Camponotus vicinus (Mayr) is a common ant species found in the Pacific Northwest. It is an important predator of many forest insect pests, a potential biological control agent, and is also a serious structural pest. However, little knowledge is currently available about its nest location and distribution. The study is designed to examine the biotic and abiotic factors in affecting the distribution of carpenter ants. Investigations during 1993 and 1994 showed that in conifer forests in northern Idaho, C. vicinus was found nesting mostly in fallen logs and tree stumps. The diameter of logs used as nest sites was 5–55 cm, but most nests were found in logs with diameters between 15 and 35 cm. Tree bark, duff, and wood beneath stones were also used as nest sites. Most nests were found in dry areas associated with an opening in the forest canopy. This kind of site can be called a C. vicinus carpenter ant zone. To study the effect of biotic and abiotic factors on nest aggregations of C. vicinus, five factors were tested in conifer forests of northern Idaho: habitat availability, food abundance, competition, moisture, and temperature. Competition is not a main factor in restricting the distribution of C. vicinus because food and habitat are relatively abundant throughout the forests. The main factors that restrict the distribution of the carpenter ant, causing colonies to aggregate in open and dry forest areas are an interaction between temperature and moisture during the daylight hours.