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General DescriptionBombus melanopygus 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). Bombus melanopygus has a large body densely covered in long, fine pile (Franklin 1912). Abdominal segment 1 is yellow, segments 2 and 3 are red or orange, and the remaining segments (4-6) are black. The anterior scutum and the vertex of head and face are covered in a mixture of black and yellow pile and appear clouded (Thorp et al. 1983; Curry 1984). Males tend to have less black pile on the face and the third antennal segment is shorter than the fifth but longer than the fourth (Franklin 1912). Body size and wingspan varies between castes: queens are 15 to 18 mm with wingspans of 29 to 36 mm, workers range between 11 to 15 mm with wingspans of 25 to 29 mm, and males are 9 to 13 mm with wingspans of 21 to 26 mm. Wings are darkly stained brown (Franklin 1912). The penis valve is rounded at the apex with a sharp angle at middle of apical curvature. The gonostylus is short and sternite 8 is uniformly thick (Thorp et al. 1983).