There are many people who are terrified of spiders. There are many people who are terrified of a zombie apocalypse. There is probably a Venn diagram of the two groups and there are undoubtedly a good number in the middle who are terrified of both. Well, get ready for your fears to become reality. Mechanical engineers at Rice University in Houston have figured out how to turn big dead spiders into zombie robots that can grasp large objects like a mechanical gripper does. Do you think this is just one of those ‘fun’ projects scientists sometimes dabble in? Not this one … they’ve actually given their new zombie robotic spider science a scary name – necrobotics. What are they planning next? A real necrobotic zombie spider apocalypse? What could possibly go wrong?
“We were moving stuff around in the lab and we noticed a curled up spider at the edge of the hallway. We were really curious as to why spiders curl up after they die.”
Opening scene for a horror movie? No, just the brainstorm Rice graduate student Faye Yap had that inspired necrobotics. According to the press release announcing the publication of their study published in the journal Advanced Science, Yap and Daniel Preston, an assistant professor at Rice’s George R. Brown School of Engineering and founder of his own lab there, took an engineer’s look at the dead spider’s leg mechanisms. While humans have ‘antagonistic’ muscles – biceps and triceps controlling opposing movements, the wolf spider, and spiders in general, only have flexor muscles controlled by hydraulics. The flexor muscles cause the spider’s legs to curl under it, while hydraulic pressure inside the prosoma (the area where the head and the thorax are fused together) pushes open the valves in the legs. When the pressure ends, the valves close and the legs automatically fold back in. it’s no wonder this procedure intrigued mechanical engineers like Yap.
“At the time, we were thinking, ‘Oh, this is super interesting.’ We wanted to find a way to leverage this mechanism.”
Like curious kids discovering their first dead insect, the engineers probed the dead spider they found and others in the area (Why does Rice University have so many dead spiders? That is for another study to solve.) and determined that the valves in their legs still worked and the legs still flexed – no rigor mortis in these arachnids. However, the hydraulics system was still dead. What the engineers needed was mechanical version to replace it. Good old all-American post-graduate ingenuity stepped in.
“Setting up a spider gripper was fairly simple. Yap tapped into the prosoma chamber with a needle, attaching it with a dab of superglue. The other end of the needle was connected to one of the lab’s test rigs or a handheld syringe, which delivered a minute amount of air to activate the legs almost instantly.”
A squeeze of the bulb opened the now zombie spider’s legs just as if it were alive. (Photos and illustrations here.) The first question they pondered was how long would these legs continue to operate. Professor Preston said that one zombie performed 1,000 open-close cycles successfully in a manner that was “fairly robust” before it began to show some wear and tear. Spiders obviously perform this operation many more times without problems (have you ever seen a spider rubbing its legs with a topical analgesic heat rub?), so Preston diagnosed the problem as a lack of lubrication caused by dehydration of the joints and recommended a mechanical engineering solution:
“We think we can overcome that by applying polymeric coatings.”
Once the zombie spider’s leg valves were working normally again, it was time to see if they could perform other spidery functions while under the control of humans. Instead of just opening and closing the legs, they first tested to see whether they could grip an object. Using a small ball and a gauge, the zombie spiders gripped a small ball with a peak grip force of 0.35 millinewtons. (A ‘newton’ is the force required to accelerate a mass of one kilogram by one meter per second per second – this was one-thousandth of that force.) So, the zombie spider now has strength. Can that strength be regulated to give it a delicate touch? After all, real spiders are able to carry flies and other dead insects without crushing them, and crawl over delicate webs without tearing them apart.
“They then demonstrated the use of a dead spider to pick up delicate objects and electronics, including having this necrobotic gripper remove a jumper wire attached to an electric breadboard and then move a block of polyurethane foam.”
The Rice team showed they could put a zombie spider to work in a lab or on an electronics factory floor preforming tasks with objects that might be too fragile for mechanical grippers. Necrobotics has suddenly gone from creepy to potentially useful – Preston points out that the zombie spider showed the capability to perform thousands of repetitive talks without any signs of breakdown – a problem in applications requiring tiny mechanisms. What else can it do?
“They also showed that the spider could bear the weight of another spider of about the same size.”
So, a zombie spider can grab and carry a dead or living spider. Does this sound like a plan to create a zombie spider army for a zombie spider apocalypse? Preston has a cover story – he foresaw an application where unsuspecting spiders and insects could be studied in nature using camouflaged zombie spiders equipped with cameras and other equipment. Adding one more ‘noble cause’ to the project, Preston points out that zombie spiders are biodegradable – no junkyards filled with broken-down grippers and rusting parts. Of course, that also means no evidence that zombie spiders caused an apocalypse. Does that sound sinister to you?
“Despite looking like it might have come back to life, we’re certain that it’s inanimate, and we’re using it in this case strictly as a material derived from a once-living spider. It’s providing us with something really useful.”
That may sound reassuring … except the last line of the press release notes that “a NASA Space Technology Graduate Research Opportunity award supported the research.” Is NASA planning a zombie spider force to explore and conquer space? Does it know that aliens are afraid of spiders too?
Spider zombie apocalypse aside – this Rice University necrobotics project shows once again that nature has a lot of solutions to our problems that we need to study before we have no more nature to study.