Western bumble bee, Bombus occidentalis

The Western bumble bee, Bombus occidentalis, was until recently the most widely distributed bumble bee species across Washington state. The range map below shows just how wide spread it was.

Then a disease outbreak spread from captive raised bumble bees used for tomato hothouse operations wiped out an estimated 95% or more of the wild population.

Even now, over two decades later, the numbers of Western bumble bees have not rebounded. They can reliably be found in and around Colville, but in other parts of the state encounters are much more sporadic.

Please reference the Embedded Range Maps page to better interpret
the # of observations per ecoregion.

Field ID Tips

The golden yellow scutum, black body and large white T4 and T5 are the classic field marks for the Western bumble bee. Also note the black head and face.
There is a color morph found in the Blue Mountains, and in Oregon, which has the scutellum (rear of the thorax) yellow, rather than black. It should still be distinctive as a Western bumble.

Similar Species

No other species has white on the end of its’ abdomen and golden yellow on the front of the thorax.

I do find that that in the field, Western bumble bees can feel a bit like Bald faced hornets, with white at the end of the abdomen. Could it be an example of mullerian mimicry?

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One Response to “Western bumble bee, Bombus occidentalis”

  1. B. Bailey says:

    Please do not import or farm-raise bumblebees! It is not worth the risk of wiping out whole populations of native bumblebees.

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