Illustration by Glenn Harvey.

Between a sidewalk and a cinder-block wall grew seven mushrooms, each half the size of a doorknob. Their silver-green caps were barely coming up, only a few proud of the ground. Most lay slightly underground, bulging up like land mines. Magnolia bushes provided cover. An abandoned syringe lay on the ground nearby, along with a light assortment of suburban litter.

Paul Kroeger, a wizard of a man with a long, copious, well-combed beard, knelt and dug under one of the sickly colored caps. With a short, curved knife, he pried up the mushroom and pulled it out whole. It was a mushroom known as the death cap, Amanita phalloides. If ingested, severe illness can start as soon as six hours later, but tends to take longer, 36 hours or more. Severe liver damage is usually apparent after 72 hours. Fatality can occur after a week or longer. “Long and slow is a frightening aspect of this type of poisoning,” Kroeger said.

He and I were in a quiet neighborhood of East Vancouver, British Columbia. Across the street, behind St. Patrick Elementary School, kids were playing basketball, and their voices echoed between the occasional passing cars. Kroeger likes kids. As we’d hunted mushrooms from the sidewalk earlier that day, he had cooed at every stroller, then stopped the parents to warn them about the death caps in the neighborhood.

As he shook the mushroom free of its soil and added it to the others he’d lined up on a sheet of wax paper, he surveyed the collection and said, “Enough here to kill an entire Catholic school.”

The death caps were slightly domed, with white gills and faintly greenish stems. At the bottom of each stem was a silky slipper, called the volva, which was a purer white than the rest of the mushroom. The Amanita phalloides species accounts for more than 90 percent of mushroom-related poisonings and fatalities worldwide.

Kroeger, who studied the biochemistry of medicinal mushrooms while working as a lab assistant and technician at the University of British Columbia, is a founding member and the former president of the Vancouver Mycological Society, and the go-to authority on mushroom poisonings in western Canada. When Amanita phalloides first appeared in British Columbia in 1997, he took careful note. It had never before been seen in Canada. The single reported specimen was found among imported European sweet chestnut trees near the town of Mission, an hour east of Vancouver.

The species appeared again a year later, under a large, ornamental European beech tree on the grounds of a government building in the provincial capital, Victoria, on southern Vancouver Island. Ten years later, death caps began to appear in Vancouver, in a neighborhood shaded with mature European hornbeam trees. Kroeger recruited volunteers to search neighborhoods, and put out the word to mushroom hunters. During the first year, they documented about 50 locations in Vancouver. Kroeger wanted to know where the mushrooms were coming from, and where they’d turn up next. Sooner or later, he feared, they would have deadly consequences.

The first serious poisoning in British Columbia was reported in 2003, and another occurred in 2008. Both victims survived. Then, in 2016, a 3-year-old boy from Victoria died after eating mushrooms found outside an apartment complex. Kroeger thought he had anticipated the worst, but he was not prepared, he said, “for a wee child to die.”

Without fail, Kroeger noted, death caps appeared in urban neighborhoods, not in deep woods or city parks. They showed up most often in the strip of grass between sidewalks and streets.

For the past few years, Kroeger and his network of fungiphiles have been putting up posters in infected neighborhoods. The BC Centre for Disease Control sends out his warnings in press releases, and he sets up a booth at street events in order to warn anyone willing to listen that death caps should be left alone. When I joined him in East Vancouver, most of the people he stopped on the sidewalk—parents with strollers and passersby with groceries—had already heard of the invader. A man in a tool belt coming off a house remodel said he’d seen death caps a few blocks away in East Vancouver, and Kroeger scribbled down the address. I asked the man why he was so interested in mushrooms; he said he just liked to know what was growing in the neighborhood.

The first death cap Kroeger found that day had been in front of a house decorated for Halloween, which was two weeks away. He dug into the leafy ground cover, revealing several more greenish domes. Like a leaping gnome, he jumped across the sidewalk, grabbed a plastic human skull off a post, and brought it back to his find. Nestling the skull into a nest of purple periwinkle beside the emergent death caps, he laughed to himself and took a picture. Sometimes, he almost seems to side with the death caps. He appreciates their mysterious tenacity. He greets each one with an excited smile, talking to it: “There you are.”

