Giant ‘murder hornets’ can decimate honeybees. This is how screaming helps their defense

When Vespa soror – giant hornets found in parts of Asia – attack a honeybee hive, they kill as many bees as possible, decapitating them and scouring the hive to harvest their young.

To protect their hives from such a catastrophe, some species of honeybees have developed an arsenal of defensive techniques. They may forage for other animals’ feces and place it at their nest’s entrance to repel predators, a tactic called “fecal spotting.” Or, in a technique known as “balling,” a cluster of honeybees may engulf a hornet, vibrate their flight muscles and produce enough heat to kill the enemy.

Now, a new study published in Royal Society Open Science says honeybees have another defense: screaming.

More precisely, the bees in the study produced a noise known as an “antipredator pipe” – not something that comes out of their mouths, but rather a sound they produce by vibrating their wings, raising their abdomens and exposing a gland used to release a certain kind of pheromone.

To human ears, the result is a high-pitched whine. To bees, the frantic vibrating is likely a “rallying call for collective defense” against the hornets, the study says.

Yet bees don’t “hear” like humans, explained Heather Mattila, a biologist at Wellesley College and a co-author of the study. Except in certain circumstances, bees transmit and receive vibrations via “substrate,” meaning vibrations are sent through a surface and picked up by sensors in the bees’ legs.

So while the piping sound is not technically a “scream” – a sound produced by vocal cords – it serves a similar function and shares “acoustic traits with alarm shrieks, fear screams and panic calls of primates, birds and meerkats,” the study says. Plus, Mattila acknowledged that screaming is a useful metaphor – and it’s close enough that she and her team referred to the high-pitched vibrations as “screams” as they studied the bees. “All my spreadsheets say ‘screams,’ ” Mattila told The Washington Post.

To Mattila, the discovery of honeybee distress signals shows that communicating danger may be a universal experience for animals. “These sounds in particular are disturbing,” she said. “And I think it is because they have these properties that are sort of universally alarming – they’re meant to be alarming for anyone who’s listening.”

Giant hornets have received much attention in the United States after the first “murder hornets” were spotted in 2019 in Washington state. With large mandibles capable of dismembering and masticating honeybees en masse – and stingers that can puncture beekeeping suits – the V. mandarinia has become an increasing threat to honeybee hives in the U.S. The hornets in the study released Wednesday are a “sister species” to the ones found in Washington, researchers wrote.

“Everything about these two species is the same. The size is the same; the way they hunt is the same,” Mattila said. “If anything, Vespa soror actually has bigger colonies.”

For more than seven years, Mattila and her colleagues have studied interactions between giant hornets and honeybees in Vietnam, according to a news release. Having recorded about 30,000 signals made by colonies of bees, they believe that a beehive is in constant communication – a “bustling signaling space” – even when the bees are relaxed, the study says.

But during stressful events, those signals increase dramatically. When the V. soror hornet was threatening to wipe out a hive, the bees’ signals increased sevenfold, the study found. They may come in the form of hisses, quick bursts of vibration or the loud, high-pitched whine that had not been previously studied.

The researchers recorded the bees’ reactions to five hornet attacks, including ones by the V. soror and a slightly smaller hornet called the V. velutina. They placed microphones inside the hives and video recorded the hives’ exteriors to capture defense activities.

While Mattila and her team knew the honeybees had been using the distress signal, they couldn’t figure out how the bees behaved while making the sound. After all, individual actions are difficult to spot during a giant hornet’s attack on a honeybee hive – a chaotic “melee” in which honeybees frantically run around and hornets swoop in and out of the hive, Mattila explained.

But late one night in March, while watching one of the videos, Mattila was able to isolate the sound and movement of a single bee making the noise. The bee raised its abdomen while rapidly buzzing its wings and exposing its Nasonov gland, which releases a pheromone used to guide bees back to a hive.

It was a breakthrough.

“So then I started watching a whole bunch of other videos, and I could pick them out immediately because they really do have a characteristic posture,” Mattila said.

The study says there are more questions to answer, such as whether the alarm piping is used to call for a specific defense, such as balling or fecal spotting. Furthermore, additional research needs to be done on how the signals are sent and received, the study says.

Nevertheless, the “research shows how amazingly complex signals produced by Asian hive bees can be,” Gard Otis, one of Mattila’s colleagues and a professor emeritus in the School of Environmental Sciences at Canada’s University of Guelph, said in a news release.

“We feel like we have only grazed the surface of understanding their communication,” he added. “There’s a lot more to be learned.”