The greater the number of bees that make up the winter cluster, the more...
- its surface-to-volume ratio increases.
- its surface-to-volume ratio approaches that of a sphere.
- its surface-to-volume ratio decreases.
Show answer
Correct answer: 3.
Its surface-to-volume ratio decreases.
Why?
The larger a winter cluster is, the faster its volume increases relative to its surface. In other words, the surface exposed to the cold becomes proportionally smaller.
This is important for the bees, because heat losses occur mainly through the surface of the cluster. A large cluster therefore loses less heat per unit of volume than a small cluster.
Conversely, a small cluster has proportionally a great deal of exposed surface. It must therefore expend more energy to maintain a temperature compatible with the survival of the colony.
What to understand
The winter cluster functions as a collective structure. The bees of the outer mantle limit heat losses, while bees further inside can produce heat through muscular contractions.
The surface-to-volume ratio explains why the size of the colony is a critical factor in winter. A colony that is too weak has more difficulty conserving its heat, even if each bee takes part in the collective effort.
This logic does not mean that a very large colony never has any winter risk. The stores, the humidity, the health status, the presence of varroa, the quality of the winter bees and access to food remain decisive.
Key points
When the cluster increases in size, its surface-to-volume ratio decreases.
A large cluster loses proportionally less heat than a small cluster.
This is one of the reasons why small colonies overwinter with greater risks, especially if they lack stores or good-quality winter bees.
Further reading
► Sense and nonsense of thermal insulation of hives
► Overwintering in the honey bee
► Insulation of hives put to the test of the collective thermoregulation of bees