basilisk

A basilisk is a fearsome creature most notable for it's ability to turn other creatures to stone with its gaze. While they are technically natural, many consider them dangerous enough creatures that they are hunted and killed where possible.
Basilisks are a noted enemy of spiderkind, though the origin for this enmity is not well known. The common wisdom is that since spiders have many uncloseable eyes, they make for particularly easy prey for a basilisk. Spiders generally do their best to avoid any location they know contains a basilisk.
Part of the basilisk's digestive tract reverts stone back into flesh; careful removal of these structures (called gastroliths) may allow them to be used for that purpose independent of the creature.
Basilisks lay eggs, but their properties are not well known. It may be possible to domesticate a basilisk born in captivity, but significant skill would be involved.