Nagapanchami

Nepalese people have great respect for Nagapanchami Day, which falls every year on the fifth day of bright fortnight of Shrawan (July-August). They celebrate it by posting colorful portraits of nagas (serpents) on the walls above the main doorways.
Nagapanchami has very ancient origin. The tradition of serpent-worship seems to have originated from the Dravidian culture. So this tradition is in its basic from very non-Vedic. The Aryans did not initially worship the snakes. They were always afraid of the snakes and tried by all means to keep them away. The Vedas have very little to say in praise of serpent-gods. (There is a reference about an interesting method of neutralising snake venom in the Rigveda. Taittiriya Samhita prescribes snake sacrifice for one's peace, protection and prosperity.) It was only in the puranic period that the Aryans made some rooms for the snakes in their religious functions. But later, the Puranas started speaking very highly of the significance of the serpent-worship. And thus the tradition of serpent-worship came to be recognized as an integral part of the Vedic religion.
The Puranas have plenty of verses devoted to the nagas. To illustrate, the Garuda Purana says that worshipping of the nagas on the Nagapanchami Day brings peace and prosperity to the devotees. The Skanda Purana says that if one offers cow milk to the snakes on this day one is sure to be safe from snakebites for the whole year. The Bhavishya Purana says that one who worships the nagas with single minded devotion will always be able to keep the thunder away.

Another reason is that the Kathmandu Valley has long been regarded as the legendary lake home of the nagas. Karkotak, their king, is still believed to be living in Taudaha lake, about seven miles south of the Kathmandu city. Kathmandu Valley was also called Nagarhida, which means the ancient abode of the nagas.In any case, the Nagapanchami Day reminds us that many snakes by nature are poisonous and dangerous. And yet, they are very useful to the ecosystem as they keep check on pests like rats, insects, etc.

Nepalese people have been maintaining this tradition from time immemorial. Snakes in Nepal are generally belived to roam about in disguise of a certain god or goddess. So when they see a serpent crawling in or around their houses they never forgot to burn some incense in its honour. However, the Nepalese people seem to worship the snakes more as rain-god than as any other gods. One possible reason is that Nepal has long been an agricultural country. More than ninety percent of the people here still depend on agriculture for their livelihood and monsoon rain is still the main source of irrigation for farming. And the legend has it that the nagas are the sole agents of the monsoon and drought. It also talks about Naunaga (nine very important snakes) seated on which Yoga Gorkhanath performed deep penance to stop the rain for twelve long years all over Nepal. So Nepalese farmers always regard nagas as the most powerful water spirits.