Many species of wood rats build complicated stick houses in which they live. In Washington, elaborate stick houses are sometimes built but are usually not occupied. In the attic of an old building near Pend Oreille Lakes, Stevens County, two large and complicated houses were discovered. These were built of sticks, paper and other debris and measured more than three feet in diameter. Three small, cup-shaped nests resembling those of a bird, made of soft grasses, moss, and shredded paper were found on the attic floor ten feet or more from the stick houses. These nests gave every indication of being used, while the piles of sticks contained no nests and seemed never to have been occupied. Near Moses Lake, Grant County, a wood rat house built in the rafters of an old shed was constructed entirely of tumbleweeds (_Salsola pestifer_). This house was spherical in shape and measured more than five feet in diameter. It appeared to be unoccupied and a wood rat, probably its builder, was living under the floor of the shed. Most wood rat houses consist of a half-dozen sticks arranged in a crevice in a rock pile or a cave. Wood rats were placing fresh material on a house in the Wenatchee National Forest on January 17, 1939, when there was two feet of snow on the ground and the temperature was hovering around zero. The house measured about one cubic yard and consisted of _Ceanothus_ leaves and steins, with some twigs of fir (_Abies_). It was built under a bunk in a broken-down cabin left by deer hunters. The collecting habit of the wood rat has gained it the name "pack-rat." Taylor (1920A: 91) lists the following materials from a wood rat nest on Mt. Rainier: _Nesting material_: rags, leaves, paper, thumb of a glove, string, thongs, oakum; _Food_: apple core, onion peel, bacon rind, raisins, 10 bars of chocolate, figs, puff balls, bread crust, meat scraps, cantaloupe rind, potatoes, dried apricots, lemons, mushrooms, beans, peanuts, banana, 15 lumps of sugar; _Miscellaneous_: dime, coffee can cover, paraffin from jelly glass, bones, 19 pieces of candles and several cakes of soap. As a rule only one or two wood rats are trapped at a given locality, indicating that the species is not gregarious. The presence of wood rats in a building, cave, mine tunnel, or talus slide can be detected in several ways. The white, mineral-like incrustation formed by the urine of many generations of wood rats is usually conspicuous on rocks near their homes. A strong musky odor pervades the atmosphere in every habitat occupied by wood rats. Wood rat feces, consisting of hard, black cylinders one-half inch long and three-sixteenths of an inch in diameter, are invariably found scattered on stones or exposed areas of ground. [Illustration: FIG. 108. Distribution of the bushy-tailed wood rat in Washington. A. _Neotoma cinerea occidentalis._ B. _Neotoma cinerea alticola._]