The Nevada bumble bee, Bombus nevadensis, may well be our largest bumble bee in Washington state. Notice in the picture above its size relative to a native Iris. When I give talks I describe it as being “as large as my thumb”. That may be a bit of an exaggeration, but it is definitely a distinct presence when present.
Field ID tips
The Nevada bumble bee is identified by its larger size, the golden thorax with a black spot in the center, and T1 thru T3 a similar golden brown to the thorax. In some places, T1 may show some black (as in the photo below) but in general T1 is golden/yellow.
Similar species include Brown-belted bumble bee, Bombus griseocollis and the Morrison bumble bee, Bombus morrisoni.
The Brown belted bumble bee has brown on T2 or if yellow (queen) has black on the edges of the yellow on T2. T3 is black.
Morrison bumble bee lacks a black dot on the center of the abdomen. It also shows some yellow on T3. Relative to the long cheek of nevadensis, morrisoni has a short cheek.. If in doubt, look at the shape of the face. Hand lens can be handy. Once you have seen them both, you should feel confident in distinguishing between them.
Nevada bumble bee is an east side species. There are a few records on the west side, but it is not regularly seen there (that I am aware). I found it at the Turnbull NWR on a couple of separate occasions.