These little things have recently made their way from nearby Australia. It is not well suited to the colder and wetter conditions of New Zealand so it is unlikely that it will ever become well established here. As a result, its numbers are very small and you are very unlikely to see one. The white-tail is a bit more common and does bite, although it is not particularly painful and won't cause any problems.
Female redback guarding egg sac
Image Courtesy of Wiki Commons