Other bumbles may show white, but those species are also striped, so look for them in that grouping.
Western bumble bee, Bombus occidentalis
The Western bumble shows white on T4 and T5.
The White-shouldered bumble is a large bumble bee with white on the front of the Thorax and a golden yellow abdomen. Lisa’s father-in-law describes it as “wearing white oversized shoulder pads”. Just in time for football season!
White-shouldered bumble bee, Bombus appositus
See individual species accounts for more details and images.
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.
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?
