They come in two kinds. The first are "New" Grubbers (given this adjective in the Concept Art) who wander the ruins, carrying lights or just watching the floodwater in the cavern. They wear only a ragged loincloth and carry staves. Their behaviour is not consistent - when Zoë Castillo encounters them, they attack her, but April Ryan seems to frighten them away. The second are larger "Warrior" Grubbers who are summoned by normal Grubbers when they are afraid, and dispatched as guards or foot soldiers by the Prophet. They are heavily muscular, capable of killing a human in a few blows, and have sharpened teeth. The implication of the differing adjectives may describe an evolution (or devolution) of the Grubbers, from Warrior to "New".