The title says it all, are there snakes in New Zealand? The short answer is NO, there are no native species of snakes living in the New Zealand wilderness. Read along for the more complicated and long answer.
While it is true that New Zealand does not have native land snakes, it has sea snakes that can travel long distances, even all the way from Australia and the smaller islands of South Pacific. The yellow-bellied sea snake and banded sea krait are both poisonous and potentially dangerous to humans and animals. Majority of sea snakes or the Elapidae family are poisonous. A close relative for the sea snake would be the more commonly known Cobra. The scientific name of the banded sea krait is Laticauda colubrina and the yellow-bellied is called Pelamis platurus. Luckily both sea snake species are very rare, and it is not likely you will encounter either of them in nature in New Zealand.
Because New Zealand has never had a snake population, the local wildlife would be very vulnerable against them. That is the reason why the authorities are very strict about snakes and proceed to eliminate the threat as soon as possible. Sometimes snakes find their way into New Zealand accidentally in ships or container transports, and the officials are generally quick to take action in such cases. New Zealand has lost more than one-third of its native bird species since the introduction of humans to the island, so this might explain the extreme measures taken against foreign fauna.
In ancient times when New Zealand was joined with Australia, there probably existed some snakes or similar creatures, but the change of temperatures and several ice ages made sure that the snakes in modern day New Zealand had to chance to survive. This would have taken place around 85 million years ago, which is a pretty long time ago considering that New Zealand has been inhabited by humans only about 700 years. In general, snakes do survive in colder climates, or they might hibernate during the colder months.
All in all, it is pretty remarkable that New Zealand does not have native snake populations, because the neighbouring Australia has all of the top 10 most dangerous snakes in the world.