Countries that have no native snakes include Ireland, New Zealand, Iceland and Newfoundland. Hawaii is one part of the United States that is also free of native snakes.
There are several reasons why snakes are not native to certain islands. One such reason is that snakes cannot get to isolated islands surrounded by vast amounts of water. In the case of Ireland, not only did the land bridge between England and Ireland disappear thousands of years ago due to rising waters, but Ireland's climate is too cold for cold-blooded animals. In fact, the only reptile native to Ireland is the viviparous lizard. According to legend, St. Patrick eradicated the snakes himself centuries ago.
Because snakes are so invasive, they are outlawed in those countries to which they are not native. They compete with the native species for food, putting native species at risk. It is a felony to possess snakes in Hawaii. New Zealand has a strict policy in regards to snakes: if a snake is spotted in the wild, specialists are sent to the area to eradicate the problem before reproduction grows out of control. Ireland is occasionally visited by sea snakes that swim to the country from neighboring islands or Southeast Asia.