Honey bees in Vietnam have a surprising defense against murder hornets

Murder hornets earned the accolade of the Internet's most feared insect in 2020, and for good reason. These beastly creatures can grow up to two inches long and reports recount how they brutally decapitate bees with such ferocity as to wipe out entire colonies in a matter of hours.

But nature is resilient. In new research published in the journal PLOS ONE, researchers reveal how the Asian honey bee employs a surprising, smelly solution to deter the fearsome Asian giant hornet: poop.

What's new — The researchers observed bees deploying a defensive tactic they call "fecal spotting," in which the honey bees scout for nearby animal dung, and then apply it to the entrance of their hives in response to a hornet attack.

Beyond dung, the researchers observed the bees picking up other smelly defensive tools.

"The Asian honey bees we studied collected other substances in addition to dung. In one instance, a hive showing all of the 'spotting behaviors' reeked of urine, and I found the bees drinking urine to apply to the hive front," Gard Otis, University of Guelph professor and co-author on the study, tells Inverse.

Curiously, Otis and his colleagues did not spot fecal spotting in attacks against other types of insect predators, suggesting perhaps that there is something unique to the way giant hornets react to animal dung.

"We speculate that dung contain compounds inherently repellent to hornets or that it simply masks bee odors," Otis says.

By comparing bee colonies that had been visited by hornets and those that had not, researchers saw a clear correlation between fecal spotting and hornet attacks. As the study states:

"Fecal spotting increased after colonies were exposed either to naturally occurring attacks or to chemicals that scout hornets use to target colonies for mass attack."

How they did it — Otis and his colleagues spent more than two months watching bee colonies in Vietnam, examining how honey bees responded to attacking murder hornets.

In their short time, the researchers recorded a whopping 276 hornets visits to these bee hives on camera.

They also set up a control colony to ensure that they had a test group the hornets would not visit. To achieve this, the researchers stood near the control hive and waved plastic bags tied to sticks to frighten away the hornets.

What we don't know — Despite the clear success of the honey bee's smelly strategy, it's not clear why dung thwarts hornets but not bees.

"Because we don't know what the bees are seeking in feces, we can't say at this point why it repels hornets but is acceptable to the bees. The fact that this is the case, however, is very interesting," Heather Mattila, lead author on the study and associate professor of Biological Sciences at Wellesley College, tells Inverse.

It's also worth noting that feces are not the Asian honey bee's only line of defense against these hornets, or other types of hornets.

In fact, these honey bees have effectively adapted to "a suite of defensive strategies" to defend their colonies from all manner of invaders — including a terrifying technique where they form hotter and hotter balls to cook the murder hornet alive, Mattila says.

"We have no idea about the relative importance of the defensive behaviors of Asian honey bees in preventing attacks by hornets," Oris agrees. "I would not say that hive spotting is more or less effective as a defense."

It's also unclear whether fecal spotting is always an advantageous battle tactic, as it may interfere with the bee hive's goal of quickly banding together its workers to defend against a mass hornet attack.

"It may be that hive spotting interferes with the recruitment of nestmates observed during the mass-attack phase of giant hornets," Otis says. "Some of our data indicate that when hives have been heavily spotted, the hornets less frequently switch from catching single bees to mass-attack."

Why it matters —  Human beekeepers could stand to learn something from the honey bees' smelly strategy, using feces to protect their hives from hornet invasions. But, the researchers are skeptical. There's still too much that we don't understand about this defensive strategy.

"If we understood more about what bees are seeking in feces to protect their homes, then we could envision the possibility of humans applying that repellent to colonies in a safer manner," Mattila says.

"I think the optics of doing that for honey customers could be very bad," Otis adds.

Instead, Otis suggested to a colleague in Vietnam that he try applying essential oils to bee colonies.

"He set up a nice experiment, but he failed to detect differences between treated and control colonies," Otis says. "However, the hornets stopped visiting the apiary, so perhaps the strong odors drifted throughout the area and acted as a general repellent to the hornets."

What's next — A different variety of murder hornet (Vespa mandarinia) has now made its way to North America, where the honey bees are unfamiliar with their deadly behavior. The reports of murder hornets in the Pacific Northwest have prompted concerns they could wipe out local bee colonies and terrify humans in these areas, who fear these hornets' painful sting.

Lacking the evolutionary knowledge of their Asian counterparts, bee colonies in the United States will be highly susceptible to the murder hornet's vicious takeovers.

"We have not seen how our Apis mellifera honey bees in North America might react to smelly substances placed at their hive entrance, given that they lack defenses against hornets that we see in Apis cerana of Asia," Otis says.

If murder hornets do became a frequent presence in North America, we'll need to explore any means possible to take them down. Including poop, potentially. There is still time, however.

"At this point in time in North America, Vespa mandarinia is still exceedingly rare," Otis says.

"If that species — or Vespa soror — do become established in North America, researchers and beekeepers will need to explore repellents, hornet traps, hornet excluders, etc. that would need to be incorporated into hive management, Otis says.

Abstract: Honey bees (genus Apis) are well known for the impressive suite of nest defenses they have evolved to protect their abundant stockpiles of food and the large colonies they sustain. In Asia, honey bees have evolved under tremendous predatory pressure from social wasps in the genus Vespa, the most formidable of which are the giant hornets that attack colonies in groups, kill adult defenders, and prey on brood. We document for the first time an extraordinary collective defense used by Apis cerana against the giant hornet Vespa soror. In response to attack by V. soror, A. cerana workers foraged for and applied spots of animal feces around their nest entrances. Fecal spotting increased after colonies were exposed either to naturally occurring attacks or to chemicals that scout hornets use to target colonies for mass attack. Spotting continued for days after attacks ceased and occurred in response to V. soror, which frequently landed at and chewed on entrances to breach nests, but not Vespa velutina, a smaller hornet that rarely landed at entrances. Moderate to heavy fecal spotting suppressed attempts by V. soror to penetrate nests by lowering the incidence of multiple-hornet attacks and substantially reducing the likelihood of them approaching and chewing on entrances. We argue that A. cerana forages for animal feces because it has properties that repel this deadly predator from nest entrances, providing the first report of tool use by honey bees and the first evidence that they forage for solids that are not derived from plants. Our study describes a remarkable weapon in the already sophisticated portfolio of defenses that honey bees have evolved in response to the predatory threats they face. It also highlights the strong selective pressure honey bees will encounter if giant hornets, recently detected in western North America, become established.