Why there are no snakes in Ireland

To explain why there are no snakes in Ireland, a brief history of the geography is in order.

For tens of thousands of years on at least two occasions during the past 2 million years, Ireland must have looked like Greenland and Antarctica at the present day: frozen.  

Some 60,000 years ago, as the climate cooled at the beginning of each of the episodes of polar climate, the snows of winter would linger through the year until a time when one season's snow hadn't melted before the next winter's accumulation began.  The thickness of the snow would be so great that the underlying layers would compact into ice.  The ice and snow were hundreds and perhaps thousands of feet deep.  

When pressures a the base of the ice became to great, it behaved as a very thick molasses, rather than a solid and the ice masses began to ooze outwards in all directions from their core area.  The movement was slow, but the immense mass of the ice made it a irresistible force as it advanced over the land.  Any loose rocks and soil would be swept along at the base of the ice, and would be used as tools to abrade and pluck at the more resistant obstacles - a gigantic rasp scouring the surface, leaving only the strongest landforms surviving.  (David Drew, Department of Geography,  Trinity College, Dublin, Ireland, The Shape of the Land, 1989, Wolfhound Press, Camelot Press, U.K.)

The prevailing cold climate and the thick ice sheets that advanced across the country during the Ice Age combined to wipe out most, if not all, of the pre-existing wildlife or at least forced it to migrate to warmer areas.

In order to live and thrive in any location each organism requires an adequate supply of food and water and a suitable range of environmental conditions.  (Roy Alexander, Department of Geography, Chester College, Chester, Wildlife in the Countryside, 1989, Wolfhound Press, Camelot Press, U.K.)

It is true that Ireland is one of the few inhabited places in the world without snakes.  New Zealand is another.  Because snakes are cold-blooded, they also don't live in areas that are frozen year-round, such as polar regions. 

Only after the great freeze finally ended in Ireland some 15,000 years ago would a snake have been able to survive in Ireland -- and by then 12 miles of icy North Channel ocean water barred the way from England and Europe, a barrier no terrestrial snake could breach.  There are no snakes in Ireland today for the simple reason there is literally no way for a snake to GET to Ireland.  

Simply put, snakes cannot migrate across water.  That is the reason there are no snakes in New Zealand, a much larger island that Ireland situated across the Tasman Sea from Australia.  Saint Patrick never visited New Zealand.  There are no snakes there because the Pacific Ocean's water isolated New Zealand from Australia and Asia long before snakes evolved. 

Source: National Geographic World, May 1996, v. 247, Snakes are Almost Everywhere, p.7

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