Why do death cap mushrooms not warn of their poison?

Why do death cap mushrooms not warn of their poison?

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This has been puzzling me for a long time now. There is an evolutionary predilection for living things which have evolved strong defensive measures (that may not themselves be visible) to give distinct visual or audible warnings advertising these measures.

Wasps, hornets, snakes, and bees are all brightly coloured. Snakes may even have rattles to advertise their venom. These things by in large don't want to have to use their poison in a defensive capacity. Getting revenge on a predator who has mortally wounded you is a Pyrrhic victory.

These warnings are so potent that many animals without such measures will mimic these warnings in order to piggy pack on a general evolutionary bias towards an instinctive avoidance of anything that warns of being poisonous.

But take the death cap mushroom.

This innocuous fungus looks identical to completely harmless mushrooms. It has no foul smell. In fact, evidence shows that it actually has a pleasant taste! That picture above actually looks pretty tasty in my opinion.

This fungus has gone to the trouble of developing one of the most potent poisons in nature (humans have a seriously robust digestive systems by animal standards, and yet a single death cap can easily kill an adult human).

So why so secretive about its arsenal?

I know this same question about evolving poisons that are not well advertised could be applied to a large number of animals, insects, and particularly fungi, but I think the death cap is the most extreme example in both the lethality of the poison considered, and combined lack of advertising.

Most of this type of evolutionary question are generally worthless, IMHO. You can rationalize anything post hoc and then go away with the misapprehension that you have been involved in science.

To add a few of those possible post hoc explanations (which took longer to type out than think up):

1) The poison is only accidentally a poison. It serves some other function in the mushroom's metabolism. There are numerous possible examples of this. For instance, the stalks of rhubarb are edible, while the leaves are poison; potatos are edible unless they've turned green from exposure to sunlight…

2) The poison might not be directed at humans. The mushroom might have some warning that would be obvious to other species, for instance a smell or markings visible in UV (such as many flowers have). We have lots of examples of poisonous plants that we grow because they're attractive to us: datura, lily of the valley, foxglove, oleander, delphinium…

3) If I'm not mistaken, mushroom poisoning takes rather a long time to kill, which argues against it being a defense. The poison might have evolved as an aid to reproduction. Mushrooms are the fruiting body of the fungus. If an animal eats it, it consumes the spores. If it dies hours or days later, it has transported those spores to a distant location, and the corpse provides nutrition for the new fungi.


Doesn't the all-white toadstool look distinctive and memorable to you? It doesn't look remotely like the field mushrooms or other edible mushrooms I would collect. What edible fungus would you confuse it with?

Hepatoprotective Effects of Picroliv

1.11 Picroliv Protects Against Amanita phalloides-Induced Hepatotoxicity

Amanita phalloides , commonly known as the death cap, is one of most toxic mushrooms. It is a highly poisonous species of mushroom, and the principal toxic constituent α-amanitin is known to cause severe liver derangement culminating in hemorrhagic liver necrosis. Studies have shown that Picroliv protected rats against the A. phalloides-induced hepatotoxicity ( Dwivedi et al., 1992b ). Picroliv (50 mg kg −1 ) decreased the activities of hepatic 5′-nucleotidase, gamma-glutamyltranspeptidase, acid RNAse, and SDH and increased the levels of glucose-6-phosphatase, affirming their hepatoprotective effects ( Dwivedi et al., 1992b ).

In California, Poisonous Death Cap Mushrooms Are The Forager's Bane

Donna Davis thought she had hit the jackpot with the two bags of mushrooms she collected in the woods of Northern California's Salt Point State Park. Instead, she ended up in the hospital, facing the possibility of a liver transplant, after mistakenly eating a poisonous mushroom known as the death cap.

The 55-year-old life coach and her boyfriend had collected chanterelles, matsutakes and hedgehog mushrooms, all sought-after edible species.

That night, Davis made mushroom soup for herself, her boyfriend and a group of their friends. "It was amazingly delicious," Davis says. So good, in fact, that she had two bowls.

Mature death caps in West Marin's Point Reyes National Seashore in December. Gabriela Quirós/KQED hide caption

Mature death caps in West Marin's Point Reyes National Seashore in December.

And she felt fine. Until the next afternoon.

"I slept for three days," says Davis, of her illness in December 2014. "I was kind of in and out of it, just drinking water and not being able to really hold anything down."

When she dragged herself to a mirror, she realized she had turned yellow.

Davis isn't the first or only forager who has fallen victim to the death cap.

