The life cycle of the bumblebee queen, a large, fertile female, defines the annual existence of a Bombus colony. Bumblebees are highly efficient pollinators, and their success is tied directly to the queen’s ability to initiate and grow a temporary society single-handedly. She is noticeably larger than her worker daughters, reflecting her sole responsibility for reproduction and the continuation of the species. The queen’s life begins each spring.
The Solitary Spring: Overwintering and Nest Selection
The queen begins her year in a state of suspended animation known as diapause, having spent the winter alone in a sheltered spot called a hibernaculum. This overwintering site is typically a small, self-excavated chamber located in loose soil, under leaf litter, or within a rotten log. To survive the cold, the queen synthesizes a biological antifreeze, such as glycerol, to protect her cells from freezing temperatures.
Once spring temperatures rise, the queen emerges, needing to feed and replenish her energy stores. She immediately forages on early blooming flowers to fuel her ovaries, which begin to develop after she breaks diapause. Her next task is searching for a suitable nest site, an endeavor she undertakes entirely by herself. She explores cavities in search of a dry, protected space, often selecting abandoned rodent burrows, grass tufts, or thick moss. This solitary phase is the most vulnerable time in the queen’s life, as failure to find a home or sufficient food ends her future colony.
Founding the Colony: From First Brood to Worker Support
Upon selecting her home, the queen begins colony foundation by building two structures from wax she secretes. She constructs a wax pot, provisioning it with collected nectar to serve as a food reserve for herself when weather prevents foraging. Next, she collects pollen, forming it into a clump on the nest floor, where she lays her first batch of fertilized eggs, creating the “brood clump.”
The queen is solely responsible for incubating the eggs and larvae, generating heat by vibrating her flight muscles. She maintains a temperature inside the brood clump of approximately 25 to 32 degrees Celsius. She must continuously forage for pollen and nectar to feed her developing young, a demanding cycle that lasts for several weeks. When the first generation of female workers emerges, they are often smaller because resources were limited during the founding period. This marks a major transition, as the new workers immediately take over all duties of foraging, nest maintenance, and caring for the subsequent brood, freeing the queen to focus exclusively on laying eggs.
The Annual End: Producing New Queens and Males
The colony enters its peak growth phase in mid-to-late summer, supported by the numerous female workers. Determined by colony size and resource availability, the queen initiates the production of the next generation of reproductives. She begins to lay unfertilized eggs, which develop into males, also known as drones. Simultaneously, she lays fertilized eggs destined to become new queens, or gynes, which are reared differently than the workers.
The female larvae intended to be new queens receive a significantly richer diet of pollen and resources, ensuring they develop the necessary size and fat reserves. Once these new queens and males emerge, they leave the nest to mate with individuals from other colonies, preventing inbreeding. The original founding queen often dies shortly after the new reproductives emerge. The workers and males perish with the arrival of the first hard frost. Only the newly mated gynes survive, using their fat reserves to seek out a suitable hibernaculum, ensuring the annual life cycle begins anew the following spring.