The Wyrm was an extraterrestrial organism living beneath The Evertree, trying to break free. The Wyrm was trapped in an egg encased in roots, although its tiny parasites had been wriggling out. Zerif was using these parasites to seize spirit animals under the command of the Wyrm, who also controlled Zerif himself. The Wyrm's egg originally landed on the Evertree, creating the gigantic crater seen in The Evertree. The explosion and shockwave caused by the strike of the Wyrm egg killed and destroyed animals in their radii and also wrecked the surrounding area. The 15 animals who survived became the Great Beasts. The Wyrm is actually the maker of the spirit animal bond, using the Evertree which regrew right above it. This was because the Wyrm wanted a source of food for when it waked up. The Wyrm died when the Hellan weapon activated, reversing Zerif and the Wyrm's bond. Zerif threw himself and the Wyrm into lava, killing them both. The release of the Wyrm's life bond power infused Erdas, basically turning every part of nature into a "mini-Evertree."
The Wyrm is a powerful alien that arrived on Earth thousands of years ago in a nearly indestructible egg casing strong enough to survive passage through the atmosphere. It is a slick, black creature with four red eyes and roughly a dozen tentacles. On its "face" it has a radula with many rows of teeth for devouring prey- Marked people. It has many parasites it can create from bits of its flesh, which it can control to infect animals and people, bringing them also under its control. It can induce different levels of freedom in its bond, ranging from mindless (the Many) to normal intelligence and some degree of independence(Zerif), and in-betweens such as Conor. The Wyrm can also form a symbiotic bond with people. In The Burning Tide, it bonded with Zerif, which transformed Zerif into the Thing. The Thing had grey skin, writhing black eyes, and veined flesh. It retained the Wyrm's strength and allowed the Wyrm to speak in Common instead of its native alien tongue. The Thing had the powerful ability to suck the life forces out of animals and people, which it did to a Redcloak named Shadow and nearly did it to Essix and Rollan.
The Wyrm is not as endurant as its egg, dying in lava, which can be up to 2,100 degrees F, while atmospheric entry can be up to 3000 degrees F. The Wyrm is very strong, being able to simultaneously crush many attacking Redcloaks with its tentacles with ease.
When a Wyrm parasite infects a spirit animal, it buries itself into the animal's skin (either directly into the forehead or it slowly makes it way towards the forehead). It has the same effect on humans, causing them to lose their memory and go insane to various degrees. Conor had a parasite inside of him until the end of the series.
- The concept of the Wyrm infecting The Evertree may have been based off of a story from Norse Mythology, which included a dragon called Níðhöggr who chewed at the roots of the mythological world tree, Yggdrasil.
- It was thought to be a dragon, but that was proven false in The Burning Tide, the Wyrm being a tentacled creature.
- According to Meilin's dream in Broken Ground, it was a shape-shifting shadowy blob. In her dream it could talk and imitate voices.