From A Wiki of Ice and Fire
Firewyrms are creatures that breathe fire but have no wings, and are possibly related to dragons. They can bore through rock, soil, and stone. According to old tales, firewyrms were in the Fourteen Flames of the Valyrian peninsula even before the dragons came. Their young are not much bigger than a child's arm, but as they age they can grow to immense sizes. They have no love for men.
Firewyrms were encountered by slaves of the Valyrian Freehold in the mines of the Fourteen Flames. Burnt and blackened corpses were often found in shafts where the rocks were cracked or full of holes.
Septon Barth's book, Dragons, Wyrms, and Wyverns: Their Unnatural History, discusses firewyrms.
- ↑ 1.0 1.1 1.2 A Feast for Crows, Chapter 22, Arya II.
- ↑ A Dance with Dragons, Chapter 50, Daenerys VIII.
- ↑ A Dance with Dragons, Chapter 14, Tyrion IV.
- ↑ The World of Ice & Fire, Ancient History: The Rise of Valyria.