Bombus insularis, or the indescriminate cuckoo bumble bee is a social parasite. The females of this species will invade the nests of other bumble bees, kill the queen and lay her eggs inside the host nest. The host workers will then tend to her nest while her offspring look for other nests to invade. Male bees measure 13 -16mm and females measure 16 – 19mm. Host species include Bombus appositus), Bombus fervidus), Bombus flavifrons, Bombus nevadensis), and Bombus ternarius. In Canada they are most active from June to August. The bees prefer the flowers of Aster, Meliotus, Rubus, Senecio, Solidago, Trifolium, and Vaccinium.