Logworms were enormous, dangerous worms found in the Deepwoods, which resembled large logs while resting. Active logworms suspended themselves with blasts of air on their undersides, like hover-worms. Ferociously active predators, logworms sucked in massive amounts of air to inhale their prey, then crushed them by arching their spines.
During the Rook trilogy, logworms were attracted to the Silver Pastures in large numbers because of the vast herds of livestock in the area. Rook, Stob Lummus, Magda Burlix, and Hekkle ran into one on the way to the Free Glades. The logworm ate their prowlgrins, but they managed to escape.