Pack rats, properly known as woodrats, are native North American rodents belonging to the genus Neotoma. These solitary creatures are recognized for their habit of hoarding materials, which earned them their popular nickname. Woodrats build and maintain elaborate shelters in diverse habitats, from deserts to forests. They are primarily nocturnal, meaning they are most active under the cover of darkness, which helps them avoid predators and extreme temperatures.
The Defining Behavior of Collecting
The woodrat’s compulsive hoarding of objects gave rise to the name “pack rat.” This collecting instinct is not limited to natural building materials; they are notoriously attracted to small, unusual, or shiny human-made items. Objects like keys, bottle caps, jewelry, coins, and pieces of foil are often carried back to their nests.
This behavior sometimes leads to “trading.” If a woodrat is carrying an item and encounters a more attractive object, such as a glittering coin, it will drop the less-valued item to pick up the new one. This exchange leaves the original item behind, earning them the secondary moniker “trade rat.”
Construction of the Midden
The collected items, both natural and man-made, are used in the construction of the woodrat’s home, a massive structure called a midden. These complex shelters often reach up to four feet across, resembling a beaver dam built on land. The midden is built from an assortment of materials like sticks, twigs, plant debris, rocks, and cactus spines, which serve as fortification against predators and buffer against extreme temperatures.
Inside, the woodrat creates a softer nest chamber lined with shredded plant fibers for sleeping and raising young. The longevity of these structures is remarkable because the woodrat’s viscous urine, high in crystallized calcium compounds, solidifies the detritus and acts as a preserving glue. This process can mummify the contents, creating fossil middens that persist for tens of thousands of years.
Diet and Foraging Habits
Woodrats are primarily herbivores, consuming a wide variety of plant materials available in their specific habitat. Their diet includes leaves, seeds, nuts, fruits, and bark, and they will also consume insects opportunistically.
A notable adaptation, especially in desert species, is their ability to consume plants that are toxic or high in defensive chemicals, such as certain cacti. They obtain all necessary moisture from the plants they eat, meaning they do not require a separate source of standing water. Woodrats cache food within their middens, storing plant material to ensure sustenance, especially during colder months.