During 1837-40 the first Australian brushtail opossums (Trichosurus vulpecula, more commonly known as possums ) were introduced and liberated in New Zealand by private individuals and Acclimatization Societies wanting to establish a fur industry. Up until 1930 the spread of these nocturnal marsupials was accelerated by further releases, both authorized and illegal, of New Zealand-bred stock.

As early as the 1890s people were advocating control because the potential for damage to orchards and gardens was becoming evident. However, in 1920 a Professor of Botany and Zoology at the then Victoria University College of Wellington released a report supporting the possum, and stating that the harm to native forests was negligible. There followed a series of ineffective regulations until 1947, when heavier penalties for harbouring and liberating opossums were brought into effect and all restrictions on the trapping or killing of possums were cancelled. Finally, in 1951, a control measure was introduced - a bounty of 2s 6d a head to be paid on all killed possums from which skins had not been taken - a scheme that continued until 1960.

Possums number in excess of 70 million, even pushing sheep into second place, and it is thought that they currently munch their way through 21,000 tonnes of vegetation every day. They are also carriers of bovine TB, an added menace to the dairy, beef and deer industries. They pose a threat to the survival of native bush and to the indigenous fauna that rely on the tree fruits and flowers for food, to say nothing of the eating of eggs and killing of chicks.

Most travellers will encounter possums either when walking the tracks or when driving. Road kill possum is know colloquially as "road pizza": the relatively cute-looking, furry little creatures engender an almost pathological hatred in even the most mild mannered Kiwis who will swerve all over the road in order to run them over. Many believe a return to the old possum hunter days would provide the best solution to the problem with hunters getting a few dollars for each pelt and creating employment. The Department of Conservation continue with the controversial policy of poisoning which in the past has led to casualties amongst non-targeted bird species. But whatever the solution it is clear that if the possums are allowed to continue unchecked they will turn New Zealand into a barren wasteland