Honey bees' secret heat

By Richard Gray, Science Correspondent

 
The secret of honey bees' success has been discovered living deep inside their hives - a special type of bee which acts like a living radiator, warming the nest and controlling the colony's complex social structure.

The "heater bees" have been found to play a crucial, and previously unappreciated, role in the survival of honey bee colonies.

They have found that these specialised bees, whose body temperatures are considerably higher than other bees in the colony, not only keep the hive warm but also control the social make-up within a colony.

Bees, and other social insects such as ants, share jobs within a colony so each individual has specific role that benefits the colony as a whole.

It is this division of labour that has allowed bees to become so successful as they behave like a highly organised, single "superorganism" rather than a cluster of selfish individuals.

Heater bees are responsible for maintaining 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.

The scientists discovered that the 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 that never leave the nest, 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."

The findings will be revealed later this month in a new BBC series Richard Hammond's Invisible World, where technology is used to give a glimpse into previously unseen worlds.

Thermal imaging cameras reveal how individual heater bees warm up the nest to precisely the right temperature.

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."

Temperature is known to have an influence on the development of young in other animal species.

In crocodiles, the sex of hatchlings is determined by the average temperature of the eggs during a key point in the incubation period, so if they are kept above 34.5 degrees C the offspring will be male.

Many species of fish and turtles also use temperature to determine the sex of their young.

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."  The Telegraph