Sandworm

Sandworms – known by the Fremen as Shai-Hulud and given the scientific name Geonemotodium arraknis in the Dune Encyclopedia – are gigantic annelid-like creatures which dwell underground on planet Arrakis.

These non-sapient worms can grow up to 400 meters in length (although much larger individuals have been rumored to exist) and have a three-jawed mouth filled with sharp crystalline teeth. They usually feed on large quantities of sand and sand plankton – which consists of a massive amount of tiny organisms living in the sand, including minuscule larval Sandworms – but will also prey on larger desert creatures. Every segment of a Sandworm's body has a separate nervous system, making the creature extremely hard to kill. Their skin is tough and covered by scales. They are aggressive, territorial beasts and move around by sensing the vibrations on the ground.

Sandworms can live for thousands of years. Their biochemistry is poorly known, and it is possible that they are not carbon-based. What is known is that the chemical reactions going on in the Sandworms' bodies produce enough oxygen to compensate for Arrakis' near lack of flora, and that water is poisonous to the adult worms.

Sandworms begin their long lives as minute larvae living in the sand and which make up the sand plankton. If not eaten by their adult counterparts, they will grow up to the next larval stage, which is known as Sandtrout and resembles a large leech or slug. At this stage, they are able to withstand water, but also consume it, destroying water bodies at an untold rate so that the adult Sandworms will be able to live more safely. A plague of Sandtrouts is able to turn a whole Earth-like planet into a desert planet within a few centuries. Indeed, since Arrakis is known to have had oceans in the past, it has been speculated that Sandworms may not be native to the planet. After centuries, or even millennia, the surviving Sandtrouts will have matured into fully grown Sandworms.

Besides being one of the most important species in the ecology of Arrakis, Sandworms are also important figures in the religion, daily life and economy of the native Fremen, which breed Sandworms for the spice they produce, known as Melange.