Is the biggest living thing on Earth a fungus under an Oregon forest?

Possibly yes. A honey fungus called Armillaria ostoyae in Oregon's Malheur National Forest is possibly the largest living organism on Earth by mass, area and volume. It covers about 3.5 square miles (2,200 acres) and weighs as much as 35,000 tons. You would walk right over it: the fungus grows and spreads primarily underground, so the bulk of it is not visible from the surface.

Only in autumn does the hidden part show itself, when it produces honey mushrooms as surface fruits. Below, the mycelium invades the sapwood of trees and spreads under the bark or from tree to tree as black cords called rhizomorphs, nicknamed shoestrings. It is highly pathogenic to commercial softwoods such as Douglas-fir, true firs, pines and Western Hemlock, which is why forest managers care about it.

The age of the Oregon colony is uncertain. One estimate puts it at some 8,000 years old, while another says 2,400 years, possibly older.

The story of how we learned that a fungus can be this big began by accident. In the early 1990s, researchers in Michigan's Upper Peninsula were working on a project about extremely low frequency radio stations, which were being investigated for talking to submerged submarines. In the same forest, red pine seedlings planted among rotting oak stumps were killed by a fungus, Armillaria gallica. DNA tests showed that one colony covered 15 hectares and weighed over 9,500 kilograms. Media outlets from around the world visited, and the fungus got a nickname: the humongous fungus.