Bumble Bees of Washington State

The California bumble bee, Bombus californicus, has two distinct color morphs. The first is similar to the Yellow-Faced bumble bee, Bombus vosnesenskii, but California bumble bee lacks yellow hairs on the face.

The California bumble bee, Bombus californicus can be found on both sides of the Washington Cascades. On the west side, it is a regular member of the pollinating community associated with our native prairies, as documented by Dr. Susan Waters and her team conducting pollinator pathway studies on the remnants of our west side prairie habitats.

californicus or fervidus?

Bumble bee taxonomists are having discussions about whether Bombus californicus is a full species or a subspecies of Bombus fervidus, based on gene pheneology and mitochondrial markers.  Bombus californicus shares the same mitochondrial marker cytochrome-oxidase I (COI) with B. fervidus, supporting the single species perspective (Williams, et al. 2014).

Those findings are not aligned with results from a five (5) gene phylogeny study which concluded that B. californicus and B. fervidus were different species (Cameron et al, 2007).

The two species/forms meet along the eastern side of Columbia gorge.  I have not sampled there myself yet, but my understanding is that the individuals seen fit the field marks for one or the other species, suggesting some level of cross-breeding barrier.

Reasons to list B. californicus as a separate species on this site comes from two totally unrelated personal experiences (DJ).  First, when I was an young birder I learned the Oregon Junco as part of my wildlife biology training.  At that time there were two distinctly different forms: slate-side and Oregon (now there are at least 4!).  Because I only had to learn “Oregon Junco”, my brain has refused to easily remember the distinguishing characteristics—sad but true. We learn to the test. Sadly.

The second reason is political.  Our state and federal wildlife conservation laws offer much more protection for distinct species rather than subspecies or ecotypes.  By recognizing these as distinct species, it may make it easier to get one of them the protection they deserve when needed.

Third, what is a species? I once thought there were firm barriers between species, but then I took a Dendrology class in Forestry School and had learn the southern Oaks…and also learned how oaks hybridized across “species” to the extent that our responses to questions required identifying which two species were likely involved in the hybrid individual in question. Some very nice work was done on finches in the Galapagos Islands (Beak of the Finch). I find myself to be a splitter, focusing on adaptations to local conditions driving natural selection.

Field ID tips

The California bumble bee, Bombus californicus, has two distinct color morphs.
The black form has a yellow scutum and yellow T4. The face is black (this is a key field mark).
The yellow form is predominantly yellow and shows some black on T2 and T3. It also has a black alar (wing band)

Similar Species

Similar species for the black form are Yellow-faced bumble bee, Bombus vosnesenskii and the Obscure bumble bee, Bombus caliginosis. The California bumble bee is easily separated from these two similar species because it is the only one of the three with a black face.

The yellow form is very similar to the Yellow bumble bee, Bombus fervidus. The Yellow bumble bee has a totally yellow abdomen (T1 thru T4 yellow). The dark bands on abdominal tergites T2 and T3 of the California bumble bee are the key to separating the yellow form of this species from the Yellow bumble, B. fervidus.

This species and the Yellow bumble bee are sharing landscape level habitats in the Willamette Valley of Oregon. Seems like a great site for a field trip!