Honey Bees Fight Back: The Stinky Way They Defend Themselves From Giant Hornets

How can smaller honey bees defend their nests from being taken over by brutal giant hornets? As it turns out, one honey bee species in Vietnam uses animal dung to deter the fearsome predator.

The invasive Asian giant hornet (Vespa mandarinia), dubbed "murder hornets," is a threat to North American honey bees that may not know how to defend themselves. But the ones that have lived with the Vespa hornet species already know how to protect their hives.

In a new study published in PLOS ONE, a team of researchers found the interesting way that the Apis cerana honey bee species in Vietnam protect themselves from another Vespa species, the V. soror, using animal dung.

As the news release from the University of Guelph (U of G) explained, the researchers first learned about "fecal spotting" after asking local beekeepers about the dark spots at the entrances of beehives. The researchers found that the spots were, in fact, animal dung.

This behavior behavior hasn't been previously observed in honey bees.

Considering the possibility that the dung was to defend themselves from V. soror, which prey on the A. cerana honey bees similar to the aggressive way that V. mandarinia do, the researchers observed the bee colonies and found that a high percentage of them actually foraged for dung and applied it around the entrances of the hives in response to a V. soror attack.

"This response was sustained for several days after hornet attacks ceased and, for some colonies, resulted in a substantial coating of filth that extended outward from nest entrances," the researchers wrote in their study.

The researchers also extracted the chemical pheromones that the V. soror uses to mark their target hives and applied them to the hives' entrances. In response, the honey bees applied dung to their hives.

According to the researchers, the dung resulted in a reduced likelihood that the hornets would visit and chew on the entrance. Even if they did, the time they spent attempting to breach the nest was also reduced. In addition, the hornets were also less likely to strike mass attacks on the hives that were heavily spotted with dung.

Interestingly, the honey bees only responded with fecal spotting after a V. soror attack, the researchers said, but not after attacks by another Vespa species, the V. velutina. Apparently, V. velutina do not attack as aggressively as the V. soror do. Instead of attacking the entire hive, they attack individual bees outside of the hive.

"The difference in the defensive response by bees to V. soror and V. velutina likely reflects the hornets' respective hunting tactics and the level of threat they pose to colonies because of the intensity of their attacks," the researchers said.

Simply put, the researchers found a very interesting way that the A. cerana honey bees in Vietnam protect their colonies from the aggressive V. soror using dung. Apart from showing an interesting adaptation to living with the predators, it also presents evidence of tool use among bees for the first time.

As the U of G news release explains, there is still debate on whether animals can use tools. However, the researchers found that the bees used the dung for a specific purpose, in this case, to protect their hive.

"The bees clearly use the material to alter the hive with purpose, said Otis," the news release said, quoting U of G professor and study co-author Gard Otis. "And they shape and mould it with their mouth parts, which he said meets the test of holding or manipulating a tool."

Although it's still unclear whether the smell of the dung repels the hornets or if it simply masks the smell of the honey bees, the finding shows the incredible ways that honey bees have adapted to living with predatory hornets. In Japan, for instance, the honey bees protect their hives by essentially "cooking" the Asian giant hornet by surrounding the invader and vibrating their wings until they reach a temperature the hornet cannot survive.

In the new study, the researchers found how the bees prevent hornet attacks using a rather unique tool.

"This study demonstrates a fairly remarkable trait these bees have to defend themselves against a really awful predator," study lead Heather Mattila said in the U of G news release.