When does the Waterwraith appear in the Submerged Castle in Pikmin 2?

On the first four sublevels, if you stay there for five miutes or longer, it will appear; a cutscene heralds the first time it arrives. You are unable to defeat or damage it until you reach the final floor, where you'll find Violet Candypop Buds; Purple Pikmin can force the Waterwraith into solidity, making it possible for any Pikmin to damage it.