The animal itself
Snakes shed the skin in one piece, including the eye caps, several times a year. They go temporarily near-blind before each shed, which is when they are most defensive.2 of 2 calendars · 2,400 searches a month
Snake
Shedding what no longer fits.
Which calendar assigns it, and when
Celtic calendar
18 February – 17 March
Its tree
Ash
Native American calendar
23 October – 22 November
Its zodiac sign
Scorpio
Unusual: snake appears in both calendars. The two systems agree on only 17 days of the year out of 365, so an animal claimed by both is the exception rather than the rule.
What it stands for, and where that came from
Shedding what no longer fits — renewal that requires discarding a whole former surface.
Honoured in: The rod of Asclepius still marks medicine; Ouroboros as the cycle; Genesis as the one culture that made it the villain.
The symbolism usually grew out of the behaviour rather than the other way round — which is the part worth keeping when the rest is set aside.