The Underground Web: How Mycelium Connects the Forest

Under your feet, right now, a secret city is working! In a forest in Oregon, there is one giant fungus whose underground threads stretch across 2,385 acres. That is bigger than 1,800 football fields! Scientists call it the Humongous Fungus, and it is the largest living thing on Earth. Its secret? An underground network called mycelium.

By the end of this lesson you will: • Know what mycelium is and where it grows • Understand how trees share food using mycelium • Describe what mycelium looks like up close • Build your own mycelium web model

A mushroom is just the top part of a fungus — like an apple on a tree. The real body of the fungus is underground: it is called mycelium. Mycelium is made of millions of tiny threads called hyphae. Each thread is thinner than a strand of your hair! These threads spread out in all directions through the soil, connecting to rocks, roots, and other fungi. When you see a mushroom pop up after rain, the mycelium underground has been growing for weeks or even years.

Here is the most amazing part: mycelium connects different trees together! Scientists call it the Wood Wide Web. When a big old tree has extra sugar — made by its leaves from sunlight — it can send that sugar through the mycelium threads to a smaller, shadier tree that needs food. A sick tree can even receive water and nutrients from its neighbors this way. In return, the fungus gets sugar from the trees. It is a fair trade: trees share food, fungi share minerals and water. Everyone wins!

If you could shrink down and look at mycelium up close, you would see a lacy white web — like a spider web made of white threads, but much thicker and more tangled. You can actually see mycelium without a microscope! Lift up a rotting log in the forest and look at the white, fuzzy film on the wood underneath. That white fuzz is mycelium eating the dead wood and turning it into rich soil. Fungi that break down dead things are called decomposers. Without them, forests would be buried in dead leaves and fallen trees forever!