Takshak Naag was the eldest son of Maharshi Kashyap and one of his 13 wives Kadru. Kadru had many sons as Naag. Garud had cheated on Kadru, because Indra stole that Amrit and replaced it with poison after Garud's mother gave it to Kadru to become free from her slavery. Kadru gave that poison to her sons and since then it stayed in their mouth. Now they had become very fierce and full of poison. (read the full story here) They were at war with men too. Devtaa in Swarg trembled seeing them lest they end the race of men for ever.

One day Kadru called them for some matter, but they being mischievous, refused to obey her. At this Kadru got very angry and cursed her children - "You all shall perish in the fire sacrifice made by the King Janamejaya." It had never happened that some race was finished by their mother's curse only. All heard this curse. Brahmaa Jee also heard this curse. Devtaa got very happy to hear this.

When Shesh Naag heard this he went to do Tapasyaa and pleased Brahmaa Jee. Pleased Brahmaa Jee appeared before him and asked him to ask for a boon. He said - "I don't want to be with my brothers, they are not kind to Vinataa and her sons." Brahmaa Jee said - "You don't need to be worried about your brothers. Ask for any other boon." Shesh Naag said - "Let me be happy in virtue and penance." "So be it. You may go and stabilize this Earth on your head." Shesh Naag entered the Earth and kept it on his head.

When Vaasuki heard this curse, he got worried and said - "We should do something so that Janamejaya's this Yagya does not take place." He consulted his brothers also about it. Many types of suggestions came from them to escape from the curse but Vaasuki didn't like any of them and asked some time to think. The then Elaapatra said - "Brothers, Listen to me carefully, Sacrifice cannot be stopped. Whoever is afflicted by fate, has to recourse his fate alone, he cannot be saved. This is written in our fate so this will have to happen. Still listen to what I say. When our mother gave us Shaap, I was lying in her lap. I heard Devtaa telling Brahmaa Jee with grief - "Who else other than Kadroo could curse her children like this. And you also said "So be it." Why didn't you stop her doing so?"

Brahmaa Jee said - "The snakes have multiplied a lot. They are cruel, poisonous and terrible. Only those snakes will die in that Yagya who will be like that, not the ones who are not poisonous, harmless and who are virtuous. And when the time will come they will escape from this calamity. A Rishi, known as Jaratkaaru, will be born in Yaayaavar's family. He will have a son named Aasteek, he will put a stop to that Yagya and the virtuous snakes will escape from that sacrifice." Devtaa asked - "How he will have a son?" Brahmaa Jee said - "He will marry a girl of his own name." Vaasuki further said - "So O brothers, We have a sister named Jaratkaaru. Let us give her to him in alms. This is the only means of saving our lives which I heard."

Therefore Vaasuki started taking care of his sister carefully. Not after long Saagar Manthan took place and Vaasuki was used as a churning rope. As this event was over, Vaasuki went to Brahmaa Jee along with Devtaa and Devtaa said to Brahmaa Jee - "Father, Vaasuki is greatly suffering from the fear of his mother's curse. Please remove his fear so that his race can flourish." Brahmaa Jee said - "Vaasuki should do whatever Elaapatra has said to him, at the appropriate opportunity he gets." Then Vaasuki asked other snakes to keep an eye on Jaratkaaru that whenever he is in a search of his wife, they should inform about him to him because now their race depends on him only."

(Read further How the Naag Were Saved)