The Hydra made its lair in Lake Lerna, hence its name. According to the myth, beneath the lake was an entrance to the Underworld, and the Hydra was it's guardian. Most of the time, it stayed in the spring of Amymone, a deep cave , only coming out to terrorize neighboring villages.
After slaying the Nemean Lion, Heracles was sent to kill the Hydra. Outside its lair, he covered his mouth and nose to avoid it's poisonous breath. He fired arrows into the cave, then pulled out either a scythe, sword or his famous club, depending on the different retellings of the myth, but soon learnt that he couldn't kill it, as with every head he cut off, 2 more would take it's place.
Realizing 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 of using a firebrand to scorch the neck stumps after each decapitation. It is possible that this was inspired by Athena. Heracles cut off each head and Iolaus cauterized the open stumps. Seeing that Heracles was winning the struggle, Hera sent a large crab to distract him, but he crushed it under his foot. The Hydra's one immortal head was cut off with a golden sword given to him by Athena. Heracles placed it under a great rock on the sacred way between Lerna and Elaius, and dipped his arrows in the Hydra's poisonous blood, thus completing his second task.
- Regeneration - With every head removed, the Hydra would grow two more.
- Poison - The Hydra's poison was so powerful, even those near it when it breathed would be killed.
- Immortality - This only relates to one of the Hydra's heads, although another god or the weapons of a god could kill it.