The California Department of Public Health has warned people against foraging for mushrooms this year due to an “unprecedented outbreak of severe illness and deaths,” because people are unwittingly gathering poisonous wild mushrooms and eating them. There were 40 cases of illness, including 4 deaths, and well as a few liver transplants, from mid-November 2025 to February 7, 2026. Death cap mushrooms resemble harmless varieties, so they are thought to be to blame for these illnesses. Western Destroying Angel Mushrooms are another deadly type of mushroom that could be found in California and mistaken for an edible variety.
Scientists have now learned more about the biochemistry of death cap mushrooms (Amanita phalloides), and have suggested this invasive species is quickly spreading in the US, and its biochemistry was altered when it moved to the US from Europe. The findings have been reported in the Proceedings of the National Academy of Sciences (PNAS).
"What we hope people take away from this paper is that scientists are actively studying this serious issue. We're working hard to understand why it's happening,” said senior study author Nancy Keller, a Professor at the University of Wisconsin-Madison.
Death cap mushrooms probably came to California in the 1930s from Europe in tree roots, and then spread around the West Coast. Pringle lab graduate student Cecelia Stokes noted that they can now be found growing north of the Canadian border and as far south as Mexico. They have been identified in the New England region more recently too, but don’t seem to be spreading as fast on the East Coast, yet.
"I have no doubt these invasive mushrooms are impacting native ecosystems, but we are still working towards understanding the actual consequences and bigger picture," noted Stokes. "We do know death cap mushrooms are popping up in dense patches in forests from year to year. You can find more than 40 mushrooms under one tree, and this is abnormal, especially in comparison to the native mushroom species."
The researchers have determined that the California death cap mushrooms are generating natural products that have not yet been described. This mushroom chemistry is not only different from what is found in Europe, but has also never been isolated from any other fungus.
The investigators have also recently reported another study in The ISME Journal on death cap mushroom genetics. Now, they want to known more about the bioactivity of these compounds.
Sources: University of Wisconsin-Madison, Proceedings of the National Academy of Sciences (PNAS)
