Bombus (Thoracobombus) californicus Smith, 1854 California Bumble Bee

Bombus californicus is known from coastal California, Oregon, and Washington and throughout the intermountain western U.S. from Colorado and Utah north to Idaho and Montana. Individuals have been recorded as far east as South Dakota (Koch et al. 2012). It is not a commonly collected bumble bee and is a species that may be in decline (Koch et al. 2012). In Montana, this species has been collected in mountainous regions of the west, but is relatively uncommon.

Recorded Montana Distribution

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Sheridan> Gallatin
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Bombus californicus has several different color morphs, some more cryptic than others. Characters used to identify B. californicus include a longer-than-wide cheek and black hairs on the face. There is always yellow on abdominal T4 while T1-T3 are variable in color, though there is always at least some black. Some forms have T1-T3 completely black while others have T1-T3 almost completely yellow with only small patches of black on the sides of T2. Identification is complicated by a spectrum of intermediate color patterns between these two extremes (Koch 2015).

Similar Species

This species is most easily confused with B. fervidus and some keys treat them as one species. Bombus fervidus in Montana has only yellow hairs on T1-T4.