By the end of the day, Kroeger had collected a couple of dozen death caps, each placed in wrinkled wax paper and then into one of the plastic boxes he carried in a faded, bucket-style day pack. They’d be dried and stored at the university. Most were from new locations. Before rolling a thin cigarette for himself, he fished out a damp cloth to clean his hands. He explained that he couldn’t use a moist towelette with alcohol because it could facilitate the passage of toxins through the skin. While he thought the mushrooms could usually be handled safely, a whole day of repeated touching was risky, since it was always possible to forget and touch one’s face, nose, or lips. “Just to be safe,” he said, wiping his hands and offering the cloth to me.

***

Dr. Kathy Vo, a medical toxicologist in San Francisco, publishes case studies on rare or unusual poisonings. Amanita phalloides poisonings, she told me, are some of the worst. “When the liver starts to fail, you see bleeding disorders, brain swelling, multi-organ failure. It’s very, very rough,” she said.

The levels of fluid loss, Vo said, are some of the most dramatic she’s seen. The body flushes everything it has. “There’s not an antidote,” she said. “That’s what makes this particularly deadly. We institute a variety of therapies, but there’s not an A, B, C, D. It’s not always the same. The best bet for the patient is fluid, fluid, fluid; keep watching the liver, and if the liver is failing, go for a transplant.”

On average, one person a year has died in North America from ingesting death caps, though that number is rising as the mushroom spreads. More than 30 death-cap poisonings were reported in 2012, including three fatalities, while 2013 saw five cases and no deaths. In 2014, two people died of death-cap poisoning in California; a third died that year in Vancouver after a Canadian man traveled to California, ate the mushrooms as part of a meal, and returned to Vancouver, where he became ill and died.

Amanita phalloides are said to be quite tasty, and a person who eats one could feel fine for a day or two before illness sets in. The poison is taken up by the liver cells, where it inhibits an enzyme responsible for protein synthesis; without protein, the cells begin to die, and the patient may start to experience nausea and diarrhea—symptoms that can easily be attributed to general food poisoning or other ailments. “If the patient doesn’t realize the connection, doesn’t see the illness as a result of eating a mushroom a day or two earlier, it’s a hard diagnosis,” said Vo.

The first death caps to appear on the West Coast hit Northern California in 1938. Since then, Amanita phalloides has been a constant menace to people in the Bay Area. Vo said that an outbreak of poisonings typically follows a rainy season; in November of 2016, after a long spell of warm weather and copious rain, the Bay Area Mycological Society got in touch with the California Poison Control System hotline, warning that death caps were sprouting up. “Five days after that, we started getting calls,” she said.

As part of a cluster of 14 poisonings in the fall of 2016, a Bay Area family grilled wild mushrooms gathered by a friend, not knowing they were death caps. They were eaten by the young mother and father, their 18-month-old daughter, and two other adults. The parents and a third adult underwent aggressive fluid treatments and were released from the hospital after a couple of days, while the fourth adult and the child required liver transplants. In the process, the little girl, who reportedly ate half a mushroom cap, suffered what Vo described as permanent neurological impairment, and is no longer able to feed herself or follow commands.

“Every year we get lots of calls about mushroom ingestion,” Vo said. “A kid finds one in the backyard and eats it. We ask them to send a picture and usually it’s not a big problem. We call them ‘little brown mushrooms.’ They cause irritation, sometimes nausea and vomiting. But Amanita phalloides is a different case. Flip the mushroom over and tell me if the gills are white. If they are, I’m really concerned.”

***

The death cap is a global traveler, but only in the past century has it caught its stride. Long after feral cats spread across Australia, long after pigs and mongooses were running loose in Hawaii, Amanita phalloides was still home in Europe, where it grew mostly in deciduous forests and was the leading cause of mushroom poisonings from the Balkans to Russia to Ireland.

While historical records are inconclusive, the first suspected death caps in North America were reported on the East Coast in the early 1900s. The first in California were spotted on the grounds of the Hotel Del Monte in Monterey in 1938, growing from the roots of a planted, ornamental tree. After that, the species landed hard in the Bay Area, where it is now common, having spread into wild oaks; it is becoming more abundant in California than in its native European habitat. After the Bay Area, it was reported in a string of Pacific Northwest cities, each one farther up the coast.

