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Bombus occidentalis Greene, 1858
Bombus proximus Cresson, 1863; Bombus howardii Cresson, 1863; Bombus howardi Cresson, 1863, emend; Bombus perixanthus Cockerell and Porter, 1899; Bombus proximus var coloradensis Titus, 1902; Bombus (Bombus) occidentalis nigroscutatus Franklin, 1913; Bremus terricola var severini Frison, 1926; Bombus (Bombus) occidentalis occidentalis Greene, 1858

Life   Insecta   Hymenoptera   Apoidea   Apidae   Bombus
Subgenus: Bombus

Bombus occidentalis, -face 2012-07-26-16.24.16
© Copyright source/photographer · 9
Bombus occidentalis, -face 2012-07-26-16.24.16

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IDnature guides

    Williams, Paul H., Robbin W. Thorp, Leif L. Richardson, and Sheila R. Colla. Bumble Bees of North America: An Identification Guide. Princeton University Press, 2014. http://www.jstor.org/stable/j.ctt6wpzr9.

    - has the best modern color guides for identification of both sexes, microscopic identification characters, range and natural history notes.

    Often considered a subspecies of Bombus terricola, but recent DNA Barcodes support this as a separate species (Williams et al. 2014).

    Abruptly declined across much of its range in the 1990s following an attempt by the commercial bumble bee industry to develop this species as the greenhouse pollinator for western North America.

    Known as the Western Bumble Bee.

  • Hosts
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Bombus occidentalis, -side 2012-07-26-16.30.28
© Copyright source/photographer · 9
Bombus occidentalis, -side 2012-07-26-16.30.28
Bombus occidentalis, female, face
Smithsonian Institution, Entomology Department · 9
Bombus occidentalis, female, face

Bombus occidentalis, female, side
Smithsonian Institution, Entomology Department · 9
Bombus occidentalis, female, side
Bombus occidentalis, female, top
Smithsonian Institution, Entomology Department · 9
Bombus occidentalis, female, top

Bombus occidentalis, female, wing
Smithsonian Institution, Entomology Department · 9
Bombus occidentalis, female, wing
Bombus occidentalis FEM mm -x f
© Copyright Laurence Packer 2014 · 7
Bombus occidentalis FEM mm -x f

Bombus occidentalis MALE mm -x f
© Copyright Laurence Packer 2014 · 7
Bombus occidentalis MALE mm -x f
Bombus occidentalis, Diane Wilson
Diane Wilson · 5
Bombus occidentalis, Diane Wilson

Bombus occidentalis, F, Back, Utah Co., Utah
© Copyright source/photographer · 5
Bombus occidentalis, F, Back, Utah Co., Utah
Bombus occidentalis, F, Face, Utah Co., Utah
© Copyright source/photographer · 5
Bombus occidentalis, F, Face, Utah Co., Utah

Bombus occidentalis, F, Side, Utah Co., Utah
© Copyright source/photographer · 5
Bombus occidentalis, F, Side, Utah Co., Utah
Bombus occidentalis, F, Back, Utah Co., Utah
© Copyright source/photographer · 5
Bombus occidentalis, F, Back, Utah Co., Utah

Bombus occidentalis, F, Face, Utah Co., Utah
© Copyright source/photographer · 5
Bombus occidentalis, F, Face, Utah Co., Utah
Bombus occidentalis, F, Side, Utah Co., Utah
© Copyright source/photographer · 5
Bombus occidentalis, F, Side, Utah Co., Utah
Extracted from Jonathan Koch, James Strange, Paul Williams.2012. Bumble Bees of the Western United States. A product of the U.S. Forest Service and the Pollinator Partnership with funding from the National Fish and Wildlife Foundation

Western bumble bee

Status: Rare throughout much of its range; in decline but may be locally common.

