Confirmed: Spiders Are Even More Terrifying Than Previously Thought

By Megan Garber
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Shutterstock/Valentyn Volkov

Spider webs are architectural marvels. Their silks are similar in tensile strength to alloy steel. Their adhesive properties adjust to movements of prey ensnared in them. Yet they are, for many of the spiders that weave them, edible.

And spider webs, it turns out, may be one more thing, too: actually attractive to the very prey they're meant to lure. New research suggests that the webs may be effective at their primary jobs -- catching prey for the creatures that wove them -- not only because of their stickiness, and not only because of their strength, and not only because of their unique shape ... but also because of their responsiveness to electricity itself.

Yes. According to the research, the webs and positively charged objects -- like, say, insects flying by -- seem to be attracted to each other. Electrically attracted to each other. Unavoidably attracted to each other. Insects' wings, after all, don't simply keep their owners in the air as they're flapping; they also, in the process, generate electrical charge. Honeybees can generate enough charge -- up to 200 volts -- to detach pollen from flowers. And spider webs may take advantage of that in a way that is both evolutionarily ingenious and totally insidious at the same time, capturing prey by essentially sucking their victims in. Talk about animal magnetism.

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Web deformations produced by a charged honeybee (a), a fruitfly (b), and a water drop (c). Images are three sequential video frames (filming speed: 1,500 frames s−1). The bee, fruitfly, and drop sizes are 12 mm, 3 mm, and 1.5 mm, respectively, with the image gamma increased to 1.5. (Victor Manuel Ortega-Jimenez and Robert Dudley)

The study, conducted by U.C. Berkeley's Victor Manuel Ortega-Jimenez and Robert Dudley and published in the journal Scientific Reports, tested webs' responsiveness to, in particular, the electrostatic charges of insects and water droplets. Their research, the authors note, builds on previous work that has documented webs' deformations in response to prey. We know, or think we know, that spider webs shift their shapes in order to capture that prey; the question is how they do it.

The researchers thought electricity might be the answer, and they thought that, in part, because of a toy. Ortega-Jimenez, Live Science notes, had the electricity-as-hunting-tool idea while playing with his daughter -- with, specifically, an electrostatically charged "magic wand" that helps light objects that come into contact with it to levitate. The pair passed the wand in front of a spider web -- and the web deformed in response.

So Ortega-Jiminez and Dudley tested the magic wand's effect in a lab setting. They gathered webs of the cross spider, or garden spider, from around the UC Berkeley campus. They ran a series of experiments, testing the webs' reaction to passing objects like honeybees, green bottle flies, fruit flies, aphids -- and, for good measure, water droplets.

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Spider web deformations produced by statically charged insects -- bees, flies, aphids, fruit flies -- and water drops (Victor Manuel Ortega-Jimenez and Robert Dudley)

Their findings? The webs and positively charged objects did indeed seem to be attracted to each other. The silk threads in the web, for example, curved toward each other underneath a charged honeybee that was falling toward it -- which would make it likelier that the bee would become entangled in the web. Video sequences, both of positively charged insects and of water droplets falling towards a web, revealed "rapid and substantial web attraction." Radial and especially spiral silk threads, the authors write, "are quickly attracted to the electrified bodies." By contrast, control trials using uncharged insects and water drops showed no such deformation.

And the deformations they're describing were significant: they were, on average, nearly half the length of the insects themselves.

"Our experiments show clearly that positively charged insect bodies induce rapid attraction of silk threads in the webs of cross-spiders," the authors sum it up, "indirectly supporting a prior hypothesis that static charges of insects increase the prey capture success of orb-webs." Put less scientifically: it might be even more terrifying than previously assumed to become the prey of a spider.

This article available online at:

http://www.theatlantic.com/technology/archive/2013/07/confirmed-spiders-are-even-more-terrifying-than-previously-thought/277544/