The Brown-belted bumble bee is very much an east side species. It is not that partial to mountainous areas either, more often found in drier lowland areas. I have picked it up near the Canadian border near Sinlaheiken WMA, on a USFWS Milkweed field that is grown for monarch butterflies. That area is very hot and dry, so it fits within the expected habitat preferences.
Field ID tips
From an identification perspective, this species is relatively easy, with just a possible couple of gotcha’s. The worker is distinctive, with a yellow thorax (small to medium spot between the wings), a yellow T1 and a brown T2. T3 thru T6 are all black
Queens, which fly early in the season and again as summer wanes, have a slightly different appearance. T2 is not brown, instead it is similar in color to T1, but with black on each side. See picture above.
- Thorax yellow with very small to medium black spot
- T1 = yellow
- T2 = yellow with black on edges for queen
T2 = brown for workers
- T3 = black
- T4 = black
- T5 = black
Similar species include the Nevada bumble bee Bombus nevadensis, Half-black bumble bee B. vagans and the Eastern common bumble bee B. impatiens.
The Nevada bumble bee has a yellow T3 and a distinctive thorax spot.
Half-black bumble bee is generally smaller and has a more delicate feel. The two species feel very dissimilar in body shape and behavior. Once you have identified one, when you encounter the other species it will feel like a very different species.
The Common eastern bumble bee currently is restricted to areas west of the mountains with the current (but spreading) population documented as far south as King County. It is not expected to expand into the east side, based on some preliminary “suitable range” analysis done by the excellent team of entomologists at the Washington state Department of Agriculture. The Common eastern bumble bee has a black T2