The apsara explains her curse by a brahmana
Arjuna has just dragged a giant crocodile from a sacred river, only to see it transform into a beautiful celestial woman. He asks who she is and why she was living in the water, committing the sin of preying on ascetics. She tells him the story of a temptation that went terribly wrong.
The woman who had been a crocodile stood before Arjuna, divine and radiant in her true form. She answered his question.
She was an apsara named Varga, she said, one who used to roam the forests of the gods. She was a favorite of Kubera, the lord of riches. She had four beautiful friends, all capable of going anywhere at will: Sourabheyi, Samichi, Budbuda, and Lata. Once, the five of them were traveling to the abode of the protector of the worlds.
On their way, they saw a brahmana. He was rigid in his vows, extremely handsome, and studying alone in his solitude. The entire forest was radiant with the energy of his austerities; he seemed to illuminate the region like the sun.
Witnessing the extraordinary sight of his terrible austerities, they descended. Their purpose was to create an impediment. They went to the brahmana together. They sang. They laughed. They sought to tempt him.
But the brahmana did not pay any attention to them, not even for an instant. The immensely energetic and pure one did not waver; he remained fixed in his austerities.
His indifference turned to anger. The brahmana cursed them. For their attempt to obstruct his sacred pursuit, they would become crocodiles and live in the water for a hundred years.