Jumping spiders don’t build webs, but like their arachnid kin, they can produce silk. Some species are known to spin fine threads as they leap, presumably to stabilize takeoff and ensure a more controlled landing. Since these draglines aren’t tasked with entangling struggling prey, researchers have wondered how they compare to the silks made by other species. Spider silk is considered a very robust natural biomaterial, with research finding it stronger than steel.
Harvard neurobiologist Paul Shamble and his colleagues decided to examine the silk produced by zebra jumping spiders (Salticus scenicus). Little did they know they were in for what Shamble says was “a huge surprise”: the strength of this spiders’ silk parallels—and even surpasses—that of most orb weaver spiders, which produce the strongest silks known.
First, to measure the speed of the spiders’ spinning, Shamble and his team collected the animals locally in Cambridge, Massachusetts, and recorded them leaping across a 3-cm gap with a high-speed camera. “One of the real kickers of this project is that the spiders are moving so fast when they’re [producing silk], that we didn’t even really know what to expect. They’re just going way faster than any spider that’s been studied for silk spinning,” he says. Indeed, the videos revealed the spiders produce their draglines at an impressive 500 to 700 mm/s—about 25 to 35 times faster than the average web-spinner.
The team then collected the draglines that the animals produced and analyzed their physical appearance using scanning electron microscopy (SEM). This part proved challenging because the electron blasts from the microscope burned the silk, says Shamble. But, after troubleshooting the microscope’s power settings, the team was able to progress with the physical analysis. They also conducted tensile tests to determine how much the dragline could be stretched and how much energy it could absorb before it broke.
Those tests revealed that the draglines' average toughness was 281.9 megajoules per cubic meter, the team reports November 8 in Current Biology. That’s more than twice the reported toughness of the silk produced by the orb weaver Nephila clavipes. In fact, the jumping spider’s silk is only bested by that of the Caerostris darwini orb weaver, which weaves the largest webs in the world and produces a silk with a toughness averaging 350 megajoules per cubic meter.
Part of the explanation for the draglines’ toughness is that they’re the same kind of silk as the lines that run from a web’s center to its edges, Shamble explains: “Those are the lines that are responsible for absorbing a bunch of energy” when something lands in the web. Still, it’s not clear why the animals need tougher silk than much of their kin do. Shamble speculates that “it might just be that [jumping] actually has really high demands on the silk.” Previous research suggests that jumping spiders use their draglines as a mechanism for controlling their orientation mid-jump.
Next, Shamble wants to explore how draglines are used in jumps and the mechanisms behind jumping spider silk production. He emphasizes that before this paper, jumping spiders were not widely talked about in the context of silk. He hopes these findings excite other researchers so they reevaluate using this group in silk research. “A lot of people have thought really hard [about spider silk], including some really cool synthetic biology types about making artificial silk. But all of that has always been based on just orb weaver spiders. . . . I think this is a pretty exciting launching point [for studying jumping spiders].”