Bees are remarkably intelligent creatures capable of abstract thought (they can count and grasp the concept of zero) and use symbolic language. But that’s not all. In a new study, researchers have shown that honey bees (Apis cerena) in Southeast Asia are collecting animal dung to defend their colonies from potentially devastating giant hornet attacks. This is the first time tool use has been documented in bees.
While working on other projects in Vietnam, Gard Otis, a professor at the University of Guelph who specializes in honeybee behavior and co-author of the new study, noticed fecal spotting on some hives. Upon investigating, he learned from beekeepers that the bees were reacting to attacks by the giant Asian hornet (Vespa soror). One of the beekeepers even said that he witnessed worker bees foraging on dung in water buffalo fields. That got everybody’s attention and it turned out it was true.
“We first determined through observation that bees were in fact foraging for animal dung, carrying it back to their hives, and then applying it around their entrances,” Heather Mattila, associate professor of biological sciences at Wellesley College and co-author of the study, told ZME Science.
“Through a series of field trials, we figured out that Asian honey bees started spotting after their colonies experienced naturally occurring visits by V. soror, they would continue to spot for days (even after attacks ceased), and they spotted even if they were presented with only the glandular extracts that the giant hornets use to mark colonies as targets.”
“However, fecal spotting was the strongest if the colonies were exposed to real hornets. We also determined that colonies didn’t spot in response to attack by Vespa velutina, a smaller hornet that is not as strong a predator and hunts without coming into contact with hives or nests. Finally, we determined that V. soror, the giant hornets, were much less inclined to try to break into colonies that were moderately or heavily spotted, thus limiting their ability to execute group attacks, which can result in devastating colony takeovers.”
Although honey bees are famous for foraging materials produced by plants, such as nectar and pollen, they had never been seen retrieving solid material from any other source until now.
Mattila and Otis have been studying giant hornets and Asian honey bees in Vietnam for several years, conducting fieldwork in apiaries with colonies housed in wooden hives managed by local beekeepers.
“In the early stages of the study, we spent a few days hanging out on farms and seeing if we could find bees foraging on livestock dung. Eventually, after sitting in a chicken coop for a few hours, I was able to take a few dimly lit videos of bees collecting chicken dung, so it was a very exciting moment. I remember running back to our study apiary, bursting with the news I wanted to share with everyone, that we had finally confirmed that bees were collecting dung. After that, we brought piles of dung to the side of our most active apiary and we were able to observe many more bees collecting it,” Mattila wrote in an email.
After the researchers confirmed that the bees were collecting animal dung, they then cleaned the colonies to track how exactly the bees were designing their defenses using fecal spotting. As they monitored the bees’ behavior, they observed how giant hornets were repelled from nest entrances, where they focus their attacks.
This seems like an innate behavior, “just like how taking up foraging for other things, like food from flowers, is instinctual,” Mattila said. “Bees learn a lot as individuals as they forage, like how to become more efficient as they do it, but it is unlikely that the fecal spotting strategy is a culturally transmitted defense,” she added.
As for why the hornets find the feces so repelling, scientists aren’t sure yet. But since it acts like a chemical weapon, it’s likely that specific chemical properties keep hornets away, while not affecting bees in any negative way.
“At this point, we know little about how the foraging effort for dung collection is organized. We know from research conducted in Japan, where this honey bee species has been documented collecting plant material in response to hornet attacks, that bees perform what are called “emergency dances” to boost foraging. We saw the same kinds of dances performed outside of some of our study hives, but a lot of work remains to be done to figure out how bees organized this process, as well as what exactly workers are seeking from dung when they go foraging,” Mattila said.
“Many scientists disagree over whether certain animals, let alone insects, use tools,” Otis said in a press release. “To qualify as tool users, animals must meet several criteria, including using an object from the environment–in this case, dung. The bees clearly use the material to alter the hive with purpose, in addition to meeting the requirements of holding or manipulating the tool.”
In the future, the researchers plan on conducting more follow-up field studies that examine the acoustic signals shared by workers when they are under attack by hornets. However, because of travel difficulties due to the pandemic the researchers had to postpone travel. Instead, they’ve sent hornet samples to colleagues to “figure out more about how the hornets mark colonies for attack.”
“Our study adds another defense to the already impressive list of ways that Asian honey bees fend off attacks by hornets, and especially giant hornets, which are particularly deadly predators. It also makes clear why honey bee species that haven’t evolved with these predators are so vulnerable to their attacks because they lack these important defenses that result from exposure to this predatory pressure over evolutionary time,” Mattila concluded.
The findings appeared today in the journal PLOS ONE.
