Alarka is a parasitic worm, with shape is like a micro pig, eight legs, with sharp teeth, and covered with numerous needle-like fur. This worm bit Karṇa (Karna), the famous warrior in Mahābhārata (Mahabharata).
It was an incident that occurred, when Karṇa, assuming the identity of a brāhmaṇa belonging to the Bhārgava (Bhargava) clan, came to Paraśurāma (Parasurama), to take lessons of weaponry. Karṇa was then very happy, after receiving Brahmāstra (Brahmastra) from Paraśurāma. One day, Paraśurāma, exhausted after fasting, went to sleep, laying his head in the lap of Karṇa. When he was in sound sleep, the worm, feeding upon flesh-and-blood, bit deeply in the thigh of Karṇa, Fearing that his guru’s sleep would be disturbed, Karṇa could not kill the worm, nor could he throw it away. Blood oozed out of his thigh, and when that blood fell into the body of Paraśurāma. Feeling the impurity of blood upon his body, Paraśurāma asked Karṇa about it. Karṇa told him everything. Paraśurāma saw that eight-legged, pig like creature. That worm was called Alarka. The moment he looked at the worm with a gaze of ascetic energy, that blood-soaked worm died, and it turned into a rākṣasa (rakshasa, monster). When Paraśurāma asked him about his identity. He said, in the previous birth, he was a monster, antagonistic to the gods; and his name was Daṃśa (Damsa). He was of the same age of Paraśurāma’s great grandfather Bhṛgu. Once he tried to abduct the wife of Bhṛgu, he was cursed that he would be dwelling in naraka (hell), being a blood-consuming worm. But at the pleading of the monster , Bhṛgu said that he will be redeemed by the gaze of his descendant Paraśurāma. Saying all these, the monster offered his regards to Paraśurāma, and took his leave.