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Scope Series 4 RTÉ Two, Thursday, 7.00pm

Why Ireland has no snakes

SnakeLegend has it that back in the fifth century St. Patrick drove the snakes from Ireland. Standing atop a hill he used his staff to herd the slithering creatures into the sea, banishing them for eternity.

While it's true that aside from zoos and pets there are no snakes on the emerald isle, in fact, there never were any snakes in Ireland. Contrary to legend, however, this has more to do with geography than feats of St. Patrick.

Snakes evolved from their lizard forbearers about 100 million years ago during the late Cretaceous period, about the same time that Tyrannosaurus rex appeared. At this point Ireland was completely underwater.

During the Cenozoic era, 65 million years ago, the world began to dry out and vast grasslands came to dominate much of the northern hemisphere.  Predecessors of modern boas and pythons were widespread throughout this area about 50 million years ago with vipers and cobras following about 25 million years ago.

Now snakes are found in deserts, grasslands, forests and mountains virtually everywhere in the world. Everywhere, that is, except New Zealand, Iceland, Greenland, Antarctica and, of course, Ireland.

Notice these few snake free parts of the world are surrounded by water. So far, no serpent has successfully migrated across the open ocean to a new terrestrial home.

SnakeAs the world's oceans have risen and fallen over the millennia, land bridges have come and gone between Ireland, other parts of Great Britain and the European mainland, allowing animals and early humans to cross. However, any snake slithering its way to Ireland would have frozen during the ice ages.

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, can’t survive where the ground is frozen year round.

Ireland thawed out the last time only 15,000 years ago. Since then, 12 miles of icy water in the Northern Channel separate Ireland from Scotland, which does harbour a few species of snakes. Ireland has no snakes because they simply cannot get here.

How did the myth of St. Patrick and the snakes originate? Most scholars agree that snakes symbolize paganism, which St. Patrick is also credited with banishing. As symbols of evil, snakes are prevalent throughout Judeo-Christian mythology, most notoriously as Eve’s tempter in the Garden of Eden. However, ancient Egyptians venerated snakes and Ben Franklin advocated making the rattlesnake the symbol of the United States.

Herpetologists, scientists studying snakes, reptiles and amphibians, point out that snakes play an important role in ecosystems by controlling rodent populations, and snake venom has been used to treat diseases including cancer and haemophilia.

Some 200 species of snakes are threatened or endangered, their greatest menace being habitat loss. Unless humans take more interest in their survival, snakes may find themselves banished from more places than just Ireland.


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