Between 2010 and 2015, five people died in California and 57 became sick after eating these unassuming greenish mushrooms, according to the California Poison Control System. One mushroom cap is enough to kill a human being, and they're also poisonous to dogs.

"Dogs die in droves," says Debbie Viess of the Bay Area Mycological Society.

The trouble is, people feel fine for six to 12 hours after they've eaten death caps, says Dr. Kent Olson, the co-medical director of the San Francisco Division of the California Poison Control System. But during that time, a toxin in the mushroom is quietly injuring their liver cells. Patients then develop severe abdominal pain, diarrhea and vomiting.

"They can become very rapidly dehydrated from the fluid losses," says Olson. Dehydration can cause kidney failure, which compounds the damage to the liver.

When Davis went to the hospital, doctors put her on intravenous fluids. They also pumped her stomach full of activated charcoal to help absorb the poison out of her body, although some doctors question the usefulness of this treatment when many hours have elapsed since the poisoning occurred.

For the most severe cases, the only way to save the patient is a liver transplant, says Olson. (Davis didn't end up needing one and went home before Christmas.)

Researchers are looking for better treatments. One group of scientists is testing the drug silibinin, which can protect a patient's liver and make a transplant unnecessary.

Death cap mushrooms have gills from which they launch spores in order to reproduce. Josh Cassidy/KQED hide caption

Death cap mushrooms have gills from which they launch spores in order to reproduce.

And other scientists are trying to learn more about death caps — hoping to find a weakness they can exploit to defeat them.

The death caps arrived in California from Europe as early as the 1930s and '40s, says Anne Pringle, a biologist at the University of Wisconsin, Madison. She discovered this timeline through genetic testing of death cap samples collected in California during this era. She says death caps likely sneaked into California from Europe attached to the roots of imported plants — and they got really comfortable, spreading all over the state.

Through genetic testing, Pringle is trying to better understand how death caps propagate, and how long they live. In mushroom-producing fungi like the death cap, much of their body lies under the earth's surface. (The mushrooms are just there to help the fungus spread spores and reproduce.) Pringle wants to know how long the underground bits last — would simply plucking the mushrooms to prevent them from spreading their spores through the air be enough to kill off individual death cap fungi? Or is the death cap more resilient — does each individual develop a vast underground network that would be near-impossible to eradicate?

For now, it's looking like the death caps are here to stay.

With this year's mushroom foraging season well underway, health workers and experts are warning aficionados to be careful. Death caps, which are abundant in California, can easily be confused for other edible mushrooms, growing mainly under coast live oaks. Death caps have also been found under pines, and in Yosemite Valley under black oaks.

And it's not just amateurs who mistake death caps for edible mushrooms like coccora or paddy straws. "I've seen expert mycologists arguing good-naturedly about whether a mushroom they were looking at was the deadly one," says Dr. Kent Olson, co-medical director of the San Francisco Division of the California Poison Control System. "At certain stages of development, the mushrooms can be confused."

In hindsight, Davis thinks she confused young death cap mushrooms — which have a rounded yellowish-green cap — for hedgehog mushrooms, which are yellow and rounded.

Death caps under a tree at the University of California Botanical Garden, in Berkeley, California. Death caps are popping up in California year-round in irrigated areas like gardens. Josh Cassidy/KQED hide caption

Death caps under a tree at the University of California Botanical Garden, in Berkeley, California. Death caps are popping up in California year-round in irrigated areas like gardens.

Hedgehog and death cap mushrooms are fairly different-looking. While hedgehogs don't have any gills — ribs under the mushroom cap — death caps do have gills.

"It is easy for folks to make ID mistakes," says Viess, "which is why I encourage strong caution for beginners."

Mature death cap mushrooms are big, smooth and an olive green color. And if you pull one out of the ground, you'll see it has a little cup that holds it up.

"Assume nothing, and learn for several seasons before you eat any wild mushrooms," warns Viess from the Bay Area Mycological Society. "Use good, regional books, find a mentor, and have your initial IDs checked by more knowledgeable and trusted identifiers."

As for Davis, after temporarily losing her taste for mushrooms, she is now looking forward to foraging again. But she says she'll be much more cautious.

"I don't need to collect all that I see," she says. "I'm good with just, you know, a handful."

A longer version of this post originally appeared on the website of KQED's science series Deep Look. For more information on the death cap, you can visit the websites of the Bay Area Mycological Society and the North American Mycological Association.

