A possum (plural form: possums) is any of about 70 small- to medium-sized arboreal marsupial species native to Australia, New Guinea, and Sulawesi (and introduced to New Zealand and China). The name derives from their resemblance to the opossums of the Americas(the name is from Algonquian wapathemwa, not Greek or Latin, so the plural is possums, not possa or possi).
Possums are quadrupedal diprotodont marsupials with long tails. The smallest possum, indeed the smallest diprotodont marsupial, is theTasmanian pygmy possum, with an adult head-body length of 70 mm (2 3⁄4 in) and a weight of 10 g (3⁄8 oz). The largest are the two species of bear cuscus which may exceed 7 kg (15 lb 7 oz). Possums are typically nocturnal and at least partially arboreal. The various species inhabit most vegetated habitats, and several species have adjusted well to urban settings. Diets range from generalist herbivoresor omnivores (the common brushtail possum) to specialist browsers of eucalyptus (greater glider), insectivores (mountain pygmy possum) and nectar-feeders (honey possum).
Threat to native plants and species
The common brushtail possum was introduced to New Zealand by European settlers in an attempt to establish a fur industry. There are no native predators of the possum in New Zealand, so its numbers in New Zealand have risen to the point where it is considered a serious pest. Numerous attempts to eradicate them have been made because of the damage they do to native trees and wildlife, as well as acting as a carrier of bovine tuberculosis. By 2009, these measures had reduced the possum numbers to less than half of the 1980s levels – from around 70 million to around 30 million animals.
Since 1996, possum fur, obtained from about two million wild-caught possums per year, has been used in clothing with blends of fine merino wool with brushtail possum fur – variously known as Ecopossum, Merinosilk, Merinomink, possumdown, eco fur or possum wool. Possum fur is also used for fur trim, jackets, bed throws, and possum leather gloves.
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.
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.
Residual trap catch index
A method for estimating possum abundance based on sampling populations by means of traps.
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.