Background/Question/Methods   Beetle banks are raised strips of grass that run across agricultural fields. In the United Kingdom these structures are widely used to provide over wintering habitat to ground beetles and other generalist predators that augment agricultural pest management. In European trials, Dactylis glomerata was shown to support higher populations of generalist predators than other grasses. In the northwest United States farmers are interested in whether native bunch grasses species perform as well as the best exotic species. Five species of native grasses and D. glomerata were sown on a beetle bank on an experimental farm. The objective of the study was to determine which grass species supported the highest numbers of predators. A secondary objective was to identify the functional factors associated with high beetle numbers, specifically vegetation structure and biomass and its temperature moderating effects. Beetle communities were sampled by taking soil cores and extracting the invertebrates with a berlese funnel. Vegetation cover was sampled with point intercept plots, structure with height measurements, and biomass was collected and weighed. Soil surface temperatures were measured with data loggers and compared with the temperature on a non-vegetated bank to estimate the insulation and shading effect of the stand of vegetation. p>Results/Conclusions   The tested grasses differed in biomass and vegetation structure. They also differed in their shading or insulation effect. The insulation effect increased from the second to third year, but the shading effect did not change between years. Grass species differed in the mean number of generalist predators per core. When the generalist predator guild was broken apart rove beetles (Staphylinidae) had significant differences, while spiders did not. Ground beetle (Carabidae) abundance did not differ significantly between grass species when grouped as a family, but some individual ground beetle species had significant differences, while others did not. The grass species that supported the highest predator abundances were also the species with the most vegetative biomass and the largest insulation effect. These functional factors were found to be significantly correlated with increased populations of several groups of predators in linear regression models. This study demonstrated that northwest native bunch grass species are at least as effective at supporting high generalist predator populations as the most effective species from European studies. The important factors are the ability of a grass species to create a dense layer of vegetation and litter that can moderate cold winter temperatures and increase the survival of generalist predators.