Select food plant genera: Melilotus, Cirsium, Trifolium, Centaurea, Chrysothamnus, Eriogonum

Tongue Length: Short

Distribution: Historically from the Pacific coast to the Colorado Rocky Mountains; severe population decline west of the Sierra Cascade Crest, but populations are known from the Great Basin, the Rocky Mountains and Alaska; several subspecies have been suggested

Can be confused with B. crotchii, B. mixtus, and B. terricola.

Thorax anterior to black band between wing bases yellow, scutellum black or yellow, T1 black, T2 and T3 black or yellow, T4 often white at least apicolaterally, T5 white, face round.

Mid leg basitarsus with the distal posterior corner rounded. Cheek length slightly shorter than width. Hair of the face and top of head predominately black with yellow sometimes intermixed. On the side of the thorax, the lower anterior surface with predominantly black hair, sometimes with yellow intermixed, corbicular fringes red. Hair length medium and even.

Extracted from Wallace E. LaBerge and Morgan C. Webb. (1962). The Bumblebees of Nebraska (Hymenoptera, Apidae, Bombinae). University of Nebraska College of Agriculture.

This western species has been collected only twice in the northwestern corner of the state. There is extensive color variation in B. occidentalis which is not described fully here; Stephen (1957) should be consulted for a complete description with diagrams.

Females: Head hairs chiefly black with some while or yellow surrounding antennal fossae and on vertex: thorax with sides with hairs black except on and surrounding posterior pronotal lobes, dorsum pale yellow to yellow anteriorly, with broad interalar band of black, scutellum entirely yellow or black mediobasally; tergum I with pile black; tergum 2 with pile mostly black, often yellow along apical margin; tergum 3 with pile pale lemon-yellow to brownish yellow; tergum 4 with pile black in Nebraska specimens, often entirely white or white apically; terga 5 and 6 with pile white to pale yellow; leg hairs black except corbicular fringe somewhat rufescent; malar space about as long as broad near apex or slightly shorter: ocelli placed on supraorbital line.

Males: Head hairs black except clypeus, face surrounding antennal fossae and vertex with at least some pale hairs; thorax with sides with hairs pale anteriorly and black posteriorly, dorsum yellow anteriorly with interalar band of black, scutellum yellow; tergum 1 with pile black, terga 2 and 3 with pile cinereous to brownish yellow (Often black at base of tergum 2); tergum 4 black: tergum 5 cinereous or white, occasionally entirely black; terga 6 and 7 cinereous; leg hairs chiefly black but often coxae, trochanters and lower surfaces of femora yellow and fringe of long hairs on tibiae rufescent; tibiae with outer surfaces bare and impunctate; malar space about as long as broad; compound eyes not swollen; ocelli placed on or slightly above supraorbital line; first flagellar segment subequal to third and slightly longer than second.

Extracted from Bumble Bees and Cuckoo Bumble Bees of California by Thorp, R. (1983).

Discussion. B. occidentalis is most closely related to B. franklini and can be distinguished from it by the characters mentioned under that species. Franklin (1913) considered B. nigroscutatus as a subspecies of B. occidentalis based principally on California specimens, but included individual variants from the Rocky Mountains which had similar coloring. Stephen (1957) redefined the subspecies, limiting it to coastal California populations. Although populations from the San Francisco Bay region are distinctively colored (except when com-pared to specimens from the San Francisco Mountains of northern Arizona), there is such a broad zone of intergradation from Mendocino County northward that recognition of this color form as a subspecies is unwarranted. Indeed, Milliron (1971) went so far as to place B. nigroscutatus and franklini in synonymy with occidentalis and then reduced occidentalis to subspecific status under B. terricola Kirby. Since the area of sympatry is the eastern slopes of the Rocky Mountains, we cannot resolve the question here. However, Stephen (1957) found no intergradation between them in British Columbia, and Hobbs (1968) found them distinct in southern Alberta, where they coexist Since these data fit with the few specimens we have seen from the area of sympatry, we prefer to treat occidentalis as a species distinct from terricola. Color variation in B. occidentals is extensive (Figs. 113, 140). There is a broad area of gradation from the nigroscutatus form near San Francisco to the occidentalis pattern in northern and eastern California. The only apparent general trend in this highly polychromatic species is for the appearance of increasing amounts of yellow hair in populations from north to south in the Rocky Mountains, the Cascade-Sierra Nevada, and the North Coast Ranges of California. The biology of B. occidentalis is discussed by Hobbs (1968). We have taken nests of this species in the San Francisco Bay area and in Humboldt County. All were underground except for one beneath a house in San Francisco, where the bees entered through a hole in the basement door and crossed over the dirt floor for about 3 m, under an old refrigerator to an old comforter, behind which the nest was established in the cotton stuffing. Hobbs (1968) identified invading females of all three species of Psithyrus (suckleyi 17; insularis, 6; and fernaldae, 1) in nests of 8. occidentalis, and at least one nest produced adult progeny of P. suckleyi.

