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 name gives you a sense of it’s preferred habitat.
Please reference the Embedded Range Maps page to better interpret
# of observations per ecoregion.
Field ID tips
The Fogbelt bumble bee has a yellow face, yellow scutum 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).
The only similar species to the Fogbelt 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 short even hairs while the Obscure bumble bee has hair a little more unkempt.
It is not always easy or possible to get a good shot of the stergites. A field mark easier to document may be the length of the cheek. The Fogbelt bumble bee, Bombus caliginosis, has a long cheek. Vosnesenskii bumble bee Bombus vosnesenskii, has a short cheek. Check the face shape and pattern. Over time recognizing if the cheek is distinctively long or short can be key for confident identifications (in the absence of the specimen).