First documented in the 1980s, the Armillaria gallica mushroom in Crystal Falls, Michigan, was dubbed the "humongous fungus" because it spans 91 acres and weighs 440 tons.
Wikimedia CommonsHoney mushrooms of the gargantuan Armillaria gallica.
When people think of the Earth’s largest organisms, they usually imagine whales, elephants, or even dinosaurs. But some of the largest organisms on Earth aren’t animals at all, but sprawling fungi dubbed “humongous fungus.”
Armillaria fungi, known as “honey mushrooms,” is a unique species of fungus capable of growing to jaw-dropping sizes both underground and on decaying stumps or logs. The original “humongous fungus,” located in Michigan, has grown across such an impressive area over the last several thousand years that today it’s roughly the size of Vatican City.
But while the humongous fungus of Michigan was originally thought to be the largest humongous fungus in the world, scientists now know that there are even larger species of Armillaria out there.
The Discovery Of The Original Humongous Fungus In Michigan
Wikimedia CommonsFrom above ground, the humongous fungus looks like multiple organisms.
Scientists came across the original humongous fungus in Crystal Falls, Michigan by chance. As local media in Detroit reported in 2018, the sprawling fungus was discovered during a Department of Defense project in the 1980s studying the properties of Extremely Low Frequency (ELF) radio waves.
Researchers wanted to determine if these frequencies could be used to communicate with submerged submarines. Because of the public concern about the effects these radio waves might have on the environment, a study was launched to study the effect of EFL radio waves on trees and plants.
During the course of this study in Crystal Falls, researchers began to notice a fungus, now known as Armillaria gallica, eating some of the trees. As they observed the fungus, they began to realize that it was big — very big. They ultimately determined that the fungus covered at least 15 hectares (37 acres) and weighed about 110 tons. It was able to grow so big and heavy, they said, because it was roughly 1,500 years old.
“This is the first report estimating the minimum size, mass, and age of an unambiguously defined fungal individual,” the researchers wrote in their 1992 study on the fungus. “Although the number of observations for plants and animals is much greater, members of the fungal kingdom should now be recognized as among the oldest and largest organisms on earth.”
The story gained media traction, and the press dubbed the discovery the “humongous fungus.” The nickname stuck. But Michigan’s humongous fungus was actually even bigger, and older, than the researchers thought.
The Michigan Armillaria Was Even Larger Than The Researchers Thought
Igor PavlovA forest of trees dying due to damage from Armillaria.
In 2018, researchers returned to Crystal Falls, Michigan to study the humongous fungus anew. They took 245 samples of the fungus, and confirmed through DNA analysis that the sprawling honey mushroom consisted of the same individual organism. They found that it had been growing far longer than previously estimated, for about 2,500 years.
What’s more, they established that Crystal Falls’ Armillaria gallica was even larger than they had previously thought. It was not 37 acres, but 90. That meant that the humongous fungus covered an area double the size of New York City’s Grand Central Station.
And with the fungus’ larger size came a greater weight. The researchers determined that the fungus weighed about 440 tons, or about the size of three blue whales, the largest animals in the world.
Though the humongous fungus is visible above ground as clumps of honey mushrooms, the bulk of its 400-ton body is located underground. It’s made up mostly of subterranean black tendrils called rhizomorphs which can extend miles beneath the earth in search of sustenance.
Lairich RigArmillaria rhizomorphs.
Armillaria infects living trees, then consumes the trees once they’re dead. For this reason, Armillaria can often be detected above ground by large swaths of dead or dying trees. That said, they’re ok for humans to eat. But they do need to be very well cooked in order to avoid stomach problems.
And though the fungus can be devastating for trees, it’s widely celebrated in Michigan. Crystal Falls hosts a “Humongous Fungus” festival every year — even though scientists now believe that the Michigan fungus is not the largest fungus ever documented.
The Largest Humongous Fungus In The World
Since the discovery of humongous fungus, Michigan has celebrated its unique, natural attraction. The town of Crystal Falls even holds a “Humongous Fungus Festival” each August.
Humongous Fungus Festival/FacebookPeople dressed up for the 2025 Humongous Fungus Festival in Crystal Falls, Michigan.
The festival includes an array of fungus or mushroom themes activities. The city also hosts an annual parade and t-shirt design contest. Needless to say, locals have embraced the humongous fungus.
But while the Armillaria gallica in Crystal Falls, Michigan is truly humongous, it is not the largest of the Armillaria mushrooms ever documented. That title goes to an Armillaria ostoyae in Oregon’s Blue Mountains.
After the discovery of Michigan’s humongous fungus, scientists elsewhere began to take a closer look at Armillaria in their own backyards. In 1988, a sprawling Armillaria ostoyae was discovered by a Forest Service employee in Oregon. This fungus covers more than 2,000 acres and weighs an estimated 35,000 tons. Scientists believe that it’s roughly 8,000 years old.
Similarly to its Michigan cousin, the Armillaria ostoyae grows rhizomorphs underground, infecting tree roots, and eventually killing the tree.
Alan Rockefeller/Wikimedia CommonsAn example of Armillaria ostoyae, the mushroom that makes up Oregon’s humongous fungus.
While these organism are certainly huge, there have been some debate if they can be categorized in the same way other large species like blue whales or red wood trees are. In a book published a few years after the 1992 Armillaria gallica paper, author Jack Wilson questioned what really makes an organism biologically “independent.”
But no matter the technical or scientific categorizations of these impressively large fungus, people still love them. There are certainly some formidable fungus among us.
After learning about the gigantic Armillaria gallica mushroom, check out these fascinating photographs of Cordyceps, the killer fungus that takes an insect host. Or, look through this collection of some of the strangest mushrooms in the world.