The species wasn’t just spreading from tree to tree, gradually expanding its range. Instead, it landed like an isolated bomb, colonizing outward from each impact. While this pattern suggests that the mushrooms in British Columbia may have started in California, Kroeger began to suspect that they represented a separate invasion.

When Kroeger put together maps of the first death-cap outbreaks in Vancouver, he had no problem seeing the pattern. They were showing up in neighborhoods built in the 1960s and ’70s, growing under broadleaf trees that had started off in nurseries.

Ilustration by Glenn Harvey.

Most mushrooms propagate in the form of spores that fly into the air and land like seeds. Death-cap spores are especially fragile; they degrade in sunlight, and don’t travel far or well. By any measure, the species should have remained a rare European endemic, but somehow, it successfully hitched a ride all the way to North America—not once but many times.

Most of any mushroom is underground, invisible. The majority of its biomass consists of mycelia, a network of living threads that send up occasional fruiting bodies in the form of mushrooms. Death-cap mycelia live only in tree roots. They form a symbiotic bond with certain trees, growing into a web that dramatically extends the reach of their roots.

As the web penetrates the root structure, becoming an inseparable part of the tree, the fungus begins to live off the sugars stored in the roots—while offering the tree greater access to water, nutrients, and chemical messages from surrounding trees. The relationship is called ectomycorrhizal: ecto (outside), myco (mushroom), rhyzal (root). If a sapling with ectomycorrhizal fungi were to be dug up and moved, the fungi would travel with it. In this case, Kroeger surmised, the fungi had been inadvertently carried across the Atlantic to southern British Columbia.

Kroeger can stand on a hill in Vancouver, or look from a freeway, and pick out the neighborhoods where he is most likely to find death caps. He looks for a combination of mature broadleaf trees and European ornamentals, especially hornbeams, mixed with what he calls mid-century modern domestic architecture, where the longest wall of the house is built parallel to the street rather than tucked back into a landscaped lot. This dates a neighborhood, and its trees, to the 1960s and early ’70s.

According to Kroeger, although there is some dispute among experts in the field, death caps appear in these neighborhoods decades after planting, because the mushroom lies dormant for that long. Its mycelia live in the roots of a host tree until the tree reaches maturity—when it stops pouring energy into growth and starts storing sugars. For these European imports, that’s about half a century. When surplus sugars enter the fungal web, the first fruiting bodies emerge.

Shadowing Kroeger along streets pillared with old broadleaf trees is like pursuing a fox, not a creature of sidewalks. The matrix he follows is underground. Cutting between parked cars, smoking one of his thin cigarettes as he traveled, he seemed to know every grassy back way, every portage around apartment complexes and medical facilities.

Wearing sneakers and a red flannel jacket, he glided swiftly and paused often. Most of what he found were red and white Amanita muscaria, a showy native species. Like A. phalloides, this Amanita attaches to tree roots, and rings of its fruiting bodies rise like fairy kingdoms around the trunks. Poisonous and hallucinogenic, they had been brought out by the rains, and they were all over the city, some as big as dinner plates, some like cherry-colored doorknobs dotted with white flakes. Kroeger crawled on the ground with his camera, capturing tableaus, tapping on their tops, feeling their firmness in the ground. Passersby stopped to comment, amazed at how beautiful and numerous they were.

The death caps were lurkers. They had to be searched for. Rooting around in a strip of vines and flowers in front of a house where he’d found new specimens, Kroeger looked up as a woman cracked open the front door.

“What are you doing in my garden?”

Kroeger stammered that he was a professional mycologist. He clearly enjoyed talking to mushrooms more than to people. He stood upright and lifted a death cap in his hand like a freshly removed appendix. Did she know that deadly mushrooms were growing in her garden? When she didn’t answer, Kroeger said in his gentle, earthy voice, “I’m just here to collect these.”

“Okay,” she said. “But stay out of my garden.”

He waited a moment after the door slammed, making sure she was gone, then reached into the base of a shrub, using his curved knife to pry up another silver-green mushroom.

As we packed up and moved on, he said, “The development style of the city set the stage for their introduction and proliferation. They will never go away, not, at least, through any known human decision.”

Once an ectomycorrhizal fungus is in the ground, even killing the host tree won’t stop it. A proposal was put before the city to chop down every hornbeam, the major source of death caps. “But then you have to cut the lindens, sweet chestnuts, red oaks, English oaks. That’s a lot of the city, and you still won’t get rid of [the death caps],” Kroeger said.

