How do honey bees keep their hive warm?
Honey bees do not heat their hives the way we heat our homes. Instead, they concentrate on keeping the cluster warm by vibrating their flight muscles. The center of the cluster is the warmest part of the hive, and the temperature drops as you move out from the center.
The interior of the hive is warmer than the outside air because heat escapes from the cluster and the hive itself offers a small amount of insulation. But the bees do not attempt to keep the entire space warm. In fact, the air inside the hive can be quite cold.
Because hot air rises, the warmest place outside of the cluster is right above the cluster. A beekeeper can help keep the hive slightly warmer by placing insulation above the cluster to capture some of this escaping heat.
Bill’s hive temperature experiment
In order to help explain this phenomenon to new beekeepers, Bill Reynolds of Minnesota decided to monitor the temperature inside his hives as the colonies plunged into winter. According to Bill, he purchased an inexpensive desktop weather forecasting station with three remote wireless sensors for his project. He used a fourth sensor to monitor the ambient outside air.
The weather cooperated for his experiment. Bill says, “Here in Minnesota we are experiencing bone-chilling temps around zero each morning and mid-twenties, if we are lucky, by noon.”
Bill set up three hives, each with three deeps topped with a quilt box. One hive contained a colony of Carniolans, one a colony of mutts, and one was empty. In each hive he centered the sensor over the third deep but under the quilt box. He did not attempt to place the sensors at the core of the clusters. During the measurement period, the clusters were two deep hive bodies below the sensors.
The hives were not wrapped. All three setups were on the south side of a house with a straw-bale wall blocking northwest winds. According to Bill, “Other than the sensors, there is nothing different between these hives and any other hive one would find in a backyard.”
Partway through the experiment, Bill began recording separate readings for the outside air and empty hive. He made this change because he noticed that the temperatures increased and decreased at different rates inside the empty hive and outside of it. It became apparent that the wooden boxes themselves influenced temperature fluctuations.
Warmer inside, but only slightly
The graph below shows temperature readings for each sensor. It is quite clear from this simple experiment that temperatures inside the active hives rose and fell with the outside temperature, but overall the inside remained warmer than the outside. But far from being cozy, the inside temperatures dropped down into the 30s on the coldest days. It is interesting to see that the two colonies were very consistent with each other, rising and falling in tandem.
It also became clear that the interior of the empty hive box was somwhat warmer than the outside air. I suspect a combination of sun and minimum air movement through the boxes increased the temperature slightly.
Thank you, Bill, for your experiment and awesome graph. Nicely done!
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