Snakes or Nagas are constant companions of Muruga – who is
also known as Subramanian, Kartikeya and Skanda. The reason why nagas are
associated with Muruga is a story of repentance. Legend has it that once Muruga
asked Brahma the meaning of Pranava (OM). Brahma was not able to provide a
satisfactory answer. An angry Muruga imprisoned Brahma.
Later Shiva intervened and the matter was settled.
Muruga then felt that he did not act properly by imprisoning
Brahma. For the sin committed, he took the form of a huge snake and started
living in this form.
Goddess Parvati was unhappy with the snake form of Muruga.
She complained to Shiva.
Shiva then asked Goddess Parvati to observe 108 Sashti
Vratam to get back her son.
When the 108 Sashtis were completed, all the gods arrived to
witness the meeting of Muruga and Goddess Parvati.
Muruga gave away the serpent form and appeared in his
original form.
There
is a slight difference regarding the final part of the story in some
scriptures. It is Vishnu that advices Goddess Parvati to observe the Vrata. On
the 108 Sashti day Muruga appears as a huge snake. He gets back the original
form when Vishnu touches the snake.