The woylie or brush-tailed bettong (Bettongia penicillata) is a small, critically endangered mammal native to forests and shrubland of Australia.

A species was first described by J. E. Gray in 1837,[3] based on the skin and skull of an adult male obtained by the Zoological Society of London, and placed with the British Museum of Natural History.

The ring around the eye of the woylie is pale, and its muzzle is longer and more pointed than the boodie, and less than Gilbert's potoroo (Potorous gilbertii), with which it once shared an overlapping distribution range.

The population in south-west Australia persisted into the twentieth century, seemingly surviving the mass extinction of similar mammals in the previous decades, and was collected at temperate locations near Margaret River, by G. C. Shortridge in 1909, and by Charles M. Hoy in 1920.

Gilbert noted woylies on the tidal flats of the Swan Coastal Plain and river itself, and their nests amongst clumps of grass and the hollows of trees, observing a preference for woodlands of Eucalyptus wandoo.

The decline was probably caused by a number of factors, including the impact of introduced grazing animals, accompanied by land clearance for pastoralism and agriculture.

The introduction of the European rabbit (Oryctolagus cuniculus), may have also placed the population under pressure, especially in arid and semi-arid regions, by direct competition or the degradation of habitat.

[20] Although it may eat tubers, seeds, insects, and resin exuded from Hakea laurina, the bulk of its nutrients are derived from underground fungi, which it digs out with its strong fore-claws.

[21] The austral summer and autumn seasons provide woylies with the fruiting bodies of hypogeous fungi, and around 24 fungal taxa are known to be consumed.

[22] Woylies have been observed eating the large seeds of Australian sandalwood, Santalum spicatum, a nutritious food that the animal is known to place in a shallow cache for later consumption.

Populations of woylies introduced to an island off the coast of South Australia consume mainly plant material, tubers and roots, seeds and leaves, and beetles, a diet regarded as unusual for the species.

The species was used for meat during the earlier colonial period, although that practice did not persist amongst the colonists because, while it was readily available and easily captured, the skinning of the animal is said to be difficult.

Although similar species of marsupials were often regarded as agricultural pests, the woylie did not always acquire this reputation, and was sometimes identified as a non-destructive native animal.

[10] Native predators of the woylie include the wedge-tailed eagle (Aquila audax), a large raptor thought to have been a significant influence on their mortality.

[24][17] Woylies are natural excavators, dubbed an "ecosystem engineer" by one researcher, moving about six tonnes of soil annually in its quest for food.

[10] The body is arched as the animal hops away, with the head held low and the tail extended, using a bipedal motion in lengthy bounds to evade a potential predator.

The exact cause of the rapid population crash was uncertain, although researcher Andrew Thompson found two parasite infestations in woylie blood.

A major program to control feral cats has seen the number of both woylies and numbats begin to increase, although populations remain vastly reduced from even recent decades.

[17] In 2011 the species was reported as living mostly in open sclerophyll forest and Mallee Woodlands and Shrublands eucalypt assemblages, with a dense low understorey of tussock grasses.

[31] The reintroduction of control programs for predators saw the species successfully conserved at sites including Perup, Tutanning and the Dryandra Woodland reserves.

[32] It was reintroduced to large fenced landscapes at Newhaven in the Northern Territory in August 2021[33] and to Mallee Cliffs National Park in NSW in September 2021.

[36] It is a key species in the faunal reconstruction project within the Dhilba Guuranda–Innes National Park on South Australia's Yorke Peninsula, formerly named the Great Southern Ark (2019),[37] renamed Marna Banggara in June 2020 in honour of the Narungga people, who are the traditional owners of the region.

A trapping survey estimated that there are over 200 in Dhilba Guuranda-Innes National Park as a result of the Marna Banggara project as of March 2023[update].