Know your deadly mushrooms this rainy season

by Iris Kwok

Feb. 11, 2025, 2:39 p.m.Feb. 11, 2025, 2:40 p.m.

Mycologists and mushroom foragers rejoice in the rainy season as it’s when many of their favorite species can be found. But some can be deadly and so, as it does every year around this time, the East Bay Regional Park District (EBRPD) is warning of the danger posed by toxic mushrooms.

California Poison Control System operates a free hotline at 1-800-222-1222

Two of the world’s deadliest types of shrooms thrive in the East Bay: the Amanita phalloides (death cap) and the Amanita ocreata (Western destroying angel). 

Both are associated with oak trees, and can be found growing anywhere oak roots are present, according to the park district. Both the death cap and the destroying angel contain amatoxin, a lethal chemical compound that causes liver failure. Symptoms of mushroom poisoning typically appear around 12 hours after consumption.

Mushrooms tend to thrive after heavy rains, but when it comes to deadly amanitas, it’s not a hard and fast rule, Debbie Viess, a retired zoologist who founded the Bay Area Mycological Society, told Berkeleyside in 2023. 

“Mushrooms don’t behave the same all the time. They have windows of fruiting and they have times that they like to fruit,” Viess said. “Amanitas share resources with many other mushroom species on the same tree. Sometimes they take turns, and sometimes they compete, so there’s really no predicting what’s going to come.”  

Other species of mushrooms, including the Lactarius rubidus (candy cap) — great in ice cream — and the plump, orblike Calvatia gigantea (giant puffball) — which can be sliced into discs and turned into a “pizza” — also thrive in the East Bay’s parks. But if you’re hoping to forage any, you’ll have to do it elsewhere, as mushroom collecting is prohibited in Tilden and other EBRPD parks. 

Experts generally advise against eating foraged mushrooms — especially when it’s one you can’t identify with utter certainty. 

In 2016, there were 1,328 emergency department visits nationwide and 100 hospitalizations from accidental mushroom ingestion, according to a 2021 report by the Centers for Disease Control and Prevention.

The California Poison Control System, which advises people to use caution and eat mushrooms from grocery stores, not friends, received 33 calls for human mushroom exposures in Alameda County in 2023. Eight of those were for young children ages 5 and under; 11 were for children between 6 and 19 years old; and 14 were for people ages 20 and above. 

Pets are also at risk. In early 2023, one Berkeley resident spoke out to warn others after her puppy died from eating a death cap in Codornices Park. A Berkeley animal hospital said it sees about 20 suspect pet poisonings annually.

To safely learn more about fungi, explore the East Bay Regional Park District’s toxic mushroom page which contains handy photos of mushrooms to avoid.

A version of this story was originally published in January 2024.