Similar to electrostatic dust cloths, spider webs attract electrically charged prey. The electricity, in this case, is derived from flapping.
The discovery, outlined in the latest issue of Scientific Reports, could help to explain how spider webs evolved. Light, flexible spider silk easily deforms in the wind and electrostatic charges to aid prey capture. Were it not for such flexibility, the flying insect could just bounce off and zip on its way.
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"Electrostatic charges are everywhere, and we propose that this may have driven the evolution of specialized webs," Victor Manuel Ortega-Jimenez, a UC Berkeley researcher who worked on the study, said in a press release.
Ortega-Jimenez most often studies hummingbird flight, but he had a light bulb moment while playing with his 4-year-old daughter.
"I was playing with my daughter's magic wand, a toy that produces an electrostatic charge, and I noticed that the positive charge attracted spider webs," he said. "I then realized that if an insect is positively charged too it could perhaps attract an oppositely charged spider web to affect the capture success of the spider web."
To test this, he gathered a bunch of cross-spider webs and brought them into his lab. Then, like Dr. Frankenstein, he used an electrostatic generator to charge up dead insects. These included aphids, fruit flies, green-bottle flies and honeybees. Once charged, all were then dropped one by one onto a neutral, grounded web.
"Using a high speed camera, you can clearly see the spider web is deforming and touching the insect before it reaches the web," he said. Insects without a charge did not do this. "You would expect that if the web is charged negatively, the attraction would increase."
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Insect-generated electricity has also been shown to help bees to communicate with plants and vice versa. There's been a fair amount of focus on electrically charged bees and insects these days, with all kinds of interesting findings like this. (See an electrically charged bee fall into a spider's web).
The electricity from our perspective is minimal, although insects easily develop several hundred volts of positive charge from the friction of wings against air molecules or by contacting a charged surface. By comparison, we develop several thousand volts of electricity when walking across a rug, or even when petting a cat. That's why you can get a shock right afterward when you touch something metal, such as a metal doorknob.
The electrostatic charge of a bee is sufficient to draw pollen off a flower before even landing, saving the bee a lot of work.
In the future, Ortega-Jimenez hopes to find out whether static charges on webs attract more dirt and pollen. If so, that could be why many spiders rebuild their webs on a daily basis.
Image: gradders52, Flickr