World’s fastest swimming insects could inspire US Navy’s next drone boat

If there ever was to be an Olympics for , Whirligig beetles would stand out as the undisputed champions in swimming. These diminutive beetles, the speedsters of the insect world, can hit a staggering peak acceleration of 100 meters per second and cruise at a top velocity of 100 body lengths per second (equivalent to 1 meter per second).

But what’s propelling them forward? It’s been believed that whirligigs rely on a drag based thrust system, requiring their legs to outpace their swimming speed, but a new study exposes a paradigm shift. The findings not only reveal the secret behind whirligigs' Olympic worthy speeds but also provide insights for designers of water robots and unmanned boats.

The team of researchers employed state of the art high speed cameras, revealing that these minuscule, one centimeter insects achieve their astonishing speeds using a technique shared with swift marine mammals and waterfowl. Chris Roh, assistant professor of biological and environmental engineering, remarked in a , "The fastest swimmer and drag based thrust don't usually go together in the same sentence." Instead, the revelation unveils a lift based thrust mechanism, which is somewhat similar to the principles of lift used in aviation.

When whirligigs swim, they move their legs in a special way. This movement creates a force called "lift," kind of like how an airplane's wings lift it into the sky. But for the beatles, this lift happens underwater, and it pushes them forward. High speed cameras, synchronized at different angles, captured the whirligig's legs engaging in a partial propeller like rotation, creating thrust perpendicular to the water surface.

This lift based thrust eliminates drag, allowing for a more efficient and speedier momentum. “In biology, it’s hard to rotate things,” said Roh. “We’re machines based on contraction. So, you could say the whirligig beetle’s legs are a partial propeller that rotates about an angle and then they retract before they reset and rotate partially again.” An inspiration for unmanned boats Roh draws parallels between the whirligig's propulsion and the aerodynamics of an airplane wing.

He notes, "That angle of attack allows it to actually generate lift." Remarkably, this study extends the application of lift based thrust to the tiniest of organisms, with whirligig beetles becoming the smallest known users of this propulsion method for swimming. The research suggests potential inspiration for bio inspired and unmanned boat design.

Roh believes this discovery could also contribute to the US Navy's pursuit of smaller, more flexible naval vessels. The was funded by the National Science Foundation and published in the journal . Whirligig beetles (Gyrinidae) are the fastest swimming insects. The one centimeter long aquatic beetle can reach a peak acceleration of 100 m s–2 and a top velocity of 100 body lengths per second.

Previous studies have suggested that drag based thrust by their hind legs is responsible for their propulsion. For the drag based thrust to be effective, however, the leg stroke velocity must exceed the swimming velocity. Therefore, for fast swimming whirligigs, it is unlikely that the drag based thrust is the main source of acceleration.

Here, we demonstrate that lift based thrust enables the rapid swimming of the whirligigs..