Tuesday, March 17, 2015

Happy Snakes Patrick's Day!

Happy St. Patrick's Day!

Every year on St. Patrick's Day, I share pictures of snakes. 

One of the legends surrounding St. Patrick is how he rid Ireland of snakes.  The story says that Patrick was in the middle of a 40 day fast when he was attacked by snakes.  Enraged by this intrusion, he chased the snakes into the sea and banished them from Ireland forever.

The real story of why Ireland has no native species of snakes does not involve an angry saint.  Instead, Ireland's lack of snakes can be attributed to ice.  During the last glacial maximum (ice age) which peaked around 11,000 years ago, three-quarters of Ireland was covered by a sheet of ice.  The remaining fringe of land was too cold to be inhabited by snakes (and most other animals). 

As the glaciers retreated, Ireland was temporarily connected to Great Britain and mainland Europe by a land bridge.  The existence of this bridge allowed some species to repopulate the island, but not snakes.  When the glaciers melted this land bridge was covered by the sea, severing the connection and limiting the number of native terrestrial species on the island.

Mid-Michigan was covered by glaciers during the same glacial maximum, chasing away our snakes and most other species as well.  However, because Michigan is not an island, we have not experienced the same post-glacial isolation.  In the last 11,000 years many species have recolonized Michigan, including seventeen species of snakes. 

Here are three of those snakes.

Northern Water Snake (Nerodia sipedon)

Eastern Hognose Snake (Heterodon platirhinos)

Common Garter Snake (Thamnophis sirtalis)

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