Bone Serpent

The Bone Serpent is the strongest non-boss burrowing enemy, second only to the Eater of Worlds. They follow the Worm AI. Bone Serpents are immune to lava.

The best way of killing one is the same as killing any other worm, by using weapons that can hit multiple enemies simultaneously like the Blade of Grass or a flail. When fighting them it is recommended to have a lot of potions, end game armor and weapons to be able to stay alive for extensive periods of time.

Drops
Each Segment of a Bone Serpent can drop loot; however, since they are usually defeated by destroying only one section of their bodies, they seem to drop only one item. Causing a large amount of damage to multiple body sections at once, with Dynamite for example, will result in potential loot from every destroyed Segment. This can drastically increase the loot gained from a single Bone Serpent. (Note that as of 1.0.6, The Sunfury and Flamelash no longer drop from Serpents, and are instead found randomly in Shadow Chests.)

Serpent d'os Костяной змей