Imagine trying to bend an inflated bicycle tire tube in half. It’s a bit difficult, though not impossible. When you let go, the pressure inside snaps the tube back to its normal shape, as if spring-loaded.
What you’re doing when you bend the tube is essentially storing energy inside it, to be released all at once when you let go. The trick isn’t very useful when it comes to bike tires, of course, but scientists have found that a species of midge has found a unique way to put this technique to use in nature.
When surprised, the larva of the goldenrod gall midge do something odd: They crane their heads around and grab onto their tails, forming a ring shape. Then, all at once, they let go, flinging their head skyward and launching their entire bodies into the air for a tumbling flight that can take them over 30 body lengths away. It’s unexpected, ungainly and, the scientists say, surprisingly efficient.
Researchers from Duke University were studying gall midge larvae of a specific type that like to burrow into goldenrod flowers while they’re young. They normally hide patiently within the flowers, but as one surprised researcher confirmed when he was removing them for study, they’ll take flight when surprised.
“I looked in the petri dish and there were only two larvae in the dish,” said Michael Wise, now a biologist at Roanoke College, in a press release. “They were jumping all over the office!”
The jumping motion had been known about for years, but the specifics of how it worked were unknown. The Duke researchers used a high-speed camera to watch them fly and uncovered the secret of their leaps. Their atypical brand of locomotion comes thanks to special adhesive plates on their heads and tails that stick together when put in contact with each other. The plates are covered in microstructures that likely act as an adhesive, the researchers found, though how exactly they work is unclear.
Once stuck head-to-tail, the gall midge larva will pressurize its body by pumping internal fluids to its lower regions and then use that force to flick its head upwards for a liftoff. They travel an average of about 27 body lengths and sometimes up to almost 40, the scientists reported at the 2018 meeting of the Society for Integrative and Comparative Biology.
The larvae seem unfazed by the rough landings they endure, the researchers say, and their jumps end up being far more efficient than crawling like other larva do. Add to that the unexpected nature of the movement, and it could be that the jumps evolved to help them evade predators, they say. Other closely related species also make the same jumps, in some cases to leave plants to find soil to pupate in.
Their work could help inform future experiments into soft robotics, the researchers say, perhaps providing the groundwork for a new class of machines that flick and tumble themselves across the ground. No one said flying has to be graceful.