For a human, losing a limb is an extremely traumatic experience. For a spider, not so much. They can pop off a leg or two as a form of defense without experiencing much disruption to their movement. Tonia Hsieh, Associate Professor of Biology, and Andrew Spence, Associate Professor of Bioengineering, are digging deeper to discover how spiders adapt to limb loss to keep their stability. Their study might lead to the development of search and rescue robots that can save lives faster. 

Hsieh, who has also explored tail loss on lizards, began to wonder if there was an animal that could adapt to a more extreme change. This led to the idea of testing how spiders adjust to limb loss. It was essential to the study that the spiders voluntarily remove their limbs, not only for ethical reasons, but also because spiders are designed to remove their own limbs in a very specific way. Spiders' bodies are pressurized, when a spider chooses to eject a limb the wound coagulates, and the spider losses no blood. Each spider was made to eject two legs from its body. Hsieh's team then recorded and analyzed hundreds of gigabytes of high-speed video showing spider movement to see how they dealt with the considerable change to their normal forms of movement.

When spiders walk, they use only four of their eight legs at a time, which keeps them stable and fast. It made sense to assume spiders with six legs would use a similar tactic—using three legs at a time. While most spiders did just that, a significant number used two of their six legs at a time, then transferred to four, almost like they were limping. To the surprise of Hsieh and Spence, these spiders lost little in terms of stability and speed. Learning how spiders can take limb loss in stride, so to speak, would be of great use in the robotics industry, specifically when it comes to search and rescue.

Robot movement is still in its early stages. Although great progress is being made, it is still not very robust. Simple things like stepping off a curb, or moving from grass to concrete, can cause a robot to fail. Now imagine how losing a leg would impact a robots functionality. Search and rescue robots will have to navigate difficult terrain so they need to be able to adapt to extremes. Hsieh and Spence's research could support the development of more robust and adaptable robots in the not-so-distant future.

You can learn more about Hsieh's research on spider science or read about her other work here. You can find Spence's research here.