SeasonalityFlight period of queens ranges from late March to late August; workers: late April to late September; males: late May to late September (Thorp et al. 1983).
IdentificationBombus flavifrons belongs to the diverse subgenus Pyrobombus Dalla Torre which is characterized by a malar space of medium length but longer than its apical width and antennal flagellum 2.5 to 3x the length of the scape. The penis valves of the males are usually hook shaped (Thorp et al., 1983).
The robust body of B. flavifrons is densely covered in coarse yellow and black pile. The face and head are primarily yellow (Franklin 1912) and mixed with black on the anterior scutum (Thorp et al. 1983). Abdominal segments 3 and 4 are typically black but males may have yellow pile and females, reddish pile on the apical portion (Thorp et al. 1983). Pile at the base of the legs is light and the wings subhyaline (Franklin 1912). Body size and wingspan varies between castes: queens are 13 to 16 mm with wingspans of 27 to 34 mm, workers range between 9 to 12 mm with wingspans of 19 to 27 mm, and males are 11 to 12 mm with wingspans of 25 to 26 mm (Franklin 1912). The male genitalia is very similar to B. centralis with smoothly rounded, sickle shaped penis valves, narrow valsellae and a weakly trilobate sternite 8 that is apically membraneous (Thorp et al. 1983, Franklin 1912).