When people search for “wild rats,” they usually refer to two highly successful and invasive species: the Norway Rat (Rattus norvegicus) and the Roof Rat (Rattus rattus). Their common names—Brown Rat and Black Rat—suggest a simple difference in coloration. However, the reality of wild rat appearance is more complex, as many factors can alter their coat. While color provides an initial clue, proper identification requires looking beyond the shade of the fur.
The Color Profiles of the Two Major Wild Species
The Norway Rat, often called the Brown Rat, typically displays a coarse, grizzled grayish-brown or reddish-brown coat. This coloration is not uniform; the upper parts are generally darker, while the belly is much lighter, often appearing gray or a dull yellowish-white. This species has a robust, stocky build. Adult Norway Rats are the larger of the two main species.
The Roof Rat, conversely, is commonly known as the Black Rat, and its typical coloring ranges from a sleek, solid black to a dark, smoky gray. Their fur is generally smoother and softer in texture than that of their brown counterparts. Unlike the Norway Rat, the Roof Rat’s belly often shows less contrast with its back, sometimes being a paler gray or a light brown. This species possesses a more slender body type.
Why Color Can Be Misleading
Relying solely on color for identification can easily lead to mistakes because rat coats are subject to inherent variability. A so-called Black Rat may sometimes be dark brown, and a Brown Rat might appear quite gray depending on the light and the individual’s genetics. Young rats often have a darker, softer “baby coat” that they shed around six to eight weeks of age as they transition to their adult coloration.
Environmental and physiological factors can also alter the perceived shade of a rat’s fur over its lifespan. Older, darker-colored rats can exhibit a phenomenon known as “rusting,” where the black or dark fur develops patches of brown, sometimes due to age or dietary factors like a copper deficiency. Genetic variations like melanism can result in a completely black individual, even within a species typically considered brown. Conversely, albinism, resulting in a total lack of pigment, produces a pure white rat with pink eyes in either species.
Key Physical Features for Positive Identification
Since color is unreliable, a definitive identification relies on several consistent morphological differences between the two species. The most reliable physical characteristic to observe is the tail length compared to the body length. A Norway Rat has a thick, scaly tail that is always shorter than its head and body combined.
In contrast, the Roof Rat has a long, slender tail that is noticeably longer than its head and body combined, which aids in its arboreal lifestyle. Beyond the tail, facial features provide further clues. The Norway Rat has a blunt muzzle and small ears that do not reach its eyes when pressed forward. The Roof Rat has a distinctly pointed snout and large, nearly hairless ears that easily fold forward to cover its eyes.