SPIDERS OF GAVROK. BtVS Demon/Monster/Villain.
Mystical beings acquired by The Mayor (Faith kills the man delivering the box containing them at the Sunnydale airport) in preparation for his Ascension).
In "Choices" Angel and Buffy steal the box but must return it in exchange for Willow, who had been taken captive. During the exchange in the Sunnydale High library, Principal Snyder, convinced a drug deal is transpiring, brings in the police, and two of the Spiders escape. After one policeman is killed and the now indestructible Mayor is attacked, Buffy kills one by crushing it, and Faith impales the other on the wall with the knife the Mayor gave her as a present. (Buffy will later use the knife in her epic battle with Faith in "Graduation Day," Part 1 and as a lure for the ascended Mayor in "Graduation Day," Part 2.)
In "Graduation Day," Part 1 The Mayor explains to Faith how the Spiders will be used:
FAITH: What next?
MAYOR: The Ritual of Gavrock. I have to ingest several of the inhabitants of this box.
FAITH: Ingest?
MAYOR: Eat.
FAITH: You're wicked gross.
MAYOR: (chuckles) Well, you don't have to watch. Just, you know, go home, take it easy. It's a big day tomorrow.
Later in the episode we do see The Mayor ingesting the Spiders, which leads him to comment:
Mmm. My god, what a feeling. The power of these creatures. It suffuses my being. I can feel the changes begin. My organs are shifting, changing, making ready for the Ascension. Plus these babies are high in fiber. And what's the fun in becoming an immortal demon if you're not regular, am I right?