Reports filter in occasionally that the Kojun Desert, the area to the North of the mountain range known as the Spine of the World, is home to massive snakelike monsters which burrow several leagues under the sand. We now know that these accounts are correct. They are very rarely seen but that is most likely due to the small number of people who travel as far as these remote regions and return to Yarnolth alive.
Many believe that these creatures are nocturnal. This rumour is only partially correct. I, personally, do not believe that Sandworms ever truly sleep at all. These creatures have an unusual metabolism reminiscent of reptiles: Their body temperature must be kept above a certain level. During the day, they achieve this by lying on the surface of the desert and absorbing sunlight. While they sunbathe, they are content to the point of lethargy. Some people claim that this is a kind of sleep, but I think it is more like a trance, as there have been reports that they can react to events. At night, when the desert’s air temperature drops, Sandworms go underground, where they have to burrow at full speed throughout the night in order to maintain their body temperature. If their temperature drops below a certain level, they freeze and turn into crystals, which is often the fate of older Sandworms. The crystal deposits found so commonly in the desert are elderly Sandworms who could no longer keep up the necessary pace to stay warm.
Sandworms can go weeks without food, but when they do, they get very hungry and start eating anything in sight, even sand, in an attempt to sustain themselves. This, I believe, is the reason why they are often seen by adventurers with sand falling out of their maws.
Despite the fact that their eyes and ears are nearly impossible to discern, Sandworms have surprisingly acute sight and hearing. They are very sensitive to vibrations, and are able to detect the footsteps of animals or people walking on the sand even from a great distance.