Agrenia riparia is a widely distributed northern species, with records from Norway, Sweden, central Alaska (Fairbanks), northwestern Siberia (S Taimyr: Putorana) (Babenko, 2002), and northeastern Siberia (Magadan). In Scandinavia it tends to replace A. bidenticulata as a stream bank species in the forested regions, whereas A. bidenticulata is more common in arctic and alpine tundra. In the zone of overlap the two species can be separated by the mucronal seta (present in A. bidenticulata, absent in A. riparia). In winter animals the mucro and claws are shortened. Reproductive males have shorter and finer setae on Abd. IV–VI than nonreproductive males.