Spinning at night, it makes four radial spokes that converge at a point, an apex line that connects that point to a nearby branch, and sticky capture threads that run across the spokes. Once finished, it sits on the apex line, cuts it, and uses its own body to bridge the two separate threads. Its front legs grab the end leading to the web. The silk-making spinnerets on its backside grab the end anchored to the branch. Then, by walking its back legs along that anchor line, as a person hauling along a rope, it slowly winches the web taut. If an insect hits the web, Hyptiotes lets go with its back legs, allowing the web (and its body) to spring forward.
Thanks to this springing action, several of the sticky capture threads slam into the insect. And since Hyptiotes is still holding on to the anchor line with its spinnerets, it can repeatedly recock and relaunch the web. Again and again, the triangle pulls back and springs forward, each time entangling the insect even more. Finally, when the victim is well and truly trapped, the spider scampers over and starts to feed.
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Wilder described all of this in 1875, and while others have studied Hyptiotes since, no one had studied the physics of its attack. Sarah Han from the University of Akron did so recently using high-speed video cameras, and the numbers she got came as a shock.
When the spider releases the anchor line, its body accelerates at 770 meters per second squared (more than 2,500 feet per second squared)—almost 80 times greater than a free-falling object, and 60 times greater than a sprinting cheetah. That’s only possible because the spider stores energy in its stretched web. If it tried to accelerate that hard on its own power, it would need 20 times its body weight in muscle.
Many animals use special energy-storing structures in their body to amplify the power of their muscles. Fleas compress a springy pad when they cock their legs, and the energy released when that pad expands powers the insects’ incredible jumps. Mantis shrimps—a group of aggressive crustaceans—use a similar structure in their arms to deliver the world’s fastest punches. Chameleons launch their super-fast tongue strikes by pulling the tongue back as if drawing an arrow on a bow, and then releasing it.
In all these cases, energy is stored within the animal’s body. By contrast, very few animals store energy in an external tool. Humans, with our bows, slingshots, catapults, and ballistae, are one. Hyptiotes, with its spring-loaded web, is another. The ray spiders (aka slingshot spiders) can also join the club: They spin traditional circular webs and then stretch the center back to create a spring-loaded cone. Symone Alexander from Georgia Tech, who studied one of these spiders, showed that they can achieve even greater accelerations than Hyptiotes. And “though Hyptiotes face their web, slingshots face away, indicating that there are perhaps some differences in prey-sensing and web-release strategies,” Alexander says.