Why are there no snake in Ireland?

The common story states that Saint Patrick was requested to rid the country of snakes. He cast the serpents into the sea, and his prayers prevented replacements. While not a bad myth, it is false. The last snake in Ireland died out during the last ice age, some 10,000 years before Patrick was born. Modern herpetologists claim the reptiles' extinction was due to habitat destruction. Some argue they simply were unable to adapt to the extreme cold and harsh conditions. Today, the climate of Ireland is ideal for reptiles, and there are over 50 reptile species in the British Isles. However, the native reptiles in Ireland are two lizard species—common lizard and viviparous lizard.

As for why St. Patrick was specifically requested to rid the country of the serpents, there is a theory, but also no hard proof. Many historians think that snakes, specifically the phallic symbols, represented pagan religion. So Patrick getting rid of them symbolized the beginning of Christianity in Ireland.