Surf Cat

If their honey-making and pollination prowess weren’t enough, there’s a new reason to appreciate honeybees: They’re world-class surfers.

Beyond pollinating flowers, worker bees — which are all females — are given the job of searching for water to cool their hives. But if they fall into ponds, their wings get wet and can’t be used to fly. A team of researchers at the California Institute of Technology found that when bees drop into bodies of water, they can use their wings to generate ripples and glide toward land — like surfers who create and then ride their own waves.

Gnarly, right?

“When they fall in the water, they have to find a way to get to shore as a matter of survival,” said Chris Roh, a Caltech research engineer and lead author of the study, published Monday in Proceedings of the National Academy of Sciences. “It’s a ‘to bee or not to bee’ situation.”

As with many scientific advances — Isaac Newton’s apple or Benjamin Franklin’s lightning bolt — Dr. Roh’s experiment began with a walk. Passing Caltech’s Millikan Pond in 2016, he observed a bee on the water’s surface generating waves. He wondered how an insect known for flight could propel through water.

Dr. Roh and his co-author Morteza Gharib, a Caltech professor of aeronautics and bio-inspired engineering, used butterfly nets to collect local Pasadena honeybees and observe their surf-like movements.

The researchers fashioned a wire harness to constrain each bee’s bodily motion, allowing close examination of their wings. They found that the bee bends its wing at a 30-degree angle, pulling up water and generating a forward thrust. Bees get trapped on the surface because water is roughly three orders of magnitude denser than air. But that weight helps to propel the bee forward when its wings flap. It’s a strenuous exercise for the bees, which the researchers estimate could handle about 10 minutes of the activity.

The researchers said the surf-like motion hasn’t been documented in other insects and most semiaquatic insects use their legs for propulsion, what’s known as water-walking. It may have evolved in bees, they speculate, so the workers could collect fluid without getting stuck in the water and dying. The closest motion is seen in stoneflies, but their movement is more like paddling than surfing.

Dr. Roh and Dr. Gharib plan to use their observations to design robots capable of traversing sky and sea. They have already made a mechanical model that simulates the bee’s surfing motion. Next, they will make one light enough to fly.

Howard Stone, a professor of mechanical and aerospace engineering at Princeton, said nature is a helpful guide for technological innovation because “evolution has had lots of years to try out solutions” to common physical problems.

Dr. Gharib’s lab has previously studied underwater locomotion by looking at jellyfish, and energy harvesting by looking at leaves rustling in the wind. He envisions numerous practical applications for bee surfing.

“You could imagine an amphibious system that can move on the surface of water and fly without hassle,” Dr. Gharib said. “This could be useful for search and rescues, or for getting samples of the surface of the ocean, if you can’t send a boat or helicopter.”