Brood temperature is one of the earliest signals about the condition of the colony. A healthy colony keeps it with surprising precision, and every deviation means something.
What is normal
Bees maintain brood temperature between 32 °C and 35 °C. Not approximately, but really precisely. It is necessary for proper brood development. When overheated, bees ventilate and cool by evaporating water. When temperature drops, they generate heat through muscle activity.
This regulation costs the colony energy. The colder it is outside, the more is consumed. A smaller colony is less efficient at this than a strong one.
What a change signals
A deviation from a stable 34 °C is not random. It can signal:
- A missing or non-laying queen when egg-laying stops, the brood area gradually cools and the temperature loses stability
- Preparation for swarming because colony behaviour changes even before the swarm leaves
- The seasonal end of brood rearing in autumn, the queen slows egg-laying and brood temperature gradually drops
In the graph above, you can see brood temperature that was first stable around 34 °C and then started to fluctuate and fall. The cause was a late summer nectar dearth and the queen slowed egg-laying.
The queen started laying without opening the hive
The opposite case is just as interesting. If the colony had no brood, after making a split or after replacing the queen, stabilization of brood temperature reliably signals that the new queen has started laying.
This graph shows a hive after a new queen was introduced. Brood temperature stabilized at 34 °C after 6 days, and without disturbing the bees, we know the queen was accepted and is laying.
Spring: the first signal of the new season
In spring, brood temperature rises and stabilizes before anything is visible on the hive from the outside. It is one of the first reliable signals that the brood-rearing season has started.
Practical use
You follow brood temperature in the app together with weight. The combination of these two curves gives a picture that you would otherwise get only by opening the hive:
- Weight stagnates + brood temperature unstable -> a problem with the queen
- Weight falls + temperature stable -> normal winter consumption
- Weight rises + temperature stable -> nectar flow is running, colony is fine