Honeybees Do "the Wave" to Fend Off Attackers

Ker Than
for National Geographic News

September 12, 2008

Like sports fans performing "the wave" at a stadium, honeybees can create a dazzling ripple effect by splaying their shiny wings and flicking their abdomens up and down, new research reveals.

The exact purpose of this "shimmering" phenomenon has been a source of speculation for several decades.

But a new study provides the strongest evidence to date that it is a defense mechanism aimed at repelling wasps and hornets, the bees' mortal enemies.

(Watch bees battle Japan's "hornets from hell".)

Unlike other bee species, Southeast Asian giant honeybees form "open nests" lacking outer protection.

Thousands of bees, layered several rows deep, cling to each other around a central comb to create a living hive.

This leaves them vulnerable to predators such as hornets and wasps, which hunt and feed on the bees and their honey.

Ready, Set, Wave!

Gerald Kastberger, a bee researcher at the University of Graz in Austria, and colleagues used cameras to record more than 450 interactions between bees and hornets on water towers in Nepal.

The team found that shimmering was triggered in giant honeybee colonies when hornets flew too close to the nests.

The closer the hornets flew to the hives, the stronger the shimmering became.

Each "wave" lasted only a few hundred milliseconds, but the bees could keep up the shimmering indefinitely.

"If you use a dummy wasp or a tethered wasp, you can easily arouse the test colony over hours without any sign of exhaustion," Kastberger told National Geographic News in an email.

The rippling effect caused the possibly confused hornets to veer away, creating a safety zone around the hive that extended about 1.5 feet (50 centimeters).

(Watch a hornet attack a praying mantis.)

The bees were also not above resorting to violence. Colonies would deploy specialized fighter bees after enemies undeterred by shimmering.

Scientists have also observed a honeybee attack called "heat balling." If a wasp manages to land on the surface of the living hive, it is immediately overwhelmed by a mass of warm bees and smothered to death.

(Related: "Bees Smother Invading Hornets to Protect Hive" [September 17, 2007].)

The research was detailed online recently in the journal PLoS One.

Innate Ability

Shimmering is one of the most remarkable examples of self organization in nature, and could provide important insights into how social systems in nature communicate, Kastberger said.

"For example, the colony has to 'decide' that the group of bees participating in shimmering should remain at the nest for the collective defense action and should not fly toward the approaching predator," he said.

Randall Hepburn is an entomologist at Rhodes University in South Africa who was not involved in the study. Hepburn said the new study is the first to directly test the defense-mechanism theory for shimmering and called the results strong evidence in favor of it.

"Other studies are more observation. Gerald's is detailed video analysis," Hepburn said.

Micheal Breed, a biologist at the University of Colorado at Boulder who studies social insects, said the study reveals new details about how the bees coordinate their belly-waving.

"Because the bee is responding to the bee next to it, there's a little delay," Breed said.

Western honeybees are not known to shimmer, but that might be because they are not exposed to the same pressures as their Asian relatives, Breed added.

"This study makes me wonder if this capacity to shimmer is present throughout the genus, and our bees have lost the ability because we don't have that kind of wasps in Europe and North America," Breed said, "or whether each species has independently evolved this in response to the wasps."