Synonyms and other taxonomic changes
Species status for Bombus californicus is controversial as some authorities regard it as merely a subspecies or color variety of Bombus fervidus. Many Bombus californicus, especially from northern and eastern sites, are extensively yellow and therefore closely resemble Bombus fervidus, differing only in presence of black hairs on Terga 1-4. Lack of strong divergence in DNA barcodes and other molecular markers also indicate that this species pair is less distinct than other controversial species pairs.
Color pattern of typical Californian females as in vosnesenskii but with all black hairs on head instead of extensive yellow hairs. Also malar space long and legs gangly. In the eastern portion of its range its color converges on fervidus, and the most extensively yellow californicus specimens are very difficult to separate from typical fervidus (see comments on taxonomy above) but have at least some black hairs on the terga (these can be inconspicuous) which are lacking in fervidus.
In California often found in oak woodland savannah at relatively low elevation
Often visits California poppies and Mariposa lilies (as do other bumble bees). The Hosts section of its Discover Life species page
lists known floral associations based on specimen records and images.