Across from the Catholic school where Kroeger had collected death caps a few hours earlier, a mature hornbeam tree towered over the neighborhood, its deciduous canopy shading both sides of the street. The house of the woman who had scolded him stood 30 feet from another stately hornbeam. Kroeger has maps of land use over the century, detailing development block by block. To him, they are maps of present and future death-cap distribution. Decade by decade, like an underground echo, more and more appear. Kroeger wonders how long it takes people to learn how to avoid a common and deadly mushroom. It is not common yet, but he knows that it likely will be, and that the first fatality in British Columbia from a local death cap, in 2016, will not be the last.

***

Britt Bunyard, the founder, publisher, and editor in chief of the mycology journal Fungi, has tasted a death cap. “Very pleasant and mushroomy,” he told me. “A nice flavor, and then you spit it out.”

For the amatoxin poison to begin to work, it needs to enter the intestinal tract. A quick bite without swallowing has little effect.

“Poisonous snakes, reptiles, plants, [and] fish have aposematic coloration that shows off that they are poisonous. Mushrooms don’t,” Bunyard said. “The dangerous ones are all mostly drab or brown, green-brown, bronze. There’s nothing in the taste that tells you what you are eating is about to kill you.”

A large portion of people who are poisoned by death caps in North America are Hmong or Laotian immigrants. They mistake the species for a prized edible from home, what is called the “white Caesar,” Amanita princeps.

Death caps are not only a North American problem. They have spread worldwide where foreign trees have been introduced into landscaping and forestry practices: North and South America, New Zealand, Australia, South and East Africa, and Madagascar. In Canberra, Australia, in 2012, an experienced Chinese-born chef and his assistant prepared a New Year’s Eve dinner that included, unbeknownst to them, locally gathered death caps. Both died within two days, waiting for liver transplants; a guest at the dinner also fell ill, but survived after a successful transplant.

“Because the mushrooms don’t taste bad, they’re probably not meant to be poisonous to ward off being eaten or foraged,” Bunyard said. “Mammals, not even all mammals, are the only ones affected. Some squirrels and rabbits can eat them without being harmed. Why it’s so toxic to humans—who knows? Some poisons are used as communication molecules, and just happen to be poison to us.”

To Bunyard, the death cap’s journey is only a symptom of a larger phenomenon—the global mobilization of the entire Fungi kingdom. With their blowing spores and underground mycelia, mushrooms can travel in as many ways as humans can carry them. Bunyard, who has a Ph.D. in plant pathology, is concerned about how mushrooms might displace and change their new ecosystems. “The way bacteria are the primary pathogen for animals, fungi are the primary pathogens for plants,” he said. “What’s going on is under the soil, what we don’t see. Some of the native mycorrhizal fungi are being displaced, which will in turn displace plants.”

How a newly introduced mushroom and its underground cobweb impacts the life around it is poorly understood. Much about the life cycles and taxonomy of fungi remains elusive. Fungi were not given their own kingdom—now known as the “fifth kingdom”—until 1968. Before that, mushrooms were categorized as plants. Genetically and evolutionarily, they are closer to animal than plant. Mycology is a relatively new science, and researchers are only now beginning to understand how instrumental fungi are in almost every ecosystem, not only in breaking down and recycling organic matter, but also in concentrating nutrients for plant life and acting as chemical communicators.

Kroeger has reported that death caps are now moving from their imported European host trees to an oak species native to British Columbia. The first identified species jump was in 2015. This was seen in California decades ago, when they began moving into coast live oak trees. Tree roots mingle underground and mycelia reach across, taking up new residence. Death caps have begun to naturalize, spreading without external aid.

“They could get rid of a lot of humans and dogs,” Kroeger said. The occasional fatality is a risk Kroeger tries to mitigate, but, like Bunyard, he worries more about what he calls the “unexpected consequences” of a biological invasion following paths of modern civilization. What does it mean to move a tree-root mushroom to a distant continent? The steamship gave living plants and mushrooms their first chance to enter global commerce. Now, container ships and airplanes can get them anywhere. “I think anything humans do has a chance of going wrong,” Kroeger said. “The monkeys have a bad history.”

