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.