We’ve probably all killed a spider or two in the past, but what if that arachnid carcass could be repurposed into something useful? Well, researchers at Rice University in Texas think it can and are pioneering the field of “necrobotics” by injecting dead spiders with air to use to grab small objects.
When Rice University assistant professor of mechanical engineering Daniel Preston was setting up his lab, he and graduate student Faye Yap wondered why a dead spider in the corner of the room had its legs curled up. It turns out that spiders extend their legs using hydraulic pressure, which comes from fluid pumped into their legs from a central cavity, meaning that when they die, their legs permanently retract. Preston and Yap wondered if they could hack that hydraulic process by injecting air into a dead spider’s legs to force them open. They found they could, and their study of this macabre opportunity to make a biological clamp was published in advanced science on Monday.
“[Spiders] they really just have muscles to flex,” Yap said in a video call, meaning the spiders can stick their legs in, but they don’t have muscles to extend them. “The way they extend their legs is by using hydraulic pressure.”
This pressure comes from the spider’s prosoma, the spider’s cephalothorax, where its legs join its body, which sends fluid to the arachnid’s legs, allowing it to walk; the individual legs are controlled by the opening and closing of valves in the spider’s anatomy. Preston, Yap and their colleagues found that if they carefully inserted a syringe into the prosoma of a dead spider, they could mimic hydraulic pressure with air, extending and retracting all of the spider’s legs at once. This meant that the spider could be used as a pincer. But why try something so disturbing?
“We’re interested in using them for things like sample collection,” Preston said. “They have intrinsic compliance because of this hydraulic or pneumatic actuation that we can apply that helps protect fragile samples or even other live insects, for example, if we wanted to collect them in the field.”
The properties of the repurposed arachnid are incredibly promising: the team found that a spider claw could last for over 1,000 open/close cycles and could be used to lift 130% of its own body weight.
The researchers primarily used wolf spiders for the work on this particular manuscript, but believe other spider species could be used as well. Interestingly, Yap says the group found that spiders with a larger body mass, like the Goliath spider, could only lift objects that were 1/10 their body weight, while smaller spiders, like jumping spiders, could lift as much as twice your body weight.
As for how those outside the lab reacted to the project, Preston says most were supportive and even excited when they saw how effective the clamp was. Others, however, weren’t too happy to have spiders around.
“One of the employees who works in our main office really doesn’t like spiders. So we had to call the main office every time we had another delivery to use for the project and just let them know,” Preston said with a smile. The team ordered their spiders from a biological supply company, but sadly, some of them didn’t arrive dead. Yap explained: “Sometimes they are inanimate, but sometimes we have to put them down. So we looked for the most humane way to kill them in literature.”
While the project may seem strange, Preston believes it fits perfectly within his lab’s research scope to study soft robotics. “We look at anything at the intersection of energy, materials and fluids,” he says. “Soft robotics generally applies non-traditional materials, things that are not your typical hard plastic metals, but things like hydrogels and elastomers and unique actuation modes like magnetism and light.” Preston and Yap are very interested in using this as a starting point for further research on necrobotic pincers, such as figuring out how to open and close individual legs.
As researchers around the world work on bio-inspired robotics, Preston, Yap and the rest of the team cut to the chase and used the biology itself, extracted from the soil of their lab. This creative work, inspired by nature, is clearly mad science at its finest.
