With tens of thousands of residents in a single hive, you would have thought that bees are pretty used to being knocked about a bit. But new research has found that this hasn’t stopped honeybees from emitting a little “whooping” noise whenever they're startled or surprised.

Researchers have known about the odd noise, which is really a vibrational pulse, for some time now, but explanations for its use have varied. Initially, it was thought that the bees made the pulse to beg for food from their hive-mates, but this was then revised.

It was also suggested that the signal was used to warn others of potential dangers when out foraging. The pulse was believed to be used by one bee to stop others from performing the waggle dance to describe where rich pickings are to be found, if the former new danger lurked in that area. It now seems that both of these theories might well be wrong, as new research suggests the “whooping signal” is more likely to be an expression of shock or surprise.

By placing ultra-sensitive vibrational sensors, known as accelerometers, into the comb of two hives in both the UK and France, researchers were able to continually monitor and eavesdrop on the vibrations emitted by the colony over an entire year. They found that not only was the vibrational pulse occurring too often to be a “stop” signal as previously thought, but it was also happening at the wrong time of the day.

If the bees were sending the pulse to prevent another from doing the waggle dance, then the researchers expected the pulses to be more frequent when more dances were being performed, which tends to be in the middle of the day. But they found the opposite to be true, as the bees were most likely to pulse at night, and that it increased when the weather was bad and the bees were stuck inside. In fact, some sensors recorded the pulse occurring more than five times per minute over successive days, far more frequently than if it was a “stop” signal.  

“We have found that this signal is remarkably common, much more than previously thought,” says Nottingham Trent University’s Dr Martin Bencsik, who co-authored the study published in PLOS One, in a statement. They now suspect that the pulse is instead made when the bees bump into and startle each other, and have recommended that it should now be called the “whooping” signal.

This would explain why it is more common at night and during bad weather – there are simply more bees inside the hive, increasing the chance they will knock into one another.