Spiders are experts at creating tension. They make many people nervous, of course, even though they're mostly harmless — and often helpful — to humans. But they also create a more literal kind of tenseness, weaving webs that stay uncannily taut despite being stretched and compressed while insects fight for their lives.

Spider silk is already famous for its superpowers, from extreme strength, flexibility and stickiness to antimicrobial, biodegradable and hypoallergenic qualities. One strand is thinner than a human hair, yet five times stronger than steel of the same width. It can stretch to many times its original length, but also resists sagging when it slackens — almost as if loose silk is reeled in by hidden spools.

Actually, that's exactly what happens, according to a new study: Tiny, prey-trapping glue droplets on a spider's "capture silk" double as automatic reels when the strand contracts, spooling up slack so the strand stays tight. And on top of demonstrating this spooling phenomenon in natural spider silk, the researchers also developed their own spinoff version, which they describe as "liquid wire."

This video includes footage of both spider silk and liquid wire in action:

"The thousands of tiny droplets of glue that cover the capture spiral of the spider's orb web do much more than make the silk sticky and catch the fly," says co-author Fritz Vollrath, a silk expert and zoologist at Oxford University, in a statement. "Surprisingly, each drop packs enough punch in its watery skins to reel in loose bits of thread. And this winching behaviour is used to excellent effect to keep the threads tight at all times, as we can all observe and test in the webs in our gardens."

The spooling technique relies on a subtle balance, the researchers explain, between fiber elasticity and the surface tension of droplets. Yet despite the precision required, they were able to recreate it in a lab using oil droplets and a thin plastic filament. This artificial system effectively mimics a spider's natural silk, they write, with filament spooling and unspooling inside oil droplets as the thread extends and contracts.

Here's more video of the synthetic silk being tested:

"Spider silk has been known to be an extraordinary material for around 40 years, but it continues to amaze us," says co-author Hervé Elettro, a doctoral researcher at Pierre and Marie Curie University in Paris. "While the web is simply a high-tech trap from the spider's point of view, its properties have a huge amount to offer the worlds of materials, engineering and medicine."

This study, published in the Proceedings of the National Academy of Sciences, is just the latest reminder that spiders are not our enemies. Aside from protecting crops and killing pests like mosquitoes and flies, they produce incredible substances we can imitate — like venom that inspires safer pesticides, or silk that leads to stronger synthetic materials. The newly discovered "liquid wire" technology, for example, could have a variety of uses in robotics and electronics, or to create artificial muscles.

"Our bio-inspired hybrid threads could be manufactured from virtually any components," Elettro adds. "These new insights could lead to a wide range of applications, such as microfabrication of complex structures, reversible micro-motors, or self-tensioned stretchable systems."

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.