Bombus vagans Smith Half-Black Bumble Bee

Bombus vagans is a common bumble bee known from eastern Washington to New England, primarily along the Canadian border (Koch et al. 2012), and south through the Appalachian Mountains (Williams et al. 2014). The database shows patchy records of B. vagans in Montana. It’s been collected throughout the mountainous northwestern counties, in the south-central counties, and in two counties in far eastern Montana. This patchy distribution suggests the need for more sampling throughout the state.

Recorded Montana Distribution

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Sheridan> Gallatin
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Bombus vagans has a cheek that is longer than it is wide (though sometimes it may appear to be as long as it is wide) and a hair pattern of abdominal T1 and T2: yellow and T3-T6: black. Sometimes the yellow hairs on T2 are only along the front edge, with the hairs further back black. The hairs on the face are black, but there are usually shorter yellow hairs inconspicuously mixed in, especially near the base of the antennae. The sides of the thorax are yellow.

Similar Species

This species is most easily confused with B. bimaculatus, B. griseocollis, and B. perplexus. In B. bimaculatus, T2 is black with yellow hairs only in the middle, often in a W- shape. The sides of the thorax are extensively black in B. perplexus (which is not yet known from Montana) and B. griseocollis has a cheek that is shorter than wide.

There is a dark form of B. flavifrons that looks very similar to B. vagans, though this form has not yet been recorded from Montana. The dark form of B. flavifrons can be distinguished from B. vagans by having yellow hairs on the sides of T3 and T4 and having S3-S5 extensively yellow.