No, St Patrick didn’t drive them out (nor the snakes, as I found out last year), apparently they never made it there at all. Here’s Professor Ian Montgomery from Queen’s University to explain:
“The origin of the Irish mammal fauna is very interesting because the major process is one of glaciation.
“During the last ice age, most parts of Ireland were covered, as was Britain, and as the ice retreated animals from the south moved northwards.
“They moved through continental Europe. They got into Britain, but they didn’t get into Ireland because the sea level rose too quickly.
“As a result, Ireland was left without moles, whereas moles managed to get into Britain.”
He goes on to say that we’re actually missing out on loads of brilliant animals in Ireland, like weasels, some bats and the pygmy shrew. It’s why David Attenborough never comes to visit.
Another side-effect of not having any moles is that there’ll never be an Irish remake of Infernal Affairs/The Departed.