Bombus flavidus, commonly known as the yellowish cuckoo bumble bee is a relatively small bee, with male measuring 13 -15mm and females measuring 15 -17mm. In 2021 the species Bombus fernaldae was reclassified as Bombus flavidus, making it the most widespread species of bumblebee worldwide. In Canada they are most active in May, but in the United States they are active from June to September. The discrepancy in activity is largely due to their nesting habits. Cuckoo bees parasitize other bumble bee colonies by laying their eggs in other solitary bee hives, after which their larva hatch and eat the other bees food stores for their young. Unlike many other species of bumble bees, these bees are solitary and do not form small colonies. For food sources the bees prefer Cirsium, Meliotus and Senecio. Yellowish cuckoo bumble bees are quite rare, and so despite being widespread across the globe studying them has proven difficult.