Bombus sitkensis Nylander, 1848

Bombinae, Apidae, Hymenoptera, Insecta, Arthropoda, Animalia

Matthew P. Kweskin

31 Mar 1997

Thorax Head Abdomen
Pile of scutum and scutellum yellow mixed with black; pleura yellow. Pile of face yellow with black. Gastral terga 1 and 2 yellow, at least laterally; terga 3 black; terga 4 yellow basally; terga 5 and 6 yellow.

Identification- It is very difficult to distinguish female B. flavifrons from B. sitkensis in the Olympia, Washington area. In other regions there is less difficulty. According to Stephen (1957), B. sitkensis females always have reddish pile on gastral terga five and six and they lack a median ridge on the hypopygium. Therefore, B. flavifrons females have dark hair on gastral terga five and six or they have a median ridge on their hypopygium.

B. sitkensis B. flavifrons
T5 and 6 with brownish red hairs T5 and 6 with mostly dark hairs
Hypopygium without ridge Hypopygium sometimes with ridge

B. sitkensis can also be confused with B. mixtus. There are some differences in pile coloration and the size of the malar region can be used to distinguish the species. The fourth gastral tergum of B. sitkensis is all black, while in B. mixtus, this tergum is orange colored medially. The pile of the first and second gastral terga of B. sitkensis tend to be lighter in color than those of B. mixtus. Finally, in B. mixtus, the malar space is longer than wide. Where as in B. sitkensis, the malar space is as long as, or shorter than wide.
B. sitkensis B. mixtus

Geography- B. sitkensis is found in the western parts of the Pacific coast states from Southern British Columbia to Central California. It is also found more inland in central British Columbia to Idaho.

Page author: Matthew P. Kweskin
Last modified: 31 Mar 1997
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