Fig 1. Annual cycle of social bumblebees.

The cycle begins when mated queens emerge from their overwintering sites in early spring and search for suitable nest sites. Once a suitable nest site has been found, the queen collects and stores floral resources (nectar and pollen) to raise the first brood of workers, which emerges in late spring. A subset of the workers emerging become ‘foragers’ and leave the nest to collect floral resources for the queen and the rest of the workers in the colony. The number of workers (foragers and nest bees) in the colony continues to grow over the summer months. From late summer into the fall, the colony starts to produce new queens and males (reproductives) instead of workers. Reproductives leave the nest soon after emergence and search for a suitable mate until late fall. Once mated, queens search for an overwintering site and once located, reside there until the spring. Males and colonies (founding queen and workers) do not survive the winter, thus completing the cycle.