Heracles journeyed to Lake Lerna in a speedy chariot, and with him he took his nephew and charioteer Iolaus, in search of the dreaded Hydra. When they finally reached the Hydras' hiding place, Heracles told Iolaus to stay with the horses while he drew the monster from its hole with flaming arrows. This brought out the hideous beast. Heracles courageously attacked the beast, flaying at each head with his sword, (in some versions a scythe) but he soon realized that as one head was severed another grew in its place. Heracles called for help from Iolaus, telling him to bring a flaming torch, and as Heracles cut off the heads one by one from the Hydra, Iolaus cauterized the open wounds with the torch preventing them from growing again. As Heracles fought the writhing monster he was almost stifled by its obnoxious breath, but eventually, with the help of Iolaus, Heracles removed all but one of the Hydras' heads. The one remaining could not be harmed by any weapon, so, picking up his hefty club Heracles crushed it with one mighty blow, he then tore off the head with his bare hands and quickly buried it deep in the ground, placing a huge boulder on the top. After he had killed the Hydra, Heracles dipped the tips of his arrows into the Hydras' blood, which was extremely poisonous, making them deadly.
Other versions say that while Heracles fought the Hydra the goddess Hera sent down a giant crab which attacked his feet). This legend comes from a marble relief dating from the 2nd century BCE found at ancient Lerna, showing Heracles attacking the Hydra, and near his feet is a huge crab. Also other legends say that a stray arrow set alight the forest, and it was the burning trunks which Heracles ripped up and used to cauterize the open wounds.