December 2007 Archives

Canine Scent Line-ups

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Does the cold nose know?
Canine "nose witnesses" may be more convincing than reliable.

Copyright Jessica Snyder Sachs, as first appeared in Popular Science

Nothing brings a little light into a dismal courtroom like the goofy grin and thumping tail of a hound. And as witnesses go, nothing beats a canine for sincerity and trustworthiness.

"The jury eats it up," says police K-9 handler Pat McAlhany, a veteran of the Miami-Dade County Sheriff's Office. "From a prosecutor's standpoint, there's nothing better than my actually bringing my dog into the courtroom for a demonstration."

Indeed, the practice of using dogs as "nose witnesses" to finger, as it were, the accused is rapidly growing. A rape case that passed through the Los Angeles court system last year illustrates the procedure. A young woman came into the police department and described a brutal attack. Two men had dragged her from a bus stop in an industrial part of the city into an alleyway, where they sexually assaulted her. Traumatized, she initially did not report the attack. But two days later she found a necklace she thought one of the rapists had ripped from her neck. It lay outside the school where she worked. Did one or both of the attackers live in her neighborhood and know her daily habits? She also spotted a man at a local market who reminded her of one of the attackers. Now terrified, she went to the police.

The delay meant a rape kit could not provide DNA evidence. Not a problem. Enter Reilly, a confident, experienced expert witness with boundless enthusiasm for his job. Under the leash of volunteer scent-evidence K-9 handler Joseph D'Allura, this chocolate Lab's scent-detection skills had put killers behind bars. For the rape case, D'Allura created a "scent lineup," using a scent transfer unit that worked like a Dustbuster, sucking the perpetrator's odor off the snatched jewelry and onto a sterile gauze pad placed over the vacuum's air intake. He then vacuumed a piece of clothing taken from the neighborhood resident who had aroused the rape victim's suspicions in the local market.

D'Allura prepared the scent lineup by placing the suspect's pad alongside three decoys infused with scent from other individuals. Finally, he presented Reilly with the necklace scent pad and directed him to find its match. Passing over pad number one, the dog gave the second sample a wag and a bark--an "alert" in dog-handling lingo. The police had a positive ID.

Or did they? Juries may love a dog show, but some experts remain skeptical. "In all honesty, we don't know what a dog is picking up on when it alerts," says Lawrence Myers, an Auburn University sensory and behavioral biologist called as an expert witness for the defense in the rape case. Over the past 21 years Myers has trained more than 50, and studied hundreds, of scent-detecting dogs under laboratory and field conditions, mostly for federal agencies wanting to perfect the use of dogs for finding explosives, drugs, trapped disaster victims and hidden graves.

Myers considers the canine nose the ultimate odor-detection system in use today. But in many ways, he says, "we're still dealing with a black box." Scientists have yet to fully understand the process of canine odor identification. Neither have they defined the limits of a dog's sense of smell, nor isolated any universal "scent factor" that dogs use to distinguish one person from another.

The widely held view is that dogs pick up on variations in the chemical makeup of the skin flakes and perspiration residue we all continually shed. But no one knows which aspects of this microscopic brew grab a dog's attention as it plays a forensic game of mix and match. Might racial or gender differences skew results? Or, for that matter, some yummy-smelling food the person ate the previous day?

When it comes to something as complex as human scent, Myers believes that different dogs likely tune in to different things. And no dog is perfectly consistent. Myers's research has shown that something as mundane as dental tartar can have a ruinous effect on a dog's powers of discrimination. "Clean the teeth and you get an almost immediate recovery of smell," he says. Scent dogs also have off days, suffer allergies, get colds. "Trouble is," he says, "you can't cross-examine a dog and ask, 'Are you sure?' "

So Myers has deep misgivings about the growing number of calls he's getting to testify in rape and murder cases that hinge largely on a doggie's positive ID. "It's like the floodgates have opened," he says.

