Bumble Bees of Montana
Bombus (Pyrobombus) sylvicola Kirby, 1837 Forest Bumble Bee
Bombus sylvicola is a boreal-alpine species that is common throughout high elevation habitats of the western U.S., north to Alaska and across the northernmost parts of Canada (Williams et al. 2014). In Montana, it has been collected throughout the mountainous counties in the west, though most of the records are from the Beartooth Mountains of Carbon County where the Beartooth Highway makes access to true alpine habitat easily accessible.
Bombus sylvicola has body hairs that are relatively long and uneven. It also has a square cheek and hair pattern of abdominal T1: yellow, T2 and T3: orange, T4: yellow, T5: black with yellow tufts on the side, and T6: black. The black hairs on the face are interrupted by a circle of yellow hair at the base of the antennae. The yellow hair on the thorax behind the wings is divided by a line or triangle of black hairs in the middle.
This species is most easily confused with B. huntii, B. ternarius, and B. melanopygus, though collecting at higher elevations reduces the likelihood of an individual being B. huntii or B. ternarius. Bombus huntii does not have black interrupting the yellow hairs on the thorax behind the wings, the face has only yellow hairs, and T5 is completely black. Bombus ternarius will often have yellow hair on the front coxae (first leg segment) and T5 will be completely black. Bombus melanopygus has many black hairs intermixed with the yellow on the thorax in front of the wings, making the thorax appear dirty or cloudy.
There is a form of B. sylvicola in which the orange hair on T2 and T3 is replaced with black. This form has not been recorded in Montana, and is known primarily from the Sierra Nevada Mountains of California.