Bees make a chilling warning noise when killer hornets attack their colonies

(CNN) – When a swarm of giant hornets attack a hive of bees, the slaughter is brutal and swift.
The hornets descend en masse after a scout has identified the target hive, killing the defending adult bees, occupying their nest, and harvesting the brood from the bees to feed their own young. Hornets can decimate a hive in hours.

But honey bees are not defenseless against so-called killer hornets, which are native to Asia but first appeared in the United States in 2019. Bees have their own survival strategies, including a unique and frenzied warning signal that triggers movements. defensive, which has now been documented by scientists for the first time.

“I get a gut reaction when I hear them because the bees are obviously agitated,” said Heather Mattila, associate professor in the Department of Biological Sciences at Wellesley College, who was part of a team of scientists who identified the warning noise.

Mattila described the warning signal, known as a harsh and loud “anti-predator screech,” with varying lengths and pitches similar to the screeches, screams and panic calls that mammals such as primates and meerkats use when afraid.

“The individual screeches have different durations, but the worker bees chain many of them into longer signals. They also change a lot in pitch and irregularly, which makes them stand out.”

The researcher points out that this sound seems to be used by Asian honey bees (Apis cerana) only when giant hornets attack the colonies of Vietnam studied by the team. The research was published Tuesday in the journal Royal Society Open Science.

“Our study showed that the bees did not make the sound if there were no hornets. They did so very infrequently in response to the smaller hornets, a little more often if the bees smelled a giant hornet (but didn’t see it), and they did them distinctly when a giant hornet was directly out of its nest, “Mattila said by email.

“We haven’t tested all the predatory scenarios that Asian bees might encounter, but this is good evidence that a real wasp attack is needed to trigger this response.”

The signal is used to trigger some of the defensive mechanisms that bees have in their arsenal to deploy against killer hornets, he said.

Among them are strategies such as manure detection, when bees collect manure from animals and apply it at the entrances of their colony to repel and confuse hornets, and the formation of swarms to neutralize the enemy, which is known as “Balling” or “swarming” of bees.

Balling consists of hundreds of bees surrounding a hornet in a matter of seconds, squeezing it and restricting its ability to breathe.

The bees raise their body temperature to a level that is lethal for the hornet, Mattila explained.

Giant hornets are native to Asia, but have been seen recently in the United States.

“They act like an overheated collective boa constrictor,” he said.

The first United States sightings of the Asian giant hornet occurred in Washington state in 2019. It is unclear how they got there from their native Asia, but they may have arrived with international container ships, purchases shipped to the United States. or travelers who visit or return. There were 14 sightings and three nests were found in Washington state in 2021.

Asian bees have developed some defensive strategies to scare off giant hornets.

Unlike their Asian counterparts, western honey bees (Apis mellifera) have not developed any strategy to defend themselves against giant hornets.

“US honey bees do not have the historical experience of developing defenses against giant hornets. They are not expected to react to the sounds that Asian bees make, and they also do not perform many of the other important defenses against hornets that uses Apis cerana, “said Mattila.

“When people use our American honey bees for beekeeping in Asia, the giant hornets preferentially attack them because they are so defenseless.”