According to the Grímnismál (35), Nídhögg gnaws at Yggdrasil from below. Snorri Sturluson specifies (Gylfaginning, 15) that it is the third root of Yggdrasil that the serpent gnaws, the one above Niflheim and the spring Hvergelmir.
Through the squirrel Ratatosk, Nídhögg exchanges messages with the eagle that lives on top of Mount Peymisse (Gylfaginning, 16; Grimnismál, 32, only mentions the eagle's messages to Nídhögg, but not their nature or the dragon's answers).
In the Völuspá (39), Nídhögg is presented as living in Náströnd, where he sucks the corpses of perjurers, murderers and adulterers. Snorri repeats this information, with the difference, already mentioned, that Nídhögg lives in Hvergelmir (Gylfaginning, 52).
The last stanza of the Völuspá (66) describes the arrival of Nídhögg flying over the plain, carrying corpses in his wings. The meaning of this scene is disputed: for some3 , it closes the episode of Ragnarök: the dragon carries away the bodies of those who died during the events; for others4 , it announces on the contrary its beginning. In the version of the Poetic Edda corrected and translated by Genzmer, the author sees it as a possible last gasp of the dying world: "at last the waves swallow him up", with him the old order ends.