SeasonalityFlight periods of queens ranges from early April to late October; workers: early April to late September; males: early May to late September (Thorp et al., 1983).
IdentificationBombus mixtus 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).
Abdominal segment 3 of the large bodied B. mixtus is typically covered in black pile with reddish hair on the apical portion (Curry 1984; Franklin 1912). The remainder of the segments are yellow, cloudy yellow, or reddish yellow (Curry 1984; Franklin 1912). The pleura and the face are primarily yellow (Franklin 1912) and the mesonotum has an extensive amount of black pile between the wing bases but it does not form a distinct band (Curry 1984). There is large colour variation in males and they may look similar to B. edwardsii or B. sitkensis however, B. mixtus males have very distinct hair fringes on the inner faces of the antennal flagellomeres (Thorp et al. 1983). The malar space is as long as it is wide (Thorp et al., 1983). Body size and wingspan varies between castes: queens are 11 to 15 mm with wingspans of 27 to 31 mm, workers range between 7 to 11 mm with wingspans of 17 to 25 mm, and males are 8 to 11 mm with wingspans of 21 to 25 mm. Wings are lightly stained brown (Franklin 1912).