***

The next day, on a Chinatown-bound city bus, Kroeger moved toward the back like a gentle ghost. His ponytail lay down his back, neatly combed. He sat with his pack on his lap, plastic bins empty for another day of hunting and gathering. As the bus traveled down Main Street near East Vancouver, he rubbed his hands together with some excitement, saying, “We are about to pass the 13th Street location; we must genuflect.”

He was referring to the crop of death caps he’d found the day before, across from the Catholic school. Every year he finds more, new appearances along sidewalk edgings and corner gardens. Soon, he fears, they will move from the city into the surrounding woods. Southern British Columbia could be the next Bay Area in terms of death-cap abundance, with fatalities or life-affecting illnesses after every good rain.

As the bus stopped and started toward the edge of downtown Vancouver, Kroeger ticked off the ways mushrooms get around the world: volcanic pumice rafts, ship ballast, animal stomachs, packing crates, live plants, peat. Human activities that introduce mushrooms to new habitats tend to bring in other non-native species too. “Most of the time you’d never know it’s happening,” he said. “It’s only because this mushroom kills people that we’re paying attention.”

In 1987, Kroeger identified a mushroom previously unknown to science. He found it growing in clumps at the University of British Columbia Botanical Gardens—in mulch beds, on the wet, marshy edges of ponds, and along trails. “Pretty little thing,” he said, as if describing something precious. “Gray gills and an amber-colored cap.” As he does when he talks about any mushroom, he sounded like he was in love.

Kroeger and a colleague named this new species Hypholoma tuberosum, and it was not long before other sightings were reported in New York, Japan, Germany, Belgium, and Australia. The species wasn’t native to British Columbia, but it wasn’t a new arrival, either; it had simply not been noticed by anyone willing to go to the trouble to name it. Since it seemed to favor landscaped grounds, mycologists began looking for its source, thinking that like the death cap, it must have been incidentally carried by humans. The source appeared to be a single nursery in metropolitan Sydney, Australia, where peat carrying H. tuberosum was being used for potting plants, which were then shipped worldwide. That peat had been collected from a bog 130 kilometers away—the likely native source of a mushroom that could have easily remained an obscure local, but has become a global cosmopolitan.

As the bus slowed in downtown Vancouver, Kroeger lifted his pack, saying, “Our stop.”

We got out on Hastings Street and moved along a wide, crowded sidewalk, bedsheets and flattened cardboard stretched out in what looked like a blocks-long flea market. Half the vendors were curled up or sprawled semiconscious next to their wares; it was early in the day in a rough part of town. Kroeger said he’s been hesitant to put up signs in neighborhoods around here: “People with psychiatric issues, suicidal, possibly even with malicious intent. I don’t want them intentionally going after death caps.”

Several blocks away, in a shaded neighborhood, he stopped in front of a house on the corner of East Georgia Street and Princess Avenue. Moving back a fern frond with his hand, he said, “Speak of the devil.”

In the shade of the underbrush was a metallic-colored mushroom, pale green verging on gold. There are 96 hornbeam trees on this chain of blocks, Kroeger said, and he had already found death caps under eight of them. Now the count was up to nine.

Kroeger stopped not just for death caps but for every troop of mushrooms. Anything bright or emergent caught his attention. “Nicely poisonous,” he said about a button-topped Agaricus growing on a corner lawn. “Not near as poisonous as phalloides,” he added.

Later in the day, his plastic containers were full, and he’d gone through five or six thin cigarettes. He found one last death cap, a mature one growing in the grass near the base of a rock wall. He looked around, noting the nearest intersection, committing the location to memory. Then he moved on, leaving the mushroom behind. It had been a long day, and Kroeger is not on a crusade to remove every death cap. He wants to know what they are up to, and he wants to take out enough to matter. He loves kids and dogs, after all.

The death cap he passed up, grown from the roots of a nearby hornbeam, stood clear of the grass on its slender white stalk. Digging it up would not slow what is happening underground; it would not change the worldwide flow of soils and roots, and the fibrous bodies living within them. Digging it up would be almost a symbolic act, less than a drop in the bucket. So Kroeger left the mushroom in place—a nod to the fifth kingdom, the unstoppable.

Craig Childs is a writer based in Colorado. His work has appeared in The New York Times, the Los Angeles Times, and The Last Word on Nothing.