Bees exhibit remarkable strategies for surviving the cold. While individual bees are susceptible to low temperatures, a colony’s collective adaptations allow them to endure harsh winter conditions.
Temperature Limits for Bee Survival
The ability of bees to withstand cold varies significantly depending on their species and social structure. Individual honey bees cannot survive freezing temperatures on their own. Their bodies enter a state of chill coma if temperatures fall below approximately 10°C (50°F), leading to immobilization and eventual death if not warmed. Honey bee colonies (Apis mellifera) demonstrate impressive resilience, capable of surviving external temperatures well below freezing, even down to -20°C (-4°F) or colder, provided the colony is strong and healthy.
In contrast, solitary bees and bumblebees employ different overwintering strategies. Most solitary bee species, which do not form colonies, typically overwinter as dormant larvae or pupae within protective cocoons, often underground or in sheltered cavities. These developmental stages possess natural cryoprotectants, acting like antifreeze, that allow them to endure sub-zero temperatures. Bumblebee colonies do not survive the winter; instead, only new queens, fertilized in the fall, hibernate by burrowing into the soil or under leaf litter, entering a state of diapause where their metabolism slows significantly until spring.
How Bees Survive Cold Temperatures
Honey bee colonies primarily survive cold temperatures through a collective behavior known as clustering. When the ambient temperature inside the hive drops to around 10-14°C (50-57°F), the bees form a tight, spherical cluster. The outer layer of bees in this cluster pack together closely, creating an insulating shell that minimizes heat loss. These outer bees remain relatively still, with their heads often pointed inward, while their abdomens are exposed to the colder air.
Inside this insulating mantle, bees actively generate heat through a process called shivering thermogenesis. They rapidly contract and relax their flight muscles without moving their wings, much like how humans shiver to warm up. This muscular activity consumes energy and produces heat, which warms the core of the cluster. The core of a honey bee cluster is maintained at a remarkably stable temperature, typically between 24-30°C (75-93°F), and can even reach 32-37°C (90-100°F) if brood is present. Bees continuously rotate between the warmer core and the cooler outer layers, ensuring that no individual bee becomes too cold.
The primary fuel source for this heat generation is honey, which bees consume to power their metabolic processes. As outside temperatures decrease, the bees’ metabolism increases, leading to higher honey consumption to maintain the cluster temperature. The queen bee remains at the warm center of this dynamic cluster, protected by her worker bees.
Key Factors for Winter Survival
A strong colony with a large population of healthy “winter bees” is better equipped to form an effective heat-generating cluster. These specialized winter bees have larger fat bodies and live significantly longer than summer bees, typically four to five months compared to a few weeks, which is essential for sustaining the colony through the long, non-foraging period.
Adequate food stores, primarily honey, are paramount. A healthy colony in temperate regions needs between 60 to 90 pounds of honey to fuel its heat production and sustain itself through winter. Pollen reserves are important for providing essential nutrients, particularly for the development of long-lived winter bees and early spring brood.
Moisture control within the hive is often more important than the cold itself. Bees generate significant water vapor as they metabolize honey, and if this moisture condenses on cold hive surfaces and drips onto the bees, it can lead to hypothermia, mold growth, and disease. Proper ventilation, such as a small upper entrance or a moisture-absorbing quilt box, helps to remove excess humidity without creating detrimental drafts.
The health of the colony, including the absence of diseases and parasites like Varroa mites, significantly influences winter survival. Varroa mites weaken bees by feeding on their fat bodies and transmitting viruses, reducing their lifespan and ability to thermoregulate effectively. The hive’s location and protection from environmental elements also play a role. Placing hives in areas sheltered from strong winds and with some winter sun exposure can help reduce energy expenditure for the bees.