In the Morte'lumin War, a rogue primordial brought primordial sand worms from Chaos to Bal-Kriav. The chaotic nature and uncontrollability of these creatures was such that not even the primordials wanted them in their armies. As a result of a falling out between Storralk and his general Hon'palos, primordial sand worms found a new home in the Sands of Hell. These creatures were so disruptive that they separated a large force of workers from Storralk. These workers, the Dezellâm, went into hiding for the rest of the Creation War and actually did everything they could to stay out of sight of both primordials and their adversaries.
Primordial sand worms get up to twice as large as the largest purple worm specimens of the Underdark. Their most dangerous attribute is a gut that is a rift to Chaos. Those unfortunate enough to be swallowed by a primordial sand worm may be drawn through this rift and cast into Chaos. The fact that they have a rift inside them has led to them being used to open rifts to this realm of entropy. In the March of Resalth, the Dragon Lord Balfroglemis did just this when he dropped a young primordial worm into a Sphere of Annihilation. This created an even bigger rift in the Web of Magic leading to some terrible effects in Feykro Silon.