Brushtail possums are New Zealand's most destructive introduced pest. Brought from Australia in the nineteenth century, they now number in the tens of millions, devastating native forests, killing native birds, and spreading bovine tuberculosis. New Zealand spends millions annually on control, and the possum merino fibre industry has become a key part of the economic case for sustained trapping.
Before European settlement, New Zealand's forests had never known a browsing mammal. Its trees, birds, and plants evolved over millions of years in their absence — developing no defences against something that climbs, eats everything, and breeds without limit. When brushtail possums arrived, the result was a slow-moving ecological catastrophe that is still being reckoned with today.
A Deliberate Introduction
The brushtail possum was first released in New Zealand in 1837, brought from Australia to establish a commercial fur trade. This wasn't an accident or an act of ignorance — it was organised, funded, and enthusiastically supported by acclimatisation societies: government-backed organisations whose stated purpose was introducing European and commercially useful animals to make New Zealand feel more familiar to settlers.
The commercial logic was straightforward. Possum fur was valuable in European markets — soft, warm, and suited to coats, hats, and trim. New Zealand's vast, largely untouched forests looked like ideal habitat. The societies released animals across Southland first, then pushed releases progressively northward over the following decades. There were 38 recorded liberations from Australia between 1837 and 1898. Even as late as the 1930s, acclimatisation societies were lobbying for closed seasons to allow possum numbers to recover — actively protecting the very population they had created.
What the societies didn't — couldn't — fully account for was the absence of any natural check. In Australia, possums are kept in balance by predators: dingoes, pythons, large owls. New Zealand had none of these. It had, in fact, no native land mammals at all beyond two small species of bat. The forests were, in every ecological sense, defenceless.
Māori and the Paihamu
For Māori, the possum arrived as something entirely foreign — a creature without name, without place in mātauranga Māori, and without precedent in the ecosystems Māori had lived within and cared for over centuries. The word paihamu, used in te reo today, is simply a transliteration of the English word "possum" — a linguistic adoption that reflects the animal's colonial origins rather than any traditional relationship.
The forests being invaded were not abstract wilderness. They were wāhi tapu — places of significance, sources of food, medicine, and material, home to birds and plants woven deeply into Māori culture and cosmology. Kererū, kōkako, tūī, rātā, kōwhai — these were not background scenery but living connections to whakapapa and to the land itself. Their destruction by an introduced pest was, from a Māori perspective, an assault on the whenua that the colonists had neither the framework nor the inclination to fully understand.
Māori communities did adopt possum fur practically once the animal was established — as they incorporated many introduced materials — but there was no traditional knowledge of the paihamu to draw on, no customary relationship to guide its management. That framework, kaitiakitanga, would eventually inform how Māori approached possum control — but that is the second part of this story.
The Fur Trade: Rise and Collapse
Commercial possum trapping became a significant rural industry through the early twentieth century. Skins were processed and exported to European fashion markets, appearing as trim on coats and collars in department stores from London to Paris. For a time, the trade seemed to justify what the acclimatisation societies had built.
But the industry carried a structural problem it never solved: possums reproduce faster than they can be trapped. A single female produces young twice a year, and with no natural predators, every animal that escaped a trap lived to breed. Trapping peaked in 1981, when 3.2 million skins were exported — but even at that volume, it was nowhere near enough to meaningfully reduce the population.
Then demand collapsed. In the decades following World War II, synthetic alternatives flooded fashion markets. Attitudes toward fur shifted. Possum skin prices fell, trappers left the industry, and the commercial incentive that had partly sustained ongoing control evaporated. The population, already enormous, was left without any meaningful check.
The industry that introduced possums for profit, exploited them for profit, and walked away when the profit dried up left New Zealand with an ecological crisis that would take generations to confront.
What Possums Actually Do
Possums are opportunistic omnivores. They eat leaves, buds, fruit, flowers, fungi, insects, eggs, and chicks. They have particular favourites — rātā and kamahi suffer disproportionate damage — and they occupy tree hollows that would otherwise serve as nesting sites for kākāriki and saddlebacks. The volume of consumption across millions of animals prevents forest regeneration entirely in heavily affected areas.
