Honeybees found using tools, in a first—to repel giant hornet attacks

In Vietnam, Asian honeybees use feces to ward off the cousins of “murder hornets." The finding could help protect bees in other countries with invasive wasps.

Published 10 Dec 2020, 10:31 GMT
Asian honeybees have evolved a variety of tricks to ward off attacks from giant hornets.

Asian honeybees have evolved a variety of tricks to ward off attacks from giant hornets.

Photograph by Satoshi Kuribayashi, Minden

In East Asia, honeybees must contend with never-ending attacks by a formidable foe: giant hornets. These predators pick off individual bees, but also stage group invasions of hives. In a brutal onslaught, these large wasps first decapitate every bee they encounter, then occupy the hive and take their time devouring the bees’ larvae.

To defend themselves against hornets, Asian honeybees have evolved various creative tactics, such as swarming invaders with hot “bee balls,” roasting them to death.

But in new research from Vietnam, scientists have discovered an even stranger bee trick: Coating the hive entrance in animal dung.

This “faecal spotting” not only repels giant hornets—it’s the first clear example of tool use in honeybees, says Heather Mattila, an entomologist at Wellesley College in Massachusetts and co-author of the study, published December 9 in the journal PLOS ONE.

Before this study, researchers had not investigated what caused the black marks often seen covering beehive entrances in Vietnam and elsewhere in Southeast Asia. Mattila and colleagues verified that the dark material is actually faeces of various animals, such as chickens and cows. The researchers also documented that the feces repel a species known as Vespa soror, commonly called giant hornets.

To finally figure out what the bees had been doing “was pretty stunning,” says Mattila, whose research was partially funded by the National Geographic Society. It’s “one of the coolest things our [research] group has ever explored.”

The study takes on even more significance because Vespa soror is the closest relative to Vespa mandarinia, also known as Asian giant hornets, or “murder hornets,” whose recent discovery in the Pacific Northwest of the United States has fuelled worldwide intrigue.

Understanding how the Vietnamese bee behaviour repels hornet attacks could have applications for protecting honeybees in other countries, Mattila says.

Not to mention, she quips, “the combination of ‘murder hornets’ and poop is pretty appealing.”

Dung deterrent

Mattila and colleagues, who spent hundreds of hours observing bees at a Vietnamese apiary, found that honeybees began adding feces to their hive entrances after natural attacks by giant hornets. By analysing more than 300 filmed hornet attacks, the team determined that the hornets were less likely to linger at a hive entrance or initiate an invasion as the hive became more covered in faeces.

The researchers also found that placing a paper soaked in extracts from giant hornet bodies near the hive entrance caused the bees to begin coating it in dung.

It’s unclear yet how exactly the faecal coating repels the hornets. It appears that the insects don’t like the smell, but they also may not want to chew into a nest covered in dung, a behaviour that enlarges the hive opening for easier attack, Mattila says.

The faeces may also function as a kind of olfactory camouflage. “Bee hives normally smell like honey and sweet things,” and hornets can use this scent to find them, says Lars Chittka, who studies bee perception and behaviour at Queen Mary University of London. “It's possible the faeces has an unpleasant smell and masks [this scent].”

Asian giant hornets (Vespa mandarinia) attacking honeybees in Japan. New research shows that these hornets’ closest relatives, Vespa soror, which look and act similar, are repelled by dung the bees can pile near hive entrances.

Photograph by Mark MacEwen, Nature Picture Library / Alamy

Murder hornet mania

Since Asian giant hornets were first observed in northwestern Washington State in late 2019, entomologists have been furiously working to prevent the species from becoming established, with some success. In October, state biologists discovered and removed the first known live nest of these voracious insects.

One reason the invasion has received so much attention is that Asian giant hornets are known to attack European honeybees which, unlike Asian honeybees, have no defense against the predators. (Learn more: First 'murder hornet' nest found in U.S., a key step in preventing spread.)

European honeybees are responsible for pollinating many plant species. They also make up most commercial honeybee hives and are more efficient at producing honey than their Asian counterparts.

Mattila says it's possible that once researchers discover what exactly about the dung repels the hornets, beekeepers could potentially use this substance to coat hive entrances to discourage hornet attacks. But much remains unknown.

There are possible downsides to the behaviour, for example. Honeybees are normally quite clean and fastidious—one reason why the finding came as such a shock, Mattila says—so it’s possible that using dung as a deterrent could complicate safety standards for producing honey.

The buzz on tools

This newly discovered use of animal dung qualifies as a form of tool use by bees because the animals are “taking something and manipulating it” to shape their environment. It’s a “pretty groundbreaking finding,” says Susan Cobey, a California-based independent honeybee breeder and geneticist not involved in the paper. (Related: The tools animals use.)

The literature on animals’ use of tools is complex and at times contentious, depending on what definition of “tool” one uses, Mattila says. Other insects have been shown to use them; for example, some thread-waisted wasps use stones to tamp down soil and protect their nests. Tools needn’t be items like sticks or stones, though, they can also be materials like dung.

Some researchers are unsure faecal spotting qualifies, however: “It’s a bit of a stretch to say this is [the first demonstration of] tool use,” Stephen Martin, an entomologist at the University of Salford in the United Kingdom, says by email. “The species also uses leaves to stain hive entrances, and nests are built from paper”—behaviours that could also be classified as tool use, he says.

Bob Jeanne, a wasp expert at the University of Wisconsin-Madison, says the authors are “correct in calling this the first example of tool use by a honeybee... I think they’re applying a reasonable definition.”

Both Martin and Jeanne agree the behaviour is fascinating. “The ability of social insects to astound us continues,” Martin says. “We still know so little of their behaviour, and this is another great example.”

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