Mnemosyne — Classical Greek Myth Library

The second labor was to kill the Hydra of Lerna, a creature reared in the swamp, with a huge body and nine heads—eight mortal, the middle one immortal. She would raid the cattle and the land. Heracles took Iolaus with him. Finding the Hydra on a rise by the springs of Amymone, he forced her out with burning shafts, seized her, and crushed heads with his club; but for every head destroyed two grew in its place. A giant crab, sent by Hera to aid the Hydra, bit his foot; he killed the crab and called Iolaus for help. Iolaus fired part of the nearby wood and, as Heracles cut each mortal head, seared the stump so that nothing could regrow. Heracles then struck off the immortal head, buried it while it still hissed, and set a heavy rock over the place. He slit the body and dipped his arrows in the gall, so that thereafter any wound from them was deadly. Athena’s counsel stands behind the joint success in Hesiod’s brief notice. Eurystheus refused to accept the labor as valid, arguing that Heracles had not conquered the Hydra alone but with Iolaus’s aid—an administrative quibble that does not undo the deed in the narrative itself. Hera, for her part, is said to have set the crab among the stars as the Crab (Cancer); the Hydra’s defeat becomes both a purge of the Argive marshes and the origin of Heracles’s poisoned shafts, which will later wound Chiron and, inadvertently, the hero himself.