For mushroom collectors in California, the risk of selecting the wrong species of mushroom and plucking something deadly rather than edible is rising. Death cap mushrooms, an introduced species, are now abundant in the state and are continuing to spread. They can sometimes be mistaken for edible paddy straw mushrooms or other similar-looking species, and they apparently taste delicious — at least according to the people unfortunate enough to ingest them.
Slate writes that the death cap is "now present on every continent except Antarctica. It became such a world traveler because humans spread the mushroom’s spores around like glitter at a kids’ glitter party." Not that we necessarily did it on purpose.
The mushrooms have a symbiotic relationship with trees and as people imported various trees and plants to the U.S., among the roots were death cap spores and mycelium. Death caps have been present in the U.S. for decades, and are spreading across California. The Bay Area Mycological Society writes, "Death Caps now occur around the world, from Australia to South America, but nowhere have they found a place more to their liking than in the oak-strewn State of California."
According to KQED, "In California, death caps have established a very successful relationship with coast live oaks... Death caps have also been found under pines, and in Yosemite Valley under black oaks."
This video explains what death caps are capable of doing to a person, and the research going in to how to deal with the mushrooms.
Biologist Anne Pringle, of the University of Wisconsin, Madison, is currently researching the species to learn more about its lifecycle. If the mushrooms are short-lived, it could be possible to eradicate them from certain areas like one's garden by plucking them before they have a chance to spread their spores. Clearing them out of an area is important because they can be deadly to pet dogs as well as people. KQED writes that "two people died from death cap poisoning in California in 2014. Last year, nine poisonings were reported to the California Poison Control System and all the victims survived."
So if you're foraging where death caps are known to live, be extra, extra careful when collecting.