Several years ago, Harvard University roboticist Robert Wood made headlines when his lab constructed RoboBee, a tiny robot capable of partially untethered flight. Over the years, RoboBee has learned to fly, dive, and hover. The latest improvement: RoboBee has learned how to stick the landing, thanks to biomechanical improvements to its landing gear modeled on the crane fly, which has a similar wingspan and body size to the RoboBee platform. The details of this achievement appear in a new paper published in the journal Science Robotics.

As previously reported, the ultimate goal of the RoboBee initiative is to build a swarm of tiny interconnected robots capable of sustained, untethered flight—a significant technological challenge, given the insect-sized scale, which changes the various forces at play. In 2019, Wood's group announced its achievement of the lightest insect-scale robot so far to have achieved sustained, untethered flight—an improved version called the RoboBee X-Wing. In 2021, Wood's group turned its attention to the biomechanics of the mantis shrimp's knock-out punch and built a tiny robot to mimic that movement.

But RoboBee was not forgotten, with the team focusing this time around on achieving more robust landings. “Previously, if we were to go in for a landing, we’d turn off the vehicle a little bit above the ground and just drop it, and pray that it will land upright and safely,” said co-author Christian Chan, one of Wood's graduate students. The trick is to minimize velocity when approaching a surface and then quickly dissipating impact energy. Even something as small and light as RoboBee can generate significant impact energy. The crane fly has long, jointed appendages that enable them to dampen their landings, so the insect served as a useful model for RoboBee's new landing gear.

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The white-necked jacobin (Florisuga mellivora) is a jewel-toned hummingbird found in the neotropical lowlands of South America and the Caribbean. It shimmers blue and green in the sunlight as it flits from flower to flower, a tiny spectacle of the rainforest.

Jay Falk, a National Science Foundation postdoctoral fellow at the University of Colorado, Boulder, and the Smithsonian Tropical Research Institute (STRI) in Panama, expected to find something like that when he sought this species out in Panama. What he didn’t expect was a caterpillar in the nest of one of these birds. At least it looked like a caterpillar—it was actually a hatchling with some highly unusual camouflage.

The chick was covered in long, fine feathers similar to the urticating hairs that some caterpillars are covered in. These often toxic barbed hairs deter predators, who can suffer anything from inflammation to nausea and even death if they attack. Falk realized he was witnessing mimicry only seen in one other bird species and never before in hummingbirds. It seemed that the nestlings of this species had evolved a defense: convincing predators they were poisonous.

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