This group contains some of my favorite species to encounter in the field. Some can pose a bit of an ID challenge.
Two form bumble bee, B. bifarius
California bumble bee, B. californicus
Yellow-faced bumble bee, B. vosnesenskii
Obscure bumble bee, B. caliginosus
van Dyke bumble bee, B. vandykei
The Two form Bumble shows an inverted black triangle on her scutellum.
T1 = yellow/white
T2 = black
T3 = black
T4 = yellow/white
T5 = black
This form of the California bumble bee looks a lot like the next two species, except this species, the California bumble bee has a BLACK face.
The Yellow-faced bumble bee has a yellow face, scutum and T4. It’s stergites are black.
The Obscure bumble bee has a yellow face, scutum and T4. Stergites S4 and S5 are white.
On the van Dyke bumble, T3 shows yellow, in contrast to the Two form bumble bee, where T3 is black.