First Look

The Amanitas Are Blooming. Don’t Eat Them.

Death caps and Western destroying angels, both common in Oakland, thrive after rainfall, the East Bay park district warns.

January 4, 2024

This story was first published in Berkeleyside, an independent, nonprofit news site.

December pours spread fungal spores. 

The rainy season means a blooming of a colorful array of mushrooms—some of which are deadly—in wooded areas in and around Oakland. 

As it does every year around this time, the East Bay Regional Park District (EBRPD) is warning of the danger posed by toxic mushrooms—reminding park visitors that two of the world’s deadliest types of shrooms thrive in the East Bay: Amanita phalloides, or death cap, and Amanita ocreata, the Western destroying angel. 

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

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 last year

“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 candy cap, or Lactarius rubidus—great in ice cream—and the plump, orblike giant puffball (Calvatia gigantea)—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. 

The California Poison Control System, which took 71 calls for human mushroom exposures in Alameda County in 2021 and 2022, advises people to use caution and eat mushrooms from grocery stores, not friends. Most of those calls came from patients between 1 and 3 years old and those in their 20s, who were presumably “getting into stuff more deliberately,” CPCS executive director Stuart Heard has told Berkeleyside

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

Pets are also at risk. Last January, 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) or visit the Tilden Fungus Fair on January 20 and 21, from 10am to 4:30pm at the Tilden Nature Area.

Left, a death cap; right, a western destroying angel. Both of these deadly poisonous Amanitas are classic-looking mushrooms in pale colors. Each bears a characteristic Amanita egg-like sack called a “volva” at its base (it hatches out of this sack, and if you cut into one you can see the baby mushroom), as the left picture shows, and a skirt around its stalk. (Death cap by averypommee via iNaturalist, CC-BY-NC; destroying angel by Dean Lyons via iNaturalist, CC-BY-NC)

About the Author

Iris Kwok covers the environment for Berkeleyside through a partnership with Report for America. A former music journalist, her work has appeared in the San Francisco Chronicle, KQED, San Francisco Examiner and San Francisco Classical Voice, among other publications. In her spare time, you can find her petting street cats or playing cello. She joined Berkeleyside in June 2022.