Snakes in Ireland explanations

St Bede claimed that even a stowaway adder would die as soon as it took a breath of Irish air when the boat neared the shores.
But I'd imagine it's mostly seen as allegorical- still,why mainland Britain should have snakes and close by Ireland not is mysterious (consider the similarity of fauna between Papua New Guinea and Australia, particularly Queensland for comparison; New Guinea even has it's own dingo, called the whistling dog). I only learned recently that it became mandatory to cut Wimbledon lawns neatly in the early days of the tennis tournament after a player was bitten during a game.

Another explanation could be the casting-into-the-sea of some thing or things of serpentine appearance after Christianity took hold, note following piece from Irish LIbrary:

"Rude carvings of snakes adorn the pyramidal stones overlooking the plains of Dundalk in Louth County. This is on Killing Hill. The marvellous megalithic temple of New Grange, one of the finest antiquities of Ireland, has its curled serpentine monument.
The legends still floating about among the peasantry of the country parts of Ireland have frequent reference to the Piastra, Piastha, Worm, or Serpent. This creature is always in some lake, or deep pond. The Fenian heroes are recorded in ancient songs to have killed many of them. Fionn, in particular, was the traditional dragon-killer of Ireland."

We do have native reptiles in Ireland and I am not referring to politicians. I was greatly surprised to see lizards sunning themselves in the Bluestack mountains in South Donegal on a hike many years ago.