They are peaceful, but very rare creatures that can spawn on nearly every solid natural block (most likely not on crafted blocks though) and in every biome, during day and night. If a Keepa (of any kind) is near, you will be "alerted" by an Arcstone-symbol showing up on your compass-bar on top of your screen that radiates light blue semi-circles for a second or two. If killed, Golden Keepas will drop nearly the same materials as all Keepas do, but in larger amounts. The same goes for their harvest if you tame them to become your Pets.