Rodentia is an order of mammals also known as rodents, characterised by two continuously-growing incisors in the upper and lower jaws which must be kept short by gnawing.
Common rodents to Australia are rats and mice.
Rats are various medium sized rodents. Rats are distinguished from mice by their size; rats gernerally have bodies longer than 12cm.
The best-known rat species are the Black Rat and the Brown Rat. The group is generally known as the Old World rats or tru rats, and originated in Asia.
A typical rat will be 15cm to 20cm long with a further 20cm of tail. The Black Rat is nocturnal and omnivorous, with a preference for grains.