Thermoregulation of the Honey Bee Colony
It is unsurprising that the honey bee caste system has been described as a “superorganism”. The colony itself is a highly functioning social unit, with each sub-group of bees working together in the nest or hive in one of nature’s most evolved and well-oiled machines. As described in The Caste System of the Honey Bee, this involves each social group taking on very specific responsibilities so that the colony can thrive. This capacity is seen once again as these complex animals self-regulate the internal temperature of the bee colony through a variety of cooperative methods.
The brood—or pre-adult bee life, including larvae and pupae—requires a very controlled temperature to survive and thrive. Like many aspects of the bee life-cycle, honey bees have developed sophisticated methods to ensure that this temperature is maintained between 32°C and an optimal 34°C. This will ensure that the brood develop healthily, as even small deviations in this climate adversely affecting the young: research has shown that any deviation of more than 0.5°C have significant influence on the health of the resulting adult bee. The method for maintaining this colony temperature is to fan the air out of the nest, or use evaporation cooling mechanisms, when the temperature is too high; when the mercury drops, honey bees generate metabolic heat by contracting and relaxing their flight muscles, uncoupling their wings. Their muscles heat up and this heats the air. Just like you might warm your car up on a winter’s morning, many insects use this process of vibration to heat their muscles before flights; however, bees have cleverly taken this one step further, and maximised on their muscle warmth to thermoregulate their home.
Once optimal temperature is reached, strict thermo-control and stabilisation of this colony climate is achieved in various ways. The brood cells are capped with a seal of beeswax. To heat the cells, honey bees press their thoraces, or middle sections, down on the cell to transfer their own body heat to the pupae inside. A “heater” bee, with a body temperature of around 43°C, can hold their position for up to 30 minutes, while other bees thickly pack the comb around it to keep the warmth in. Another intriguing method is for these same heated bees to actually occupy empty brood cells (approximately 5-10% of the entire colony) that have been strategically positioned around the nest or hive. Due to this intense process of heating their bodies to a high temperature, these special thermo-bees expend tremendous amounts of energy in the form of a highly-concentrated honey that is brought to them by other workers. This very concentrated substance is the best food to maintain the energy of the heater bees, surpassing them feeding on nectar found in the brood area. In contrast, cooling the colony is a less demanding process, and is achieved by fanning their wings, evaporating water inside the bee-home and, at times, partially evacuating the nest. This method of thermoregulation is yet another sophisticated example of how the honey bee shares tasks to ensure quality of life and growth in their species.