This species occurs along the Pacific Coast, from southern California to southern British Columbia, with scattered records from the east side of California’s Central Valley.
Analyses suggest very high population decline range-wide, including range size reductions, persistence reductions, and relative abundance declines. The level of population decline is difficult to ascertain, with more surveys needed within this species’ historic range. This is because the species co-occurs with Bombus vosnesenskii (a very common bee that is difficult to discern from B. caliginosus in the field) which may lead many collectors/observers to mis-identify this species. Read More