Honeybees tell hornet predators to buzz off

Hornet worker approaching honeybee colony (c) Masato Ono/Tamagawa University The closer the hornet flies to the colony, the more intensely the guard bees shake

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Asian honeybees signal to their enemies - bee-eating hornets - to let them know they have been spotted.

An international team of scientists watched the bees as they guarded the entrance to their hive.

The researchers described how the bees shook their abdomens when a hornet approached, a signal that triggered the hornet to retreat.

They published their findings in the journal Animal Behaviour.

Researchers already knew of this "characteristic shaking signal", in which all the guards bees simultaneously vibrate their abdomens from side-to-side for a few seconds when a hornet approaches the colony.

In the wild, this produces a spectacular "Mexican wave" of vibrating bees.

Start Quote

The bees can back up their signal by killing the hornet if it lands”

End Quote Dr Benjamin Oldroyd University of Sydney

This study, carried out on a small bee hive, revealed the hornets (Vespa velutina) responded directly to the bees' shaking signal.

Warned wasps would retreat from the colony and try to catch bees in flight instead.

To find this out, the researchers tethered live hornets to lengths of wire and held them at a variety of distances from the hive entrance.

The closer the tethered hornet was held to the hive, the more intensely the bee guards shook their bodies.

To confirm that the bees were specifically "talking to" the hornets with this signal, the team carried out the same tethering experiment with a harmless butterfly species (Papilio xuthus).

This insect is slightly larger than the hornet and has very similar yellow and black markings.

Despite the similarity, the bees did not respond to the butterflies, no matter how close they came to the hive.

'I see you'

The researchers say this is an example of insect prey communicating with their predators.

"Our study proved that it is a real signal that the predator responds to," lead researcher Dr Benjamin Oldroyd from the University of Sydney told BBC Nature.

This communication, he explained, benefits both the bees and the hornets.

See a "mob" of honeybees overpower a giant hornet

"The bees can back up their signal by killing the hornet if it lands," the scientist explained.

By reacting to the bees' signal, the hornet avoids a rather grisly demise, as the research team described in their paper.

"If a hornet lands at the hive entrance," they wrote, "it is pounced on by the guards, which then form a dense ball of up to 500 bees around the hornet."

This kills the hornet with a combination of heat and suffocation.

Dr Stephen Martin, an expert in social insects from the University of Sheffield told BBC Nature that the bees' signal was a "classic co-evolution scenario".

"The [Asian honeybee] has co-evolved with the hornet and the two species are in this continuous arms race," he said.

Honeybee colonies, he explained, are a good food source for the wasps.

But as the bees have learned to defend themselves, the wasps "have had to change their approach to the bees".

"Rather than land on the colony, the wasps have to take the bees on the wing, which is much harder," Dr Martin explained.

Dr Oldroyd added: "Honey bees are a wonderful model organism for addressing fundamental questions in behaviour, social organisation, self-organising systems, evolution and genetics.

"This is just one more example of where honey bees have shed new light on an old question."

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