The Death Cap Mushroom . . . It’s as Bad as it Sounds

A lot of things in life don’t make sense, and it seems I spend half my time trying to explain and rationalize these to my three young girls. They ask a lot of questions. A lot.

  • Why do we park on a driveway?
  • Why is something called a “free gift”, aren’t gifts always free?
  • What’s a pineapple? There’s no pine or apple in it.
  • If wizards can regrow bones, why does Harry Potter still need glasses?
  • Why the hell would someone throw a pair of shoes on the power line?

They also swear, which they get from their mother. Seriously. But at least there’s one name I won’t have to explain to them: the Death Cap mushroom. Like vomitoxin , it’s self explanatory.

The Death Cap mushroom, Amanita phalloides, is a nondescript mushroom native to most of Europe and has a symbiotic relationship with many species of hardwood trees, like the chestnut, beech, and oak. The fancy scientific word for this is “mycorrhiza” and involves the fungal colonization of a plant’s roots. The fungus gets carbohydrates, the tree gets minerals. Win-win.

Amanita phalloides by Seattle Roamer (CC BY-NC-ND 2.0)

Though non-native to the United States, the Death Cap mushroom was likely introduced in the 19th century as spores hitchhiked across the Atlantic with chestnuts or wood products from Europe, but was not conclusively identified until the early 20th century (1). What took so long for it to be identified? Well, it’s a pretty plain looking mushroom. White stalk, annulus, and volva – don’t laugh, those are real words. The cap is white too, and turns shades of brown, yellow, and green with age. Unless you’re a well trained forager or mycologist that knows what to look for, Amanita phalloides doesn’t scream “poison, ” until it’s too late.

The poisons involved are two groups of bicyclic peptides, the amatoxins and phallotoxins, made up of eight and seven amino acids, respectively. But while the phallotoxins are present in a higher concentration, in every part of the mushroom (2), it is the amatoxins that get the blame, particularly α-amanitin. The amatoxins do their dirty work by inhibiting the enzyme RNA polymerase II (3). That sounds important…do we need one of those? Yeah, you do. One of the functions of RNA polymerase II is catalyzing the transcription of DNA to messenger RNA. That sounds important too…I suppose we need that as well? Short answer, yes. Messenger RNA is really a single-stranded copy of a gene that becomes translated into proteins – it makes you, you, and enables the growth and repair of your body.

Death Cap toxicity occurs chronologically in the systems that came into contact with the peptide poisons: the GI system first, then the liver. It’s the disruption of the GI system that clues you in that you were poisoned, but it’s the liver failure that kills you. Your liver is responsible for metabolizing and excreting the vast majority of chemicals and drugs that enter your body, and without it you die. Without your liver able to replicate and repair itself from the amatoxin induced damage, you’re in for a painful journey.

Symptoms are delayed and start approximately 6 to 12 hours after ingestion, and present with nausea, vomiting, diarrhea, and general abdominal pain. At this point people may think they have “food poisoning” and that it will pass. And it does after about 24-48 hours, like the calm before the storm, or being in the eye of a hurricane (I’ve experienced that, it’s true). But it’s during this “recovery” phase that irreparable liver damage is kicking in, with liver failure just around the corner. At this point, liver transplantation is usually the best, or only, option for survival (4). Supportive care is of course provided, but other treatments are often considered, such as antibiotics and silibinin, a chemical from milk thistle extract that may offer protection to liver cells. Silibinin has received a lot of attention in recent years, but the medical community still seems to be split on the issue (5, and for a review of current therapies).

The next obvious question is: How much is lethal? There aren’t any clinical trials for these sorts of things, or rather not many people signing up for them. But the LD50 (the amount needed to kill 50% of the population) is estimated at approximately 0.3 mg/kg for the amatoxins in various species – it could be more or less in humans, but it’s a good starting point (6). For an average 70 kg person, that’s 21 mg – or about 1 grain of rice. The cap of the Death Cap contains about 0.36 mg of amatoxins per gram of mushroom (2), so one would only need to eat 58 grams, or 2 ounces of mushroom, for it to be potentially fatal. Other portions of the fatal shroom contain higher concentrations of amatoxins, such as the ring, where only 7 grams (!) could prove lethal. Overall mortality rates range from 10% to 25%. Why the range? It depends upon course of treatment, with liver transplantation affording the best chance for survival, but also on proper identification of the mushroom ingested. I have a feeling many people become ill from eating mushrooms, but the exact species is not conclusively identified and many labeled as a Death Cap – it sounds better and makes for a better story – so their survival tends to deflate the mortality rates.

