Asian honey bees collect animal feces and place it near the entrances of their nest to deter giant hornets, according to research from the University of Guelph. Hornets were found to be less likely to land on nest entrances with large amounts of dung, and those that did land spent 94 percent less time chewing at the entrance to reach their prey.
While honey bees have evolved a collection of strategies to ward off predators, including synchronized visual displays, the current study is the first of its kind to document their use of tools.
One single sting from an Asian giant hornet contains about seven times as much venom as that of an ordinary honeybee. In 2019, “murder” hornets were first discovered in North America, appearing in British Columbia and Washington.
“Giant hornets are the biggest wasps that threaten honeybees. They are one of their most significant predators,” said study co-author Professor Gard Otis, who conducted the research in Vietnam. He said the hornets could ultimately carry out similar honeybee hive raids in North America as well.
Professor Otis explained that the hornets recruit nestmates to participate in organized attacks on honey bee nests. They kill the bees and carry away larvae and pupae to feed their own developing brood.
Beekeepers in Vietnam normally attempt to control hornets by standing guard and swatting away individuals to prevent them from escalating their attacks. “If you allow them, a group of hornets assembles, attacks the colony and takes over,” said Professor Otis. “The beekeepers control them every day by moving among their hives and whacking hornets.”
The researchers discovered that honey bees are not only aware of the impending danger, but also proactively prepare for the raids by collecting animal dung and applying it to hive entrances.
“This study demonstrates a fairly remarkable trait these bees have to defend themselves against a really awful predator,” said study lead author Heather Mattila, who is currently a Biology professor at Wellesley College.
Unlike their Asian counterparts, honeybees in Canada lack similar defenses, said Professor Mattila. This means that beekeepers in North America will have to rely on destroying the hornet nests, or hope that the climate will limit the spread of the hornets. Matilla noted that honey bees commonly found in Canada have not yet had the opportunity to evolve defenses. “It’s like going into a war cold.”
Professor Otis initiated the research after asking Vietnamese beekeepers about dark spots at the hive entrances of Asian honeybees. One of the beekeepers explained that the substance was buffalo dung, and all of the beekeepers linked these hive spots with hornets.
“Dung collection is a behavior never previously reported for honeybees, and no one had studied the phenomenon,” said Professor Otis.
With funding from the National Geographic Society, the researchers gathered dung from water buffalo, chickens, pigs, and cows, and placed it in mounds near a collection of beehives. By the end of the day, about 150 bees had visited the piles, showing a preference for the stronger smelling manure of pigs and chickens.
Individual bees were marked so that they could be identified once they were back at their hives. Moments after collecting the manure, the bees were seen applying it at hive entrances.
The study revealed that hornets spent less than half as much time at nest entrances with moderate to heavy dung spotting. They were also less likely to launch mass attacks on the more heavily spotted hives.
It is not yet clear what deters the hornets. They may simply be repelled by the odor, or the smell of the dung may mask the signature scents emitted by honey bees.
In one experiment, the researchers extracted the chemical pheromone applied by hornets when marking their target hive and applied it to honey bee nest entrances. The honey bees quickly responded by distributing dung throughout the hive.
“The use of animal feces by Asian honey bees showcases the impressive suite of weapons they have evolved to defend their colonies against one of their most dangerous predators,” wrote the study authors. “It also highlights the reasons why European honey bees, which don’t have these defenses, succumb to giant hornets so easily when they are introduced into each other’s range.”
The study is published in the journal PLOS ONE.