
Hindus worship Snakes or Nag on the fifth day of the bright half of sravana month . The day is known as `Nagpanchami`. The festival falls during the onset of monsoons and believed to counter the increased possibility of snake biting during this time. Hindus deify snakes and regard them with veneration. The snakes are thought to be associated with some gods like Lord Shiva, Goddess Manasa etc. Sesha or Ananta is the thousand-hooded king of serpents, who forms the couch for Lord Vishnu. The King of serpants Vasuki adorns the neck of Lord Shiva like a necklace. The day of Nagpanchami is dedicated to snakes and they are worshipped with milk and fruits.
The five Nagas worshipped on Nagpanchami are Ananta, Vasuki, Takshak, Karkotaka and Pingala. According to the Puranic myth, Brahma`s son Kashyapa had four wives, who gave birth to Devas(god), Garuda, Nagas and Daityas (demons) respectively. The third wife of Kashyapa was Kadroo, who gave birth to Nagas. Nagas are thus also known as Kadrooja. The Nagas are the rulers of the `Patal Loka`.
People visits temples specially dedicated to snakes and worship them. Shiva temples are the most favored place for veneration of Nagas as snakes are considered dear to the Lord. In South India people sculpt images of snakes made up of cow dung, which are then placed at the either side of the entrance to the house. In some other parts of Southern India, people draw figures of snakes with red sandal hood paste on wooden boards. Some other times clay images of snakes that are colored yellow or black are purchased. These are then worshipped and offered milk, as snakes are believed to be fond of milk. Some go find the holes of anthills to worship the snakes. A five hooded snake is made by mixing `gandh` (a fragrant pigment), `halad-kumkum` (turmeric powder), `chandan` (sandal) and `keshar` (saffron) which are placed on a metal plate and worshipped.

On this day, devotees pour milk into all the holes in the ground around the house or near the temple to satisfy the snakes. Sometimes, a small pot of milk with some flowers is placed near the holes so that the snakes can drink it. If a snake actually drinks the milk, the devotee is considered to be extremely lucky.
Legend says that the serpents have the capability to change their shape and form at their will. When they take the human form, they are depicted as beautiful women and handsome men. The victory of Krishna over the Kaliya snake is also commemorated on this day as the other herdsmen who were friends of Krishna celebrated his victory and serve milk to the serpent since the Kaliya did not do any harm to Krishna.
Nag Panchami is observed in different ways in different parts of India. It is one of the oldest festivals on which many women fast. In fact the Nagpanchami Vrata even finds mention in the Puranas. It is believed to be one of the most auspicious days of the entire year. According to the Bhavishya Purana, when men bathe the snakes called Vasuki,

Takshaka, Kaliya, Manibhadra, Airavata, Dhritarashtra, Karkotaka and Dhananjaya with milk on the fifth day of the bright fortnight of Shravan, they ensure freedom from danger for their families.
On this day snake charmers wander about with all the snakes to which people offer milk. They are also offered some money for allowing this serpent worship. The main psychology behind worshipping snake-god in Nag Panchami is people`s fear of serpents for which they want to satisfy them to save the life of their family. In the Ashyalayana Grihasutra, the Paraskara Grihasutra and other Grihasutras , a ritual called `Sarpabali` or offerings to serpents were performed on the full moon night of Sravana (monsoon season). However, the reason for shifting the actual day of vrata from full moon day to fifth night of the bright fortnight is may be due to the slight change of time on the onset of the rains.
The Vrata is also observed in modern India. At Sirale a fair is held on Naga panchami when snakes are specially caught worshipped and then set free. At Vitthal in South India there is the temple of Ananteshwara,where snakes are worshipped and appeased.