Bees, like all insects, are ectotherms, meaning they cannot generate internal heat to regulate their body temperature. As the environment cools and floral resources disappear, their survival faces a serious challenge. The methods bees use to get through the cold months are diverse, ranging from collective warmth to deep, solitary dormancy. The strategies employed depend entirely on the species’ social structure; a hive-dwelling honey bee has a dramatically different winter than a solitary mason bee. The successful survival of bees through the winter secures the pollination needed for the coming spring.
The Social Strategy of Honey Bee Colonies
Honey bee colonies survive winter as a unified, active social unit, not by hibernating. When the temperature inside the hive drops to about 57°F (14°C), the worker bees form a tight structure known as the winter cluster. This collective acts as a “superorganism” to generate and conserve heat.
The cluster has a dense outer mantle of tightly packed bees that acts as an insulating layer. Bees on the inside vibrate their flight muscles without moving their wings, similar to shivering, which generates metabolic heat fueled by stored honey reserves.
The workers actively regulate the temperature within the cluster. The core temperature is maintained around 64–85°F (18–29°C) when no developing young are present. If the queen begins to lay eggs, the temperature is raised to 91–96°F (33–36°C). The queen remains safe and warm in the center, surrounded by worker bees.
To prevent individual bees on the outside from freezing, the workers continuously rotate, moving from the cold outer shell to the warmer core. This movement ensures that collective body heat is shared throughout the colony. The cluster will tighten or expand as the external temperature fluctuates, minimizing heat loss.
How Solitary Bees and Bumble Bees Cope
The vast majority of bee species are solitary, relying on a different, non-social strategy to survive the cold. Most adult solitary bees, such as leafcutter and mason bees, complete their life cycle and perish before winter arrives. Survival is entrusted to the next generation, which is sealed inside individual nest cells.
The young of solitary bees overwinter as eggs, larvae, or pupae inside their protected nests in a state of suspended animation called diapause. Diapause is a hormonally regulated physiological state where development is halted and metabolism slows dramatically. These developing bees remain dormant within hollow stems, tunnels in wood, or underground burrows, relying on the food provisions left by their mother.
Bumble bees do not overwinter as a colony; only the newly mated queen survives. The rest of the colony, including the workers and males, dies with the onset of cold weather. The fertilized queen finds a protected underground location, such as loose soil or an abandoned rodent tunnel, called a hibernaculum.
The queen enters diapause for up to nine months, relying on fat reserves built up in the late fall. Her body produces a chemical, like glycerol, which acts as a natural antifreeze to protect her tissues. She will emerge alone in the spring to begin founding a new colony.
Preparation and Winter Provisions
Honey bee colonies begin preparations for winter long before the first frost, focusing intensely on resource management. Worker bees spend the late summer and fall accumulating massive stores of honey and pollen within the hive. The stored honey serves as the carbohydrate fuel that powers the muscle contractions needed for the winter cluster to generate heat.
An average colony requires 60 to 90 pounds of honey reserves to survive a typical winter in colder climates. This resource conservation leads to the eviction of drones. Worker bees stop feeding the male drones and forcefully expel them from the hive in the fall, eliminating individuals that would otherwise consume precious food stores.
Brood rearing is also reduced or temporarily ceased by the queen in late fall, minimizing the energy and food required to maintain the high temperatures of the brood nest. Beekeepers aid this natural process by ensuring hives have adequate food stores and protection. Assistance includes reducing the hive entrance to keep pests out and sometimes adding insulation or supplemental sugar feed if stores are low.