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The Hydra is a vicious nine-headed monster that can grow back its heads.


The Hydra

The Lernaean Hydra was born to Typhon and Echidna. While not the most powerful of its siblings, the Hydra was a fearsome and vicious monsters with nine heads (at birth). The monster terrorized the Kingdom of Lerna, chasing all of the inhabitants away with the toxic acid and fumes that it spewed at them and killing livestock. When one of the Hydra's heads was decapitated, two more snake-heads would grow in its place.

Percy Jackson's Greek Heroes

As the second of his Twelve Labors, Hercules was tasked by King Eurystheus to kill the Lernaean Hydra. The hero eventually defeated the monster by having his nephew Iolaus cauterize each stump after he had cut it, then tearing off the immortal head with his bare hands and crushing it under a giant rock. After defeating the monster, Hercules dipped the tips of his arrows in the Hydra's bile, rendering the weapons extremely venomous. However, Eurystheus said that labor did not count as he had help, so he Hercules had to do an extra labor make up for it.

Percy Jackson and the Olympians

The Lightning Thief

When Percy Jackson visits the Oracle of Delphi in the Big House Attic, he notices a stuffed Hydra head amongst the collected spoils of war.

The Sea of Monsters

When Percy Jackson sent Tyson to look for powdered doughnuts so he could talk to Annabeth, Tyson went out and came upon a Monster Donut store. Tyson, being a monster, was somehow able to summon the outlet bringing the Hydra with it. It was large and lizard-like, with long necks and nine heads to match. It had many rows of razor-sharp teeth, its hands were clawed, had a tail, and spat acid. According to Annabeth, another Monster Donut shop popped up every time it grew another head. She says that Hermes' children found a way to use the Hydra's life-force to make a new chain of stores. Percy initially tries to defeat it by slicing off its heads, but succeeded only in making more. Percy, Annabeth, and Tyson were saved by Clarisse who completely obliterated the Hydra with cannon fire from the CSS Birmingham.

Later, when Tyson creates a shield for Percy, one of his designs on it is of Tyson battling the Hydra as he holds aloft a box of Monster Donuts.

The Heroes of Olympus

The Mark of Athena

Percy fights a Hydra when he, Piper McLean, and Jason Grace arrive to rescue Nico di Angelo from the giants Ephialtes and Otis. During the fight, Percy attempts to find a rocket launcher that he'd spotted earlier, but he instead find a device rigged to launch all kinds of explosives. When Percy fires it at the Hydra, the monster is instantly vaporized by the blast.

The Trials of Apollo

The Dark Prophecy

Apollo tells Meg McCaffrey that the red-bellied hydra was one of the monsters that started to fade from mortals' collective memory. This resulted in them regenerating less often in Tartarus, so the gods have to let them breed and repopulate. A few thousand years ago, a proposed temple of Poseidon in Sicily had to be relocated because the land was found to be the nesting area of a red-bellied hydra. Yet, those kinds of hydra are not nearly as rare as Yales.


The Hydra is described in The Sea of Monsters to be a huge and scaly lizard-like monster with nine heads, each one diamond-shaped with a mouth lined with razor-sharp teeth. Each mouth spits toxic acid. If one of its heads is severed, the hydra grows two heads in the place of the lost one.

In The Sea of Monsters, the Hydra is seen wearing a plastic bib reading "I'M A MONSTER DONUT KID!"

Spoil of War

In the attic of the Big House in Camp Half-Blood, a Hydra head was left as a spoil of war. This Hydra was defeated in Woodstock, New York in 1969.

Powers and Abilities

  • It can spew acid from its mouth.
  • It has multiple heads.
  • Two heads will grow back for each head that is cut off.
  • The monster as a whole possesses incredible superhuman strength.



Percy Jackson and the Olympians: The Lightning Thief

Percy Jackson, Annabeth Chase, and Grover Underwood encounter the Hydra in the form of five Security Guards at the replica of the Parthenon in Tennessee, after Percy Jackson takes Persephone's Pearl (originally Poseidon's in the book) from Athena's statue. Ignoring Annabeth's warning, Percy cuts off each of the Hydra's Heads with Riptide, causing ten heads to regrow. Grover managed to defeat the Hydra using Medusa's Head - a possible reference to some accounts of Perseus slaying Cetus, the monster that Andromeda was going to be sacrificed to. It should be noted that the Hydra is depicted as breathing fire in the film instead of acid. After Percy cuts its middle head, two of the Hydra's head breathe fire.



  • Hydra, the largest of the modern star constellations, is named after the monster.
  • Hydra is also the name of a satellite of the dwarf planet Pluto.
  • Hydra, a species of simple fresh-water animal, is named after the monster.
  • In Greek Mythology, the Hydra terrorized the Kingdom of Lerna, so it is fully called the Lernean Hydra.
  • The Hydra is the only monster which reforms in The Heroes of Olympus series after being defeated in the Percy Jackson and the Olympians series.
  • The Hydra did not have one immortal head in Percy Jackson and the Olympians: The Lightning Thief.
  • The existence of the red-bellied hydra confirms that there are multiple hydras in the riordanverse, unlike actual Greek mythology in which the Lernean Hydra is the only hydra
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Friendly Monsters: Argus | Blackjack | Briares | Bombilo | Chiron | Cottus | Don | Ella | Festus | Gleeson Hedge | Gray | Grover Underwood | Guido | Gyges | Lysas | Mrs. O'Leary | Ophiotaurus | Peaches | Peleus | Porkpie | Rainbow | Scipio | Tyson | Tempest | Sssssarah
Enemy Monsters: Antaeus | Agrius and Oreius | Arachne | Cacus | Carthaginian Serpent | Charybdis and Scylla | Chimera | Chrysaor | Clazmonian Sow | Colchis Bulls | Echidna | Euryale | Geryon | Kampê | Karkinos | Kekrops | Lamia | Manticore | Medusa | Minotaur | Nemean Lion | Polyphemus | Python | Skolopendra | Sphinx | Stheno | Sun Dragons | Typhon | Trojan Sea Monster
Neutral Monsters: Cerberus | Erymanthian Boar | Gray Sisters | Furies | Ladon | Orthus | Sybaris