There are two meanings of the term Naga -
Sarpa has originated from the Sanskrit root सृप् meaning something which crawls on the ground.
Snake with hood is called Naga.
Sarpa is the common name for all kinds of snakes.
Kadru was Daksha Prajapati's daughter.
Her husband was Kashyapa Prajapati.
Kadru desired to have 1,000 strong sons.
She expressed her desire to Kashyapa.
As a result of their union, she laid 1,000 eggs that hatched into snakes.
All the snakes are descendants of these.
Vasuki.
The mother of serpents,
Kadru made her sister Vinata her slave through cheating.
Sheshnag (Adi Shesha) was very righteous.
Some of his brother serpents also took part in this.
Sheshnag was disgusted and did not want to continue any relationship with his family.
He observed tapas.
Brahma sent him down to Pathala-loka with the responsibility of holding the earth upon his hoods.
विषेण हन्मि ते विषम् - Vishena hanmi te visham - Atharva Veda 5.13.4
According to Vagbhatacharya a snake bites for eight reasons:
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