Field ID tips
The thorax area in front of the wings (anterior thorax) is cloudy-a mixture of yellow and black hairs. The two front segments of the abdomen (T1, T2) are yellow. T3 is black. The end of the abdomen (rear of T4, T5, T6) has faint orange/pale hairs.
Two species that should be ruled out are Yellow head bumble bee, B. flavifrons and Fuzzy-horned bumble bee, B. mixtus. In the first instance, the pale hairs at the end of the tail can be missed (flavifrons). In the second, the red/pale hairs of sitkensis are not as prominent as exhibited by most B. mixtus. Mixtus may also show orange on T3.
As seen in the picture above, the anterior thorax is cloudy, T1 and T2 are yellow. T3 is black. T4 may show lots of black also, but will also have pale hairs. The pale hairs on T5 at the end of the abdomen are also visible.