In Minnesota, Bombus insularis 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. Bombus insularis females then use 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 insularis 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 insularis is uncommon to rare and found in the northern an eastern part of the stae.

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Bombus insularis females have yellow hairs on the thorax and a central black spot. The abdomen has entirely black hairs with yellow hairs on the lateral edges of the third and fourth tergites (T3 and T4). Males have black hairs between the wing bases that extend in a triangular pattern to the rear of the thorax. There are yellow hairs on the first four tergites (T1-T4), as well as the edge of the fifth and sixth tergite (T5 and T6). The remainder of the abdominal tergites have black hairs. Both males and females have yellow hairs on the vertex; females have yellow hairs on the face, males black hairs.