Honey bees, for survival, must maintain a constant temperature between 32°C to optimally 35°C within their hives. As temperatures drop, these clever creatures make a tight group within the hive to stay warm; clustering around the queen, keeping her warm.
In summer the worker bees fan their wings to keep her from overheating. You can hear the gentle beating of those wings from a few feet away. This is a precision process. And the secret of how its done can be found deep inside their hives as a special type of bee, acting like a radiator warms the nest.
These ‘heater’ bees are key to the colony’s survival and in determining what roles new bees will play in the colony.
Researchers have found that these bees, who have higher body temperatures than the other bees, not only keep the hive warm, but also control the social make-up within a colony. In a highly organised manner, behaving like a single superorganism each honey bee has a task. As Richard Gray, Science Correspondent for the Telegraph writes so succinctly, “the heater bees maintain the temperature of the brood nest in a hive, where young bees, known as pupae, are sealed into wax cells while they develop into mature bees”.
He continues that these scientists discovered that “heater bees work to subtly change the temperature of each developing pupae by around a degree and this small change determines what kind of honey bee it will become. Those kept at 35 degrees C turn into the intelligent forager bees that leave the nest in search of nectar and pollen. Those kept at 34 degrees C emerge as “house keeper” bees, conducting chores such as feeding the larvae and cleaning the nest.
Professor Jürgen Tautz, head of the bee group at Würzburg University, in Germany, said this allows the heater bees to control what sort of job a bee will fulfil when it matures and so ensure there are always enough bees filling each role within the colony. He said: “The bees are controlling the environment they live in to make sure they can fill a need within the colony. “Each bee in a colony performs a different profession – there are guard bees, nest building bees, brood caretaking bee, queen caretaking bee and forager bees, which are the ones we are familiar with as they leave the colony. “By carefully regulating the temperature of each pupae, they change the way it develops and the likelihood of the role it will fulfil when it emerges as an adult.”
By beating the muscles that would normally power their wings, heater bees increase the temperature of their bodies up to 44 degrees C – nearly 10 degrees hotter than a normal bee. They then crawl into empty cells within the brood nest, transmitting heat to the surrounding cells where the bee pupae are developing. The waxy cells also help circulate the heat around the rest of the hive. In the past beekeepers have seen these empty cells as undesirable and have attempted to breed queens that did not leave them empty, but Professor Tautz now claims they are an essential part of ensuring the health of a bee colony. Warmth is essential for bees as they need a body temperature of around 35 degrees C to be able to fly.
The heater bees, which can number from just a few to many hundreds depending on the outside temperature and size of the hive, also press themselves against individual cells to top up the temperature of each pupae to ensure it develops into the right kind of bee.
Professor Tautz added: “The old idea was that the pupae in the brood nest were producing the heat and bees moved in there to keep warm, but what we have seen is that there are adult bees who are responsible to maintaining the temperature.
“They decouple their wings so the muscles run at full power without moving the wings and this allows them to raise their body temperature extremely high.Their body temperature can reach up to 44 degrees centigrade. In theory they should cook themselves at that temperature, but somehow they are able to withstand this high temperature.”
“By creeping into empty cells, one heater bee can transmit heat to 70 pupae around them. It is a central heating system for the colony.
“Now we know that these empty cells are important, then bee keepers can try to avoid selecting for queens that don’t leave these cells empty. It can help to ensure that colonies can regulate their temperature properly and have the right mix of individuals.”
Dr David Aston, chair of the British Beekeepers Association’s technical and environmental committee, said: “There has never been a good reason for the presence of individual empty cells across the face of the comb.
“Now Professor Tautz has provided an explanation and beekeepers will look more closely at the brood combs to see if they can observe heater bees at work.”
Professor Tautz has asked us to make clear that the temperature changes brought about by the heater bees alter the probability of the tasks that will be performed by larvae when they mature.”