According to this article: Among the legends associated with St. Patrick is that he stood atop an Irish hillside and banished snakes from Ireland—prompting all serpents to slither away into the sea. In fact, research suggests snakes never occupied the Emerald Isle in the first place. There are no signs of snakes in the country’s fossil record. And water has surrounded Ireland since the last glacial period. Before that, the region was covered in ice and would have been too cold for the reptiles.