Many people assume bees hibernate during winter, much like some mammals. However, most bee species, particularly honey bees, do not enter a state of true hibernation. Instead, they employ distinct survival strategies to endure cold months, allowing them to persist until warmer weather returns.
Honey Bees’ Winter Survival
Honey bee colonies survive winter by forming a tight cluster inside their hive when temperatures drop below 50-57°F (10-14°C). This cluster acts as a collective warm-blooded organism, generating heat to keep the colony alive. Worker bees vibrate their flight muscles without moving their wings, a process that produces warmth. This shivering can maintain the core temperature of the cluster, where the queen resides, between 90-100°F (32-37°C), even when outside temperatures are much colder.
The cluster is organized into layers, with a dense outer mantle of bees that insulates the warmer, looser core. Bees on the exterior rotate inward, allowing others to take their turn on the colder outer layer and preventing any single bee from over-exerting or starving. To fuel this heat production, the bees consume their stored honey. The cluster slowly moves across the frames within the hive, following the honey stores to ensure a continuous food supply.
Other Bees’ Winter Strategies
Unlike honey bees, many other bee species do not maintain a full colony through winter. Bumblebees, for instance, have an annual life cycle where only new, mated queens survive the cold season. The worker bees, male drones, and the old queen all perish with the onset of colder temperatures. These new queen bumblebees enter a state of true hibernation, often burrowing alone into soft soil, leaf litter, or under logs and stones. During this dormant period, their metabolism significantly slows, and some produce a natural antifreeze, like glycerol, to prevent ice crystals from forming in their cells.
Solitary bees, which comprise the majority of bee species, also have diverse winter survival methods. For many solitary bee species, the adult bees from the previous season die off, and it is their offspring that overwinter. These developing bees, typically in their larval or pupal stages, remain in a protective cocoon within their sealed nest cells, often located underground or in cavities like hollow stems or wood. They enter a state of torpor, a sleepy state different from hibernation, where they consume stored “bee bread” (a mixture of pollen and nectar) for sustenance until they emerge as adults in the spring.
Preparing for Winter
Bees undertake several preparatory actions in the months leading up to winter to enhance their survival chances. Honey bee colonies focus heavily on accumulating substantial honey stores throughout the spring and summer. As autumn progresses, the queen bee reduces or stops egg-laying, leading to a decrease in the colony’s population and conserving food resources. Honey bees also seal small cracks and openings in their hive with propolis, a resinous material, to help insulate the hive and protect against drafts.
For other bee species, preparation involves individual efforts. New queen bumblebees, before hibernating, forage intensely to build up fat reserves which will sustain them through their dormant period. They then seek out sheltered locations to establish their hibernaculum. Solitary bees prepare individual larval cells with sufficient provisions of pollen and nectar, ensuring their offspring have enough food to develop and survive the winter within their protected nests. These proactive measures ensure the successful overwintering of various bee populations.