As canopy trees die, the understorey loses protection. Ground-level plants disappear. The insects, lizards, and birds that depend on them follow. Possums have been recorded killing adults or young of tītī, kāhu, pīwakawaka, and tāiko, as well as destroying the nests of kererū and North Island kōkako. The damage cascades through entire ecosystems in ways that aren't always visible from the ground — which is precisely what makes it so dangerous.
Population estimates carry significant uncertainty — the terrain is vast, the animals nocturnal, and survey methods have varied over time. By the 1980s the population had reached an estimated peak of around 70 million — roughly equal to the sheep population at the time — though subsequent analysis suggests earlier estimates may have been high. What is not in doubt is the scale of damage: DOC has described possums as "one of the greatest threats to our natural environment."
The Damage You Can't See From the Ground
In the Papakai block of the Coromandel Forest Park, Department of Conservation staff captured aerial images that make the invisible visible. The images were taken during seed collection work connected to protecting native species from myrtle rust — a tree disease with the potential to weaken and kill pōhutukawa, mānuka, and rātā. What the aerial perspective revealed went beyond the myrtle rust mission.
The images show two adjacent sections of the same forest: one where predator control has been maintained consistently for more than 25 years, and one where control has been carried out only twice in the last decade.
The difference is stark. In the long-term control area, rātā trees show their distinctive red-brown flowering — healthy canopy, full leaf coverage. In the adjacent uncontrolled section, multiple dead rātā are clearly visible, stripped bare over time and standing above the surrounding bush.
"Those dead specimens really stick out," said Nick Kelly, DOC's Coromandel Operations Manager. "They're a trigger for what we term a 'top-down collapse' of the forest ecosystem." As canopy trees die, biodiversity at every level below them is compromised — birdlife, insects, native plants, and the rare species that depend on all of them.
The Coromandel forest being protected is home to Archey's frogs, Coromandel brown kiwi, Coromandel striped gecko, and what is believed to be one of the last populations of woodrose — an extraordinarily rare parasitic plant pollinated by short-tailed bats and destroyed by possums and rats. "You can wander through the forest and not necessarily see the impact of these introduced pests," Kelly noted. "What the aerial imagery shows us is what people do not see when they're out for a walk or a tramp."
Where Things Stand
Current estimates put the possum population at around 30 million — though as with all possum population figures, this number is difficult to establish with precision and the true figure may be higher or lower. What is clear is that despite sustained effort by the Department of Conservation, regional councils, and thousands of community trapping groups across the country, possums remain one of the most ecologically damaging species in New Zealand's history.
Predator Free 2050 — a national programme to eliminate possums, stoats, and rats from New Zealand entirely — represents an extraordinary level of national commitment to reversing what the acclimatisation societies began nearly two centuries ago. Progress is real and measurable: where control is consistently maintained, forests regenerate, bird populations stabilise, and the cascade of damage described above begins to reverse.
The challenge has always been sustaining that control economically over the long term. That challenge, and the unexpected answer found in the early 1990s, is the second part of this story. Read part two: From Pest to Premium.
Sources
- Department of Conservation. "Possums: New Zealand animal pests and threats." doc.govt.nz
- Hutching, Gerard. "Possums." Te Ara — the Encyclopedia of New Zealand. teara.govt.nz
- Parliamentary Commissioner for the Environment. "Possums, rats and stoats." pce.parliament.nz
- Predator Free NZ Trust. "7 surprising facts you should know about possums." predatorfreenz.org
- New Zealand Deerstalkers Association. "Possums in New Zealand." deerstalkers.org.nz
- Department of Conservation, Coromandel District. Aerial imagery and quotes: Nick Kelly, DOC Coromandel Operations Manager.
- Te Aka Māori Dictionary. "Paihamu." maoridictionary.co.nz
