The root eater, Nidhogg

Nidhogg is a dragon that lives in the Niflheim, where one of the roots of the Yggdrasil tree grows, which gnaws incessantly until Ragnarök comes and everything is destroyed. It is a dragon of the Lindwurm type, with a very hard skin covered with rock in some parts. It feeds on the sap of the world tree itself, but that does not mean that it also feeds on other living beings. If you approach the base of the tree you can hear it gnawing the roots.