Through their manipulation of soil physical and chemical properties, earthworms have the potential to increase nutrient mineralization and benefit crop production. However, this effect is dependent on numerous factors including earthworm densities and ecological strategies. In addition to impacting density, soil environmental conditions may limit earthworm activity to specific times during the growing season, moderating their effects on nutrient availability and crop growth. The purpose of this study was to determine the active period of earthworms to better assess their potential impact on crop productivity in dryland wheat production systems in the Palouse region of northern Idaho and eastern Washington, U.S.A. Earthworm community density, age structure, diversity, and soil moisture and soil temperature were monitored over a 14-month (April 2014-June 2015) period in six dryland wheat fields. All earthworms collected were exotic species, with the endogeic species, Aporrectodea trapezoides being predominant at all sites (87% of all adults identified). Allolobophora chlorotica, Lumbricus terrestris and Aporrectodea tuberculata were collected at lower frequencies (1.8-6.4% of adults). Mean densities ranged from 14 to 75 individuals m(-2), and populations transitioned to aestivation beginning in mid-June of both years. All earthworms were active (no aestivating individuals) on 56.9% of the sampling dates in 2014 and 71% of the days in 2015. A short active period and average densities at most sites of less than 100 individuals per m(2) suggest that the impact of earthworms on crop growth may be limited in conventional, dryland agricultural fields of this region.