Bumble Bees of Montana
Bombus (Pyrobombus) mixtus Cresson, 1878 Fuzzy-Horned Bumble Bee
Bombus mixtus is known to be common throughout most of its range, which extends from the Pacific Coast through the Rocky Mountains north into western Canada and Alaska. There are scattered records as far east as the upper Midwest, northern Ontario, and New Brunswick (Williams et al. 2014). It is also common in Montana, with records throughout the forested, montane regions in the west.
Bombus mixtus has a cheek that is approximately as long as it is wide and there are black hairs mixed throughout the yellow on the thorax in front of the wings, making it appear dirty or cloudy. Usually abdominal T2 has yellow hair in the middle and black hair on the sides. Abdominal T5 (and often T4 and sometimes T3) is orange, though sometimes the orange is very pale.
This species is most easily confused with B. frigidus and B. sitkensis in Montana. Bombus frigidus does not have black hairs mixed with the yellow on the thorax in front of the wings and T2 is entirely yellow. Similar to B. mixtus, B. sitkensis has black hairs mixed with yellow on the thorax in front of the wings. However, the thorax behind the wings of B. sitkensis has many more black hairs than the thorax in front of the wings, so the thorax appears to have a front to back gradient of light to dark.