My take home message regarding picking and eating wild mushrooms is always “Don’t.” But if you feel the need, urge, or primitive desire, go for it! Just become properly trained first, your life isn’t worth a free mushroom. But another point that I touched on earlier, is that with the advent of efficient mass transit, it is easy for non-native species to “invade,” like Amanita phalloides a hundred years ago here in the States. So while an expert may be intimately familiar with poisonous mushrooms in their neck-of-the-woods, an unknown lethal one may spring up and cause confusion. So go foraging with the weapon of knowledge, and protect yourself from the evil Cap of Death.

** Homepage featured image of Amanita phalloides by Justin Pierce (CC BY-SA 3.0) **

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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.

D r. 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.”

T he 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.

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.

B ritt 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.”

T he 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.

* This article previously misstated the number of death-cap mushroom fatalities in 2014.

** This article previously misstated the origin of a species native to Australia.

*** This article previously misstated the name of the death-cap mushroom's California host tree.

**** This article has been updated to clarify the range of views held by mycologists.


Canberra Times - Saturday 2 November 2002 - article on a Canberra death caused by consumption of Amanita phalloides PDF

Benjamin, DR. Mushrooms: Poisons and Panaceas, WH Freeman & Company, New York, 1995.

Benjamin, a professional pathologist and amateur mycologist, has written a very readable account of the poisonous fungi and their poisons. While some sections require some medical knowledge (or a nearby medical dictionary) the bulk of this book can be read by non-medical people. Highly recommended for anyone who has to deal with cases of mushroom poisoning or is curious about poisonous mushrooms.

Bresinsky, A & Besl, H. A Colour Atlas of Poisonous Fungi. Wolfe Publishing, London, 1990

This is written at a more technical level than the book by Benjamin and is aimed at pharmacists, doctors and biologists. There are detailed descriptions (using macroscopic and microscopic features) of many poisonous species as well as photos showing both naked eye and microscopic features. The book also contains details of the toxic compounds and discussions of symptoms and treatments.

Southcott, RV. "Mechanisms of macrofungal poisoning in humans" in Fungi of Australia, Volume 1B, Australian Biological Resources Study, CSIRO Publishing, 1996.

This chapter gives an overview of the poisonous fungi in Australia.

ACT Health information

Poisoning by Amanita phalloides ("deathcap") mushrooms in the Australian Capital Territory

Why do death cap mushrooms not warn of their poison? - Biology

Even solely from the perspective of human health, there is an opportunity cost incurred by spending too much time focused on death caps. If one were to look for a fungus to worry about, one would need to look no further than the nearest hospital the yeast Candida auris is a rapidly-spreading pathogen, now found in hospital settings around the world. It can cause mortality rates greater than 50 percent among immunocompromised patients, and is resistant to the four major classes of antifungal compounds. Monitoring the spread of this pathogen has been hampered by the difficulty of accurate detection and diagnosis.

Or what about Aspergillus flavus? This fungus colonizes siloed grains and other crops, especially those that are rich in oil, like peanuts. In warm conditions, the fungus can contaminate food with a potent carcinogen called aflatoxin. This problem is only likely to increase in scope and scale as the climate warms in places like Europe, and as populations grow in tropical areas where many of the staple crops are oil-rich and prone to spoilage due to the prevailing warm and humid climate. When the risk isn’t from acute disease and mortality, but rather diffuse and long-term, it can be harder for humans to take seriously. In a more general sense, these kinds of risks are of tremendous concern from a civilization-level perspective. From climate change to automation, humans have a bad track record of myopia.

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To return to death caps, what if the broader negative impacts of this species have little to do with human health?

Further Reading:

Remember, they are an exotic species in the Western United States, and are rapidly increasing their geographic range and range of habitats. Are they outcompeting or excluding native species in the process? How would we know? We have done almost nothing to monitor changes in the assemblage of mushroom species in areas before and and after the incursion of death caps.

Nor has there been much research to determine if there are feasible strategies to manage the abundance of A. phalloides. Some researchers have hypothesized that those mushroom species which produce large numbers of aboveground biomass (like death caps) are poor soil competitors, and rely on year-to-year heavy spore production to maintain their foothold in a given habitat. Which might suggest that intensive fruitbody removal efforts could produce declines in abundance if kept up for sufficient periods of time.

However, on a state-level scale, this is probably not feasible, which leaves us to ask: if the spread of death caps is inevitable, can we at least learn what the impacts are on our native fungi? This requires close, sustained attention to areas where these fungi don’t yet occur, and continued monitoring over time. Hopefully, land managers and conservationists alike will find common ground to establish such monitoring efforts sooner than later – the baseline is already largely lost.

