Re: http://www.straightdope.com/columns/read/2192/if-st-patrick-didnt-chase-the-snakes-out-of-ireland-what-did
I can’t boil this down to a concise “question”, but I’m still not sure I understand how Ireland remained relatively snake-free.
There are just so many examples of manunkind either accidently or purposely facilitating the introduction and spread of invasive species to pristine land masses! I speak as an embittered US backyard bird-watcher, plagued with the usual suspects-- aggressive house sparrows, starlings, etc.-- who were deliberately imported into the US because of their “beauty” and insect-catching ability.
Snakes aren’t beautiful, but surely some stowed away in trade vessels. And it’s hard to believe that people didn’t invent excuses to bring in other species of snakes for some supposedly beneficial reason.
Not too long ago, Japan acquired a “plague” of non-native raccoons because the popularity of a TV cartoon raccoon triggered a fad of owning raccoons as pets. Enough of them escaped, or were abandoned, to flourish in the wild.
I presume the Irish authorities are extremely vigilant in preventing such infestations, but their success may be attributable to the Luck of the Irish. 
Hawaii, New Zealand, Greenland, and Iceland also don’t have snakes. Why aren’t those islands populated with invading snake populations? Because they haven’t yet, but that doesn’t mean it can’t or won’t happen. It just hasn’t yet.
Take Guam as an example. It has no native snake population, but the brown tree snake is all over the place. (I lived there for 2 years in the 90s, I remember.) It was supposedly introduced to the island as a stowaway after WWII and flourished without natural enemies. If something similar happened to Ireland then it could have a snake population in the future.
Perhaps the human aversion to snakes contributed to the lack of consideration for beneficial purposes. Though that hasn’t stopped, for instance, the transplantation of anacondas to Florida via the exotic pet trade.
The number of snake species that would do well in Ireland is smaller than the number that would thrive in tropical and subtropical regions.
As a general rule, the further north you go, the fewer reptiles you find. We only have a couple of native snake species (and a few small lizards) in neighbouring mainland Britain.
You’d have to have quite a number of stowaways or escaped pets to reproduce, which is pretty implausible, even if they were capable of thriving in the wild in Ireland. And the British native varieties are highly unlikely to be in a position to become either stowaways or collectors’ pets in the first place.
For stowaways to happen, the varmints in question need to find some reason to live around shipping facilities, such that they hide in boxes and crates getting loaded into ships. For snakes, that could be rodents that live in those areas because of access to grains from human transport. But that presupposes the types of snakes native to the areas live sufficiently close to find that resource.