UC Berkeley post-doctoral fellow Victor Manuel Ortega-Jimenez made an unusual discovery while playing with his daughter -- spider webs are especially good at catching insects that have built up an electric charge by flapping their wings.
"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."
Insects develop several hundred volts of positive charge from the friction of wings against air molecules or by contacting a charged surface. This is small compared to the several thousand volts we develop when walking across a rug, but is sufficient to allow a bee to electrostatically pull pollen from a flower before landing.
"Electrostatic charges are everywhere, and we propose that this may have driven the evolution of specialized webs," Ortega-Jimenez said.
To test his hypothesis, Ortega-Jimenez collected cross-spider (Araneus diadematus) webs. He then used an electrostatic generator to charge dead insects including aphids, fruit flies, green-bottle flies, and honey bees, and dropped them into a neutral, grounded web.
Images showed tiny strands of the spider silk separating from the primary strand to "reach" out for the bug.
"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."
Ortega-Jimenez plans to conduct further tests to determine whether this effect occurs in the wild, and to find out whether static charges on webs attract more dirt and pollen, providing a reason why orb web weavers rebuild them daily.