[3] Before the queen invades a nest she forages on various plants, such as asters, thistles, snakeroots, blazing-stars, mountain-mints, and goldenrods.

Members of Psithyrus are distinguished from other Bombus based on an abdomen with thick tergites, a long stinger, enlarged mandibles, loss of corbiculae, no worker castes, and a reduction in wax glands and its production;[4][5] all of these features are associated with being inquiline parasites that replace host queens.

[5][6] Bombus citrinus is believed to have originated from this line around 2 million years ago in the Eastern Nearctic region.

[6] Like all cuckoo bumble bees, the outer tibial surface of the hind leg is convex and densely hairy, rather than adapted for pollen transport.

Their heads are more teardrop shaped and the thorax is predominantly yellow including the lower sides and sometimes down to segment T4 or 5.

[9] The wings are slightly opaque ranging from a reddish brown to brownish black and yellowish during pubescence.

[12] The Dufour's gland is enlarged in the Psithyrus subgenus and believed to be the source of chemical production for bees in the genus.