In the Morte'lumin War (6115 DE - 8066 DE), a rogue primordial brought primordial sand worms from the Sea of Entropy to Bal-Kriav. The chaotic nature and uncontrollably 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. In one incident, perhaps saving them, the worms separated a large force of workers from Storralk's great work parties. These workers, the Knudmid, went into hiding for the rest of the Creation War (1486 DE - 8777 DE); staying out of the fight between the primordials and their Covenant 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 (898 HE - 933 HE), 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.