bone swords/sabers

The Swarmlord wields two pairs of serrated bone sabres.
Through the core of each blade lies a crystalline growth. These alien crystals are not indigenous to this galaxy, and the bone sabres crackle with lethal power.
...
	Boneswords are living monomolecular blades that can drain the life-force of their victims.

Codex: Tyranids 6th Edition