A dragonfly with its prey
A dragonfly with its prey. Image: Rhett A. Butler

Flying insects rule the sky

You have probably experienced many types of flying insects. Maybe you have tried swatting a mosquito as it buzzes around you, looking for the opportunity to suck your blood like a tiny vampire. Probably you’ve seen butterflies flutter by, a dragonfly darting across your path, or maybe you’ve tried sneaking up on a housefly that somehow zips away the moment you swat at it. There are more species of flying insect than any other type of flying animal.  

How do insects fly?

Insects have been incredibly successful at developing ways of flying. Biologists know that insects evolved two modes of flight. In one mode, their wing flaps are synchronized with neural signals from their brain. Activating each wingbeat with a nerve signal is called synchronous flight

A tobacco hawk moth (Manduca sexta). Photo: Rob Felt. Courtesy of Simon Sponberg and Nick Gravish

In the other flight mode, a single muscle twitch activates ultra-fast wingbeats. These wingbeats are so fast that they race past what the insect’s brain can do, such as the mosquito’s ability to flap 800 times in one second. The ability to flap wings much faster than signals from the brain can trigger is called asynchronous flight.  

Asynchronous flight exists in four insect groups: beetles, bees, true bugs, and flies. At small sizes, asynchronous flight allows insects to overcome the fundamental speed limit of how fast their brain can fire a signal to flap their wings. It leads to incredibly quick flight —and split-second aerial maneuvers— among those insect orders.

Scientists use genetics and robotics to better understand insect flight

A team of scientists used genetic analysis to study how insect groups with different flight modes evolved. They discovered that a single ancestor to today’s flying insects evolved the ultra-fast flight twitches of asynchronous flight more than 400 million years ago.

The team determined that some insects had returned to synchronous flight even though they evolved from an asynchronous flighted ancestor. Those insects are referred to as secondarily synchronous. The scientists hypothesized that secondarily synchronous insects would have muscles preserving evidence that they’d made the switch from asynchronous to synchronous flight. They found that the tobacco hawk moth (Manduca sexta) has those muscles.

A tobacco hawk moth (Manduca sexta) on a gloved hand in the laboratory of biophysicist Simon Sponberg. Photo: Simon Sponberg and Nick Gravish

The team wanted to know whether it was possible for the tobacco hawk moth to switch between the synchronous and asynchronous flight. The scientists created a mathematical equation that combined the two kinds of flight, which made it possible to look at flight patterns that could arise for an insect with both synchronous and asynchronous skills.

To test that equation, they would need to engineer a real-life model. James Lynch and his laboratory colleagues built an insect-sized robot that could flap asynchronously — the first of its kind. The researchers made the robot with materials similar to the membranes of insect wings.

The first asynchronous roboflapper, built at the size of an actual insect. Photo: Courtesy of Nick Gravish

As the team changed its inputs according to their equation, the robot swapped between synchronous and asynchronous flight — and everything in between. These transitions could mimic the evolutionary bridge that allowed insects to go back and forth in their flight patterns over time, they believe.

There is something the robot can’t do: actually fly. Though the wing portion is small, the gear powering it is far too bulky for it to soar to great heights. Still, the scientists hope their work will lead to more bio-inspired robotics in the future.

The flapping portion of the robot. Photo: Courtesy of Nick Gravish

“Insects have some of the greatest sources of biological, physical, and engineering insight trapped in their little bodies, waiting to be unlocked,” said scientist Simon Sponberg. “If we hadn’t appreciated the diversity of insects out there, we wouldn’t have made this new technological innovation.”

David Brown adapted this story for Mongabay Kids. It is based on an article by Eli Ramos, published on Mongabay.com:

Here is a link to the scientific paper that this story is about:

Gau, J., Lynch, J., Aiello, B., Wold, E., Gravish, N., and Sponberg, S. Bridging two insect flight modes in evolution, physiology and robophysics. Nature 622, 767–774 (2023). https://doi.org/10.1038/s41586-023-06606-3