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General DescriptionBombus borealis belongs to the subgenus Subterraneobombus in which females can be distinguished by small ocelli at the supraorbital line (Thorp et al. 1983), while males can be distinguished by spoon-shaped penis valvesthat are turned inwardsas well as the presence of a raised longitudinal keel posteriorly on sternum 6 (Williams et al. 2008)B. borealis individuals have white pile on the face between the eyes;the fifth antennal segment is longer than the fourth or third;the first four abdominal segments are covered with yellow pile, while the remaining segments are black;and the outer surface of the male hind tibia is concave (Franklin 1912). The length of the queen varies from 15 mm to 19 mm; her wing spread from 32 mm to 39 mm; and the width of the second abdominal segment 8 mm to 9.5 mm. Workers vary in length from 10 mm to 15 mm; in wing spread from 26 mm to 32 mm; and in width of the second abdominal segment from 6.5 mm to 8 mm. Males range in length from 12 mm to 15 mm; in wing spread from 26 mm to 31 mm; and in width of second abdominal segment from 6 mm to 7.5 mm (Franklin 1912).