Dog scent lineups aren't new, how-ever. Estimates suggest they've played a role in more than 1,000 criminal cases in the United States, going as far back as 1923. Today, most states and the District of Columbia admit dog scent evidence as valid identification of the accused, "provided a proper foundation is laid."

Despite this long history, a scientific basis for that proper foundation has never been established. Many prosecutors try to skirt that fact by arguing that scent lineups are no more than a logical continuation of the practice of employing dogs to track fugitives or sniff out drugs--uses that have long passed legal muster. Some judges buy that argument, some don't.

The courts rely on handlers to demonstrate a dog's reliability by
submitting training records. But it's widely known in handler circles that many are loathe to record a dog's mistakes, lest the errors later be used to discredit the dog's identifications.

Research reveals that even experienced and well-trained dogs sometimes misidentify individuals. In studies conducted in Europe (where scent lineups have become tightly regulated and standardized), dogs' identification scores varied from a high of 58 percent to a low of 22 percent. Researchers have conducted such studies both on-lead (with a handler holding the dog's leash) and off, in an effort to tease out or exclude a handler's influence.

That some handlers inadvertently prompt their dogs is a major criticism of scent lineups. And the critics include some of the nation's most experienced search-dog handlers. "We have a saying in dog training circles," explains police K-9 instructor Roger Titus, vice president of the National Police Bloodhound Association. "Your body language goes down the leash." A well-trained dog becomes hyperaware of its handler's every move, Titus explains. "You lean forward, it moves. You slow down, it does too. You walk down a lineup of six baseball caps, and all you have to do is think you're at the right one, and the dog picks up on it." Some call it the Clever Hans effect, after the 19th-century equine genius whose mathematical prowess turned out to be nothing more than the horse responding to the unconscious nod of his trainer's head.

Dog-evidence enthusiasts have reason to be cautious, Titus warns. Much of the precedent-setting case law, including murder convictions, behind the acceptance of scent lineups came from the now discredited work of a single handler, who was later shown on videotape to be cuing his dog.

The expanding use of scent lineups has become a hot-button issue in the police-dog handler community. The National Police Bloodhound Association and the Law Enforcement Bloodhound Association have both developed guidelines for proper lineup procedures, while their memberships remain deeply divided over the legitimacy of the practice.

"The fact that a dog might send somebody to the electric chair places a tremendous responsibility on the handler," admits McAlhany. "That said, my confidence in my dog and myself is very high. I would feel comfortable going to court and testifying that, yes, she can use a scent article and make a positive ID."

Confidence in dog and handler aside, the scent-collecting process itself is not above controversy. "Scent is a fragile creature to begin with," argues Titus. "In my opinion, the use of scent machines takes the whole idea further down the line of pipe dreams."

The scent transfer unit's inventor, Bill Tolhurst of the Niagara County (New York) Sheriff's Department, dismisses that argument. Tolhurst says he's successfully run dog scent lineups using evidence pads stored for more than 11 years in frozen, heat-sealed plastic bags. Tolhurst, a three-time past president of the National Police Bloodhound Association, says he's pulled human scent off shell casings from drive-by shootings. Among his proudest accomplishments, he says, is a conviction in a kidnapping and attempted murder case in which his bloodhound matched the defendant to scent vacuumed off the seat of a car last driven by the offender.

To date, Tolhurst has sold more than 80 of his scent-collecting machines to law enforcement agencies--including 35 to California police and sheriff's departments and 7 to the FBI.

Lawyers will be arguing about the merits of dog-witness identifications and procedures for years. In the rape case described earlier, the judge ruled Reilly's scent identification inadmissible, citing, among other things, D'Allura's lineup procedure. D'Allura stopped the lineup as soon as Reilly alerted on the second pad, rather than allowing him to proceed down the line. In addition, D'Allura couldn't recall when or from whom he'd made the lineup's three decoy pads. Were they from individuals of the same race as the suspect? D'Allura couldn't say.

