Hydra

HYDRA

In Greek mythology, the Lernaean Hydra was an ancient nameless serpent-likewater beast (as its name evinces) that had nine heads — and for each head cut off it grew two more — and poisonous breath make its attack deadly. The Hydra of Lerna was killed by Hercules as one of his Twelve Labours. Its lair was the lake of Lerna in the Argolid, though archaeology has born out the myth that the sacred site was older even than the Mycenaean city of Argos since Lerna was the site of the myth of the Danaids. Beneath the waters was an entrance to the Underworld, and the Hydra was its guardian.

Upon reaching the swamp near Lake Lerna, where the Hydra dwelt, Heracles covered his mouth and nose with a cloth to protect himself from the poisonous fumes. He fired flaming arrows into its lair, the spring of Amymone, a deep cave that it only came out of to terrorize neighboring villages. Then he confronted it, wielding a harvesting sickle (according to some early vase-paintings) or a sword. Ruck and Staples have pointed out that the chthonic creature's reaction was botanical upon cutting off each of its heads he found that two grew back, an expression of the hopelessness of such a struggle for any but the hero, Heracles. The weakness of the Hydra was that only one of its heads was mortal.

The details of the struggle are explicit in Apollodorus realising that he could not defeat the Hydra in this way, Heracles called on his nephew Iolaus for help. His nephew then came upon the idea (possibly inspired by Athena) of using a burning firebrand to scorch the neck stumps after each decapitation. Heracles cut off each head and Iolaus cauterized the open stumps. Its one immortal head Heracles placed under a great rock on the sacred way between Lerna and Elaius and dipped his arrows in the Hydra's poisonous blood, and so his second task was complete. The alternative to this is that after cutting off one head he dipped his sword in it and used its venom to burn each head so it couldn't grow back.
Heracles later used an arrow dipped in the Hydra's poisonous blood to kill the centaur Nessus and Nessus's tainted blood was applied to the Tunic of Nessus, by which the centaur had his posthumous revenge. Both Strabo and Pausanias report that the stench of the river Anigrus in Elis, making all the fish of the river inedible, was reputed to be due to the Hydra's poison, washed from the arrows Heracles used on the centaur.

When Eurystheus, the agent of ancient Hera who was assigning The Twelve Labours to Heracles, found out that it was Heracles' nephew Iolaus who had handed him the firebrand, he declared that the labour had not been completed alone and as a result did not count towards the ten labours set for him. The mythic element is an equivocating attempt to resolve the submerged conflict between an ancient ten Labours and a more recent twelve.