Apidae > Bombus > Bombus vagans / Bombus sandersoni

Half-black bumble bee (Bombus vagans) and Sanderson’s bumble bee (Bombus sandersoni) are two forest-associated bumble bees with similar patterning. Both species have long, messy light-yellow hairs on the top half of the abdomen, though some individuals of B. sandersoni deviate considerably from this standard color pattern. Although B. vagans is perhaps more likely to be encountered than B. sandersoni in most contexts, the two species are quite difficult to distinguish from each other in the field, so we treat them here as a species pair for purposes of field ID.

Phenology

Active from April through October in the northeast. Eusocial.

Range

B. vagans ranges throughout the northeast, but is generally more common than B. sandersoni in northern woods and along the Appalachians and foothills. 

Appearance

Size >honey bee

Workers: head dark; long messy hairs; typically, light yellow thorax with black spot in center, T1-T2 light yellow and remaining of abdomen black; sides of thorax all yellow; some B. sandersoni can have considerable yellow on the tip of the abdomen

Gynes: like workers, but larger 2-3x as big; B. sandersoni queens can have white-tipped abdomens

Males: head dark; thorax all yellow; abdomen often all yellow, but can range from all yellow to just T1-T2 yellow with the rest black

Similar species

• B. vagans and B. sandersoni are difficult to distinguish in the field, but B. vagans appears to be considerably more abundant and have a much larger range than the more northern B. sandersoni. The longer malar space of B. vagans can occasionally be apparent in photos, but discerning this requires extensive practice and photographs from misleading angles can easily give an incorrect impression of malar length.
• B. perplexus is a richer dandelion yellow color and appears darker due to intermixing of dark hairs across body including dark underwings.

Nesting

Eusocial. Overwintering mated gynes found new colonies in spring. Nests are primarily constructed in below-ground in abandoned rodents burrows, or cavities at ground level beneath long thatch grass or in hay piles. Little is known about the nesting ecology of B. sandersoni.

Foraging

Forages in forests and forest-adjacent open habitats. Thistles (Cirsium spp.), flowering raspberry (Rubus odorata), St. Johns Wort (Hypericum spp.), and meadowsweet (Spiraea spp.) are favorites of B. vagans. Little is known about the foraging ecology of B. sandersoni.

Natural Enemies

B. vagans is host to the social parasite Bombus citrinus.

Page last updated:
February 22, 2023