By Annie Hill
The original article in Russell Lights | Ngā Mārama o Kororāreka, June 2025 edition

Possums were successfully introduced to Aotearoa New Zealand in the 1850s to provide fur, food and ‘sport’. Not particularly valuable in any of those roles, they have become an unmitigated disaster, the damage they cause far outweighing their benefits. It took years for them to be regarded as pests and at one time it was suggested that 70,000,000 infested the country (although scientists reckon the carrying capacity of the motu is no more than 48,000,000), but extensive pest control has reduced the number to a ‘mere’ 30,000,000.

In spite of the name, Australian possums are not related to the opossums of the Americas. The 70+ species of possum, Phalangeridae, were given that name by Sir Joseph Banks when he first came across them, believing them similar to the American opossums, Didelphimorphia, the only order of marsupial still surviving in the Americas.

Possums appear quite heavy and thickset, varying widely in size, with adults measuring 65 to 95 cm long and weighing between 1.4 to 6.4 kg. The largest live in the South Island. They have dense body fur, a pointed snout, large, pointed ears and a thick, bushy, prehensile tail which enables them to move equally well in trees or on the ground. Their colours include gold, brown, silver-grey and black. They’re nocturnal and immensely adaptable, living and thriving anywhere with shelter and a varied food supply, from suburbia to dense forest.

Generally solitary, and territorial, possums use scent markings to avoid contact, and only seek each other out for mating. Although they actively compete for food sources and dens, they’re rarely aggressive towards one another and on encountering, usually just stare with their ears raised. Where resources are plentiful, young, mature females will often stay near their mothers, which gives them a higher survival rate than males, who have to travel farther in search of new nesting sites.

They’re not monogamous and some males will sire several offspring in a season, while others are completely unsuccessful. Like nearly all marsupials, the female carries her young in a pouch. After 16–18 days gestation, the 15mm long, 2g baby is born, then has to work its unassisted way up through the mother’s fur to the pouch, where it finds the teat and latches on for 4 to 5 months. It stays with its mother until it is 7–9 months old, either left in the den, or riding on her back. Females reach sexual maturity when they’re a year old; males do so at the end of their second year. Even though they have only one young per annum, possums bounce back immediately, as soon as predator control is paused. While some are predated by domestic and feral dogs and cats, this makes no significant difference to their numbers.

Because they’re omnivorous and ubiquitous, they cause a vast amount of damage to our native flora and fauna, as well as attacking orchards. While most of their diet consists of leaves, they eat native birds and their eggs, land snails such as Powelliphanta, and invertebrates, including weta. Consuming buds, flowers, fruit, berries and nectar, they compete with native birds and reptiles for food. They often concentrate on eating one tree at a time until all the edible parts are consumed, which prevents the tree recovering; favourite trees such as rātā or kamahi can be seriously affected.

In 1990, possum populations were out of control and in some parts of the country up to 90% of coastal pōhutukawa stands had been killed, which resulted in the creation of ‘Project Crimson’, planting over 300,000 pōhutukawa and rātā, to save these iconic trees. Every night, possums eat about 21,000 tonnes of vegetation: just pause and consider the sheer immensity of this.

They’ve been filmed eating the eggs and chicks of kōkako as well as the eggs, chicks and even adults of many other native birds, including kererū, kiwi, harrier hawk, fantail, muttonbird, and tūī. They also compete for nesting spaces with birds, by occupying holes in tree trunks: should they find it already occupied for example, by a nest of kea, they will happily kill and consume the chicks. Moreover, browsers like possums significantly impact the ability of our native forests to sequester carbon, which will end up costing the country even more billions in buying carbon credits.

Dairy and deer farmers have the worry of possums spreading bovine tuberculosis. While this is unfortunate for the farmers, at least it releases more money for their control than would probably be given for conservation alone. If the programme were to stop, the potential cost to the economy has been estimated at $5 billion over 10 years. (It was stopped from 1979 to 1984 and the number of infected cattle herds snowballed, while infected wild animals expanded from about 10% to 40% of the motu.)

In the 1960s, there were hardly any possums in Northland, but by the 1990s, 10–15 million were estimated to live here. Since 2022, PFR has caught 27 possums, with 22 in the last 12 months, and 19 in 2025 alone. This sudden increase may well be due to the fact that the Russell State Forest has been closed for predator trapping, while they focus on eradicating deer.

These cute, furry little animals are a terrible menace; please support PFR by reporting sightings.

Possum with bird’s egg. Russell Kiwi Protection Archive.