Saint Patrick may have brought Christianity to Ireland, but there's little evidence that he's responsible for the nation's lack of snakes. The absence of serpents on the Emerald Isle was puzzling to Europeans for hundreds of years, but modern science offers a few simple solutions to this ancient mystery.
Ireland is surrounded by water, which has protected it from natural snake migrations so far. New Zealand, Iceland and Greenland also are devoid of slithering reptiles, which is due partially to the oceans and seas that separate them from larger bodies of land. Ireland hasn't always been an island though. Continents and islands split from a single land mass tens of thousands of years ago thanks to a process called "continental drift." While the land masses move only a few inches a year, centuries of drifting has created distinct hemispheres and continents.
Ice Age and Climate
Since Ireland was once part of a large landmass, you may be wondering why snakes didn't float away with it after separation. It's actually likely that snakes once inhabited Ireland. However, the ice age that ended about 10,000 years ago would have wiped them out. Snakes rely on external sources of warmth to survive. Their cold-blooded nature would have prevented them from surviving the extremely cold temperatures of an ice age. While Ireland isn't too cold for snakes these days, it isn't exactly a paradise for slithering reptiles either. The relatively cool climate of the Emerald Isle helps discourage snakes from establishing themselves there.
St. Patrick Mythology
Since nearby England as well as other islands do support an indigenous population of snakes, Ireland's lack of serpents was a source of legend since the dark ages of Europe. According to local mythology, Saint Patrick drove every snake from the island when one of the unfortunate creatures disrupted his 40-day hilltop fast, according to National Geographic. Scientific evidence suggests that snakes actually were gone from Ireland long before St. Patrick began spreading Christianity there around 432 AD.
Pets and Invasive Species
While Ireland may not have a natural population of snakes, that doesn't mean there are none on the island at all. Snakes became a popular novelty pet in Irish households for the first decade of the 21st century. Ownership of these reptiles was seen as a symbol of wealth or unique taste. Economic decline in the following years prompted many snake owners to set their pets loose to save money, so Irish residents have had a few surprise encounters with large snakes in recent years, according to First Things. The brown catsnake and Aesculapian snake are among the several reptile species listed as potentially invasive and harmful to Ireland's ecology.
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