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 Ta-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 nearby Rockworm into a massive version of itself. Whenua managed to subdue it by using his Kanohi Ruru to blind it and force it underground.