Of course, having evidence dismissed is part of the legal process; win some, lose some. D'Allura points to several cases in which Reilly's testi-mony played a decisive role. In a major coup for scent lineup proponents, a California appeals court recently upheld Reilly's identification of a teenager convicted of a double homicide, as well as the young man's sentence of two consecutive life terms.

Does the cold nose know? Criminal juries may be happy to say yes. But the scientific jury remains out.

Jessica Snyder Sachs, a contributing editor to Popular Science, 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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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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THE DRY SEASON grips the highland savanna of eastern Africa between late May and early June. As the relentless sun drives the last bit of moisture from the soil, the verdant highlands shrivel to yellow and brown. Herds of antelope, gazelle, wildebeest, elephant and buffalo gather by the hundreds of thousands, chafing to begin their annual migration to the lowlands to find water. Lions, hyenas and other predators likewise ready themselves to follow their prey on the seasonal journey.

But none can leave the depleted highlands until the plains zebra departs--and readies lowland grasses for the grazers that follow. "They start the whole grazing succession," says Princeton University ecologist Daniel Rubenstein, who has been studying the species for the past 15 years. Because zebras have an unusual hindgut digestive system rich in fermenting microbes, they can gorge on the low-quality coarse straw available at the start of the rainy season. Buried beneath this sunlight-blocking thatch lies the tender new growth upon which all other grazers depend. This means that from the vast, acacia-dotted savannas of the Serengeti, south through Zambia's scrubby woodlands and the treeless veldt of South Africa, the plains zebra plays an unmatched role in maintaining some of the most biologically diverse habitat on the planet.

Consequently, the long-term conservation of Africa's tropical grasslands relies on the wise stewardship of this linchpin species, says Rubenstein. In partnership with the African Wildlife Foundation and Earthwatch Institute, he currently heads a broad-based project aimed at integrating zebra conservation with the rapid growth of agriculture, livestock and game-ranching industries in eastern Africa.

To the tourist on safari, the plains zebra certainly looks to be thriving. Indeed, where these zebras still occur, their inimitable stripes dominate the landscape, with a population of nearly 665,000, dwarfing that of its two gravely endangered cousins--the Grevy's zebra of Kenya and the mountain zebra of Namibia and South Africa.

"But if you actually look at the details," says Rubenstein, "you see that the plains zebra has been extirpated from much of its historic range." Today, 70 percent of its population concentrates in just two countries, Kenya and Tanzania. Ecotourism dollars have enabled these nations to protect large swaths of lowland zebra habitat inside national parks. But just outside park borders, farms and ranches have sprung up to block many of the age-old migration routes that zebras need to cross between dry season refuges and lusher uplands. Though the lengths of these migration routes vary widely, many populations travel hundreds of miles a year.


In Tanzania, for example,"there used to be nine migratory routes out of Tarangire National Park," says Rubenstein. "Now there are only two or three left, all on privately owned land." Because of the low quality of their grasses, dry-season refuges such as Tarangire can't support large populations of zebras unless the animals can fatten up in adjacent highlands during the wet season.

How this changing landscape will affect the plains zebra is unknown. But what is certain, given Rubenstein's studies, is that human activities are affecting the species' unique multilayered social structure.

At the core of plains zebra society is a breeding group, or harem, with a single breeding stallion, up to six mares and their young. Rubenstein has discovered that although the stallion defends his harem from danger and harassment, the mares generally call the shots. "The males that let their females do what they want--organize behind the scenes and choose the kind of grazing they want--those are the stallions that get the most females," he says.

As with many social mammals, female plains zebras form strong, long-term bonds with one another and stay together even after the death of a stallion. What's unusual is that the females in a zebra harem are not related. And unlike many other large mammals--such as lionesses and female elephants, which form alliances with sisters and daughters--plains zebra mares cast out all of their offspring. "In fact, it's usually the young females who get the message first and take a hike," says Rubenstein. In her second year, a maturing filly goes in search of a young stallion. A young male leaves by his third year, either to join a bachelor group or begin recruiting his own harem.

