Snakeless in Ireland: Blame Ice Age, Not St. Patrick

James Owen in London, England, for National Geographic News, March 13, 2008

During St. Patrick's Day,most revelers won't remember the patron saint of Ireland for his role as a snake killer.

But legend holds that the Christian missionary rid the slithering reptiles from Ireland's shores as he converted its peoples from paganism during the fifth century A.D.

St. Patrick supposedly chased the snakes into the sea after they began attacking him during a 40-day fast he undertook on top of a hill.

An unlikely tale, perhaps˜yet Ireland is unusual for its absence of native snakes.

It's one of only a handful of places worldwide˜including New Zealand, Iceland, Greenland, and Antarctica˜where Indiana Jones and other snake-averse humans can visit without fear.

But St. Patrick had nothing to do with Ireland's snake-free status, scientists say.

As keeper of natural history at the National Museum of Ireland in Dublin, Nigel Monaghan has trawled through vast collections of fossil and other records of Irish animals. "At no time has there ever been any suggestion of snakes in Ireland, so [there was] nothing for St. Patrick to banish," Monaghan said.

So what did happen?

Most scientists point to the most recent ice age, which kept the island too cold for reptiles until it ended 10,000 years ago. After the ice age, surrounding seas may have kept snakes from colonizing the Emerald Isle.

Once the ice caps and woolly mammoths retreated back northward, snakes returned to northern and western Europe, spreading as far as the Arctic Circle.

Britain, which had a land bridge to mainland Europe until about 6,500 years ago, was colonized by three snake species: the venomous adder, the grass snake, and the smooth snake.

But Ireland's land link to Britain was cut some 2,000 years earlier by seas swollen by the melting glaciers, Monaghan noted.

Animals that reached Ireland before the sea became an impassible barrier included brown bears, wild boars, and lynxes˜but "snakes never made it," he said.

"Snake populations are slow to colonize new areas," Monaghan added.

Mark Ryan, director of the Louisiana Poison Center at the Louisiana State University Health Sciences Center in Shreveport, agreed that the timing wasn't right for the sensitive, cold-blooded reptiles to expand their range.

"There are no snakes in Ireland for the simple reason they couldn't get there because the climate wasn't favorable for them to be there," he said.

Other reptiles didn't make it either, except for one: the common or viviparous lizard.

Ireland's only native reptile, the species must have arrived within the last 10,000 years, according to Monaghan.

So unless St. Patrick couldn't tell a snake from a lizard, where does the legend come from?

Scholars suggest the tale is allegorical. Serpents are symbols of evil in Judeo-Christian beliefs˜the Bible, for example, portrays a snake as the hissing agent of Adam and Eve's fall from grace.

The animals were also linked to heathen practices˜so St. Patrick's dramatic act of snake eradication can be seen as a metaphor for his Christianizing influence.