Heating & cooling methods as individuals and as members of a complex society.
Thermal physiology is important for bee colonies as temperatures change throughout each season. Since bees operate at air temperatures between 57 °F and 100 °F (13.9°C and 37.8 °C), keeping warm in the winter and cool in the summer become especially necessary for survival [2]. They have adapted special methods of thermoregulation to combat the effects of temperature year-round. Thermal regulation in social bee species is especially complex because they can employ multiple types of thermal regulation in order to balance their internal temperatures. Since they are flying insects, they require specialized muscles that need to be kept at certain temperatures in order to work.
As the flight muscles work, they generate heat that spreads throughout the thorax of the bee, while the abdomen remains relatively the same temperature as the air in their environment. Bees are an example of thoracic homeothermy because they are able to maintain a constant abdominal temperature, even when the flight muscles within the thorax are expelling large amounts of heat. If the flight muscles of bees, such as the worker honeybee (Bombus vagans) are not at least 30°C, the bee cannot take flight because the weather conditions are too cold and must invoke physiological or behavioral changes, such as shivering, clustering, or working harder to increase the amount of heat in its body. Similarly, bees cannot fly when their body temperatures are too high, and they will resort to cooling techniques.
Thermoregulation in Cold Weather
Brood-rearing honeybee hives tend to maintain the combs inside the hive at around 32°- 36°C (89.6°- 96.8°F) and must act as a collective colony to maintain this very narrow temperature range. The colony can even maintain this temperature range when outside air conditions are as low as -30°C. If the hive becomes colder than 32°C, the workers will cluster together inside the hive and shiver to release metabolic heat in order to keep the hive warm. When there is no brood present in the hive, the temperature may fall below this range but the bees will ensure the hive maintains a temperature well above freezing, or they will risk dying [3,4].
Thermoregulation in Warm Weather
In warmer temperatures, bees will need to use other methods to keep the hive cool. If the hive becomes too hot, the workers will fan the hive to expel the hot air and bring in cooler outside air. If outside air conditions are still too warm for the hive, the workers will disperse water droplets over the brood combs. Then they will fan the hive to cause the water droplets to evaporate into the hive. When there is no brood present, the temperatures can be higher than 36°C, but the workers will make sure the hive never reaches critically high temperatures. These thermoregulation techniques will keep the hive cooled to this range at outside air temperatures as high as +50°C [3,4].
Further Reading
FLIR® Systems, Inc. (2019, December 10). Saving Beehives. Flir. Retrieved October 25, 2020, from https://www.flir.com/discover/professional-tools/saving-beehives-with-flir-thermal-cameras/
Beepods (2020). How Honey Bees Survive Winter by Regulating Their Temperature in a Cluster. https://www.beepods.com/honey-bees-survive-winter-regulating-temperature-cluster/#:~:text=When%20the%20temperature%20of%20the,%C2%B0F%20air%20temperature%20range.
Wilson-Rich, N., Allin, K., Carreck, N., & Quigley, A. (2014). The Bee A Natural History. Princeton University Press. Pp 76.
Hill, R. W., Wyse, G. A., & Anderson, M. (2016). Animal Physiology (4th ed.). Sinauer Associates, Inc. Publishers. Pp 282-283.
claz550. (2017). Worker bees fanning hive entrance to keep it cool. Imgur. https://imgur.com/FCKcd11