In Minnesota, Bombus citrinus is one of six species of Bombus in the social parasite subgenus Psithyrus. Social parasite females take over an active Bombus nest and kill, drive out, or coexist with the host queen. The Bombus citrinus female then uses aggression and pheromones to coerce the queen's workers to help her rear her offspring. Unlike a typical Bombus nest with three castes (queen, workers, males), these social parasites have just two castes: females and males.
 

Bombus citrinus females lack corbiculae (pollen baskets) and the abdominal glands to produce wax. They have a harder exoskeleton, longer sting, and larger ovaries than nest-establishing Bombus species. In Minnesota, Bombus citrinus is the most commonly observed cuckoo bumble bee, likely because its hosts (Bombus impatiens, B. vagans, and B. bimaculatus) have relatively stable or increasing populations.

​

Bombus citrinus females have yellow hairs on the thorax and occasionally a black spot of hairs between the wing bases. The abdomen can have entirely black hairs (resembling Bombus impatiens), or have yellow hairs on the lateral edges of the third tergite (T3). Occasionally, there may be additional yellow hairs on first and second tergites (T1 and T2). Males have yellow hairs on the first three tergites (T1-T3) and black hairs on T4-T7. In addition, males have black hairs between the wing bases that extend in a triangular pattern to the rear of the thorax. Both males and females have black hairs on the face and yellow hairs on the vertex.