While there is no reason not to pay attention to death caps as a source of fascination and trepidation, it is worth remembering that there are less immediately obvious aspects of this species’ ecology, and the larger world of harmful human-fungi interactions that deserve a greater share of your concern.

Ask the Naturalist is a reader-funded bimonthly column with the California Center for Natural History that answers your questions about the natural world of the San Francisco Bay Area. Have a question for the naturalist? Fill out our question form or email us at atn at!

About the Author

Christian Schwarz is a naturalist currently living in Santa Cruz, the land of milk (caps) and honey (mushrooms). He studied Ecology and Evolution at UCSC, and now spends his time photographing, teaching about, and making scientific collections of macrofungi, and he is a co-author of “Mushrooms of the Redwood Coast”. Fungi satisfy his curiosity with their seemingly endless forms – from the grotesque to the bizarre to the sublimely beautiful. Besides dabbling in mushroom taxonomy, he’s an excitable birder, mediocre fisherman, and passionate about citizen science – particularly iNaturalist.

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World's most lethal mushroom found in Vancouver, health officials warn

A mushroom considered to be the most lethal in the world is now in Vancouver.

Health officials said Thursday that the toxic death cap mushroom had been spotted in the city. The species was found on a private property near West 10th Avenue and Yukon Street, Vancouver Coastal Health told CTV News.

No illnesses have been reported.

Eating the mushrooms, which look similar to other edible varieties, can cause liver and kidney damage and can be fatal, VCH said in a post on its website.

The mushrooms aren't found naturally in B.C. forests, but can be found in urban environments associated with species of imported trees. The mushrooms can be imported on the roots of trees planted in boulevards in Vancouver and Victoria, officials said.

They are known to be in other parts of Metro Vancouver, the Fraser Valley and Vancouver Island.

The lethal species is similar to puffball mushrooms, Asian straw mushrooms and other common Asian varieties, VCH said.

The University of British Columbia describes death caps, also known by the Latin name of Amanita phalloides, as European mushrooms that grow on the ground near broadleaved trees.

They are between three and 12 centimetres in diameter, and are rounded at first then open to convex. They can flatten out almost completely. Colour varies but UBC says they have a distinct greenish hue and white gills. Stems are between five and 13 centimetres long. More descriptors and photos are available online.

UBC's Zoology website also has detailed profiles on many mushrooms found in coastal B.C. and other parts of the Pacific Northwest.

Death caps are considered invasive, and can normally be found growing in the fall. However, they're known to be found in July and August on excessively watered lawns.

What to do, signs and symptoms

Anyone who thinks they've eaten a death cap mushroom is advised to call poison control immediately at 1-800-567-8911. They should go straight to the hospital.

Symptoms of poisoning occur within eight to 12 hours, and include cramping, abdominal pain, vomiting, watery diarrhea and dehydration. A poisoned person may feel better after 24 hours, but the BCCDC warns during this time, the toxins are damaging vital organs.

A second wave of symptoms will hit within 72 hours of consumption, and includes jaundice, liver and kidney failure, delirium, seizures, coma and gastrointestinal bleeding. Organ transplants may be required to prevent death, the BCCDC says.

In fatal cases, death occurs in seven to 10 days.

How to avoid death cap mushrooms

The best ways to stay safe include avoiding areas where death caps are known to grow.

They're especially dangerous to kids and pets, so playtime and walks should not be anywhere near the species.

Parents or pet owners should immediately remove any mushrooms from their child or pet's mouth to avoid risk of swallowing, and if any part of a mushroom was consumed, a doctor or vet should be called.

Homeowners should remove and dispose of death caps in the area by putting them in a municipal compost bin or bagging and disposing of them through regular trash.

They should avoid watering areas where death caps grow.

Home compost may not reach a high enough temperature to kill off their spores, the BCCDC says.

Mowing the lawn won't get rid of the fungus, most of which lives underground. They should be removed before mowing.

Touching death cap mushrooms is not an issue, but anyone who comes in contact with them is advised to thoroughly wash their hands afterwards.

