The White-shouldered bumble bee, Bombus appositus, is easily identified in the field by a combination of large size, bright white shoulder, black band between the wings and the entire abdomen a golden yellow.
Lisa’s father-in-law described this species as looking like they were wearing white shoulder pads. Sports analogies for the win!
It should be noted that there are three (3) additional color morphs of this species, at lease one of which can be encountered as close as Oregon’s Willamette Valley. They show mix of yellow or white on the scutum and yellow or white on the scutellum. Reference Bumble Bees of the Western United States for a visual.
Similar Species
No other species is similar in appearance.
Please reference the Embedded Range Maps page to better interpret # of observations per ecoregion.
The White-shouldered bumble bee,Bombus appositus, is one of our larger and more distinctive species. It is found mainly on the eastside, both on the east side of the Cascades, across north central Washington and then down and into the Blue Mountains, in the southeastern part of the state.
There have been detections over the years both on San Juan Island and also on the north side of the Olympic mountains, including as recently as July 2020, so it appears to not be solely restricted to the east side of the state.
Van dyke bumble bee,Bombus vandykei, photo by Lisa Robinson
I (DJ) have many fond memories associated with this species. First and foremost, I got the photo (below) and learned this species on a multi-day trip into Stehekin, NCNP to do a NPS sponsored bio-blitz with some of the rockstars of the native bee world: Jamie Strange, H. Ikerd, Terry Griswold and Chris Looney, to name drop a few. What a nice introduction to some amazing people and fun evenings around the campfire getting to know each other.
van Dyke bumble bee, Bombus vandykei
Second, the encounter documented above also shows an important reason why native bees in general, and bumble bees in particular, are the best pollinators for the money–from the perspective of the plant. It demonstrates the foraging behavior of constancy.
The general way that constancy works is that a bumble bee leaves her nest colony for the first time as a worker and stumbles across a flower that offers the needed resources: pollen and nectar.
Not really knowing what she is doing, she figures out how to get her reward. Once she figures it out she looks for a similar flower (same plant species) and is able to figure out even faster how to extract the goods and move on. Now she is efficient with this flower type.
At that point she hones in on every flower of that plant species that still has resources to offer (if the flower has just been visited, the nectar is probably gone and will need to refill over some period of time) until she is fully loaded and goes back to the colony to unload, or runs out of untapped flowers of that species. At that point, if her load is not full, she will look for another flower type and repeat the process.
This behavior, going to the same flower type time again and again is called constancy. The reason why it is so important to the plant species involved is that this greatly increases the probability that the pollen will be spread to many other plantsof the same species, resulting in successful pollination and increasing the “percent seed set” for the fertilized flower. Win-win for both plant and bee.
Please reference the Embedded Range Maps page to better interpret # of observations per ecoregion.
Field guides on bumble bees do a good job show the possible range of color combinations a given species may exhibit across its’ entire range. Trying to condense that into a visual that shows the full spectrum is challenging.
I say that because when I compare the individuals in these photos with the color schema’s shown in Bumble Bees of the Western United States, there are some inconsistencies.
These photos show that T1 sometimes shows yellow, not always black. The field guide shows the rear of the thorax (scutellum) to be black where these photos show some yellow present.
This is a good example of two different lessons. First, bee coloration is variable and may not align exactly with the examples in the book. Different than with most birds, for example.
Second, because color is variable, depending on the species, absolute identifications from photos may not be possible. Photographs rarely capture taxonomic level details like cheek shape. A collected specimen can be keyed out later as a voucher specimen of what was photographed. This should rarely be needed as a good working knowledge of our common species is relatively easy to acquire.
van Dyke bumble bee, B. vandykei
Field ID Tips
A primary field mark to distinguish the van Dyke bumble from others is that the van Dyke shows T3 with yellow.
van Dyke bumble bee can be confused with Two form bumble bee mainly because they are fairly similar is size and both striped black and white/yellow. At least, I have been confused and assumed B. bifarius because bifarius is much more common. Part of the learning curve.
The van Dyke bumble has yellow on T3. T3 is black on the Two form bumble bee. The van Dyke bumble bee also lacks a black inverted triangle on the rear of its thorax.
Based on color patterns, van Dyke bumble bee and yellow forms of California bumble bee are similar. From my experience the van Dyke bumble bee is smaller bodied.
van Dyke bumble bee, B. vandykei
When you look at the pollen gathered on her corbiculum (photo above), you can see it is first one color (orange) and then it shifts to a 2nd color (washed out brown). The bumble started with collecting pollen (and nectar) from first one species, flower after flower (orange pollen). Finally, when it became too difficult to find flowers that had not already been visited, the individual bee switched to a 2nd species of flower and is now demonstrating constancy between flower types–as shown by the change in color of the pollen collected.
van Dyke bumble bee, B. vandykei
One might see the photo above and think Yellow head bumble bee, but this individual shows T2 as black.
