San Diego Natural History Museum--Your Nature ConnectionSDNHM Field Guide
Woodrat photo courtesy Glenn Vargas, California Academy of Sciences

Neotoma species
Woodrat
(also known as "pack rats", "trade rats")

Family: Muridae

Subfamily: Sigmodontinae (includes deer mice, harvest mice, grasshopper mice, woodrats, cotton rats)

Description

Woodrats have a rat-like appearance, with long tails, large ears and large black eyes. They are distinctly larger than the deer mice, harvest mice and grasshopper mice, and usually slightly larger than the cotton rats. The three species of woodrats found in southern California and Baja California can be distinguished from each other by size and coloration.

The Desert Woodrat (Neotoma lepida) is the smallest of the three species, with a total length of approximately 282-305 mm (11.3 - 12.2 inches). It is a pale gray with light undersides, but the fur on the throat region is gray at its base; the tail is distinctly bicolored.

The White-throated Woodrat (Neotoma albigula) is also gray, with a tail that is distinctly bicolored, but the hairs on the throat region are white at the base next to the skin. This species is slightly larger in size than the Desert Woodrat, ranging in total length from 282 - 400 mm (11.3 - 16 inches). The Dusky-footed Woodrat (Neotoma fuscipes) is a medium-sized woodrat, grayish brown with a pale underside. It is approximately 260-439 mm (10.4-17.6 inches) long, and the tail, which is about half of this length, is only faintly bicolored. The woodrats can be distinguished from the "city" or Old World rats (Rattus) in two ways:
  • The throats and breast region of the woodrats are white or very pale, whereas they are gray on the rats.
  • The woodrat tail is covered with hairs and the scales are not easy to see while Rattus tails are clearly naked and scaled.

Range and Habitat

Woodrats are found throughout California and Baja California. The Dusky-footed Woodrat is found statewide in California (except in the desert regions and High Sierra) and in the northwestern region of the Baja California peninsula. The White-throated Woodrat is found in the extreme southwest desert region of California and the Valle de Mexicali in Baja California. The Desert Woodrat occurs in the southern half of California and the entire Baja California peninsula. In regions where there appears to be an overlap of range for these species, each is found usually in different habitats.

Natural History

Behavior: Woodrats are generally nocturnal. They frequently carry small items in their mouths, including typical campsite trash, and much of this is added to their houses.

The presence of woodrats is usually obvious by the large houses built from sticks, twigs, cacti, horse and cow manure, and other bits of plant materials and man-made debris. These houses are above ground, frequently beneath a rock outcrop, in a rock pile, partially under a shrub or within a large branching prickly pear cactus, or at the center of agave patches. These elaborate dwellings help protect the woodrat from seasonal temperature extremes (measurements show the inside temperature rarely exceeds 88 degrees) and predators, although rattlesnakes are known to share these nests.

Reproduction: The breeding season and number of litters per year varies with the species of woodrat. The Dusky-footed Woodrat breeds almost throughout the year, with usually more than one litter per year (rarely can have up to five per year). The White-throated Woodrat has only one small litter per year in the spring, and the Desert Woodrat (N. lepida) may have up to two litters per year, in late winter or spring. There are usually one to three young in each litter, though the Desert Woodrat may have as many as four.

According to James Cornett, the young open their eyes at twelve day and are weaned at from sixteen to forty-two days depending upon the health of the mother and the size of the litter. Lactation demands may be so great on the mother that she sometimes dies after weaning.

Diet: It is rare but not impossible to see wood rats out in the day, although their usual time to forage and collect nest material is at dusk and during the night. They eat a variety of foods depending on their habitat. The Dusky-footed Woodrat eats primarily woody plants, including the leaves, flowers, nuts and berries. It has been shown to forage above ground. It drinks water, but can survive without it, relying instead on leaves and fungi.

The Desert Woodrat and White-throated Woodrat eats a variety of buds, fruits, seeds, bark, and leaves. In desert habitats, the Desert Woodrat feeds on creosote, cholla and prickly pear; the White-throated Woodrat feeds on a variety of cacti and in some regions, branches of juniper. These desert animals do not need to drink water but require quantities of succulent vegetation including the prickly pear cactus and agave for moisture. The distribution of these plants may determine the woodrats range. The cactus spines and partially eaten cacti litter the entrance of their houses.

Metabolism: Woodrats are noted for their ability to metabolize oxalic acid, a substance that is highly toxic to other mammals. The woodrat also absorbs large amounts of calcium from the intestine and excretes it in the urine as a precipitate of calcium carbonate. Why they do not form kidney stones is unknown.

Concerns

Throughout North American deserts woodrats are an important food source for kissing bugs which live on animal and human blood. These bugs, frequent inhabitants of nests, are the vector for Chagas disease caused by the parasite Trypanosoma cruzi. This disease is not a problem for people in this country, but can be in other parts of the western hemisphere.

References

Cornett, James W. Wildlife of the North American Deserts. 1987. Nature Trails Press. Palm Springs, California.

Ingles, Lloyd G. Mammals of the Pacific States. 1965. Stanford University Press, Stanford California.

Schmidt-Nielsen, Knut. Desert Animals, Physiological Problems of Heat and Water. 1979. Dover Publications, Inc. New York.

Schoenherr, Allan A. The Natural History of California. 1992. University of California Press.


Text by Dr. Paisley Cato
Photo courtesy Glenn Vargas, California Academy of Sciences

Field Guide: Mammals | Field Guide Feedback Form