Rockworms were small subterranean Rahi that were carnivorous and poisonous.
An army of Rockworms once attacked Po-Koro, which Pohatu defended by kicking boulders into the oncoming Rockworms. Another encounter took place when Takua wandered into a cave filled with Stone Rats. Jaller then tried to rescue him but they both fell into another cavern that was filled with Rockworms instead. The two Matoran then had to dig themselves out to the surface.
The Toa Metru once battled a giant Mutated Rockworm during their fight with the Energized Protodermis Entity. The Entity used some of its substance to mutate a Rockworm that was inside the cavern to a massive version of itself. Whenua managed to subdue it by using his Kanohi Ruru to blind it and force it underground.