The Ouroboros - one of the oldest mystical symbols (shared by many ancient cultures)- depicts the serpent eating its tail, and represents renewal in the cycles of nature and the universe.

It appears in many cultures, with slightly different interpretations of the common theme of unity, balance of the light and dark, and the renewal of life. From destruction comes creation, as the serpent eats its tail to sustain life, in an unending infinite cycle.

To read about the Ouroboros, check out this article:

http://www.tokenrock.com/explain-ouroboros-70.html