    Amanita Muscaria the magical mushroom or toadstool has surprising health benefits. This red and white mushroom has associations with reindeer, Christmas, Santa Claus, children’s literature, Celtic and shamanistic practices throughout the world. So wh
    Stomach flu a virus affecting the human stomach seems to go on forever. Knowing how long the flu can last and when the virus in the stomach dissipates can make a huge difference to the sufferer. What treatment for the flu remains important as well as
    Top organic foods come from the wild foods found throughout England. Wild food remains the best food to eat as they&aposre free, high in vitamins, and beneficial to health. Choosing the right type of diet for you means foraging for natural organic foods

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2012 johndwilliams

3 Major Diseases Caused by Fungi in Humans

Some agarics (mushrooms) are poisonous to living being. The most severe type of mushroom poisoning is caused by species belonging to the genus Amanita. A mistake can result in very unpleasant gastrointestinal upset or even death. Amanita phalloides (the death cap) is very poisonous and responsible for most of the mushroom poisoning deaths.

A mixture of three toxins α-amanitine, β-amamtine and phalloidine — is the cause of poisoning. Amanita muscaria (fly agaric) and A. pantherina (panther cap) are also poisonous.

Besides Amantia, some other poisonous mushrooms are Russula, Lactarius, Boletus, Entoloma etc. Symptoms of mushroom poisoning are — nausea, vomiting, abdominal pain and visual disturbances. The affected one finally falls into a coma and may succumb.

Disease # 2. Mycotoxicosis:

Toxins produced by fungi are called mycotoxins. One of the most important mycotoxin is aflatoxin produced by some species of Aspergillus (especially A.flavus). Anatoxins can be lethal to poultry.

They may cause lever damage and are suspected to induce cancer in humans. Claviceps purpurea produces ergot alkaloids which, if mixed with rye flour, may result in severe poisoning. Fingers toes, whole arms, legs, sometimes eyes and noses become gangreneous, wither and fall off with no bleeding.

Some fungi like Stachybotrys atra, Pithomyces chartarum and some Fusarium spp. produce mycotoxins which affect large animals like norses, sheep and cattle. They develop facial eczema and liver damage while feeding on contaminated grass.

Disease # 3. Mycoses:

It is considered that around 1/5th of the global population (about 800 million) suffer or have suffered from mycoses. Mycoses can be considered of two types — superficial mycoses and deep- seated mycoses.

(i) Superficial mycoses:

Superficial mycoses are unpleasant but not lethal. Skins, hair and nails are infected. The fungi that cause superficial mycoses are called dermatophytes and the diseases they cause are called dermatophytoses.

Various species of genera Microsporon, Epidermophyton and Trichophyton are important dermatophytes. Malassezia furfur is the agent of Pityriasis versicolor (dandruff): Microsporum andouini is the agent for most cases of ring worm of scalp in children.

(ii) Deep-seated mycoses:

Deep-seated mycoses are dangerous and may become fatal if not treated. Unfortunately, the diagnosis of mycoses is often difficult because there are no specific ‘mycoses symptoms’. The isolation and identification of the pathogen is the only method to identify the disease.

About 15 deep scaled mycoses are in knowledge, e.g., Coccidioidomycosis, Blastomycosis, Candidiasis, Subcutaneous Phycomyosis, Sporotrichosis, Chromomycosis, Mucormycosis, Geotrichosis and Mycetoma.

Details of some important ones are given below:

Caused by Aspergillus fumigatus which attacks cars, lungs etc. Pulmonary aspergillosis is diagnosed as T.B.

Popular as ‘Gilchrist’s disease’. In early stages it causes cough, chest pains and weakness following the formation of subcutaneous nodules, abscesses or lesions on face and arm. Blastomyces dermitidis is the causal organism.

It is caused by Candida albicans, the mucous membrane of skin, lungs etc. are attacked. Ammons et al. (1977) have listed cutaneous candidiasis, oral candidiasis, pulmonary candidiasis, volvovaginal candidiasis and bronchocandidiasis as some of the infections.

A more or less localized and chronic infection of the skin and subcutaneous tissues by Cladosporium carrionii, Phialophora verrucosa, P. pedrosoi, etc.

Characterized by the lesions limited to the upper respiratory tract and lungs. In humans it is caused by Coccidioides immitis.

The central nervous system is affected by this disease caused by Cryptococcus neoformans, it affects the vision and causes respiratory failure.

This disease is caused by Emmonsiella capsulata. It is very widespread and serious in humans and is sometimes even fatal.

It is an oral pulmonary, bronchial or intestinal infection in humans caused by Geotrichum candidum.

However, warm blooded animals are also infected by fungi causing mycoses. Examples—Cattle (Trichophyton verrucosum), and birds (Aspergillus fumigatus, Candida albicans).