The New Zealand fauna is one of the most interesting in the world. It includes many unexpected elements and likewise lacks certain well known and otherwise widespread groups.

The New Zealand land mass may be described as subcontinental, in so far that it is probably a remnant of a more extensive land mass, but it has been isolated for a long time. Hence it has had no connection with other land masses which received many of the more advanced groups of animals and plants after its isolation. Thus mammals and other more recently evolved groups did not have access to New Zealand and this is reflected in the insect fauna. The long isolation has permitted the continued existence of primitive insects which might otherwise have become extinct through competition. The insect fauna shows some relationships to the fauna of South America and to New Caledonia, but overall most authorities regard it as being basically a peripheral one of the Australian region, for the reason that the majority of the components of the fauna have close relationship to Australian forms and also because some Australian elements are lacking often without any valid or obvious reason. Possible temporary or partial land connections with the Antarctic in the south and New Caledonia, New Guinea, north Australia in the north during the Mesozoic and early Tertiary may have made possible insect immigration from both these areas. There appears to be a faunal relationship with Tasmania due to a common source in Antarctica, and a relationship with Queensland and the lands to the north of Australia.

The uniqueness of some of the elements of the New Zealand fauna is shown in many groups. The primitive Peloridiid bugs are well represented and restricted to the southern areas of Australia and Chili and to New Zealand. This restricted distribution to southern lands is exemplified also by other families of bugs, and by some midges and beetles. Whether such a distribution points to a southern continental connection between land masses or whether it can be explained as the persistence of relics of former world-wide distributions followed by extinction in the northern continents, is still a matter for contention amongst zoogeographers.

The distance between Australia and New Zealand of 1,000–1,200 miles is not prohibitive for minute or flying insects. Such insects could make successful journeys across this distance when assisted by the prevailing westerly movement of the weather systems. There seems little doubt that successful dispersal across the Tasman Sea and South Pacific has been effected, at least over the past 20,000 years, and that successful establishment of many of the insects involved has occurred in New Zealand.

Man has been responsible for the introduction, either accidental or otherwise, of many insects into New Zealand over the last 150 years. Approximately 1,100 such species are known. A large number of these introduced insects have become pests of man, of his crops, or of his animals.