Deadly Death Cap Mushrooms Spotted Along Boise Greenbelt

Poisonous death cap mushrooms have been identified along the Boise and Garden City greenbelts, according to The Arbiter.

The presence of the Amanita phalloides marks an expansion of the toxic fungus within the region. The species was first identified in the north end of Boise in 2022 by Susan Stacy, a member of the Southern Idaho Mushroom Club (SIMC), and has since spread to the local greenbelt areas.

“Susan brought the mushroom in, gave it to me, and I ran DNA barcoding on it, and it was a perfect match for Amanita phalloides,” Michael Myhre, president of the SIMC, told The Arbiter.

The biological spread of the fungus

The death cap is not a localized occurrence that can be easily removed by picking the visible mushrooms. The appearance of a single mushroom indicates a widespread colony living in the soil and attached to tree roots.

“If you see a mushroom, that means there’s a colony under the ground that’s attached to the roots of trees, but is also pretty widespread in the soil at that point in time,” Jacob Venable, a mycology professor, told The Arbiter.

Venable said that spores are tiny and can travel via the wind. The fungus typically infects hardwoods, such as oaks, through their root systems. While the mushrooms can take years to begin bearing fruit, Myhre suggested that their growth is a matter of when, not if.

The presence of these mushrooms in Idaho is linked to the movement of trees from other regions. The fungus lives in the roots of trees that originated in Europe and British Columbia, many of which were relocated to the United States, including Oregon and California, before being moved to Boise.

Risks of accidental ingestion

The Amanita phalloides contains amatoxins, which are not neutralized by cooking. Ingesting the mushroom can lead to severe gastrointestinal distress within four to six hours. However, the most dangerous phase of poisoning often follows a deceptive period of apparent recovery.

“You can feel like you’re getting better for two or three days before you start actually having problems from the internal liver failure that’s going on,” Jacob Venable told The Arbiter.

Once liver failure begins, medical intervention may require the use of an Intensive Care Unit (ICU) or, in extreme cases, a liver transplant. Dr. Ron Kirschner, medical director of the Nebraska Regional Poison Center, said that because Idaho lacks its own poison control centers due to its smaller population, calls from the state are handled by Nebraska’s fields.

The British Columbia Medical Journal identifies the death cap as the most toxic mushroom species, attributing it to approximately 90% of all mushroom-related deaths.

Distinguishing the death cap from edible species

The death cap looks similar to the paddy straw mushroom, a valued component of Eastern Asian cuisine, creating a danger of accidental poisoning. This similarity has contributed to high death rates in California, particularly within the Asian immigrant community, where the death cap can be mistaken for edible varieties used in traditional cooking.

Venable highlighted specific physical markers to help differentiate the two:

The death cap features white gills and grows out of a white cup.
The paddy straw mushroom has pinkish gills that turn brown as they age.

“The idea is don’t put something you don’t know what it is in your mouth,” Venable told The Arbiter.

Death Cap Mushrooms (Amanita phalloides) — UK Wildcrafts

Experts advise that if a person or a pet consumes a suspected mushroom, they should seek medical or veterinary attention immediately. Myhre emphasized that if any symptoms such as vomiting or major abdominal pain arise, poison control should be contacted right away, as medical professionals may need to administer activated charcoal or a stomach pump to attempt to remove the toxin.

“If you’re foraging for mushrooms that grow in the wild, a lot of mushrooms look alike, and there can be mushrooms that are okay to eat,” Dr. Ron Kirschner told The Arbiter. “They can be very hard to tell apart from mushrooms that are dangerous.”

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