Bone Serpent

The Bone Serpent is the strongest non-boss burrowing enemy, second only to the Eater of Worlds. Bone Serpents can move through any block, and are not affected by lava or drowning. As with other worms, destroying any one part of a Bone Serpent will kill it. Hellstone does damage them.

Bone Serpents have a very rare chance of dropping a Flamelash or a Sunfury.