Scientific source:

Natural history
Williams et al. 2014 - confirmed breeding record of B. suckleyi. Likely to also be host to B. ashtoni, B. insularis, and B. fernaldae.

Supported by

Hosts · map
FamilyScientific name @ source (records)
Apiaceae  Foeniculum vulgare @ EMEC_JPS__JPS (8)

Heracleum sphondylium @ UCRC_ENT (1)
Asteraceae  Agoseris @ EMEC_JPS__JPS (1)

Aster sp @ BBSL (1)

Aster @ AMNH_BEE (5)

Centaurea solstitialis @ UCRC_ENT (1)

Chrysothamnus nauseosus @ BBSL__JPS (1)

Chrysothamnus sp @ BBSL__JPS (1)

Cirsium arvense @ BBSL__JPS (2)

Cirsium lanceolatum @ BBSL__JPS (4)

Cirsium sp @ BBSL__JPS (2); BBSL__OS (1)

Cirsium @ EMEC_JPS__JPS (28); LACM_ENTB (2); RMBL_ENT (1)

Cosmos @ EMEC_JPS__JPS (3)

Ericameria ericoides @ EMEC_JPS__JPS (16)

Ericameria nauseosa @ EMEC_JPS__JPS (1)

Ericameria? @ EMEC_JPS__JPS (1)

Ericameria? @ UCRC_ENT (1)

Ericameria? @ UCRC_ENT (1)

Eriophyllum @ EMEC_JPS__JPS (2)

Grindelia hirsutula @ UCRC_ENT (5); EMEC_JPS__JPS (19)

Grindelia squarrosa @ UCRC_ENT (3)

Grindelia @ UCRC_ENT (1); EMEC_JPS__JPS (6)

Haplopappus bloomeri @ BBSL__JPS (7)

Helianthella quinquenervis @ RMBL_ENT (2)

Helianthus @ EMEC_JPS__JPS (5)

Heliomeris multiflora @ RMBL_ENT (16)

Helminthotheca echioides @ UCRC_ENT (1)

Hypochaeris sp @ BBSL__JPS (2)

Rudbeckia montana @ RMBL_ENT (1)

Rudbeckia sp @ BBSL__JPS (1)

Rudbeckia @ AMNH_BEE (1)

Senecio clarkianus @ UCRC_ENT (1)

Senecio flaccidus @ EMEC_JPS__JPS (8)

Senecio @ RMBL_ENT (4)

Solidago multiradiata @ RMBL_ENT (1)

Solidago @ AMNH_BEE (1); UCRC_ENT (5); EMEC_JPS__JPS (1)

Taraxacum officinale @ BBSL__PUB (1); LACM_ENTB (1)
Boraginaceae  Mertensia @ EMEC_JPS__JPS (1)
Brassicaceae  Brassica @ EMEC_JPS__JPS (1)

Cakile maritima @ EMEC_JPS__JPS (7)
Caprifoliaceae  Abelia @ UCRC_ENT (6)

