Two-spotted bumble bees (Bombus bimaculatus) carry spring on their wings. Queens are often among the first bumble bees seen each year, taking advantage of a pulse of forage in the forest canopy and spring ephemerals in the understory. Colonies grow and senesce quickly, producing the earliest reproductive after less than two months of activity. A common and widespread bumble bee, B. bimaculatus can be easily identified by the two adjacent yellow spots on the second segment of the abdomen.
Active March to November, but generally uncommon by September in more northern parts of its range. Colonies begin producing males and gynes (future queens) by late May or early June, and they last until mid-July. One new generation of reproductive individuals per year. Unlikely to be observed after August.
Widespread throughout region.
Size >honey bee
Workers: thorax with long, yellow hair and black spot in center; yellow on vertex; T1 completely yellow, T2 with either adjacent yellow spots in center or mostly yellow in center with black on sides—pattern on T2 forms a wide “W” ; relatively long malar space (long face).
Gynes: pattern like workers, but 2-3x larger (similar to Xylocopa virginica).
Males: many with similar pattern to females, but some with additional yellow on sides of T4 and T5.
- B. griseocollis can appear similar and overlaps in habitat and phenology, but has shorter, darker, “buzz-cut” hair on the thorax, dark hairs on vertex, and darker wings. The curved patch of light hairs on T2 of griseocollis appears more continuous with the light hairs of T1, curving across from one side of T2 to the other, as opposed to the distinct block or spots of light hair in the center of T2 of bimaculatus.
- B. impatiens has a single yellow band on T1 and never any yellow markings on T2.
Eusocial. Mated B. bimaculatus gynes (future queens) are often the first Bombus to emerge in spring. Colonies occur in cavities, typically at or below ground-level. Likely nests in human-occupied areas including suburban gardens, cities, and woodland edges.
More associated with forests than B. griseocollis.
Generalist, foraging on a wide variety of plants, though gynes in spring are especially fond of woodland ephemeral wildflowers (particularly Dutchman’s breeches Dicentra cucullaria).
Like some other species in the subgenus Pyrobombus, B. bimaculatus may host the socially-parasitic Lemon Cuckoo-Bumble Bee (Bombus citrinus).
Page last updated:
February 22, 2023