By studying a few grains of pollen, she can trace a murderer’s footsteps

Amy Stewart

THE WASHINGTON POST – It could be the opening scene in any crime show: A man is walking his dog in the woods. The dog sniffs the air and runs off, barking like mad. When the man catches up with the dog, he stops cold at the sight of – you guessed it – a corpse, half-buried under autumn leaves.

In the next scene, the police arrive. Yellow tape cordons off the area under investigation. The forensics team goes around dropping bits of evidence into bags and snapping pictures. The coroner leans over the body and makes a pronouncement. The detective (arriving late and hung over – the detective always has a complicated personal life) asks a few questions.

We think we know this script. We’ve seen it a million times. But what we don’t know – what nobody knew, until fairly recently – is that the forest itself can tell the truth about what happened to that body.

Fungal spores, pollen grains, bits of lichen, insect wings and soil-dwelling bacteria have a way of sticking around. They cling to hair, persist on the soles of shoes and lodge in nostrils. But to make sense of those microscopic clues requires a very particular kind of expert: a forensic ecologist.

Patricia Wiltshire’s entrance into the field went exactly the way you’d want it to go, if you were a fan of crime series. As an archaeological botanist at University College London, Wiltshire’s only contact with the dead was at ancient ruins, where she specialised in analysing soil samples to determine what plants Stone Age-era people grew and ate. Picture her one quiet afternoon, bent over a microscope, surrounded by field notes, when the phone rings.

It’s a police officer in Hertfordshire. He was given her name by the staff at Kew Gardens. He says he’s working on an unusual case, one in which the presence or absence of corn pollen on the accused’s car might determine guilt or innocence. He’s hoping she can help.

In The Nature of Life and Death, Wiltshire recounts her extraordinary career in a field that she practically had to invent as she went along. While other botanists were doing similar work around the world – in New Zealand, Texas and elsewhere – all of them had been quietly developing their own methods, pioneering their own techniques and learning skills on the job that were never taught in botany classes. (For example, Wiltshire is an expert at taking apart a skull to extract pollen from nasal cavities, and she devotes three engrossing pages to a detailed description of that process.)

By analysing microscopic bits of plant residue, Wiltshire can determine with a high degree of certainty whether an accused killer was at the crime scene. She can estimate how long a body has been buried in the woods by examining the dead plants that got folded into the grave. Were there dormant buds on the ferns? It might’ve been summer. Or was there brown leaf litter? That looks more like fall. In one case, the presence of both summer and autumn plant specimens proved that a murder had been premeditated – the grave had been dug, and the killers returned later in the year to bury their victim.

But there’s more to it than simply looking at leaves and pollen grains under a microscope. Wiltshire’s work requires a knowledge of the landscape as well. In 2005, the police asked for her help locating a body based on botanical evidence found on the murderer’s clothes and vehicle. Think about that for a minute: From a mixture of pollen grains and soil samples extracted from clothing, car upholstery and tires, the police wanted her to draw a map to the spot where the victim could be found.

Believe it or not, she did it. She sounded more like a psychic than a botanist as she closed her eyes and pictured the place. “She is in a Forestry Commission-type nursery,” Wiltshire told the officer. She went on to tell him to look for a dirt road with dry, sandy soil; wet ditches alongside; and oak, beech, hazel, sycamore and elm trees, along with ivy and bramble. “Go along an open track,” she told him, “and eventually, probably quite near the path, there will be a stand of mature birch trees.” Then – incredibly – she added this: “She won’t be buried under the ground at all. She’s in a hollow, off the path, and will be covered over with birch twig litter.”

She was right. Every bit of it was correct. The image she’d formed of the dead woman’s burial ground came not only from the pollen and soil under her microscope but from her knowledge of the landscape. For instance, a particular fern spore picked up by the killer was rare in that region. Plant maps published by the Botanical Society of Britain and Ireland pinpointed the few known locations where the fern grew. She also knew how to consult with local botanists to narrow down the list of possible locations. And after the police scoured miles of back roads, they found the body – exactly as Wiltshire had described it.

The Nature of Life and Death is one of those extraordinary books that will appeal to almost everyone. If you’re a Mary Roach fan, fascinated by the macabre and grotesque, you’ll get to follow Wiltshire into mortuaries and watch her pick apart cadavers. If you’re a “Lab Girl” fan, inspired by stories of women blazing new trails in science, that’s Wiltshire’s entire career. If you’re a gardener, you will love knowing how often botany has saved the day. And if you’re a crime fiction fan – well, you’ve found your new favorite sleuth.