SpiderBot, SpiderBot SpiderBot experiments hint at echolocation to locate prey Experiments with robotic spiders and prey suggest spiders can detect differences in natural web frequencies. Jennifer Ouellette Mar 18, 2025 12:46 pm | 8 Credit: YouTube/Terradynamics Lab/JHU Credit: YouTube/Terradynamics Lab/JHU Story textSizeSmallStandardLargeWidth *StandardWideLinksStandardOrange* Subscribers only Learn moreIt's well understood that spiders have poor eyesight and thus sense the vibrations in their webs whenever prey (like a fly) gets caught; the web serves as an extension of their sensory system. But spiders also exhibit less-understood behaviors to locate struggling prey. Most notably, they take on a crouching position, sometimes moving up and down to shake the web or plucking at the web by pulling in with one leg. The crouching seems to be triggered when prey is stationary and stops when the prey starts moving.But it can be difficult to study the underlying mechanisms of this behavior because there are so many variables at play when observing live spiders. To simplify matters, researchers at Johns Hopkins University's Terradynamics Laboratory are building crouching spider robots and testing them on synthetic webs. The results provide evidence for the hypothesis that spiders crouch to sense differences in web frequencies to locate prey that isn't movingsomething analogous to echolocation. The researchers presented their initial findings today at the American Physical Society's Global Physics Summit in Anaheim, California."Our lab investigates biological problems using robot physical models," team member Eugene Lin told Ars. "Animal experiments are really hard to reproduce because it's hard to get the animal to do what you want to do." Experiments with robot physical models, by contrast, "are completely repeatable. And while you're building them, you get a better idea of the actual [biological] system and how certain behaviors happen." The lab has also built robots inspired by cockroaches and fish.The research was done in collaboration with two other labs at JHU. Andrew Gordus' lab studies spider behavior, particularly how they make their webs, and provided biological expertise as well as videos of the particular spider species (U. diversus) of interest. Jochen Mueller's lab provided expertise in silicone molding, allowing the team to use their lab to 3D-print their spider robot's flexible joints.Crouching spider, good vibrations A spider exhibiting crouching behavior. Credit: YouTube/Terradynamics Lab/JHU The first spider robot model didn't really move or change its posture; it was designed to sense vibrations in the synthetic web. But Lin et al. later modified it with actuators so it could move up and down. Also, there were only four legs, with two joints in each and two accelerometers on each leg; real spiders have eight legs and many more joints. But the model was sufficient for experimental proof of principle. There was also a stationary prey robot.The synthetic web, hung from the ceiling, was made with a combination of parachute cords and cords used for hair ties to mimic the two kinds of silk spiders used when spinning their webs. (The radial threads that make up the spokes of the web are a stronger silk, while the circling inward spiral is weaker and stickier.) The team tested two scenarios: one where the SpiderBot dynamically crouched with no prey robot on the web and one where there was a prey robot on the web. The prey robot was programmed to move only once per trial run but each time at different amplitudes. High-speed cameras monitored the web vibrations.The SpiderBot was unable to locate the prey robot without crouching if the latter wasn't moving or moving only weakly; if the prey robot made an intense movement, the SpiderBot could find it without crouching. When they analyzed the web frequency data, the team found that the crouching motion induced both robots to vibrate in the web, but each did so at its own natural frequency. The SpiderBot was able to find the prey robot because it sensed a frequency different from its own. The SpiderBot could even determine its distance from the prey robot since the induced shaking was larger the closer the SpiderBot came to the prey robot.That said, "The phenomenon we have observed, at least within the spider robot model, isn't actually echolocation; we just use it as an analogy," said Lin. "The prey robot doesn't reflect the waves produced by the spider robot but is shaken by the spider robot to create new oscillations in the web."Lin's JHU colleague Siyuan Sun is building the next-generation SpiderBot, which has eight legs and four joints per leg, with accelerometers on each joint to record vibrations. Instead of torsional springs, Sun used soft silicone materials for the joints. This new 3D-printed SpiderBot has better range of motion and hence a deeper crouch, with a connecting cable actuating a motor inside the robot's body to make all eight legs bend like actual spiders. Ideally, future SpiderBots would be pneumatically driven, per Sun, with independent leg control, although the latter is particularly difficult to achieve.Jennifer OuelletteSenior WriterJennifer OuelletteSenior Writer Jennifer is a senior writer at Ars Technica with a particular focus on where science meets culture, covering everything from physics and related interdisciplinary topics to her favorite films and TV series. Jennifer lives in Baltimore with her spouse, physicist Sean M. Carroll, and their two cats, Ariel and Caliban. 8 Comments