Poison Worms hang from the ceiling in an entangled cluster, similar to the Viper Swarms found in Super Castlevania IV. Occasionally, one of the worms will detach from this mass and crawl on the ground. These worms will poisonNathan if he touches them. They can easily be whipped while they are still falling; otherwise, simply sliding will crush them while they are crawling on the ground, or the Axesub-weapon can also be used to remove the mass from the ceiling.
The Poison Worm in Aria of Sorrow no longer appears suspended from the ceiling and is instead a big fat insect crawling on the ground, barely larger than a human. It slowly crawls toward the player; if they are behind it, it will crawl backward instead. As usual, it will poison the player on touch.
Only one Poison Worm appears in the entire game, at the beginning of the Forgotten City. While traveling the initial desert section of the level, Jonathan and Charlotte will eventually arrive to a big mound of sand; while stepping on it, the ground will suddenly split apart and a giant Poison Worm will emerge from the center of what now is clearly revealed to be a sand trap, dragging the heroes toward the monster. It attacks by curling over and expelling a big poisonous fume. As usual, touching the creature inflicts Poison status on the player as well. It is also considerably more resilient than its non poisonous counterpart, the Sand Worm (from which it is a palette swap).
Once defeated, the worm will contort violently in a shower of blood. By letting themselves get swallowed by the now vacant sand trap, the heroes will find the secret entrance to an upside down pyramid buried underground and be able to progress further into the level.