The animals commonly referred to as pack rats are actually rodents belonging to the genus Neotoma, which encompasses over 20 distinct species often known as woodrats. These medium-sized rodents are characterized by large eyes and ears, and they are not closely related to the Old World rats that are often considered pests.
The colloquial name “pack rat” or “trade rat” originates from their unique collecting behavior. When a woodrat encounters an object it finds desirable, it will often drop whatever item it is currently carrying, such as food or a twig, to carry the newly found item back to its dwelling. This habit of collecting and “trading” small items led to the common name.
North American Geographic Range
The woodrat genus Neotoma has an extensive distribution that spans the North American continent, reaching from the boreal regions of Canada down into Central America. Their range extends from the Yukon and Northwest Territories southward through the entire United States, reaching as far as Nicaragua and western Honduras. This broad geographical footprint means that different species have adapted to vastly different climates and topographies.
The Bushy-tailed Woodrat (Neotoma cinerea) claims the widest range, occupying much of western North America. The Eastern Woodrat (Neotoma floridana) is found across the eastern United States, extending west into the Great Plains. Species like the Desert Woodrat (Neotoma lepida) and the Southern Plains Woodrat (Neotoma micropus) are concentrated in the arid and semi-arid landscapes of the Southwest and northern Mexico.
Key Habitat Preferences
Woodrats occupy environments that range from low, hot deserts to cold, rocky slopes well above the timberline. All species select for habitats that provide immediate, secure shelter from predators and extreme weather conditions. This preference leads them to specific structures like canyon walls, talus slopes, and rocky crevices.
Altitude significantly influences species distribution, with some woodrats, such as N. cinerea, found at elevations up to 3,700 meters. In lower, more arid regions, the choice of habitat often involves dense, protective vegetation. For example, the White-throated Woodrat (N. albigula) frequently establishes its den at the base of prickly pear or cholla cacti, utilizing the sharp spines as a natural defense. The Southern Plains Woodrat is associated with dry grassland environments featuring cactus and mesquite growth.
The Architecture of the Pack Rat Midden
The defining feature of the woodrat’s dwelling is the midden, a complex structure built from an accumulation of collected debris. These middens are fortified, multi-chambered homes constructed from sticks, rocks, cactus joints, bones, and whatever available detritus the animal can gather. The structure offers protection because woodrats cannot survive prolonged exposure to extreme heat, cold, or direct sunlight.
The longevity and structural integrity of the midden are maintained by a unique binding agent: the woodrat’s own urine. The animal frequently urinates on the debris pile, and in the arid environment of the American Southwest, this urine crystallizes into a hard, amber-colored, resinous material sometimes called “amberat.” This crystallization acts as a cement, gluing the collected materials together into a solid mass that can persist for tens of thousands of years, making the middens valuable ecological time capsules.
Within this protective shell, the woodrat creates distinct interior spaces. These chambers include a central nest area, typically lined with soft, shredded plant material, as well as separate caches for food storage. The midden’s fortified exterior and organized interior are strategically placed in naturally secure locations, such as under large rock ledges, in caves, or around the base of a spiny yucca or cactus.