Dune novels by Frank Herbert
The sandworm was a native life-form of the planet Arrakis. It lived in the vast deserts and sand dunes that stretched across the surface of the planet. Simply put, the sandworm was 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.
The Sandworm was the predominant lifeform on Arrakis, both honored and feared; vital and deadly. The sandworms were extremely territorial; as soon as two worms sensed each other’s presence, they let out chuffing roars of challenge, bellowing melange-smelling exhaust from their cavernous throats.
By anyone’s standards, Sandworms could grow to an enormous size. Dr. Yueh cited that specimens “up to 450 meters long” were spotted by observers in the deep desert. To make a comparison, the largest animal on earth was believed to be a Blue whale measuring in at only 33 meters, or about 7% of a large sandworm’s length.
Many things commonly associated with Arrakis are surrounded in myth and mystery, and the sandworms are no exception. Some people believe that worms from 700 to even 1000 meters existed in the southern pole regions. This was neither confirmed nor denied. See Paul Atrei
des during his trial of the sandrider for further reading regarding their maximum observed size.
However there is some contention regarding these estimates as Harvester Factories were said to be 120 meters long and still the diameter of a sandworm’s maw (or at least the sand displaced by its maw) was described as twice that width. Although this particular specimen was stated to be a large example of the species, a Sandworm with jaws 240 meters in diameter would exceed in size even those of myth which could supposedly be sighted in much deeper desert than the typical spice mining region.