Legend has it that in the 5th century, St. Patrick exterminated the snakes of Ireland by throwing them into the sea.

You could say he did a good job, since there are no snakes in Ireland... but the reality is not quite like that.

The fact is that Ireland has never had snakes. And so the question arises: If snakes can be found almost anywhere in the world - from Australia to the Arctic Circle - what makes Ireland so special?

For a start, it's an island. The Irish Sea is more than 50 kilometers wide - that would be a long crossing for a land animal.

A sea snake might have an easier time, but even these live in warm tropical waters, not the icy Atlantic.

According to Popular Science, the Ice Age made the islands inhospitable for reptiles, whose cold-blooded bodies need the warmth of the environment to function.

The glaciers retreated around 10,000 years ago, exposing a land bridge between Europe and Great Britain and another between Great Britain and Ireland, allowing easy passage to the islands.

The melting of the glaciers sank Ireland's land bridge 8,5000 years ago, while Britain's stood for another 2,000 years.

Thus, animals from Europe had plenty of time to colonise the UK, and even so, only three species of snake managed to establish themselves in Britain.

None of the three seem to have felt compelled to continue moving westwards towards Ireland, so there is no evidence of the presence of crawling reptiles in Ireland's fossil record.

Other islands that don't have snakes are, for example, New Zealand, Hawaii, Greenland, Iceland and Antarctica. Even so, the absence of snakes seems miraculous, given the global pet trade and the potential for snake invasion.

However, pet snakes are not banned in Ireland, as they are in Hawaii, New Zealand and Iceland.

Pet snakes became a status symbol during Ireland's economic boom in the late 1990s, but during the 2008 recession and afterwards, hard times meant that many people let their snakes go.

The snakes have turned up in many random places, but so far they don't seem to have spread very far in the wild. If snakes ever take hold in Ireland, it will take a lot more than an intervention by St. Patrick to get rid of them.