Symphoricarpos racemosus @ BBSL__JPS (3)
Caryophyllaceae  Minuartia cismontana @ UCRC_ENT (1)
Convolvulaceae  Ipomoea @ EMEC_JPS__JPS (1)
Cucurbitaceae  Cucurbita @ EMEC_JPS__JPS (2)
Fabaceae  Lathyrus leucanthus @ RMBL_ENT (1)

Lupinus arboreus @ EMEC_JPS__JPS (3)

Lupinus argenteus @ BBSL (3)

Lupinus nanus @ BBSL__JPS (1)

Lupinus @ LACM_ENTB (2)

Melilotus albus @ UCRC_ENT (3); EMEC_JPS__JPS (21)

Melilotus officinalis @ BBSL__JPS (15); AMNH_BEE (1)

Melilotus @ UCRC_ENT (2)

Trifolium pratense @ BBSL__JPS (2)
Geraniaceae  Geranium fremontii @ UCRC_ENT (2)
Herndon, j.d.  1424 @ JRYA__OLYM (1)
Iridaceae  Gladiolus @ EMEC_JPS__JPS (3)
Lamiaceae  Agastache urticifolia @ RMBL_ENT (1)

Monardella @ EMEC_JPS__JPS (13)

Salvia sonomensis @ EMEC_JPS__JPS (1)

Stachys @ EMEC_JPS__JPS (1)
Liliaceae  Camassia sp @ BBSL__JPS (1)
Mertensiidae  Mertensia sp @ BBSL__JPS (1)
Onagraceae  Chamerion angustifolium @ RMBL_ENT (1)

Clarkia amoena @ BBSL__JPS (5); EMEC_JPS__JPS (5)

Clarkia pulchella @ EMEC_JPS__JPS (2)

Epilobium angustifolium @ AMNH_BEE (1)

Epilobium @ EMEC_JPS__JPS (2)
Orobanchaceae  Pedicularis racemosa @ RMBL_ENT (1)
Papaveraceae  Eschscholzia californica @ EMEC_JPS__JPS (1)
Plantaginaceae  Penstemon strictus @ RMBL_ENT (1)
Polemoniaceae  Ipomopsis congesta @ RMBL_ENT (1)
Polycitoridae  Salix sp @ BBSL__JPS (2)
Polygonaceae  Eriogonum fasciculatum @ EMEC_JPS__JPS (1)

Eriogonum latifolium @ BBSL__JPS (2); UCRC_ENT (1); EMEC_JPS__JPS (2)

Eriogonum nudum @ EMEC_JPS__JPS (3)

Eriogonum @ CSCA (1); EMEC_JPS__JPS (4)
Ranunculaceae  Aquilegia coerulea @ RMBL_ENT (1)

Aquilegia sp @ BBSL__JPS (5)

Clematis ligusticifolia @ BBSL__JPS (1)
Rhamnaceae  Ceanothus sp @ BBSL__JPS (1)

Ceanothus velutinus @ UCRC_ENT (1)
Rosaceae  Dasiphora fruticosa @ UCRC_ENT (1)

Potentilla fruticosa @ RMBL_ENT (1)

Potentilla @ RMBL_ENT (1)

Prunus @ UCRC_ENT (1)

Rosa arkansana @ UCRC_ENT (1)

Rubus parviflorus @ AMNH_BEE (1)

Rubus @ EMEC_JPS__JPS (2); LACM_ENTB (3)

Spiraea sp @ BBSL__JPS (1)
Rykken, j.  1361 @ JRYA__OLYM (1)

1559 @ JRYA__OLYM (2)

1562 @ JRYA__OLYM (1)
Salicaceae  Salix @ AMNH_BEE (2)
Saxifragaceae  Ribes @ EMEC_JPS__JPS (1)
Scrophulariaceae  Scrophularia @ AMNH_BEE (1)
_  Asteraceae sp @ BBSL__PUB (4)

Withheld @ BBSL (20)

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Updated: 2024-07-15 17:15:03 gmt
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