Does a winter cluster of about 2 kg of bees consume more or less energy at 2 °C than at 15 °C in the hive?
- It consumes about the same energy, because the cluster always compensates for the drop in temperature.
- It consumes more energy at 2 °C, because any drop in temperature necessarily increases the needs.
- It consumes less energy at 2 °C, because a strong cluster then stays well contracted.
Show answer
Correct answer: 3.
It consumes less energy at 2 °C, because a strong cluster then stays well contracted.
Why?
For a strong winter cluster, of about 2 kg of bees, consumption can be lower at 2 °C than at 15 °C. This result seems counter-intuitive, but it is explained by the structure of the cluster.
When it is cold, the cluster contracts. The bees thereby reduce the surface of exchange with the surrounding air and limit heat losses.
At a more moderate temperature, such as 15 °C, the cluster can loosen or partially break up. The total exposed surface then increases, which can raise heat losses and therefore energy consumption.
What to understand
The winter cluster is not a simple “heated block”. It is a living structure that contracts, loosens and regulates its heat losses according to the temperature, the size of the colony and the physiological state of the bees.
The effect is not the same for all colonies. A small cluster loses proportionally more heat than a large one, because its surface-to-volume ratio is unfavourable. It may therefore consume more and be more fragile in cold periods.
For a strong cluster, moderate cold can maintain a compact and economical cluster. Conversely, a milder temperature in the hive can favour a less compact cluster, sometimes more costly in energy.
Key points
For a strong cluster of about 2 kg, consumption can be lower at 2 °C than at 15 °C.
The main reason is the contraction of the cluster, which reduces heat losses.
This benchmark must not be generalised to small colonies: a cluster that is too weak loses its heat more easily and overwinters with greater risks.
Further reading
► Sense and nonsense of thermal insulation of hives