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Subgenus Psithyrus

Bombus unknown - Bombus citrinus - female Cuckoo bumble bee? - Bombus flavidus Bumblebee with white fur - Bombus flavidus Bombus  - Bombus flavidus - male Bombus queen & male on Goldenrod - Bombus flavidus - male - female Bombus variabilis Q - Bombus variabilis - female Lemon Cuckoo bumble bee - Bombus citrinus Indiscriminate Cuckoo Bumble Bee - Bombus insularis - female
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Hymenoptera (Ants, Bees, Wasps and Sawflies)
No Taxon (Aculeata - Ants, Bees and Stinging Wasps)
No Taxon (Apoidea (clade Anthophila) - Bees)
Family Apidae (Cuckoo, Carpenter, Digger, Bumble, and Honey Bees)
Subfamily Apinae (Honey, Bumble, Longhorn, Orchid, and Digger Bees)
Tribe Bombini (Bumble Bees)
Genus Bombus (Bumble Bees)
No Taxon Subgenus Psithyrus
Synonyms and other taxonomic changes
used to be treated as a separate genus (discussion + list and distribution of world spp.)(1)
6 spp. in our area, 30 spp. total(2)
Males are much smaller than females.
Females differ from those of all other Bombus in having the outer surface of the hind tibia convex and densely hairy (flat or concave and largely bare in other, pollen-collecting Bombus). Males have small heads and often have conspicuous bare patches on the apical terga medially.
holarctic, most diverse in Eurasia; in our area, widespread: 4 spp. are transcontinental in the north and range south along the Rockies (except B. ashtoni), B. citrinus ne. US + adjacent Canada, B. variabilis e. half of the US (+QC) to AZ in the south(2)
Social parasites of other bumble bees.
Life Cycle
There is no worker caste, the females invade Bombus nests and lay eggs there to be reared by the hosts(1)
Internet References
Mol.Phylogent. Evol. A phylogenetic analysis of cuckoo bumblebees (Psithyrus, Lepeletier) and bumblebees (Bombus, Latreille) inferred from sequences of the mitochondrial gene cytochrome oxidase I.