The Natrium Worm was a multi-headed green worm that lived on pure sodium chloride. It lived under the sands in the dunes of Bruvoldaveer, on the outer reaches of the Galactic Salt Trail. Over many thousands of years the salt was mined and the worm, desperate for food, began to attack the salt traders for their cargoes of salt. The Salt Trails developed a reputation for being cursed.
The Eleventh Doctor, Amy Pond and Rory Williams destroyed one of the worms by luring it into a watering hole where the traders' salt cargo had been dumped. While Natrium Worms had the biology to absorb large quantities of salt, their weakness was their inability to cope with other things, such as water, which caused the worm to explode. (COMIC: The Salt Solution)