The chthonic animal

In Lublin area of Poland, people believed that Snake king lives among the roots of an old Hazel tree. Every autumn he gathers all the snakes, who then slither up the tree to its branches "to see the sun for the last time" before they go under ground...

Source: "Simbolika zivotinja u slovenskoj narodnoj tradiciji" by Aleksandar Gura.

The snake on this picture is a common viper which also lives in Poland...In Poland the snake is called żmija zygzakowata, which translates as 'zigzag viper', due to the pattern on its back. 

Here we see that in this folk belief hazel tree was seen as the world tree, as Slavs believed that "the great serpent lives among the roots of the world tree"...

More about Slavic (Specifically Serbian) hazel lore can be found in my article "Hazel". 

We also see that snake is attracted to the sky and sun, which is very strange for a "chthonic animal"...

The thing is, the notion that snake is a "chthonic animal" comes from misunderstanding of the nature of snakes. Snakes are under ground, in "the other world", only during the winter, which according to Slavic tradition, is the time that sun also spends in "the other world". Which is why winter is dark and cold...When in the spring sun comes back to "our world", snakes follow it and appear above the ground...This makes a snake a solar animal true and true...

More about Slavic snake and sun lore can be found in my article "Enemy of the sun"...