One of the Oldest, Largest Living Things on Earth Is an Underground Mushroom in the U.P.

Quick — what’s the biggest living thing on the planet? Most people guess a blue whale or a giant sequoia. For a while, the answer was a mushroom in Michigan.

Beneath a forest near Crystal Falls, in the western Upper Peninsula, lives a single organism known affectionately as the “humongous fungus.” It’s an Armillaria gallica — a honey mushroom — and it isn’t one of the little caps you see popping up after rain. Those caps are just the tips. The real organism is a vast underground web of black, root-like threads spreading through the soil, all of it a single connected individual.

Scientists stumbled onto it almost by accident in the late 1980s. The U.S. military was studying extremely-low-frequency radio waves in the U.P. (a project meant to communicate with submarines), and researchers checking the radio waves’ effect on the forest noticed a fungus quietly killing trees. The more they studied it, the bigger it turned out to be.

In a 1992 study, the team estimated it covered about 37 acres, weighed around 110 tons, and was roughly 1,500 years old — one of the first times anyone had shown a fungus could be among the oldest and largest living things on Earth. When the same researchers returned with newer genetic tools in 2018, they revised the numbers way up: closer to 2,500 years old and around 440 tons — about the weight of three blue whales.

It’s no longer the record holder (an even bigger honey mushroom turned up in Oregon). But Crystal Falls doesn’t much care. The town still throws an annual Humungous Fungus Fest in its honor — proof that Michigan can celebrate just about anything, even a giant underground mushroom.