Scientists at Tufts University have designed special LED “suits” that help them understand how caterpillars crawl.
Versace might dress the likes of Shakira and Beyoncé, but Guy Levy designs for a far more unusual – and wriggly – client: the tobacco hornworm caterpillar (Manduca sexta).
The garments Levy designs are perhaps more sci-fi than haute couture: six strands of thin copper wire spider down a caterpillar’s back and along one side of its body. One strand ends at the head and another ends at the tail of the caterpillar. The remaining four strands lead to flesh directly above each of four prolegs, unjointed and stubby leg-like structures that help the caterpillar grip different surfaces. Tiny 0.3 mm2 LEDs sparkle like gems at the end of each wire, emitting infrared light.
For Levy, a postdoctoral researcher at Tufts University, and Barry Trimmer, Levy’s postdoctoral adviser and a professor at Tufts, these “suits” of LEDs and wire are a crucial tool for their research on Manduca caterpillar locomotion.
“Studying the locomotion of soft animals, [which lack] articulations, is fascinating,” said Levy, a trained neuroscientist and software engineer.
Unfettered by bony joints or rigid exoskeletons, soft-bodied caterpillars are capable of extraordinary flexibility, enabling a creative range of motion. Caterpillars are champions of climbing and crawling, able to cling to a variety of surfaces, crawl in any orientation, and contort their bodies into innumerable shapes. Understanding how these creatures perform their complex repertoire of motion could provide insight into the neuromechanics of soft-bodied organisms and also help engineers design robots that are collapsible and capable of multidimensional movement.
But because caterpillars aren’t constrained in the ways most articulated animals are, said Levy, studying their locomotion can be challenging.
Two and a half years ago, Levy started his postdoctoral position with Trimmer, who has studied insect locomotion for decades. Trimmer was eager to collaborate with Levy to begin adapting Vicon cameras and software for use with caterpillars. Vicon is a motion capture technology that has gained popularity in the video game industry. It tracks human movement by using infrared cameras to detect retroreflective markers that are worn on the clothing.
Adapting this technology for caterpillars was not trivial, however.
“To tell the truth,” Levy admitted, “There were times we felt it [could not] be done.”
One challenge was programming their custom caterpillar-specific software, which requires parallel processing across multiple servers. Another problem was that the caterpillars were too shiny: the reflective surface of their waxy cuticles outcompeted the tiny beads Levy and Trimmer attempted to use as infrared retroreflective markers. But what if they could adapt the technology to detect emitted rather than reflected infrared light?
Levy obtained LEDs that emitted infrared light, soldering them to jewelry wire to create his first caterpillar suit. Though tiny – less than 2 mm2 apiece– these LEDs were cumbersome to the caterpillars: in one early video, a suited caterpillar moves shakily along a wooden dowel before toppling over the edge.
Trimmer and Levy eventually settled upon their current version, which is dotted with miniscule 0.3x0.3 mm LEDs and does not burden its wearer. Levy anchors this suit onto an anesthetized caterpillar by carefully stitching it onto the caterpillar’s cuticle, a layer so thin that each stitch must be made under a microscope. It’s a painstaking process, Levy noted, but it’s one he’s mastered: now, it only takes him 30 minutes to dress a caterpillar.
Each suited caterpillar is then placed onto a circular treadmill. As it begins crawling, the treadmill slowly rotates, keeping the caterpillar stationary. Special cameras detect and track the infrared light emitted from the LEDs, reporting subtle changes in their positions back to a computer; custom software analyzes and interprets these changes.
Using this creative approach has enabled Levy and Trimmer to detect and measure extremely subtle changes in the different body maneuvers involved in caterpillar crawling. Levy, who will present their new method at the upcoming SICB meeting in Tampa, Florida in January 2019, believes that using their novel technique will facilitate the study of the neuromechanics of soft-bodied animals.
Next up? Levy and Trimmer intend to use their method to explore how caterpillars can crawl on many different surfaces, sending their suit-wearing caterpillars crawling down slippery, sticky, and rough textures.
Just don’t expect to see the caterpillars crawling down a runway any time soon.