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Two giant hornets (Vespa soror) on a honeycomb
Photo: Heather Mattila
In the animal kingdom, complaints and warnings are more familiar from more highly developed species. But honey bees are also able to do this. With loud alarm calls, the insects alert their conspecifics in the beehive to an attack by giant hornets. The warning calls resembled the screams of fear or the screeching of primates and birds, write researchers in the journal "Royal Society Open Science". And as they could see, the signals are also having an effect: when the warning call sounded, the workers gathered and presumably prepared their defense.
Giant hornets are among the worst enemies of the eastern honey bee (Apis cerana). As a rule, several of the many times larger hornets attack a colony of bees after a single scout has identified a suitable hive. If the attack is successful, the hornets kill the workers gathered for defense, occupy the nest and feed the defenseless brood to their own offspring.
In order to examine the bees' reaction to impending danger more closely, the team around Heather Mattila from Wellesley College (USA) listened to colonies of various beekeepers in Vietnam. The researchers hung microphones between the individual frames of the beehives and recorded the noises before, during and after one or more Asian giant hornets (Vespa soror) approached the hives. For a more detailed analysis, the scientists then graphically displayed the frequencies of the bees' sounds in spectrograms.
As the recordings showed, the beehive is often noisy anyway. The insects constantly produce noises. A special hissing sound stands out from the hum and hum, the function of which has not yet been finally clarified. An acoustic stop signal is also known, which brings conspecifics to interrupt their tasks, such as the waggle dance. This dance shows conspecifics the way to a source of food.
As soon as a hornet approached the beehive, the noise level increased eightfold and a real cacophony broke out, as the researchers report.
They identified a buzzing sound signal in the noise, which the bees presumably emitted specifically as a warning of the impending attack.
"This sound has a lot in common with numerous known mammalian alarms that immediately signal a threat," said Mattila.
While the bees warned their conspecifics acoustically, they whirred their wings and lifted their abdomen together with the Nasonov gland located there.
This gland produces fragrances that also serve for communication between the bees.
Presumably, the animals warned each other about the danger in different ways, the researchers write.
How the honey bees form and perceive the warning sound is still open. Bees do not have ears; they sense sounds rather than hear them. In their antennae there is a sensory organ that can register changes in pressure and sound, the so-called Johnston organ. They also have an organ on their legs with which they can perceive vibrations from the ground. The sound communication of bees is therefore called vibroacoustic.
According to the study, the emitted warning sounds seemed to have an effect: The researchers observed that the workers gathered in front of the entrance to the hive, possibly to initiate protective measures. It is known from previous studies that Asian honey bees place stinking dung from other animals at the entrance to ward off hornets - a behavior that is interpreted as the first documented use of tools by bees. In addition, the bees surround attacking hornets in a so-called heat ball and suffocate them in it.
Further research should corroborate the observations and conclusions, the researchers write.
"This research shows how amazingly complex the signals produced by Asiatic bees can be," said Gard Otis, one of the researchers involved.
“We have the feeling that we only scratched the surface of the way we understood their communication.
There's still a lot to learn. "
joe / dpa
