Bumble Bees of Montana
Bombus (Pyrobombus) sitkensis Nylander, 1848 Sitka Bumble Bee
The range of B. sitkensis extends from Alaska south along the coast to California as well as through the Canadian Rocky Mountains into Idaho, Montana, and Wyoming (Williams et al. 2014). It is commonly collected throughout this range. As would be expected based on its known distribution, B. sitkensis has only been collected in the northwestern corner of Montana. Since its range in Montana is so limited, it is one of the less commonly collected species in the state.
Recorded Montana Distribution
Bombus sitkensis has a cheek that is about as long as it is wide (though sometimes it may appear slightly longer than wide) and long, uneven body hairs. There are many black hairs mixed with the yellow on the thorax, with more black intermixed with yellow behind the wings than in front of the wings, making the back of the thorax appear darker than the front. Abdominal T1 and T2 are predominantly yellow, T3 is black, T4 has black hair in the front and brown/orange hair towards the back, T5 is brown/orange, and T6 is black.
This species is most easily confused with B. mixtus, which has a similar color pattern and also can have long, uneven hairs. While B. mixtus does have black hairs intermixed with yellow on the thorax like B. sitkensis, usually the front of the thorax appears darker than the back, though sometimes the amount of black hairs intermixed with yellow is similar between the front and back of the thorax of B. mixtus.