The magnesi are composed entirely of energy. Each magnese has a magnetic field that picks up magnetite and uses it to make calculations. To reproduce, a magnese will grind magnetite off a worldworm and split in two. The magnesi are known to be sentient, and they are a warlike people, feeding their enemies to the Worldworms. Since the magnesi are much faster than the Worldworms, this is the only way a worldworm can catch a magnese.
The magnesi draw their energy from the sun and the wind. They store their energy in the form of pure iron, then convert it back to magnetite when they need it. They also use iron fluoride, which is an antiferromagnet. The wispy nature of the magnesi makes them very vulnerable to more solid creatures, but they have demonstrated that this is balanced by their ability to tear apart electronics and soft bodies at close range.
The magnesi are very artistic, and tend to sculpt the worldworms into interesting figures. While they have no interest in war technology or space travel, they constantly study how to make their art survive the movement of the worldworms.