In its native land the possum is up against dingoes, bush fires and less palatable vegetation. In New Zealand there are no predators and lots of very palatable vegetation. As a result, possums have a huge impact on New Zealand ecosystems.
The Australian brush tailed possum was introduced into New Zealand in 1837 to establish a fur trade.
The possum has a thick, bushy tail, a pointed snout and long, fox-like tapering ears.
Size and weight of possums varies greatly across New Zealand. Adult possums are typically between 65 and 95 cm in length, and can weigh anywhere between 1.4 and 6.4 kg.
There are two general colour forms, grey and black, although each of these varies greatly.
- Grey possums are generally a clear grizzled grey on the body, with the face pale grey, darker around the eyes and on the side of the snout, and white at the base of the ears.
- Black possums are generally a deep, yellowish-brown, tinged with rusty red. The ears have little or no white at the base and the tail is nearly entirely black.
The sternal gland stains fur on the throat and chest a dark rusty red, more prominently in males than in females, and more prominently in grey than in black possums.
Behaviour and life cycle
Possums can live anywhere that has shelter and a varied food supply. They can be found all across New Zealand, with the exception only of the high rainfall, mountainous terrain of Fiordland.
Possum and rat both preying on a thrush nest
Forests are the major habitat, especially hardwood mixed forests, where possum densities are particularly high. Forest/pasture margins are also known to support very dense populations.
While possums feed mainly on leaves, they are also known to take buds and flowers, fruits, ferns, bark, fungi, invertebrates, native birds and eggs, land snails and carrion.
Possums are nocturnal, although in winter starving or sick animals may emerge to feed in the afternoon.
Threat to native plants and species
Possum damage on Mamaku, Pirongia Forest Park
The damage to native forests can be seen all too clearly in many areas. Possums ignore old leaves and select the best new growth. In some areas they have eaten whole canopies of rata, totara, titoki, kowhai and kohekohe.
Possums compete with native birds for habitat and for food such as insects and berries. They also disturb nesting birds, eat their eggs and chicks and may impact on native land snails.
Dairy and deer farmers have the added worry of possums spreading bovine tuberculosis.
Possums are a nuisance in suburban gardens, and sometimes even indoors.
Stoats and possums eat kea
Evidence shows stoats and possums are eating kea. Researchers using nest-cameras have witnessed the gruesome reality inside defenceless kea nests invaded by stoats and possums in South Westland. Find out more about possums eating kea.
The Department of Conservation (DOC) is charged with the care of New Zealand's native plants and wildlife. Possums are a threat to these values and in fact, the survival of whole ecosystems is affected by the possum.
DOC commits resources to possum control at priority sites to ensure long-term survival of species and the ecosystems that support them.
Signs that possums are present
Tracks (‘pads’ or ‘runs’) are often most evident where possums emerge from forests to feed on pasture. They are also visible in forests when possum numbers are high.
Frequently used trees show extensive surface scratches. Bark biting, usually a series of horizontal scars, can be seen on a variety of native and introduced trees and shrubs. Often the same trunk, marked repeatedly, becomes heavily scarred.
Faecal pellets are usually about 15-30 mm long, 5-14 mm wide, crescent shaped slightly pointed at the ends and found singly or in groups; colour and texture vary with diet. Leaves browsed by possums have torn rather than cut edges, with the midrib and lower part of the leaf often partly remaining, unlike insect browse.
Possums are distinctive feeders, leaving the ground littered with broken branches, discarded leaves, or partly eaten fruits of native plants.
Dark brown urine trails may be seen, particularly if possums have been feeding on kamahi or five-finger, both of which stain the urine.
Hunting/shooting, trapping and poisoning are the main methods of control for possums.
If you are planning a pest control operation enrol for the Animal Pest Control Methods field based course.
The course provides an overview of animal pests, their impacts and control methods (including the principles these are based on, and the task specifications DOC has developed).
The course covers all the legal requirements for animal welfare and handling toxins. Working within the law is vital to allow pest control agencies and community groups continued access to the full suite of animal pest control methods.
In particular, it describes the control methods most commonly used in DOC, and their advantages and disadvantages.
Monitoring your control
All operations require monitoring below are examples of methods used. Learn more about monitoring.
Residual trap catch index: A method for estimating possum abundance based on sampling populations by means of traps.
Wax tags: A method for estimating possum abundance based on sampling populations by means of interference with "wax tags" (scented ice-cube sized wax blocks).
Possum management in New Zealand
The National Possum Control Agencies (NPCA) was established in the early 1990s to co-ordinate strategic planning, standardise quality control and provide training and information exchange between agencies for possum control.
The member agencies of the NPCA are:
- TBfree New Zealand (formerly the Animal Health Board) is charged with eradication of bovine tuberculosis in farmed cattle and deer. To do this, it needs to control possums, which carry the disease in the wild and re-infect herds of animals adjacent to bush pasture margins.
- Regional councils have biosecurity obligations to control possums for animal health and conservation priorities. Councils are actively involved in possum control in urban and rural areas to reduce the spread of TB and to protect forestry and conservation values.
- Department of Conservation is charged with the care of New Zealand's native plants and wildlife. Possums are a threat to these values and in fact, the survival of whole ecosystems is affected by the possum. It commits resources to possum control at priority sites to ensure long term survival of species and the ecosystems that support them.
- Ministry for Primary Industries is the government agency that has overall responsibility for biosecurity issues. Possums are a threat to New Zealand's export potential because of the disease threat that possums pose. MPI keeps a close eye on all aspects of control operations.
Possum management and research websites