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New research suggests that even in turbulent wind, honeybees maintain their average flying velocity and move in a zig-zag-like pattern.
By Margaret Osborne | December 8, 2022
Credit: Bardia Hejazi
Honeybees at the Max Planck Institute for Dynamics and Self-Organization in Germany.
Honeybees are among the most important pollinators of the world’s agricultural crops. About a third of the food in our diet relies at least partially on these insects, and they’re estimated to contribute around $12 billion to the United States economy alone.
“Bees are natural pollinators and important to the environment,” says Bardia Hejazi, a physicist at the Max Planck Institute for Dynamics and Self-Organization in Germany. “It’s important to understand how they behave, how they manage to maneuver through different environments.”
Hejazi had always been interested in combining physics and animal studies, so when his institution procured three Carniolan honeybee hives, he jumped on the opportunity to work with them. With a background in turbulence research, he decided to study how honeybees fly in windy conditions — a question that could someday assist in the design of small flying robots.
At the 2022 Division of Fluid Dynamics meeting in Indianapolis, Indiana, in November, Hejazi discussed findings from his research, published in the New Journal of Physics. He found that bees’ average velocity isn’t affected by windy conditions, but that the insects tend to fly in a zig-zagging motion when they encounter turbulence.
To test how bees respond to wind, the team manufactured turbulence outside one of the hives using four fans behind a grid of flaps. The flaps could open and close independently of one another, and their movement was controlled by a computer.
“Depending on how many you move, in what sequence you move them, you can create different types of turbulence structures,” Hejazi explains.
Over a week in September 2021, they tested how bees flew in eight different turbulence scenarios and compared them to a no-wind baseline. To coax the bees to fly in the right direction, they assembled screens on either side of the hive. A fence, bordered with trees and bushes, served as a natural barrier on the opposite side of the hive. To film the bees flying, the team set up three GoPro cameras in the experiment area, each placed at a different angle.
With three different images of the same bee, the researchers used computer codes to track its path in three dimensions. The team then used this data to calculate the bees’ velocity and acceleration.
They found that the bees’ average velocity didn’t seem to be affected by the wind — not what you’d expect from a small insect battling strong gales.
“If you, for example, are walking in headwind, you're slower, you're fighting against the wind, right? And maybe your velocity is less because of that,” Hejazi says. Or the opposite could be true: If you’re riding a bicycle downwind, you’re probably going faster.
Credit: Bardia Hejazi
Hejazi and his colleagues manufactured turbulence using four fans behind a grid array with movable flaps.
“[But the bees are] maintaining that average velocity, regardless of the windy conditions that we're producing,” he says. “We thought, ‘That can't be. There has to be something going on.’”
So, Hejazi dug deeper into the data, examining exactly when the bees were speeding up and slowing down. He found that bees took a long time to accelerate, but they braked rapidly when making sharp turns, like a car that slows down around a curve. This pattern is called a flight-crash event, and it also occurs in fluid turbulence.
Further calculations showed that in conditions without wind, the bees tended to fly straight and turn sharply. But in wind, the bees didn't fly straight at all. Instead, they constantly made turns and performed evasive maneuvers. Hejazi says he could see these behaviors during the experiments, too.
“They had this really disturbed type of flight when they were trying to fight against the wind,” he explains, adding that similar movements have been observed in bacteria and fruit flies.
“It's interesting to see that it's kind of universal across different scales, different systems,” he says. “I was surprised.”
Understanding how insects like honeybees fly may help engineers design drones and other robots that can maintain their speed and control as they move. But for now, Hejazi wants to expand his research and study how bees fly in relation to each other.
“How do they know not to bump into each other?” he asks. “What mechanisms do they use to identify each other? ... Learning as much as we can about how they fly and how they behave with each other — that’s really helpful.”
Margaret Osborne is a freelance writer based in Utah.
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