Bees are incredible little critters with complex social structures. The humble bumblebee, for example, can involve itself in both rebellion and regicide. Now, a new study in the journal PLOS Biology has shown that honey bees, far from just manufacturing reams of delicious, nutritious honey, also have a slightly unusual way of signaling danger to each other: vibrating pulses that can change frequency, delivered through a headbutt.
In the same way that you may have specific text noises, ring tones or vibrations for different people, it seems that at least one species of honey bee uses different types of vibrating headbutts for individual threats.
“Surprisingly, this signal encodes the level of danger in its vibrational frequency, its pitch, and the danger context through the duration of each pulse,” said James Nieh, a professor of biology at University of California San Diego who coordinated the research team, in a statement.
Headbutting honey bees. Video via New Scientist
Six years prior to the publication of this new study, Nieh was observing the behavior of Apis mellifera, the European honey bee. He noticed that, when one is attacked, it flees back to its nest and headbutts other bees. This “stop signal” interrupts those waggle dancing, another form of communication that encourages foragers to go to a nearby food source. By preventing them from dancing, the headbutting bee stops them and others from heading out and potentially being killed by the predator that originally attacked them.
Nieh wondered if other honey bees exhibit this headbutt mechanism, so he focused his new work on another species: the Asian honey bee, A. cerana, which is found across Southeast Asia, from India to Japan. It’s under constant threat from a variety of hornets, including the world’s largest, the Vespa mandarinia, known colloquially as the “yak killer.”
Their Japanese subspecies are known to behead honey bees in midair, killing up to twenty of them in a single minute; a squadron of 30 of these hornets can destroy an entire hive of 30,000 bees in just three hours. The somewhat smaller species, V. velutina can do less harm overall but they’re still a formidable predator.
When Asian honey bees are being attacked, they form tight spheres around individual hornets and rapidly flap their wings, heating up the trapped hornet and cooking it to death. If they spot one on a foraging patrol, however, they cannot hope to fight it alone, so they dash back to their colony.
Japanese honey bees (A. cerana japonica) versus Japanese hornets (V. mandarinia japonica). Video via BBC Nature
The researchers actively encouraged these sizeable hornets to attack groups of Asian honey bees, hoping to catch them using the same type of stop signals as their European cousins. They noticed that not only were headbutts used, but that sophisticated vibrational pulses were sent with each headbutt, with higher pitched vibrations associated with larger and more dangerous hornets. In addition, both foragers and guard bees that were attacked at the entrance to the nest also produced vibrations of varying pitch, but in this context they were of a far longer duration.
The Asian honey bees’ ability to communicate predator size and location through vibrations alone took the researchers by surprise. “This is the first demonstration of such sophisticated inhibitory signaling or alarm signaling in an insect,” Nieh added, noting that similar signaling systems had only previously been observed in birds or primates.