Brood temperature is a critical factor in colony health and is precisely managed by the bees to achieve a stable temperature of 93-97ºF (33ºC - 36ºC). Thousands of individual bees work together to maintain these optimal conditions, engaging in a combination of heating and cooling activities in response to changing conditions inside and outside the hive. Heat is generated by bees vibrating their thoracic flight muscles, and the hive is cooled by workers fanning and evaporating collected water droplets. The ability of a bee colony to maintain stable brood temperature is the result of coordinated behavior and is therefore a good indicator of  colony function and health. Figure 1 below compares the brood temperature of 2 hives. You can see how the healthy queenright colony (green line) has a very stable brood temperature within the optimum range, whereas the broodless colony (red line) has a much lower and highly variable brood temperature.

Monitoring the maximum, minimum, and daily variation in temperature enables early detection deviations outside the healthy temperature range. Loss of temperature stability can be caused by  a number of different events or circumstances. Also important in temperature analysis is the time frame over which the changes occur, and the nature of the temperature changes.  For instance a sudden rise in temperature above the maximum safe threshold indicates an overheating event, this could happen during transportation, or in a badly ventilated hive in a heatwave. A sudden and complete loss of temperature stability can indicate a catastrophic event such as colony collapse.   A gradual fall in temperature and loss of stability can be caused by a failing queen or queenless hive as the brood area shrinks. Figure 2 shows a hive that loses brood temperature stability during the middle of summer.

We can see how brood temperature is such a valuable indicator of colony status, however combining temperature data with colony audio and weather data brings valuable context and enables even more detailed interpretation of colony status. Next time we'll take a closer look at some specific colony insights using sensor data. In the meantime please reach out with any questions or suggestions for topics that you would like to see covered.