The Leech Hydroe is a member of the Hydroe Family in Hey! Pikmin. They are watery creatures that are harmless and spend most of their time parasiting plants. When Captain Olimar crashlanded on the Unknown Planet, the Sparklium Converter of the S.S. Dolphin II fell near a Leech Hydroe. The parasite absorbed the converter and became extremely agressive and turned the plant it parasited into a huge and agressive predator with the ability to walk and even fly. This unique specimen is refered to as the Berserk Leech Hydroe by Olimar. After the host's death, the Leech Hydroe emerge from the dead plant and try to attack Olimar but since it has no means of attack by itself, it fall down and the Converter leave its watery body turning it back to a harmless creature. Soon after, the Leech Hydroe will run away from Olimar and the Pikmin.
"Strictly speaking, this creature is only the part that takes over a plant to drain its nutrients. Its host must then wander around to find more food. What a shock to see this harmless-looking thing emerge from that other terrible beast! The only time I was more surprised on this voyage was during my reunion with the Pikmin."
The Leech Hydroe is the first creature listed as an enemy in a bestiary in the Pikmin series that is not fought at all and is only seen in a cutscene.