(CN) — By decorating the entrance of their hives with animal feces to ward off giant predator hornets, Asian honeybees have learned to embrace the phrase “neck deep.”
Scientists discovered that some honeybees regularly forage for and apply animal feces around their hives following a hornet attack, and continue doing so for days afterward. And it works — the poop reduces the number of hornets willing to penetrate the hive and lessens the likelihood of hornets chewing on the entrance to open it up, which they normally do.
A team of researchers led by Dr. Heather Mattila at Wellesley College in Massachusetts describe this unique security measure in a study published Wednesday in the journal PLOS ONE. Their work uncovered the first example of honeybees foraging for solids that aren’t derived from plants, and the first known example of tool use by bees.
Honeybees add this admittedly disgusting technique to their existing array of home defense mechanisms, such as synchronized visual displays, hissing and covering intruders in a ball of bees to make them overheat. These defensive behaviors are most prevalent in bee populations that evolved near predators, particularly those found in Asia. Necessity is the mother of invention, after all.
“Social insects house families in centralized, resource-rich nests, a trait that has driven the evolution of defense strategies to counteract attempts by thieves and predators to exploit their bounty,” the study authors write. “Nest defense can take the form of physical, chemical, and behavioral barriers, the combination of which are known as defense portfolios. Honeybees, famous for the resources that their prolific colonies sequester, provide an impressive example of the diversity of nest-defense strategies that have evolved within a geographically widespread group.”
Vietnamese beekeepers first alerted scientists to the idea that their bees may be painting their doorsteps with dung to fend off foes. Following hornet attacks the beekeepers watched worker bees venture out and return with mouth loads of water buffalo dung, which they strategically dabbed around the opening to their nest using their mandibles.
The exact reason this works is still up for debate, but the authors present a few possibilities. They believe certain animals’ feces may contain a chemical that specifically wards off hornets, or that nearby fecal piles merely present an easy method of obtaining repellant compounds that can be found elsewhere and repel multiple insects. It may even act as camouflage.
“At this point, we don’t know what the bees are searching for in animal dung. It could be repellent or help with camouflage, or both. We know it is repellent from our field work, but what we don’t know is why — it’s either because feces itself is a deterrent or because of something specific in the feces, likely from what the dung producer ate,” Mattila said in an email. “It could mask the odor of colonies, which hornets can use as a way to find insect prey, or it could mask the pheromones that giant hornets use to mark colonies when they are starting their group attacks. More work is needed to figure out the answers to these questions.”
Giant hornets typically wreak havoc on honeybee colonies when introduced into their range, which explains why eradicating non-native hornet populations has become such an important issue of late. First, a hornet scout ventures out to find a bee colony and chemically marks its location. The hornet’s hive mates then attack the colony in swarms of up to 50, and can often eliminate the entire group in under two hours before feeding the bees’ brood to their young.
Physical shielding remains the first line of defense across honeybee species, which involves building a nest inside an enclosed space with a small entrance and posting guards at the door. From there, however, the strategies among species diverge. Asian honeybee colonies that evolved near giant hornets employ the ball-o-bees approach. This species forms larger, hotter balls that kill more hornets at faster rate than other honeybee species like European varieties, which remain more vulnerable to attack.
“The honeybee species we worked on in Asia is not the species that is kept by beekeepers in North America or Europe,” Mattila said in the email. “So the recent introduction of Vespa mandarinia, a giant hornet closely related to the giant hornet that we studied in Vietnam, Vespa soror, will pose a greater predatory threat to honey bees kept outside of Asia because they have not had time to evolve these specialized defenses.”