Armillaria ostoyae Rocky Houghtby/Flickr

The world's largest living thing is even bigger than a blue whale (which happens to be the largest animal living now).

Meet Armillaria ostoyae, or, as it's nicknamed, the Humongous Fungus.

It's an organism that covers 2,385 acres (almost 4 square miles) of the Malheur National Forest in Oregon.

But it's a lot more harmful than the nickname might suggest: The Amarillia grows by feeding off of tree roots, leaching off of them and actually killing them, causing them to decay. So, in a forest, it has a good shot of growing to a massive size (at the cost of a few thousand acres of trees).

The fungus has a huge network of roots, called mycellia, that permeate below the ground of the forest. What shows up above ground are the mushrooms that get produced about once a year, according to the USDA. They usually pop up around the base of infected or newly-killed trees.

Here's a map showing just how big the Humongous Fungus, highlighted in red, is compared to other, less humongous Armillaria (in yellow).