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Saint Patrick Expelling the Snakes

Just kidding—aside from zoos and the pet trade, Ireland actually famously has no snakes.  It is one the few snake-free large islands on Earth joined only by New Zealand, Iceland, Greenland, and Antarctica (well—everywhere far enough north or south is snake-free: the reptiles don’t really thrive in places where there is permafrost or truly cold winters).  Legend has it that it was Saint Patrick who drove the snakes out of Ireland.  Standing on a great hill he lifted up his crosier and focused divine energy upon the unlucky reptiles which then writhed en masse into the sea and never returned to the emerald island.

"Ssseriously, why are you doing thisss?"

It has always been a bit unclear to me why Saint Patrick would do such a thing. Ecoystems which undergo such catastrophic changes tend to go haywire with great alacrity!  Fortunately the story is entirely a myth.  If snakes ever lived in Ireland (and it doesn’t seem like they did), they were long gone by the time the first Christians showed up.  The real reason is even more interesting than the dramatic Moses-like power of Saint Patrick, but as with most actual answers it is also more complex.

Evidence suggests that snakes evolved 130 million years ago during the Cretaceous.  At the time Ireland was, um, underwater at the bottom of a warm chalky sea.  Early snakes slithered their way across landbridges, rafted to islands on washed away logs, and swam (like the sea snakes) from island to island but, during the Mesozoic, there was no Ireland for them to go to.

Europe in the Ice Age (the pale white area was under a huge sheet of ice)

When the Mesozoic era ended in the great ball of fire, the continents again shifted.  Snakes went through a substantial evolutionary period during the Miocene and the original python-like snakes evolved into many different forms.  These new varieties of snakes slithered into grasslands, deserts, forests, and oceans around the world, but they still could not get to Ireland (now above the waves) because a cold ocean was in their way.  Then the end of the Miocene brought an ice age.  To quote the National Zoo’s essay on “Why Ireland Has No Snakes”:

The most recent ice age began about three million years ago and continues into the present. Between warm periods like the current climate, glaciers have advanced and retreated more than 20 times, often completely blanketing Ireland with ice. Snakes, being cold-blooded animals, simply aren’t able to survive in areas where the ground is frozen year round. Ireland thawed out for the last time only 15,000 years ago.

So Ireland remains snake-free because of the world’s temperamental geology. The island was underwater or covered by ice during certain eras when the snakes might have arrived–geography has conspired against serpents coming to Eire and setting up shop.  The age of humans however has been marked by numerous introduced species cropping up everywhere.  I wonder how long Ireland will be snake free when a pet shop accident or crazy hobbyist could unleash a plague of serpents on the green island.  The fact that such a thing has yet to happen seems almost as miraculous as the original myth.

Although many people construe the whole story to be an allegory of Saint Patrick driving paganism and the old gods from Ireland (as seen here).

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