Pack rats, classified under the genus Neotoma, are native North American rodents known for collecting various items, earning them the nickname “pack rat.” Also called woodrats, these animals build large nests known as middens where they hoard plant material, debris, and sometimes shiny objects. Their size varies significantly depending on the specific species and its native environment.
Overall Size Range of North American Pack Rats
The Neotoma genus encompasses species that share a similar body plan but differ in maximum size. The total length of a pack rat, measured from the nose to the tip of the tail, falls within a range of about 12 to 18 inches (30 to 46 centimeters).
The average weight for these rodents is equally variable, spanning from approximately 4 ounces (120 grams) up to 21 ounces (600 grams) in the largest individuals. This wide weight range reflects the genus’s ecological diversity, including species adapted to arid deserts and high-elevation forests. Males are often larger than females across many species, a form of sexual dimorphism. The largest pack rats can be comparable in size to a common Norway rat, while smaller varieties are less bulky.
Significant Species and Their Corresponding Dimensions
The Bushy-tailed Woodrat (Neotoma cinerea) represents the upper limit of the genus’s size. These robust animals can reach a total length of 18 inches, with a body length of around 10 inches. The largest individuals weigh up to 21 ounces (600 grams), making them substantial native rodents in North America. This species is identifiable by its long, thick, and distinctly bushy tail, which gives it a squirrel-like appearance.
Conversely, the Desert Woodrat (Neotoma lepida) is one of the smaller representatives, suited for the arid environments of the Western United States. It measures between 11 and 15 inches in total length, with a significantly lighter average weight. Adult Desert Woodrats generally weigh between 4.3 and 12.3 ounces, rarely exceeding 350 grams.
The White-throated Woodrat (Neotoma albigula) falls between these two extremes, exhibiting a moderate size and a distinctive patch of white fur on its throat.
Physical Features That Distinguish Them From Common Rats
Pack rats are distinct from invasive Old World rats, such as the Norway rat or the Roof rat, and possess several key physical characteristics that aid in identification. The most obvious difference is the appearance of the tail. Pack rats possess a tail that is covered in hair, often dense and sometimes bushy, particularly in the Bushy-tailed Woodrat species.
In sharp contrast, common invasive rats have a tail that is noticeably naked, scaly, and lacking in significant fur coverage. Pack rats also tend to have much larger, more prominent ears that often appear relatively hairless. Their fur is generally soft, fine, and clean in appearance, often colored gray or cinnamon brown on the back with a distinct white or lighter-colored underbelly and feet.
Common invasive rats typically have a coarser, greasier coat and smaller, less conspicuous ears relative to the size of their head. These native rodents also have large, dark, bulging eyes, which reflect their mostly nocturnal nature. These combined features—the hairy tail, large ears, and soft fur—identify these animals as native woodrats rather than invasive European species.