Gigantic carnivorous worms that live beneath the desert sands

Desert worms, also called sand worms, are giganticl carnivorous worms that live beneath the desert sands. They have gaping mouths full of serrated teeth, but no eyes or other sense organs. They are able to detect vibrations within 120 feet of their location, and will attack anything that moves by bursting up from beneath the sand, gaining surprise on a 1-4 on 1d6. On a natural-20 attack roll, a desert worm will swallow any human-sized or smaller creature it is attacking whole, dealing 1d6 points of damage every round after swallowing them to its prey. The worm can only swallow one creature at a time. Creatures that have been swallowd can attempt to escape by dealing at least 15 points of damage to the worm with a small blade, such as a dagger from inside the belly of the beast, but it is extremely difficult to-hit under these circumstances, and only a roll of exactly 20 will hit. Desert dwelling peoples live in fear of the desert worms, this fear causing those who know of them to avoid making loud noises or even traveling through the worm's territory at all. Legends say that desert worms guard an ancient treasure, buried deep beneath the sand. Other legends tell of gigantic desert