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 in Fall of the Beasts, the new Evertree wasn't strong enough to hold it, and thus tiny parasites could wriggle 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 a gigantic crater. The explosion and shockwave caused by the strike of the Wyrm egg killed and destroyed the surrounding animals and area. The fifteen animals who survived the blast 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 woke 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 bond-power infused Erdas, basically turning every part of nature into a "mini-Evertree."
The Wyrm is a powerful alien that arrived on Erdas 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, or Marked people. It can create miniature parasites from bits of its flesh, which it can use to infect animals and people, bringing them under its control. It can induce different levels of freedom in its bond, ranging from mindless (the Many) to normal intelligence, 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 him 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. It nearly killed Essix and Rollan in the same way.
The Wyrm is not as endurant as its egg, as it dies 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 at 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 its 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 book 4 of the “Fall of the Beasts” series.
- The concept of the Wyrm infecting The Evertree may have been based on 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.