In fall, bumblebee colonies disband, the newly produced queens mate then seek a sheltered harborage to overwinter. In spring, the new queens will found new colonies. The first offspring are sterile females devoted to rearing the offspring of the queen. The reproductive systems of workers do not develop although they are capable. If a queen is removed from a colony, the reproductive systems of several workers will develop and they will lay eggs. These worker/queens have not mated; therefore all eggs will be unfertilized (haploid) and become males.
The control of the reproductive status of workers in a colony is not understood. The hypothesis that the queen secretes a chemical (pheromone) that suppresses worker reproduction lacks positive evidence. None of the proposed chemicals produce the predicted results. Alternative hypotheses suggest that physical contact with a queen produces internal hormonal changes in the workers or that some combination of pheromones and physical contact controls reproductive status.