Bumble Bees of Montana
Bombus (Pyrobombus) ternarius Say, 1837 Tri-Colored Bumble Bee
Bombus ternarius is known to inhabit the eastern and northern portions of the U.S. and the eastern and southern portions of Canada (William et al. 2014). Koch et al. (2012) described the distribution of this species as common in the East, but rare in the West, with records from eastern Montana and the Black Hills east to New England. In Montana, B. ternarius has been found through much of the north and east. Bombus ternarius is said to replace B. huntii in the north (Williams et al. 2014), but throughout much of Montana these two species appear to co-occur.
Recorded Montana Distribution
Bombus ternarius has a cheek that is about as long as it is wide and hair pattern of abdominal T1: yellow, T2 and T3: orange, T4: yellow, and T5 and T6: black. The face is black with yellow hairs near the antennal bases, and the yellow hairs on the thorax behind the wings are divided by a line or triangle of black hairs. Often there are yellow hairs on the front coxae (first leg segment).
This species is most easily confused with B. huntii, B. sylvicola, and B. melanopygus. Bombus huntii is found in many of the same habitats, but the yellow hairs on the thorax behind the wings are not divided by black and the hairs on the face are predominantly yellow. Bombus sylvicola is typically found at higher elevations and has longer, more uneven body hairs, plus there are yellow tufts of hair on the sides of T5. Bombus melanopygus has many black hairs mixed with the yellow on the thorax making it appear dirty or cloudy.