On feeding days, Sarah Han would lift the lid to the spider enclosure and carefully lower a struggling fly to its doom.
It only took a few tries for Han, an entomologist at the University of Akron, to notice some unusual behavior in her triangle-weaver spiders (Hyptiotes cavatus). Each time an insect brushed up against the silk, the arachnid stationed at one corner of its triangular trap would jerk in the direction of its prey, releasing the tension in the web. With each successive movement, the web’s infrastructure would crumple inward like a snapped rubber band, instantaneously shrouding the hapless fly in a billowing sheet of sticky, immobilizing silk.
The spiders’ shudders were subtle, but more than anything, they were fast. When Han filmed the spiders on high-speed video and played the tape back in slow motion, she discovered the spiders were launching themselves and their webs with accelerations up to 1,700 miles per hour per second (that is, their speed increased by 1,700 miles per hour each second). That’s about 60 times the acceleration of a sprinting cheetah. Every time they did, the spiders boosted their chances of snagging themselves an expedient meal.
Today, in the journal PNAS, Han reports the secret to these spiders’ success: A sophisticated ability to use their webs as “tools” to exceed the limitations of their own bodies—akin to a human shooting an arrow from a tightly-drawn bow.
“This is a pretty awesome thing to see,” says Symone Alexander, an entomologist and biophysicist at Georgia Tech who was not involved in the study. “These spiders don’t have superpowers like supervision or jumping. Their strategy is more, ‘How can we use a tool to catch a meal that’s much larger, faster, and stronger than we are?’”
For many other spiders, mealtimes can be a bit of a gamble. Even if an insect stumbles into a freshly woven web, there’s no guarantee it’ll stick. This puts the onus on the hungry arachnid to quickly scuttle down its silk ladder and secure its prey with a secondary straightjacket before the insect wrests itself free. And in doing so, a soft-bodied spider risks being injured by its tenuously trapped prey.
That’s why the triangle weaver’s slingshot strategy is so effective. Rather than risking their hides through physical contact with their prey, these spiders leverage their webs to subdue insects from afar.
After spinning its web, a triangle weaver spider will take up residence at one corner of its contraption and secure itself to a nearby branch with a silken anchor line. While gripping its web with its front legs, the spider then hauls itself up the anchor line in the direction of the branch, gathering the slack of its tether. The movement tugs the trap as taut as a translucent trampoline, storing energy in the spider’s super-strong silk.
Then, when an insect smacks into the trap, the spider releases its anchor line, sending itself and the web hurtling forward like an unspooling bungee jumper, collapsing silk around its prey. When the spider reaches the end of its rope, it recoils and ricochets, sending a second wave of fibers cascading around the bedeviled bug from every direction. The triangle weaver can then repeat the cycle several times over by simply ratcheting back along its anchor line and letting go again, until the entire web has become an inescapable clump of silky shrink wrap.
Before Han and her team decided to investigate, however, no one had put actual numbers to these spiders’ fleet-footed tricks. Their analysis revealed that the initial release could tangle a fly in as few as four milliseconds. Even with multiple rounds of aim and fire, the spiders didn’t need more than a few seconds total to fully snare their snacks.
Han was astounded to find that the energy wound up in the spiders’ silk could propel them forward with accelerations that would shred human innards (even accelerating at just 90 miles per hour per second can cause the average person to lose consciousness). At maximum speed, the rice-sized spiders, measuring close to 5 millimeters long, were covering 400 times the lengths of their own bodies each second—the equivalent of a 5’10” human sprinting at more than 1,500 miles per hour.
The spiders didn’t always deploy their webs when a fly made contact. If this was the case, Han found, the insect inevitably flew away. But when the web was cast, the spider’s rate of success jumped to more than 70 percent. By tapping into the power of their netlike webs, the triangle weavers had found a way to rapidly incapacitate their prey without running the risk of a physical brawl.
“This tiny little animal just cranks up stored energy in its web and turns it into...a controllable prey-catching device,” says Sheila Patek, a biophysicist and biomechanics expert at Duke University who was not involved in the study. “It’s kind of like a crossbow, where you can crank the bow multiple times to put energy into it. It’s far more than a single muscle could do.”
This web-based technique also make spiders the only known animals other than humans to store and release large amounts of energy through an external “tool” that’s not part of their own anatomy, says Angela Chuang, an entomologist and spider expert at the University of Tennessee Knoxville who was not involved in the study. “[It] highlights how much we still don't know about nature.”
What’s more, it seems that triangle weaver spiders aren’t alone in this ingenious act. At Georgia Tech, Alexander is currently studying a similar phenomenon in a Peruvian spider, which can zoom forward with an acceleration of up to 2,500 miles per hour per second. While both types of spiders can lasso lunch from a distance, Alexander’s spider builds three-dimensional, cone-shaped webs, and releases them even before insects have made contact with the silk.
This trigger-happy tactic might be a bit riskier than waiting for a fly to blunder into an actual web, Alexander says, but it also means less waiting around. Either way, both methods alleviate the need for the arduous and perhaps perilous task of rushing headlong into the path of an infuriated insect. “This completely changes the game of hunting,” Alexander says. “Now you’re less tired because the web is doing the work.”
The technique could even have the added benefit of helping spiders avoid their own predators, allowing them to springboard away from an oncoming attack, says study author Todd Blackledge, an entomologist at the University of Akron who oversees Han’s work.
But, of course, there’s no such thing as a free lunch, even for spiders. The biggest downside of this behavior is that “the web basically gets used up in a single prey capture event,” forcing the spider to reconstruct in advance of every meal, Blackledge says. “That’s potentially a real cost.”
As for the possibility of humans invoking the wrath of slingshotting spiders, Han isn’t terribly concerned. “There’s a pretty low chance you’d run into these spiders,” she says. “They’re super tiny and they live in woodsy areas.”
Even if you do chance upon a hungry Hyptiotes on a day hike, Han says, it won’t be terribly interested in catapulting into you. This sneaky spider has its sights set on a far smaller prize—an unfortunate insect who, if all goes as planned, won’t even see it coming.