Hill&Wang/FSG) and Corpse: Nature, Forensics, and the Struggle to Pinpoint Time of Death (Perseus/Basic Books).

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