Japanese scientists unfold the puzzle of ladybug’s wings
The ladybug is a tiny insect with hind wings four times its size. Like an origami master, it folds them up into a neat package, tucking them away within a slender sliver of space between its abdomen and the usually polka-dotted, harder wings that protect it.
When it is time to take off, the beetle deploys its flying apparatus from beneath shell-like top wings, called the elytra, in only one-tenth of a second.
And when it lands, it folds it back in just two.
Switching between flying and crawling many times in a day, the ladybug travels vast distances.
To the naked eye, this elegant transformation is a mystery, because the beetles close their colorful outer wings while switching from flying to walking. But scientists in Japan created a literal window into the process in a study published May 15 in Proceedings of the National Academy of Sciences.
Just how the ladybug manages to cram these rigid structures into tiny spaces is a valuable lesson for engineers designing deployable structures like umbrellas and satellites.
A ladybug’s hind wings are sturdy enough to keep it in the air for up to two hours and enable it to reach speeds up to 37 mph and altitudes as high as three vertically stacked Empire State Buildings. Yet they fold away with ease. These seemingly contradictory attributes perplexed Kazuya Saito, an aerospace engineer at the University of Tokyo and the lead author of the study.
Working on creating deployable structures like large sails and solar power systems for spacecrafts, he turned to the ladybug for design inspiration.
“Ladybugs seem to be better at flying than other beetles because they repeat takeoff and landing many times in a day,” he said. “I thought their wing should have excellent transformation system.”
Previous research could not explain the intricate folding patterns Saito observed on the beetle’s hind wings. And studying them was difficult because the elytra stay down and block the view during folding.
“I wanted to know what they actually do under the elytra,” he said.
Through teeny, tiny surgery, Saito and his colleagues swapped out part of a colorful top wing with a transparent, artificial one made of cured resin cast into the upturned shell of the original wing. It was attached to the original insect.
Then they were able to film what happens in the switch from flight to ambulation using high-speed cameras.
His team also captured super-detailed 3-D X-ray images. Together these unmasked the puzzling folding patterns.
Imagine trying to fold two 20-foot tents, with poles that do not detach, that are stuck to your back beneath a plastic case and you have no hands to help you. A ladybug does it throughout its day.
To fold, the elytra first close and align backward. The abdomen moves up and down, retracting the wings. And during the process, tiny structures on the abdomen and elytra create friction to hold the hind wings in place. The wings fold in and over and then tuck into a Z shape. The veins on the wings, springy like a tape measure, bend into a cylindrical shape, elastic under pressure. They bounce out like springs when the wings deploy.
“The beetles can fold their wing without any mistakes from the first folding,” Saito said.
Videos and diagrams can be see at bit.ly/2q7kixr.
This ladybug origami may not help with your hypothetical tent-wings, but the principles behind it are increasingly solving other engineering problems. The Japanese art has inspired self-assembling robots, a foldable lens on a Manhattan-size telescope, an inflatable heart stent, and other space and medical devices, buildings and everyday objects. Maybe one day, humans will develop our own specialized folding techniques.