Western quolls are about the size of a domestic cat. They are coloured a rufous brown and have 40–70 white spots on their backs with a creamy white underside. Their spots actually help diminish their outline from the moon at night when these animals hunt. Western quolls have five toes on their hind feet and granular pads. With large eyes and pointed ears, they are well adapted for nocturnal life. They have a black brush on their tails that extends from halfway down to the tip. Females in this species are smaller than males.
Western quolls are found in south-western corner of Western Australia. They inhabit wet and dry sclerophyll forests, including contiguous Jarrah Forest and mallee. These areas consist of open forest, low open forest, woodland, and open shrub.
Western quolls are solitary, mostly terrestrial nocturnal predators. They are most active around dusk when they hunt. These animals move swiftly on the ground, climb efficiently, and may dig or occupy existing burrows. During the day they seek refuge in hollow logs or earth burrows as dens and save energy by lowering their body temperature during sleep. Western quolls have large home ranges which they mark with their scents. Males spread out over about 15 square kilometers and typically overlap with several female ranges. Although males share their large territories with smaller female territories, females do not cross theirs with other females. Most female home ranges contains around 70 hollow log dens and 110 burrows.
Western quolls are carnivores. These animals feed on large invertebrates and any small animal they can. This includes lizards, birds, frogs, spiders, insects, and small mammals; the largest they will eat is the size of a bandicoot or parrot.
Little is know about the mating system in Western quolls. Male and female quolls meet up only to mate. As seasonal breeders, they mate between late April to July, and have a peak in June. During this time, Western quolls tend to take up large areas of habitat, and females aggressively defend their territory. Most litters range from 2 to 6. The gestation period lasts 16-23 days which is followed by the young living in their mother's shallow pouch. After another 7-15 weeks, the young outgrow the pouch and are left in the den while the female forages for food. Western quolls become independent at 18 weeks and are weaned at 23-24 weeks. They become reproductively mature at one year of age. The young disperse in November before taking up their own territories.
Main threats to Western quolls are land clearing, inappropriate fire regimes, use of pesticides by surrounding farmers, grazing by stock and feral herbivores, illegal shooting, accidental drowning in water tanks, being hit by motor vehicles, entanglement in barbed wire fencing, and poisoning are all responsible for their disappearances. Feral cats have a massive impact; both predation and competition narrow room for Western quolls. As more land became less suitable for living in, these animals are forced to move elsewhere.
According to the IUCN Red List, the total population size of Western quolls is under 10,000 individuals. This species is currently classified as Near Threatened (NT) on the IUCN Red List and its numbers today remain stable.