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.
"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.
(Related news: "Fear of Snakes, Spiders Rooted in Evolution, Study Finds" [October 4, 2001].)
Anyone in Ireland looking for serpents to exile would probably have to settle for the slow worm, a non-native species of legless lizard that is often mistaken for a small snake.
First recorded in the early 1970s, the species is thought to have been deliberately introduced in western Ireland in the 1960s, according to Ireland's National Parks and Wildlife Service.
However the reptile doesn't appear to have spread beyond a wildlife-rich limestone region in County Clare known as the Burren.
(Related: "Farming Decline Threatens Ireland's Orchid Oasis" [June 24, 2003].)
Snakes on an Irish Plain?
In the future, genuine Irish snakes are a possibility, Monaghan said.
Pet snakes deliberately released by their owners would be the most likely source, though they wouldn't be welcome.
"No alien species is without risk to well-established fauna," Monaghan explained.
"The isolated nature of an island population makes Ireland highly vulnerable to any introduction, no matter how well-meaning or misguided."
Henry Kacprzyk, curator of reptiles at the Pittsburgh Zoo & PPQ Aquarium, said that Ireland's indigenous wildlife would not be prepared for snake introductions.
Invasive snakes such as the brown tree snake have already wreaked havoc in Guam and other island ecosystems, he added.
Nor would getting rid of any such unwanted creatures be as easy as St. Patrick made it look.
"I don't want to completely burst the celebratory myth of St. Patrick," Kacprzyk said. "I want to keep some of it alive."
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