The sandworm was an autotrophic animal that inhabited the planet Arrakis. Where they originated is unknown, but were introduced to Arrakis before the events of the Butlerian Jihad. It lived in the vast deserts and sand dunes that stretched across the surface of the planet. Most importantly, sandworms are an essential factor in the creation of the Spice Melange. Sandworms lived beneath the sand. Attracted to rhythmic vibrations on the surface, they would breach in pursuit of the origin of such vibrations. This was an effort to defend their territory, of which they were highly protective. Thus to see a worm, and live to tell about it, was extremely rare, save for the mysterious fremen, who had achieved some kind of mastery over the beast.