Lernaean Hydra

In Greek mythic genealogy the Hydra is described (by Hesiod in summary traditions) as an offspring of Typhon and Echidna, situating it among the chthonic brood of monstrous beings. It is portrayed in literary and artistic sources as resident in the lake, spring or marsh at Lerna — a site reputed to be an entrance to the Underworld and an ancient sacred place — and as the lair-defending antagonist whom Heracles must confront in his canonical second Labour.

Depicted as a gigantic, serpentine lake/sea monster with multiple heads and reptilian traits. Ancient iconography and literary summaries vary in head-count (early vase imagery sometimes six; Alcaeus nine; Simonides fifty in a later account) rather than fixing a single canonical number. Descriptions attribute virulent, poisonous blood and poisonous breath; some visual traditions show a double tail. In Apollodorus' summary of the Heracles episode one head is treated as immortal and is removed and confined rather than destroyed.

Sources attribute to the Hydra poisonous breath and blood so virulent that its scent could be deadly (Hesiod as reported in secondary summaries). A regenerative property appears in later traditions: Euripides is the earliest attested source to say a severed head was replaced by two new heads, while other authors vary (Servius reports three, the Suda is silent). The monster emerges from its spring/cave to terrorize neighboring villages and defends its lair; divine agency features in its story (Hera is said to have raised it against Heracles and she sends a crab to assist). Heracles' narrative exploits against it — flaming arrows to smoke the lair, cutting heads, cauterizing stumps, and confining an immortal head — form the canonical remedies in the tradition.