Possums are small marsupials with brown or grey fur, ranging in size from the length of a finger (pygmy possums and sugar gliders), to the length of a forearm (brushtails and ringtails). 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.
The two most common species of possums are also among the largest. The Common Brushtail and Common Ringtail possums are both frequently found in urban areas, often being considered pests because of their habit of eating fruit, vegetables, flowers and tender young shoots from gardens, and nesting in roofs.
To those unfamiliar with it, the very loud hissing, crackling territorial call of the male Common Brushtail has a nightmare quality. Since it is illegal to kill a possum in Australia, it is advised that the best way to deal with invading possums is to block off entrances to the roof at night while they are out foraging, and to either trap and remove them or to install a possum nesting box to give them an alternate home.
The Common Brushtail and Common Ringtail possums were introduced to New Zealand by Europeans in an attempt to establish a fur industry. They quickly escaped into the wild and the Brushtail in particular has become established in great numbers: around 60 million individuals. There have been numerous attempts to eradicate them because of the damage they do to native trees and wildlife. For New Zealand, possums have been almost as much of an ecological disaster as rabbits have been in Australia.
Although the Common Brushtail and (to a lesser extent) Ringtail possums have adapted well to European settlement, many of the lesser-known species are reduced in number, threatened, or endangered.
About two-thirds of Australian marsupials (magnorder Australidelphia) belong to the order Diprotodontia, which is split into two suborders: the Vombatiformes (wombats and the Koala, 4 species in total); and the large and diverse Phalangerida. This suborder contains about 80 species in 9 families. The 25 different possums account for 6 of those 9 families, the remaining three families contain the solitary Musky Rat Kangaroo, the potoroos and bettongs (10 species) and the kangaroos and wallabies (about 45 species).
Families of suborder Phalangerida: