Entity
Hydra
The many-headed water-serpent of Greek myth, slain by Heracles as the second of his labors — a monster that grew two heads for every one cut away.
The Hydra — more fully the Lernaean Hydra — is the many-headed serpent of Greek myth that lived in the marsh of Lerna, near Argos, and was killed by Heracles as the second of his twelve labors. Its defining trait is the thing every later writer fixes on: for each head struck off, two grew back in its place, so that attacking it in the obvious way only made it stronger.
In Hesiod’s Theogony, the earliest surviving account, the Hydra is one of the brood of Typhon and Echidna, the dynasty of monsters that also produced Cerberus and the Chimera, and it is reared by the goddess Hera expressly as a trial for Heracles. The fuller story comes later, above all in the Library attributed to Apollodorus: the creature’s heads are many — ancient sources do not agree on how many, and one was held to be immortal — and its very breath and blood were deadly poison. Heracles solves the problem of the regenerating heads not by force alone but with help. His nephew Iolaus sears each fresh stump with a burning torch so that no new head can sprout, and the one immortal head Heracles buries under a great rock. Afterward he dips his arrows in the Hydra’s venom, which makes the wounds they inflict incurable — a detail Greek tradition follows through to his own death, since the poison eventually destroys him in turn.
The labor was read as more than an adventure. Greek and Roman authors treated the Hydra as a figure of any difficulty that multiplies under attack, and that reading has proved the durable one: a “hydra-headed” problem is one that spawns new versions of itself the moment a single instance is suppressed. Heresiologists of the early Church reached for the same image to describe the proliferation of doctrines they were trying to refute, a recurrence whose force lay precisely in its endlessness. Later esoteric and alchemical writers, who habitually read the labors of Heracles as veiled accounts of inner transformation, took the Hydra as the composite, regenerating passions or the volatile matter of the work — though such allegories are the interpreters’ construction, layered onto a story that began without them.
The name attached itself to other things. A constellation called Hydra, the longest in the sky, winds across the southern celestial sphere and was already catalogued by Ptolemy in the second century; in mapped tradition it is linked both to this monster and to the water-snake of a separate myth involving the crow and the cup. The freshwater animal Hydra, named in the eighteenth century for its capacity to regrow severed parts, carries the myth into biology. What the various uses keep in common is the original image — not the number of heads, but the futility of cutting them.