Spider webs are drawn to flying that insects that build up electrical charges, say researchers at the University of California, Berkeley.
The new findings of the new work were published July 4 in Scientific Reports, an open-access, rapid-publication website operated by the publishers of the journal Nature, and based on observations of spider-woven silk that high-speed video showed was attracted towards various inspects dropping into webs.
The positive charge created when an insect such as a bee or fly flaps their wings is strong enough to deform the spider's lair --- which is typically positively or negatively charged --- and pull it toward the buzzing insect, increasing the chances that the passerby by will end up contacting and sticking to the web, said Victor Manuel Ortega-Jimenez , a UC Berkeley post-doctoral fellow who usually studies hummingbird flight but became interested in spider webs while playing with his four-year-old daughter.
"Electrostatic charges are everywhere, and we propose that this may have driven the evolution of specialized webs," said Ortega-Jimenez.
He also noted in a press announcement that the light, flexible silk used by spiders to make making the spirals layers on top of the stiffer stands of silk that form the spokes of a web may have indeed emerged exactly for the fact it more easily deforms in the wind and the presence of electrostatic charges, aiding the capture of prey.
"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," Ortega-Jimenez 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 easily develop several hundred volts of positive charge from the friction of wings against air molecules, or by their contact with charged surfaces. Aside from moving spider webs, such charges also allow bees to electrostatically draw pollen off flowers before landing.
To test his spider web hypothesis, Ortega-Jimenez sought out cross-spider (Araneus diadematus) webs along streams in Berkeley and took them back to his lab. He then used an electrostatic generator to charge up dead insects - aphids, fruit flies, green-bottle flies, and honey bees - and drop them into a neutral, grounded web.
"Using a high speed camera, you can clearly see the spider web is deforming and touching the insect" before it actually reached the general surface of the web, Ortega-Jimenez said, and that doesn't happen to insects without a charge.
Ortega-Jimenez plans to conduct further tests at Berkeley to determine to what extent the electrical charge effect may occur in the wild, as well as try to determine if the static charges on webs attract more dirt and pollen and therefore are why orb web weavers rebuild them daily.