Everything in Mother Nature is considered sacred by the Celtic Druids, so every plant, tree, animal, fish and bird is seen as sacred too. But in the same way that some trees and plants, such as the oak and mistletoe, receive special veneration, so do certain creatures receive particular attention by the Druids. According to their particular characteristics different animals were used by the Celtic Druids to symbolise different powers, attributes or gifts. They are often connected with the world of spirits and gods.

wisdom good / fortune / healing / spiritual energy / cunning / transformation
Due to its unique characteristic represented by the cyclical shedding of its skin, the serpent was the Celtic symbol of rebirth and was widely referred as an immortal creature that came to life each year after hibernation, complete with a new skin. The serpent is both a phallic symbol and, paradoxically, a Celtic symbol of feminine power. It is associated with the element of water.
The adder is the only venomous snake found in the British Isles. The Druids carried an amulet called gloine nathair, serpent glass, which was alleged to be formed from the eggs of an adder. The snake was also thought to embody masculine power. Celtic warriors wore a torque with a two-headed snake symbol to embody this power.

The figure of the serpent biting its tail is known as the Ouroboros (a Greek term meaning 'tail-devourer') and symbolised the cyclic nature of the Universe - the Ouroboros devours its own tail to sustain its life, in an eternal cycle of life and death, creation and destruction. This mythological symbol was adopted by the Celtic populations but is found in various civilisations, beginning with that of Ancient Egypt in 1600 B.C.
The serpent is an important magical symbol in Celtic mythology, its image found in carvings and sacred jewelry. Those born near St. Keyne's Day, October 8th, are empowered with good fortune and wisdom. Because snakes shed their skin, they are symbolically creating themselves anew. Their venom, which can kill in sufficient quantity, has also been used in healing and inducing trance like states.
The Celts believed that when you see a snake while on a shamanic journey, prepare to shed something in favor of something greater and better. Daughter of Welsh King Brychan, Keyne brought the new Christianity to a land plagued with venomous snakes which her prayer turned to stone.