Adding more complexity, stallions and their harems often band together to form a much larger, loose-knit herd of several hundred, where the females freely comingle. Yet the stallions generally resist pilfering each other's mares. The purpose behind these superherds appears to be defense against raiding parties of bachelor males. "A single stallion set upon by a large group of bachelors has little chance of defending his females. As he barrels into the mob, taking on five or six of the marauders, the others just stream around him and head for the females," says Rubenstein. By contrast, a coalition of stallions can present a united front to keep the interlopers at bay. Rubenstein has observed that the more bachelors in a given area, the larger the combined-harem herds.

This elaborate social system complicates the task of conserving and managing the plains zebra. Many zebras live on private game ranches, where hunters target established stallions--the male's brighter coat makes for the most desirable trophy and the "homebody" stallions tend to be easier to find than the farther-ranging, vagabond bachelors. But increasing the proportion of bachelors causes surviving stallions and mares to band together even more, producing an unnatural herd size. "It's creating a whole new population structure," says Rubenstein, "It's not clear whether this is natural or sustainable, or what it might mean for the future."

More clear-cut is the impact that stallion hunting has on the zebra birth rate. Remove a harem's stallion and the fertility of the surviving mares drops dramatically for at least two years while young and inexperienced bachelors vie for control. "From a game management point of view, that means fewer babies," says Rubenstein, "a fact that has to be taken into consideration when setting hunting quotas if zebra populations are going to remain self-sustaining."

That said, wild populations as large as the plains zebra's can adapt to new pressures. But only if they have enough space. "Free run is the issue," says Rubenstein. "The zebras can take care of themselves."

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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Copyright Jessica Snyder Sachs, as first published in National Wildlife (photo courtesy

SOMETHING SHINY caught my eye when I glanced at the old thermostat the repairman left behind. I was about to toss it in the trash, when I realized that it contained a glass bulb filled with mercury. I had done enough reading to know that I had enough toxic metal in my hand to contaminate a large lake, rendering its fish unsafe to eat for years, if not many decades, to come. The challenge would be to safely and responsibly dispose of it. Unfortunately, thermostats are just one example of the scores of mercury-containing products found in a typical American home. Few bear any indication of their status as hazardous materials. Some contain enough mercury to pose an immediate danger if they break and release toxic vapors. All of them present homeowners with the same challenge I faced: How do you dispose of these items safely so the mercury doesn't get into the environment and return in a more dangerous form inside a can of tuna or bite of sushi?

As for the food products containing mercury that are already in our pantries and refrigerators, consumers today have good reason to think hard about what kinds of fish they're feeding their family, and in what quantity (see "Dietary Cleanup" box). "We need to look at the mercury problem through two lenses," explains Felice Stadler, national policy coordinator for NWF's Clean the Rain Campaign. "The first lens concerns what we can do to minimize our exposure today. The other lens concerns identifying sources of mercury so we can minimize environmental contamination and reduce exposure through tomorrow's food supply."

Though mercury occurs naturally in the environment-in rocks, soil, oceans and air-only in modern times has it become a pervasive and pernicious threat to health. Indeed, scientific research indicates that the rate at which mercury enters our food chain has increased considerably in recent decades.

What makes this dangerous is mercury's extreme neurotoxicity. That is, its devastating effects on the brain and nervous system. The "mad hatters" of Victorian times suffered from mercury poisoning when they rubbed the metal into felt cloth to preserve it. Mental confusion, trembling and eventually death can result from inhaling the vapors of this liquid metal, which readily evaporates at room temperature. As the dangers of mercury exposure became known in the early 20th century, acute poisonings became rare. But they still occur, as when children find and play with mercury or when someone eats large quantities of contaminated fish over a relatively short period of time.

Of far greater concern today is the harm that is done to developing fetuses, infants and young children exposed to even low levels of methylmercury. A recent report by the National Academy of Sciences concluded that the amount of methylmercury (an especially problematic form) consumed by pregnant women in this country results in at least 60,000 children born at risk of developmental harm. The risk of permanent injury continues for at least the first five years of life, as the brain and nervous system continue to develop and children consume mercury through breast milk and food.

