New Zealand's largest gecko had been thought extinct on the mainland until a dead specimen was discovered in a mouse trap at Maungatautari in Waikato last month.

The find was the first time the Duvaucel's gecko had been seen on the mainland in almost 100 years, Maungatautari ecologist Chris Smuts-Kennedy said.

Before the discovery, the gecko was thought to only live on pest-free offshore islands, he said.

The discovery meant that the gecko could be living in other areas where there was thick native bush.