Bumblebees are social insects that operate on an annual cycle; their colonies do not persist through the winter months like those of honeybees. The entire life cycle, from the queen emerging in spring to the colony’s natural end, occurs within a single year. When cold weather arrives, the vast majority of the bees die. The future of the species rests on the successful hibernation of the newly produced queens.
The Fate of the Colony
By late summer or early autumn, the original queen stops laying worker-producing eggs. The colony’s focus shifts to generating reproductive individuals: new queens and male drones. Drones leave the nest to find mates from other colonies and do not contribute to nest maintenance or foraging.
Once the new queens emerge and mating is complete, the original colony begins its natural decline. Worker bees, whose lifespans are short, die off after completing their work of tending to the brood and foraging. The old founding queen also perishes, having exhausted her reproductive capacity.
Drones do not survive the onset of winter temperatures, having served their sole purpose of mating with the new queens. This leaves the nest entirely empty, as the entire structure and all its inhabitants come to an end. This annual termination of the colony is a programmed part of the bumblebee life cycle, ensuring that only the newly mated queens survive the harsh conditions.
The Survivor: The New Queen
The only bumblebees that survive the winter are the newly emerged, fertilized queens, which enter a dormant state called diapause. Diapause is a physiological, hormone-mediated process that allows the queen to survive months without food. This state dramatically lowers the queen’s metabolism, reducing her energy needs to a minimum.
Before entering this dormant phase, young queens must engage in intense feeding, consuming large amounts of nectar and pollen to build up fat reserves. These reserves are stored in a specialized insect tissue called the fat body, which functions like a liver for energy storage and release. The fat body accumulates lipids and glycogen, which serve as the fuel source to sustain the queen throughout her hibernation.
The weight gained immediately following emergence is important for successful overwintering survival. Queens can metabolize nearly 80% of their stored fat during diapause, relying on this internal fuel until the following spring. This preparation determines her chances of surviving the long, cold period and successfully founding a new colony.
Hibernation Sites and Preparation
To survive the winter, the mated new queen must find a location that offers stable temperatures and protection from freezing and premature warming. This location is often a shallowly buried chamber in the soil, usually excavated by the queen herself. Queens often dig down more than 10 centimeters into well-drained, soft soil, or seek shelter under thick layers of leaf litter, dense moss, or within rotting logs.
Queens sometimes choose sites on slopes or raised areas, which helps reduce the risk of flooding, a significant hazard during the winter. Some queens may select north-facing locations, which receive less direct sunlight. This helps keep the temperature consistently low and prevents the queen from waking up too early during a brief winter thaw.
Once the queen has selected and prepared her site, she seals herself off and remains immobile until environmental cues signal the arrival of spring. The timing for entering this state is typically late autumn. Emergence occurs when temperatures rise consistently and early-flowering plants provide the necessary nectar and pollen to replenish her depleted reserves. A successful hibernation allows the queen to emerge ready to begin the cycle anew.