The vast majority of methylmercury in our diet turns up in large, commercially caught fish, such as tuna and swordfish, and in smaller species pulled from contaminated waters by recreational anglers. Scientists have traced the source of the contamination primarily to coal-burning power plants, certain industrial processes and the incineration of mercury-containing products.

Once mercury enters the planet's water cycle as a pollutant, bacteria convert it into methylmercury, which bioaccumulates (or concentrates) in the tissues of organisms that consume it. So it occurs at greater concentrations as it moves up the food chain. In top predators such as tuna and swordfish, methylmercury can be present at concentrations 10,000 to 100,000 times that found in surrounding waters.

The good news is that mercury-free alternatives now exist for many of the metal's uses in household and automotive products. This has encouraged a handful of states to bar the sale of easily replaced mercury devices such as thermometers and switches. Only two, Vermont and Minnesota, require manufacturers to label mercury-added devices. Until such labeling requirements become widespread, ferreting out mercury in the home takes some detective work. Understanding the metal's useful properties can help you recognize where it's likely to be found.

Thermometers and thermostats: Elemental mercury expands and contracts evenly with changes in temperature. So it has long been used in glass thermometers and the mercury-bulb switches in thermostats. Mercury switches can likewise be found inside heating elements that shut off when they reach a set temperature-such as those inside clothing irons and older microwave ovens. The most easily recognized nonmercury alternatives have digital displays-an indication of electronic sensors.

Vapor lamps: Fluorescent, neon and high-intensity-discharge (HID) light bulbs contain mercury vapor. Fluorescents more than make up for their added mercury by conserving energy and so reducing mercury emissions from coal power plants. Until mercury-free alternatives are available, the best options are low-mercury bulbs as long as they are disposed of properly; they are recognized by their green end caps.

Batteries: Over the last 20 years, U.S. manufacturers have reduced the amount of mercury in household batteries by 99 percent. Small amounts can still be found in "button" batteries, such as those used in watches and hearing aids; as a result, they should be properly disposed.

Barometers and blood-pressure gauges: Mercury expands and contracts with pressure. So it is used in conventional barometers and blood-pressure gauges. Indeed, a typical home blood-pressure device contains a whopping 1.5 pounds! Mercury-free alternatives include "Bourdon tube" barometers and "aneroid" blood-pressure gauges.

Old pesticides and latex paint: Mercury's toxicity makes it an effective preservative and pesticide. Fungicides and herbicides produced before 1994 and latex paint made before 1992 release significant amounts of mercury vapor during application. Though the sale of such items is now phased out, countless half-used containers remain in America's garages and basements.

Toys and novelties: Old children's chemistry sets (1960s vintage or earlier) often contained vials of liquid mercury. Until recently, athletic shoe manufacturers used mercury in the blinking heels of light-up sneakers. Toy importers still occasionally sell novelties that contain a drop of mercury that rolls through a maze.

Tilt switches: Mercury conducts electricity and flows when you tilt it. So it is used in switches that stop motors or turn on lights when you open a lid. Think washing machines, top-loading freezers, car hoods and trunks. Alternatives include electronic sensors and nonmercury mechanical switches (check with the manufacturer). In 1995, the International Automobile Manufacturers Association announced that it had completely eliminated mercury switches from foreign vehicles. U.S. carmakers pledged to do the same by 1997, but have been slow to fulfill their promise, says Clean Car Campaign spokesman Dean Menke.

More mercury in cars: Contrary to their pledge, U.S. automakers have actually expanded the use of mercury in cars, says Menke, who calculated more than 10,000 pounds of mercury in model-year 2000 passenger vehicles. This poses a colossal problem as neither manufacturers nor car recyclers want to take responsibility for safe disposal. Until they do, Menke advises car shoppers to ask for evidence that light switches, headlamps, antilock brakes, convenience lighting and active ride-control systems have been manufactured without mercury.

