Witness and Hear the Attack of a Giant “Murder” Hornet on a Beehive
For the first time, new research from Wellesley College demonstrates that bees employ a distinct sound to express the threat posed by enormous hornets while initiating defences against them.
The peculiar sounds honey bees (Apis cerana) make to warn other members of their hive when enormous “murder” hornets attack have been documented for the first time. These signals—which include a newly described “antipredator pipe”—are the subject of new research by Heather Mattila, an associate professor of biological sciences at Wellesley College, and her colleagues, who published their findings in Royal Society Open Science.
Mattila and an international team of researchers discovered that honey bees warn their fellow bees to defend themselves against attacks by gigantic hornets (Vespa soror), which are capable of eradicating entire colonies. When huge hornets are directly outside their hive, bees make sounds, and antipredator pipes in particular, at a frenzied tempo. It’s an unmistakable distress signal that gave Mattila the chills when she heard it. “The pipes share traits in common with a lot of mammalian alarm signals, so as a mammal hearing them, there’s something that is instantly recognisable as communicating danger,” she said. “It feels like a universal experience.”
Antipredator pipes are distinct from earlier sounds discovered in colonies, such as “hisses” and “stop signals.” These newly discovered signals are harsh and erratic, with sudden frequency changes, akin to the alarm shrieks, terror screams, and panic calls made by primates, birds, and meerkats in response to predators. Along with warning the hive of the impending arrival of giant hornets, the signals result in an increase in bees at the hive’s entrance and the initiation of defence actions such as spreading animal dung around colony entrances to repel giant hornets (the first documented use of tools by bees) and forming bee balls to collectively kill attacking hornets.
Mattila and her colleagues spent almost seven years in Vietnam studying interactions between gigantic hornets and Asian honey bees, gathering audio and video records of hornet attacks in the apiaries of local beekeepers. Microphones installed in hives recorded nearly 30,000 bee signals during the course of 1,300 minutes of monitoring.
Their recordings of colonies under active attack by giant hornets were noisy and frantic, compared to the relatively quiet and tranquil recordings of control colonies. Bees increased hive chatter to eight times its normal volume in response to hornet attacks. “[Bees] are constantly communicating with each other, in both good times and in bad, but antipredator signal exchange is particularly important during dire moments when rallying workers for colony defense is imperative,” the researchers noted in their report.
“This research shows how amazingly complex signals produced by Asian hive bees can be,” said Gard Otis, a Mattila collaborator and emeritus professor in the School of Environmental Sciences at the University of Guelph’s Ontario Agricultural College. “We feel like we have only grazed the surface of understanding their communication. There’s a lot more to be learned.”
The researchers observed that when bees construct antipredator pipes, they elevate their abdomens, buzz their wings, and run erratically, showing their pheromone-producing Nasonov gland. The behaviour of the bees indicates that they generate a variety of sorts of information in order to attract the attention of their nestmates. Mattila intends to conduct additional research into this behaviour as well.