The Yellow-faced bumble bee, Bombus vosnesenskii, is a common bumble bee on the west side of Washington state and appears to be spreading into the eastern portion. There is some speculation that the drastic decline in numbers of the Western bumble beeBombus occidentalis, during the 1990s created an opportunity for expansion of the Yellow-faced bumblebee.
Please reference the Embedded Range Maps page to better interpret # of observations per ecoregion.
Yellow-faced bumble bee, B. vosnesenskii
Field ID tips
The Yellow-faced bumble bee is a species that can be easily recognized once one has encountered them in the field. They have colonies that may contain upwards of 1,000 individuals, in contrast to most bumble bee species which have totals more in the 300-500 range.
When you encounter B. vosnesenskii you rarely just find a single individual. More often they will be numerous in the area. With their bright black coat and the distinctive and strongly contrasting yellow on the head, front of thorax (scutum) and most eye catching, on T4, they can be identified with relative confidence. Their fur is relatively even, giving them a well groomed appearance.
The Obscure bumble beeis a trickier identification challenge. The color patterns are similar, with yellow on face, front of thorax and T4. The fur on the Obscure bumble bee is less even and more shaggy. A definitive field mark is on the underside of the abdomen where the Obscure bumble bee shows white hairs.
An easier photo might be capturing the face to be able to discern if the individual has a long or short cheek/facial structure. Bombus caliginosis has a long cheek and therefor a longer face relative to Bombus vosnesenskii who has a much shorter cheek length and a shorter face.
Obscure Bumble bee, B. caliginosus
Note the white hairs on the lower abdomen of this Obscure bumble bee, an important field mark to separate B. caliginosus from the more common B. vosnesenskii.
Yellow-faced bumble bee, Bombus vosnesenskii with friend
The Western bumble bee, Bombus occidentalis, was until recently the most widely distributed bumble bee species across Washington state. The range map below shows just how wide spread it was.
Then a disease outbreak spread from captive raised bumble bees used for tomato hothouse operations wiped out an estimated 95% or more of the wild population.
Even now, over two decades later, the numbers of Western bumble bees have not rebounded. They can reliably be found in and around Colville, but in other parts of the state encounters are much more sporadic.
Historical distribution. Notice the detections across both sides of the state.
Please reference the Embedded Range Maps page to better interpret the # of observations per ecoregion.
Field ID Tips
The golden yellow scutum, black body and large white T4 and T5 are the classic field marks for the Western bumble bee. Also note the black head and face. There is a color morph found in the Blue Mountains, and in Oregon, which has the scutellum (rear of the thorax) yellow, rather than black. It should still be distinctive as a Western bumble.
Similar Species
No other species has white on the end of its’ abdomen and golden yellow on the front of the thorax.
I do find that that in the field, Western bumble bees can feel a bit like Bald faced hornets, with white at the end of the abdomen. Could it be an example of mullerian mimicry?
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.
California bumble bee, Bombus californicus
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.
Please reference the Embedded Range Maps page to better interpret # of observations per ecoregion.
californicus or fervidus?
Bumble bee taxonomists are having discussions about whether Bombuscalifornicus is a full species or a subspecies of Bombusfervidus, based on gene pheneology and mitochondrial markers. Bombuscalifornicus 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.
California bumble bee, Bombus californicus
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)
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!
aka Vancouver bumble bee, Bombus vancouverensisnearcticus
Two form bumble bee, Bombus bifarius Note the inverted black triangle on scutellum (thorax, rear of wings)
The Two form bumble bee is (was) a small bodied species common on the east side of Washington state. It can be found on the west side as well, but seems to thrive on the east side. Note the black triangle pointed at the abdomen, on the rear of the thorax (scutellum).
There is some confusion after the Vancouver bumble bee, Bombus vancouverensis, was separated from Bombus bifarius as to how to separate them and where do the two species occur separately and where do they overlap. While I (DJ) first thought B. vancouverensis was the red form found in the San Juans Islands and up north in the central part of British Columbia, now it seems that it may not be a correlation between external colors and species distinction.
I had the pleasure of putting this question to Dr. James Strange and his response was: “As for bifarius in eastern WA, they should all be considered B. vancouverensis (for now). A few of us started to look at splitting vancouverensis into two species: vancouverensis and nearcticus but we don’t have the data to do that yet. We will have to see if the data bears out the split, but for the foreseeable future vancouverensis is the name that has taxonomic precedence”.
Please reference the Vancouver bumble bee page for more discussion on the new taxonomy.
Please reference the Embedded Range Maps page to better interpret # of observations per ecoregion.
