At What Temperature Do Bees Cluster?

Bees are incredible creatures with fascinating behaviors, including their ability to form winter clusters when temperatures drop in colder months. Winter clusters are a critical survival mechanism for honey bees, allowing them to maintain warmth by gathering tightly together inside the beehive. But at what temperature do bees begin to cluster?

bee swarm

Understanding Bee Clustering

Bee clustering is a vital survival mechanism that honey bees use to maintain their colony’s temperature during cold weather. This behavior enables bees to retain heat and protect themselves and their brood from harsh winter conditions. Clustering typically begins when the outside air temperature falls to about 57°F (14°C).

The bees form a compact sphere or cluster around the brood, with the queen bee at the center. The worker bees surrounding the queen generate heat through a process known as thermogenesis. This heat generation occurs when bees vibrate their flight muscles, thus maintaining an ideal core temperature of around 95°F (35°C) within the cluster.

Workers on the outer shell of the cluster are typically at a cooler temperature, slightly above 50°F (10°C). These outer bees continuously rotate with the inner bees to keep themselves warm and share the responsibility of heat generation. 

On warm days, the cluster loosens, allowing the bees to move within the hive to obtain food, as they consume honey stored during the warmer months for energy.

Temperature Range for Clustering

When the outside temperature drops to around 64°F (17.8°C), honey bees begin to form a loose cluster in their hive to keep the queen and themselves warm. As the temperature drops further, the cluster becomes more compact to retain heat more effectively.

The bees in the cluster must maintain a temperature above the coma-inducing threshold of 5.5°C, even for those at the outer surface of the cluster. Honeybees regulate the temperature within their cluster by contracting or expanding it depending on the ambient temperature, that is, the temperature outside the cluster (Collective thermoregulation in bee clusters – NCBI).

Factors Affecting Clustering Behavior

  • Colony size: Larger colonies are typically better able to generate and maintain heat within the cluster, thanks to a higher number of heat-generating bees.
  • Hive Insulation: Proper insulation can play a significant role in maintaining the temperature within the hive, thereby affecting clustering behavior. Better-insulated hives can help the bees conserve more energy.
  • Weather conditions: Unpredictable weather patterns, such as extreme cold or frequent temperature fluctuations, may force bees to cluster more frequently or for more extended periods. This can affect their ability to access food and ultimately impact the colony’s survival.
  • Food supply: A sufficient food supply is crucial for bees to generate heat during clustering. Limited food sources can result in weaker colonies and reduced clustering efficiency, leading to poor temperature regulation.

In addition to these factors, it is essential to note that bees within the cluster actively work together to maintain the optimal temperature for the queen and brood. They collectively thermoregulate by shivering their flight muscles and transferring heat through the cluster, thereby ensuring the inner core remains warm.

Impact of Clustering on Bee Colonies

While clustering is beneficial for the survival of bee colonies in the winter, it is also energy-intensive. Bees need to consume stored honey to generate the necessary heat, which can significantly deplete their honey reserves. Consequently, beekeepers must ensure that their hives have sufficient honey stores to survive the winter months.

Moreover, poor ventilation inside the hive can result in reduced moisture regulation. The air immediately above the cluster is very warm and rises. Once it gets to the inner cover, it condenses and the cold water drips down onto the cluster, which can kill the bees. Beekeepers must manage humidity within the hive during winter.

What to Do to Get Your Bees through Winter

Since beekeepers coax bees out of trees to live in our man-made hives, it is our responsibility to get them through winter. To do so, several methods can be employed:

1. Proper Insulation: Insulating the hive is important to help bees maintain a stable environment. Adding a layer of insulation material, such as foam board or even straw, can help trap heat inside the hive and absorb excess moisture from the cluster.

2. Windbreaks: Installing windbreaks around the apiary can reduce the chilling effect of winds during winter. This can be done by setting up your apiary near shrubs, fences, or other barriers that block wind without obstructing sunlight.

3. Entrances: Reduce the hive entrance size to facilitate better climate control and protect the bees from potential predators during the cold months. However, ensure that there is still adequate ventilation to prevent condensation, which can lead to mold and disease. In case of snow, consider adding a top entrance. That way, the bees can take cleansing flights (going number 2) on sunny days even when the lower entrance is snowed in.

4. Food Supply: Ensuring the bees have enough honey stores for the winter is crucial. In some cases, providing supplemental feeding in the form of sugar syrup or fondant might be necessary, so the cluster can generate enough heat.

5. Monitoring: Regularly check the hive situation without opening it too often. You can use a Thermo camera if you can get your hands on one, which will tell you where the cluster is in the hive. You can tell the size of the cluster, health, and if they have enough stores based on where they are in the hive without opening it. If you don’t have a thermal camera, you’ll need to lift the lid and take a peak, but preferably on a sunny day and only to check if they have enough food.

The Bees Know When to Cluster, So Just Watch Them

Bees were surviving winter long before beekeepers came along. Once we exchanged their four to six-inch tree walls for our less-than-an-inch hive wall, we made things a little more difficult for them. Scientists now believe that that might be the reason they cluster. Nevertheless, now that we have altered their lifestyle, there are some things we have to do to help them survive those chilly months. And the preparation begins just as the leaves start to turn. 

We hope you’ll be ready.

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