No Snakes in Ireland?

This whole snake on the loose thing has got me freaked. So I can't stop panicking (I have a serious fear) and I've been keeping my feet up since the incident.
My final paper is due next week in Non-Fiction and as I can't get this snake thing out of my system I feel the only way to let go is through writing about it in my crazy rantings of a insane and scared snake-hater.
For the longest time I've known Ireland was snake free and that in and of itself is something for sure. But surely snakes lived there at one point before being banished by St. Patrick in Lord only knows what year, right? Otherwise how would they've been banished in the first place? If after all these years how come they haven't made their way back. Don't get me wrong I understand it's an island but what about pets and zoos and just nature taking it's course. Is it really possible to banish a species? Or is it all too good to be true? As if the drinking and fields of green green grass isn't enough of an incentive for some... I don't know I don't get it. But this is what I'm gonna find out. Hey, maybe it really is a wonderful place to live. We'll c...