A possum is any of about 64 small to medium-sized arboreal marsupial species native to Australia, New Guinea, and Sulawesi (and introduced to New Zealand). 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.) Possum is also used in North America as a short form of Opossum. The possum's rank odour is due to its large musk glands located behind each ear.
Possums are small marsupials with brown or grey fur, ranging in size and weight from the length of a finger or 170 grams (6 ounces) (pygmy possums and wrist-winged gliders), to the length of 120 centimetres (four feet) or 14.5 kilograms (32 pounds) (brushtails and ringtails). In general, though, the larger possums are about the same size as a well-fed domestic cat. All possums are nocturnal and omnivorous, hiding in a nest in a hollow tree during the day and coming out during the night to forage for food. They fill much the same role in the Australian ecosystem that squirrels fill in the northern hemisphere and are broadly similar in appearance.
Possums are commonly found in suburban areas, where they are often considered pests owing to their habit of eating fruit, vegetables, flowers and tender young shoots from gardens, and nesting in roofs. The loud hissing, crackling territorial call of the male Common Brushtail may also be a problem for suburban residents. Natural deterrents which play upon the possum's acute sense of smell are often employed to discourage them. These include cloves of garlic, camphor or naphthalene. As a native species in Australia, possums are protected by Australian regulations, even when they reside in urban neighbourhoods, and cannot be baited. If captured, regulations stipulate that they must be released within a small radius of the capture site as they are territorial creatures. Preventative measures such as blocking off their access to the roof spaces or building a possum nesting box for an alternative home are instead recommended.
Although the Common Brushtail and (to a lesser extent) ringtail possums have adapted well to the urban environment, many of the lesser-known species are reduced in number, threatened, or endangered.
They soon escaped into the wild where they have thrived as an invasive species with great numbers: around 60 million individuals estimated. There are no native predators of the possum in New Zealand. There have been numerous attempts to eradicate them because of the damage they do to native trees and wildlife, as well as acting as a carrier of bovine tuberculosis. For New Zealand, the introduction of possums has resulted in as much of an ecological disaster as the introduction of rabbits has been in Australia.
About two-thirds of Australian marsupials belong to the order Diprotodontia, which is split into three suborders: the Vombatiformes (wombats and the Koala, 4 species in total); the large and diverse Phalangeriformes (the possums and gliders) and Macropodiformes (kangaroos, potoroos, wallabies and the Musky Rat-kangaroo).