The corrupted scavenger is found in the creature keeper room within the Chambers of Xeric. It is blocking the path, and needs to be removed from its spot by feeding it until it is full. The amount of players in the raid will determine how much cavern grubs are needed to make it full.
Based on the Creature keeper's journal, this scavenger was captured by the creature keeper, who domesticated it. The creature keeper locked chests full of cavern grubs so it would be unable to get them itself. It was later pitted against several lizardmen, though the end result was unclear as the lizardmen spotted the creature keeper and poisoned him. The scavenger was unaware that the creature keeper died from the lizardman bite and patiently waits for its food.