Species Bombus occidentalis - Western Bumble Bee

Western Yellow-banded Bumble Bee

Often treated as a subspecies of its northern and eastern replacement B. terricola, but occidentalis may itself prove to be a species complex with cryptic diversity

Refers to its western distribution

White tail tip distinctive. Usually but not always with yellow band centered on T3 but this can be lacking or yellow of the metasoma may extend to other terga.

southern Alaska [update: now recognized as a distinct species B. mckayi. See https://www.tandfonline.com/doi/full/10.1080/00222933.2021.1900444], western Canada [but far NW pertains now to B. mckayi], and western USA

The Hosts section of its Discover Life species page lists known associations based on specimen records and images.

Has declined in the Pacific states including California. In the San Francisco Bay Area common until the early 1990s but now absent. Still regularly found in Colorado and elsewhere in the Rocky Mountains and has reappeared recently in small numbers at various sites in the Pacific Northwest.

Sympatric with another member of its subgenus, B. franklini of southern Oregon and adjacent northern California, which has not been seen since 2006 and is feared extinct.

https://www.tandfonline.com/doi/full/10.1080/00222933.2021.1900444