Spiders and Hydraulics

A big, hairy spider scurries across the floor of your room, you get up to remove it with a glass cup and piece of paper (since you love nature). But once you get closer to the little arachnid, its robotic like legs begin working overtime as it runs and hides under your bed. Besides the haunting dreams that you will be having tonight, ever wonder why small spiders scurry away from you rapidly in any direction when you get close to them? Well there bodies rely on hydrostatic pressure in their skeleton. If a single leg was to be punctured or lost, they risk losing pressure in their entire body and deflating. Some species have valves or sphincters to help prevent a catastrophic lose of hemolymph. The spider’s leg extension is achieved by hydraulic pressure generated in the cephalothorax. The hemolymph flows into the legs from the cephalothorax into spaces between all the soft tissues inside a leg. Thus volume inside joints and legs increase, leading to extension.


Spiders do have muscles to flex their limbs inward, they use hydraulic pressure to extend them outward. That is why when you finally “remove the blessed life from one of gods creatures” aka, there legs flexor muscles curl up in towards there abdomen since the hydraulic system has been shut off.


Different research groups have mimicked the hydraulic mechanism of spider biology to come up with creative designs for unique problems and solutions. Like, a research team at the Fraunhofer Institure for Manufacturing Engineering and Automation has developed a spider robot to track and sense information deemed too dangerous for humans.

“As a real spider would, our robot keeps four legs on the ground at all times while the other four turn and ready themselves for the next step. With its long extremities, the spider has a range of ways to get around. Some models can even jump. This is possible using hydraulically operated bellows drives that serve as joints and keep limbs mobile.”

Another remarkable engineer, from the UK, created a giant-mantis robot with hydraulic legs. The original design of the robot was used for entertainment purposes, it was meant to be cool, insect-like and fun. The machine did arise the interests of mining companies, and marine  research organisations.


The downside to spider hydraulic mechanism (which all exoskeleton animal species experience) is that the spider cannot grow very big. The mechanism has a hard time supporting large animals or objects. But consider the scaling principles of this semi-hydraulic locomotive apparatus in spiders may help to better localize its limits by understanding the design criteria and support convergence of the design of small hydraulically driven machines or robots. There could be cheap, light weight robots used to look inside pipes, or through small crevices that a conventional wheel robot would have trouble navigating. Its up to the engineer or designer to figure out the degree of sophistication needed to mimic the biological examples.


  1. http://infinitespider.com/spider-legs-work/
  2. http://jeb.biologists.org/content/215/4/578
  3. http://www.3d-printing.net/content/spider-robot-rescue
  4. http://www.bbc.com/news/technology-22231365

7 thoughts on “Spiders and Hydraulics

    1. Your Right! I should have added figures under the photos. The first photo is showing the spider limb, and gives you a reference on how the muscles move. The blood would flow out forcing the legs to expand, and the muscles only act as concentric contractors attached like wire. The second photo shows how spiders joints operate and their leg movement, using a live specimen. The third and final photo is the hydraulic inspired spider used for search and rescue missions. I tried to find a better photo of this part of the spider’s anatomy, but google just wasn’t supping


  1. This is very cool! I never knew that spiders behaved in this way. Do any other insects have this dual musculature/hydraulic system? I would like to know more about the functionality of this system as well. For example- you made it seem like the hydraulics are a mechanism for spider sense. Is that the case?

    Mackenzie (natureownsnopatents)


  2. This is super cool, I always wondered why spiders get all crunched and cramped up when they die. However, as I was reading this I was wondering, since the system relies mostly on hydrodynamic pressure, the inherent weakness is as you stated a leak or head loss in the working fluid. But in order to circumvent this downfall, what if a pneumatic system was used instead for a working fluid. If a system could use ambient air around it, pressurize it in a modulated way to achieve proper actuation, then all that would be needed to solidify the design would be a possible surrounding encapsulating layer. Essentially a thin membrane enclosing a quick seal and dry solution, would act as a fail safe to the pneumatic tubing of the robot or device if their was a puncture or leak that would cause the air pressure within the device to drop and stop proper functioning. Although, controlling a system with fluctuating pressurized segments could possibly be highly dangerous….but whatever, try it anyways right?


  3. That’s really interesting! I had no idea that our eight-legged little friends relied on pressure to get around, I always assumed they had a very similar muscular system to us. I wonder why it doesn’t scale very well, just considering the fact that hydraulic systems are very powerful, even huge tractors use them to dig holes. I would be interested to look a little further into that.



  4. Wow, a very interesting read. There are definitely a lot of these mechanical spider structures being made for events like burning man. The one thing i have noticed about these structures is they tend to have a large shock loading. I wonder if that is an unavoidable consequence of the geometry and pressure drive system. Maybe when implementing these structures at a larger scale, we may have to look into how larger animals disperse load. Anyway, thanks again for a good article.

    – Eddie


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