Disposal: Mercury sealed inside solid devices poses no immediate danger to the user. The key is proper disposal at the end of the product's useful life, followed by replacement with mercury-free alternatives when possible. (The Clean Car Campaign's national "Switch-the-Switch" exchange program, for example, enables vehicle owners to exchange mercury for nonmercury light switches. More information can be found at

Mark as "containing mercury" any device you suspect may contain the metal. Then contact your local solid waste department to determine your disposal options: Many communities have disposal sites or neighborhood pickup dates. Collected mercury in most cases is sent to recycling facilities where it is then reused in new mercury products. Environmental advocates are working on national policies to get mercury used in products or in manufacturing completely out of circulation.

Should a mercury spill occur in your home, don't panic. Elemental mercury does not readily absorb through the skin or even the digestive tract, says Lynn Goldman of the Johns Hopkins Bloomberg School of Public Health. The health danger is vapor inhalation. So in the case of a small spill-say, a broken thermometer or thermostat bulb-move children out of the room and open doors and windows to ventilate. Never try to sweep or vacuum mercury. Doing so can contaminate an entire building by scattering toxic particles through the air. Use adhesive tape or an eyedropper to collect small amounts and seal them in a plastic container. Dispose of contaminated clothing, carpeting and upholstery in sealed plastic bags. Place contaminated materials outside and inaccessible to children and animals, until they can be disposed as hazardous waste. In the case of a large spill, such as that from a blood-pressure gauge, leave the area immediately, notify your local public health agency and call your physician for possible treatment.

NWF recently published a guide to products that contain mercury, alternatives available and local actions being taken to remove mercury products from the marketplace. For copies, contact Kathleen Eales at 734-769-3351,, or see New Jersey writer Jessica Snyder Sachs is a regular contributor to this magazine.

Dietary Cleanup
Sadly, what should be one of the most healthful foods in the American diet has become potentially one of the most dangerous. Persistently high mercury levels in streams, lakes and oceans render many kinds of fish unsafe for children and women of childbearing age. Currently, 43 states have advisories against eating some or all fish caught from local waters. But don't count on finding the warnings publicized or posted. Check with your state environmental agency before eating any recreationally caught fish, and check for new advisories each season.

As for fish from the grocery store, in 2001 the Food and Drug Administration (FDA) advised that young children and women of childbearing age not eat shark, swordfish, mackerel and tilefish because such fish were found with levels of methylmercury greater than 1 part per million (ppm). That the FDA did not warn against tuna proved controversial. Though most tuna falls below the 1-ppm mercury limit, Americans tend to eat more of it.

Methylmercury studies by the EPA suggest that levels as low as 0.25 ppm may be unsafe for consumption. In recent tests by Consumers Union, canned tuna averaged about 0.31 ppm; light tuna averaged about 0.16 ppm. Based on these test results and EPA guidelines, a 132-pound woman should eat no more than 9 ounces of light tuna or 5 ounces of white tuna a week. A 44-pound child should eat no more than a third that amount. (This assumes that no other fish is consumed by the child during that time.) The FDA recommends eating no more than 12 ounces of cooked fish per week. Far less mercury turns up in smaller commercially caught fish such as flounder, haddock, butterfish, herring and sardines.

Mercury in Medicine
Medical studies have not documented any harm from the mercury used in amalgam dental fillings, but a problem nevertheless exists with disposal of mercury wastes by dentists. Currently, no federal requirements mandate safe disposal techniques. Research also has not uncovered problems resulting from the trace amounts of mercury preservatives (thimerosal, phenylmercuric acetate and phenylmercuric nitrate) used in some vaccines, nasal sprays and contact lens solutions. Importantly, thimerosal contains a form of mercury that does not bioaccumulate in the body. In any case, mercury-free options exist for all of these products. An increasing number of physicians and dentists recommend using these alternatives. (Ask your physician before having your children vaccinated.)

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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