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General DescriptionFemales of the subgenus Fervidobombus have ocelli onthe supraorbital line, and first flagellomere that are shorter than the second and third flagellomeres combined; males have can be distinguished by first flagellomere that are shorter than the third flagellomere and apically turned penis valves (Thorp et al. 1983). Bombus fervidus males have dorsal abdominal segments 1-5 covered with yellow pile with segment 6 covered with black pile; females have dorsal abdominal segments 1-4 covered with yellow pile while segments 5 and 6 have black pile (Franklin 1912). Female wings are darker stained than males; the malar space of both sexes is one-third the length of the eye (Franklin 1912). Bombus fervidus is easily confused with B. californicus, but can be distinguished by yellow pile on the scutellum, thoracic pleura, and metasomaltergites 1-3, while B. californicus has black pile in these areas (Thorp et al. 1983). Franklin (1912) gives the following morphological indices for castes of B. fervidus. Queens range in length from 15 mm to 21 mm; wing spread from 37 mm to 41 mm; and width of second abdominal segment from 8.5 mm to 10.5 mm. Workers vary in length from 8 mm to 15 mm; wing spread from 17 mm to 35 mm; and width of second abdominal segment from 3.5 mm to 8 mm. Length of males ranges from 10 mm to 16 mm; wing spread from 25 mm to 33 mm; and width of second abdominal segment from 6 mm to 8 mm.