The Forest bumble bee, Bombus sylvicola is a high altitude specialist. Here in Washington it is only found in the lofty elevations in the Olympics and Cascades. In a study done for the National Park Service, Bombus sylvicola, occurred only at sites between 1,113 and 2,023 meters in both parks.
The Forest bumble bee, Bombus sylvicola may be found in association with one or two other high alpine specialists: Frigid bumble bee, Bombus frigidus and the High country bumble bee, Bombus kirbiellus. All three show red on the abdomen. The Forest bumble bee appears to be the most common of the three species here in Washington state.
A general characteristic across these high altitude specialists relative to bumbles from lower elevations is long hair length. For this species, this would be relative to the Hunt bumble bee, Bombus huntii.
Field ID tips
First, this is one species where range is a prime consideration. Unless you are pretty high in the mountains, don’t expect to encounter the Forest bumble bee. The Forest bumble bee has a yellow scutum and scutellum, and T2 & T3 are red.
The Forest bumble bee is easily distinguished from the Frigid bumble bee and the High Country bumble bee because the red on a frigidus and a kirbiellus is at the end of their abdomen while the red on a sylvicola is on T2 and T3. The same logic holds true for separating the Forest bumble bee from the Fuzzy-horned bumble bee, B. mixtus and the Sitka bumble bee, B. sitkensis.
The Forest bumble bee, B. sylvicola, has a color pattern similar to the Hunt bumble bee, B. huntii. They both have T1 yellow, T2 and T3 orange, T4 yellow. Luckily these two species can easily be separated based on range. The Forest bumble bee is a high alpine specialist while the Hunt bumble is comfortable in hot dry sites like the Dry Falls State Park lake basin.
The scutum is yellow in sylvicola. This can help distinguish between sylvicola and melanopygus, the Black tail bumble bee. The Black tail bumble has a cloudy scutum (black hairs mixed in with the yellow).
The Red-belted bumble bee, B. rufocinctus, has the potential to be confused with the Forest bumble bee. The Red-belted bumble bee shows T2 with some yellow. The Forest bumble bee has T2 all red.
To date, I (DJ) have not captured any images of sylvicola in Washington. The quest continues…