Bombus bifarius, the two-form bumblebee, is a species of eusocial bumblebee of the subgenus Pyrobombus. B. bifarius inhabits mountainous regions of western North America, primarily the states of Colorado and Utah. Its common name refers to a historical artifact, in that it was believed that this species had a color polymorphism, with a red-tailed nominate form and a black-tailed nearcticus form present in the species. This polymorphism has recently been shown to belong instead to a cryptic sister species, Bombus vancouverensis, that occupies almost the entirety of the range of what was formerly classified as bifarius; true bifarius only has a red form, so it is not "two-formed" at all.

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