Like bees “surfing”

Floating bee

With their wings, bees create waves in the water to move. (Image: Chris Roh and Mory Gharib / Caltech)

Honeybees have many special talents. The insects memorize the way to particularly nectar-rich flowers, communicate in a complex way with their peers and even have a sense of mathematics. But not only that: as researchers now report, bees are also capable water sports enthusiasts. If they involuntarily land in the water, they generate waves with the help of complex wing movements that propel them forward. In a way, you can surf on the surface of the water – and get to the saving shore.

If you think of animal swimming masters, the honey bee will probably come last. Nevertheless, these insects manage surprisingly well in the water. If bees accidentally land in the water, they cannot immediately take to the skies again. With the help of strong wing movements, however, they manage to swim to the saving land. How do the insects do it? Chris Roh of the California Institute of Technology in Pasadena asked himself this question when he observed a bee stranded in a pond one summer day: The animal was moving purposefully towards the shore – producing shadow play on the pond bottom due to the rising sun. This made it easy to see both the body of the bee and the wave patterns generated by its wing movements.

“I was fascinated by this behavior and took the honey bee to the laboratory to find out more about it,” reports Roh. Together with his colleague Morteza Gharib, he let the insect and 32 other honeybees each swim in a container filled with water for a few minutes. Filtered light ensured that the wave movements in the water were clearly visible, as before in the pond. In addition, the researchers carried out experiments with a mechanical wing model to find out more about the secret of the bees’ swimming skills.

Ahead with 20 micron newtons

The results revealed that when a bee lands on water, water sticks to its wings and deprives it of its ability to fly. With its wings, however, it can generate waves in the water that propel it forward. As Roh and Gharib found, a wave with high amplitude and interference pattern is created in the water from the back of the bee. On the other hand, there is no big wave on the water surface directly in front of the insect. This asymmetry drives the bee forward with a thrust of 20 micron newtons. “The movements of the bee’s wings create a wave on which its body can move,” explains Gharib. “It surfs for security, so to speak.” In concrete terms, the bees’ wings act as wings, as they are known from hydrofoils. They raise the body of the bee and enable rapid movement on the water.

Slow-motion shots revealed how the wings of the insects move in the water. Accordingly, they do not simply swing up and down, but perform rotary movements downwards and upwards. The upward movement of the wings is the actually decisive movement, as the research team reports – it provides the thrust forwards. Interestingly, the top of the bee’s wings stays dry during these movements, while the bottom sticks to the water. According to the results, this gives the bees additional strength: “Water is three orders of magnitude heavier than air, which is why it can keep bees captive. At the same time, however, this weight is useful for the drive, ”says Roh. Insects don’t generate enough power to rise from the water. However, it is enough to maneuver towards the bank.

Role model for robots

However, this type of locomotion is far more exhausting for honeybees than flying. Roh and Gharib therefore believe that the insects can only “surf” on the water for about ten minutes – so they have a limited time window to find their way ashore. As the scientists emphasize, the movements in the bees documented by bees have so far been unique in the animal kingdom and could have an important biological function. Because the insects not only collect pollen and nectar. Especially on hot summer days, they also bring water to the beehive to keep the temperature there at a tolerable level. “With increased activity near the water, the risk of female bees falling on the water surface increases. The ability to push yourself to the bank could then significantly improve your chances of survival, ”the researchers explain.

In the future, the mechanism behind these saving movements will serve as a model for robots. Roh and Gharib are already working on a small construction that moves on the water surface like a honeybee. In the long term, this patent of nature could also create robots that, like insects, can do both: fly and swim. “The drive of the honeybee with wet wings shows that the system of the flapping wings is a way to generate thrust both in the air and on a water surface,” the research team concluded.

Source: Chris Roh and Morteza Gharib (California Institute of Technology, Pasadena), Proceedings of the National Academy of Sciences, doi: 10.1073 / pnas.1908857116

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