Two form bumble bee, Bombus bifarius
Field ID tips
Identification of the Two form bumble bee, Bombus bifarius is fairly straight forward for the most common color morph in Washington. There is a black band between the wings and a black inverted triangle coming from that black band down to the abodomen.
The abdomen is distinctly striped:
T1 = yellow or white
T2 = black (maybe some red)
T3 = black (maybe some red)
T4 = yellow or white
T5 = black
Similar Species
The Red-belted bumble bee, B. rufocinctus, with its’ many color morphs can be confusing to separate. Red-belted lacks a black inverted triangle, and T2 should show some yellow.Bombus rufocinctus has a very short cheek and therefor a very short face.
The non-standard color morphs of B. bifarius all show the black inverted triangle below the black wing band. The abdomen however may have some or lots of red on T2 and/or T3.
Two form bumble bee, Bombus bifarius
This color morph shows red on T3. This individual (above) was seen in the NE corner of Washington state.
Two form bumble bee, Bombus bifarius
Note the black inverted triangle under the black wing band.
The Yellow head bumble bee, Bombus flavifrons, is a common bumble bee in Thurston county. It is found around the state, but is most commonly encountered on the west side of Washington.
Please reference the Embedded Range Maps page to better interpret # of observations per ecoregion.
Yellow head bumble bee, Bombus flavifrons
Notice the cloudy front of thorax (black hairs mixed in).
Field ID Tips
The thorax is cloudy.
T1 and T2 are often bright yellow, contrasting with the black rear.
The majority of individuals I have encountered have black on T3, T4 and T5. In the San Juan Islands, and I hear from a reliable source, around the Mountain Loop highway, T3 may be replaced with red. An example is shown at the bottom of this page.
Yellow head bumble bee, Bombus flavifrons
Yellow head bumble bee, Bombus flavifrons
Yellow head bumble bee, Bombus flavifrons
Photographed on San Juan Island, WA This is a color morph that shows RED (orange). (above)
The Red-belted bumble, Bombus rufocinctus, is the species of bumble in Washington state that show the greatest diversity of color patterns. If you check Bumble Bees of the Western United States, by Koch et al, you will see that not all red-belted bumbles even show red! This is one of my most challenging species to identify. Catching one to look at under a hand lens, to confirm cheek shape may be helpful.
To quote from that reference guide: “similar to many color patterns shown by both western and eastern NA bumble bees…small bodied, short-haired, short face.” emphasis added.
Field ID Tips
I think that maybe identifying Red-belted bumble bees may be easier than I have made it out to be. They have been the species “most mysterious” from a confident field ID perspective–since there is so much variability in their color patterns.
Having said that, T2 usually shows some level of yellow, and at least as I know so far, the color morphs in Washington are all of the “shows some red” group, rather than the forms where the red is black. So, T2 with yellow, some red on abdomen.
What else. Small bodied bee, hair length relatively short and even. Very short cheek–this is one time where being able to capture an individual, cool it briefly and example the cheek ratio can be very helpful for a confidential identification.
Similar species
The next element is process of elimination from other possible bumble bees. Within Washington, there are four possible bumble species that might cause confusion: the Black tail bumble bee, the Two form bumble bee, the Hunt bumble bee and the Forest bumble bee.
The Red-belted can be distinguished from the Black tail bumble bee,B. melanopygusbecause the Red-belted’s scutum is yellow, while the Black tail scutum is cloudy.
The Red-belted can be separated from the Two form bumble bee, B. bifarious, because the Red-belted lacks the black inverted triangle.
The Fogbelt bumble bee, Bombus caliginosus, is a species I have found mainly on the southern slopes of the Olympic Mountains. It is not uncommon in that area, but is easily confused with a similar looking species, the Yellow-faced bumble bee, Bombus vosnesenskii.
The common name gives you a sense of it’s preferred habitat.
Please reference theEmbedded Range Maps page to better interpret # of observations per ecoregion.
Fogbelt bumble bee, B. caliginosus Note the white hairs on the lower abdomen.
Field ID tips
The Fogbelt bumble bee has a yellow face with a long cheek, yellowscutum and yellow on T4, with the rest of the bee being black. A key field mark can only be seen with a view of the underside of the abdomen. As seen in the pictures above and below, B. caliginosus shows white hairs on its stergites (underside of abdomen).
Similar Species
The only similar species to the Fogbelt / Obscure bumble bee is the Yellow-faced bumble bee, B. vosnesenskii. They both show yellow face, yellow scutum and yellow T4. A primary way to distinguish between the two is to look on the underside of the abodomen (stergites). Vosnesenskii has a solid black underside. As seen in the picture below, caliginosus show white hairs on its stergites (underside of abdomen). A more subtle field mark is that B. vosnesenskii has relatively even hairs while the Obscure bumble bee has hair a little more unkempt.
Obscure bumble bee, Bombus caliginosis Note the white hairs on the lower abdomen
