The giant creatures of Arrakis, also known as Shai-Hulud or 'makers', central to the planet's ecology and the production of melange. Adult sandworms could grow to enormous size, with specimens exceeding 400 metres in length. They were attracted to rhythmic vibrations and were territorial, attacking anything that produced such disturbances in the sand. The Fremen learned to summon and ride them using thumpers and maker hooks, considering the skill a badge of adulthood. The sandworm lifecycle, from sandtrout to maker, was inseparable from the spice cycle that made Arrakis the most valuable planet in the universe.