Spiders are amazing. They are useful even when they are dead.
Mechanical engineers at Rice University show how to turn dead spiders into mechanical pincers that can blend into natural environments while picking up objects, like other insects, that pass them by.
“The spider, after death, happens to be the perfect architecture for naturally occurring small-scale claws,” said Daniel Preston of Rice’s George R. Brown School of Engineering.
An open-access study in Advanced sciences describes the process by which Preston and lead author Faye Yap harnessed a spider’s physiology in a first step towards a new area of research they call “necrobotics”.
Preston’s lab specializes in soft robotic systems that often use non-traditional materials, as opposed to hard plastics, metals and electronics. “We’re using all kinds of exciting new materials like hydrogels and elastomers that can be activated by things like chemical reactions, pneumatics, and light,” he said. “We even have recent work on textiles and clothing.
“This area of soft robotics is a lot of fun because we can use previously untapped types of actuation and materials,” Preston said. “Spider falls into that line of inquiry. It’s something that hasn’t been used before but has a lot of potential.
Unlike humans and other mammals that move their limbs by synchronizing opposing muscles, spiders use hydraulics. A chamber near their head contracts to send blood to the limbs, forcing them to expand. When the pressure is released, the legs contract.
The corpses Preston’s lab put into use were wolf spiders, and tests showed they were able to reliably lift over 130% of their own body weight, and sometimes much more. They asked the grippers to manipulate a circuit board, move objects, and even lift another spider.
The researchers noted that the small spiders can carry heavier loads relative to their size. Conversely, the larger the spider, the smaller the load it can carry relative to its own body weight. Future research will likely involve testing this concept with spiders smaller than the wolf spider, Preston said.
Yap said the project began shortly after Preston established his lab at Rice’s mechanical engineering department in 2019.
“We were moving things around the lab and noticed a spider curled up at the edge of the hallway,” she said. “We were really curious about why spiders curl up after they die.”
A quick search found the answer: “Spiders don’t have pairs of antagonistic muscles, like biceps and triceps in humans,” Yap said. “They only have flexor muscles, which allow their legs to bend, and they extend them outwards by hydraulic pressure. When they die, they lose the ability to actively pressurize their bodies. That’s why they cower.
“At the time, we thought, ‘Oh, that’s super interesting.’ We wanted to find a way to take advantage of this mechanism,” she said.
Internal valves in the spiders’ hydraulic chamber, or prosoma, allow them to control each leg individually, and this will also be the subject of future research, Preston said. “The dead spider doesn’t control these valves,” he said. “They are all open. This worked in our favor in this study, as it allowed us to control all the legs at the same time.
Setting up a spider clamp was quite simple. Yap tapped into the prosoma chamber with a needle, securing it with a bit of superglue. The other end of the needle was connected to one of the lab’s test rigs or a hand-held syringe, which delivered a minute amount of air to activate the legs almost instantly.
The lab put an ex-spider through 1,000 open-close cycles to see how well its limbs held up and found it to be quite robust. “It starts to get some wear and tear as we approach 1,000 cycles,” Preston said. “We think it’s linked to joint dehydration issues. We believe we can overcome this by applying polymer coatings.
What turns lab work from cool stunt to useful technology?
Preston said a few necrobotic applications came to mind. “There are a lot of pick and place tasks that we could look at, repetitive tasks like sorting or moving objects at these small scales, and maybe even things like microelectronics assembly,” did he declare.
“Another application could be to deploy it to capture smaller insects in the wild, as it is inherently camouflaged,” Yap added.
“Plus, the spiders themselves are biodegradable,” Preston said. “So we’re not introducing a big waste stream, which can be a problem with more traditional components.”
Preston and Yap are aware that the experiments can feel like nightmares to some people, but they said what they were doing did not constitute resuscitation.
“Although it looks like it may have come back to life, we are certain it is inanimate, and we are using it in this case strictly as material derived from a once-living spider,” Preston said. “It provides us with something really useful.”
Co-authors of the paper are graduate students Zhen Liu and Trevor Shimokusu and postdoctoral fellow Anoop Rajappan. Preston is an assistant professor of mechanical engineering.
Rice and a NASA Space Technology Graduate Research Opportunity Award supported the research.