Some parts of southern India is believed to be once covered with dense jungles, during the ancient times. Snakes and cobras were abundant in the jungle during that period. When people here started converting the forest land into agricultural land, these reptiles started to become extinct or had no place. Many of them where killed without any reason. Then problems started arising one after the other. Most of these problems were because of the ancestors who killed snakes or pelted stones at these reptiles for their safety. The people had to face unknown kinds of skin diseases and other family related problems because of this. Ultimately the root of such problems were found in horoscopes and they called it "Sarpadosha".
The cobras were believed to be equivalent of a brahmin(a hindu priestly class person). The cobras in this land were treated like gods and worshipped. To get rid of this Sarpadosha, the people started following many kinds of serpent god related celebrations. They also installed the holy stones with serpent god's image carved on them, and called it as Stone serpent( Naganakallu in kannada language).
In some places they also built small shrines. These shrines were called Nagabrahmasthana or shortly as Brahmasthana. There annual celebrations such as Nema or Naga darshana were conducted. Nagabrahma mandala, Dakkebali, Ashlesha bali etc. were also conducted during some auspicious days.
Learn more about Dakkebali celebration at this famous page: http://hubpages.com/hub/dakke_bali_the_attractive_serpent_dance
Tulunadu is that part of Dakshina Kannada region(South kanara district) in Karnataka where people communicate in Tulu language. Here, Serpent or Cobra worship is done in a special way. One can see Cobra worship performed extensively here, than in any part of the world. Every town, every village and every family have the stone snakes installed for worship.
This part is also called Nagaloka(Serpent world) or Nagarakhanda(Serpent zone). There are many types in Serpent worship.
Installing stone snakes, offering of milk to serpent god, to perform Tambila, to make the serpent god possessed in someone, Ashlesha bali, Dakkebali, Nagamandala.
There are 3 ways of performing the Nagamandala:
1) ¼ mandala of sacred 4.
2) ½ mandala of scared 8.
3) Full mandala of sacred 16.
Nagamandala is performed in an open place or vast field. Nagapathris(one who gets possessed)and vaidyas make this ritual a huge success. The Areca flowers are piled up like anything, for this ritual. Nagamandala is a religious activity here.
Kukke Subrahmanya in South kanara district of Karnataka, India, is a holy place to get effective results or remedies for any kind of Sarpadosha. Here the people who are in trouble because of Sarpadosha come to the temple and ask the priests to help them perform the Ashlesha bali. This place is said to have more power than any other holy place for such a ritual related to the Nagas(cobras).
When a cobra is seen lying dead anywhere, Sarpasamskara is performed to come out of the Sarpadosha. As the cobra is said to be of the Brahmin caste, these last rites and rituals are necessary, according to Hindus.
A similar Serpent god related "Srimad Anantheshwar temple" of GSB community at Manjeshwar, Kerala State:
Rath for the Shashti celebration at Manjeshwar:
Holy chariot named Chandramandala for the Shashti celebration:
Gold Lalkhi taken for Utsav celebration at Manjeshwar, on the Panchami day:
Ratharohan at Manjeshwar temple: