St Mirin and the Snakes of Cumbrae

The story is in Wikipedia's article on Great Cumbrae, and it is a transfer of the well-known St Patrick story to a Scottish island. Wikipedia also notes that the Norwegian fleet may have used the island's east coast as an anchorage in 1263 before the Battle of Largs, and that the island once had many standing stones. The claim that there are no snakes is simply a folk claim, and no source is given.