Rats and mice are small rodent mammals that are distinguished by perpetually growing chisel-like front teeth. One pair lies in the upper jaw, while the other pair is in the lower jaw.
In Australia, the most common feral rats and mice are the Black Rat (Rattus rattus), Brown Rat (Rattus norvegicus) and House Mouse (Mus musculus). These all have yellowing enamel on their front teeth and generally live in small to large groups.
The Black Rat or Roof Rat (Rattus rattus) is a medium-sized rat. The body is slender and 350 mm to 460 mm in length, nose to tail. The coat is silky smooth and is light brown or charcoal grey on the back, with a slightly lighter-coloured belly. The head is long with a rounded face, pointed nose and long whiskers. Eyes are large. Ears are prominent, large, thin and hairless. The tail is similar in colour to the upper coat, hairless, scaly and longer than the rest of the body (185mm to 255 mm). Although it is most active at night, it can be seen during the day and is unafraid of humans. An accomplished climber, it disfavours water and swimming, and prefers to stay near the nest when finding food.
The Brown Rat, Norway Rat or Water Rat (Rattus norvegicus) is a large-sized rat. The body is stocky and 330 mm to 470 mm in length, nose to tail. The coat is coarse and is grey-brown, sometimes black, on the back and sides, with a white to grey belly. The head is long with a stunted nose and mouth (muzzle), a straight face and long whiskers. Eyes are small. Ears are close together, set into the head, small and hairless. The tail is scaly, hairless and shorter than the rest of the body (150 mm to 215 mm). It is mostly active in the early evening and at night. They are excellent swimmers and travel long distances from the nest to find food.
The House Mouse (Mus musculus) body is rounded and 135 mm to 200 mm in length, nose to tail. The coat is soft and light-brown to black on the back with a white to light yellowish-brown belly. The nose is pointed with long whiskers. Eyes are black, large, prominent and bulging. Ears are large, rounded and generally naked. The tail is slender, generally hairless with circular rows of scales and is approximately the same length as the rest of the body (75 mm to 100 mm). Although they are good climbers, jumpers and swimmers, they prefer to stay close to their nest area.