Arthropods are active during the winter in temperate regions. Many use the seasonal snowpack as a buffer against harsh ambient conditions and remain active in a refugium known as the subnivium. While the use of the subnivium by insects and other arthropods is well-established, far less is known about winter community composition, abundance, biomass, and diversity and how these characteristics compare with the community in the summer. Understanding subnivean communities is especially important given observed and anticipated changes in snowpack depth and duration with changing climate. We studied winter and summer insects and other arthropods using pitfall trapping in northern New Hampshire, where snowpack is still relatively intact. We found that compositions of the subnivium and summer arthropod communities differed. The subnivium arthropod community featured moderate levels of richness and other measures of diversity that tended to be lower than in the summer community. More striking, the subnivium community was much lower in overall abundance and biomass than the summer community. Interestingly, some groups and species of arthropods were dominant in the subnivium but either rare or absent in summer collections. These putative “subnivium specialists” included one spider (order: Araneae), Cicurina brevis (Emerton, 1890), and three rove beetles (order: Coleoptera, family: Staphylinidae) Arpedium cribratum Fauvel, 1878, Lesteva pallipes LeConte, 1863, and Porrhodites inflatus (Hatch, 1957). This study provides a detailed account of the subnivium arthropod community, presents novel concepts, and establishes baseline information on arthropod communities in the North American northeastern temperate forest.