Other Common Names
Often cited as Fernalds Bumble Bee, but use of the possessive is generally preferred when citing common names (see AOU and BOU bird checklists, e.g., Franklin's Gull).
Synonyms and other taxonomic changes
Formerly in genus Psithyrus which is now considered a subgenus of Bombus.
Explanation of Names
Author of species is Franklin, 1911.
Relatively small. Female: 14.5-17 mm. Male: 13-15 mm (no workers).
Males often have a distinctive ring-like band of yellow on T4 more or less contrasting with the color of the other tergites (T1-T3 vary from mostly black to mostly yellow) and especially with T5 which is mostly black. Similar species have more pale hairs on T5 laterally so don't have such a well-defined subterminal ring. Both sexes often have a black face contrasting with extensive yellow hairs on the vertex. The distinctive projecting and shape of the female apical sternum is rarely visible in images. Males have rather long malar spaces.
Widespread in Canada and the United States, from Alaska to California in the West, New Brunswick to North Carolina in the East.
Social parasites of other bumble bees including. Both sexes regularly visit flowers for nectar. The Hosts section of its Discover Life species page
lists known floral associations based on specimen records and images.
Overwintered, mated females can be observed seeking the hives of their hosts in the spring. In late summer and fall males and young queens can be observed on flowers.
Cuckoo bumble bees are social parasites within the hives of other Bombus species. They don't have workers and lack pollen and nectar collecting equipment.
common name reference; PDF doc
(Committee on Common Names of Insects, Entomological Society of America)