04 July 2013

Spider Webs Use Electrostatic Charge To Effectively Catch Insects

A study from biologists in University of California, Berkeley, shows that spider webs use the electrical charge in insects to help better capture them. The result of their findings is published in Scientific Reports.

The image on the left is that of a cross spider, Araneus diadematus, lying in wait in its web. The cross spider, just like most spiders, produces silk to create its web to capture its prey.

There are other researches done to study and analyze the structure of the spider web to discover what makes spider webs resilient and how these properties relate to the molecular structure of silk fibers. A key property of spider silk that helps make webs robust is that it can stretch and soften at first when pulled, and then stiffen again as the force of the pulling increases.

The UC Berkeley study states that the electrostatic charge generated by insects as they flap their wings help deform the silk web before capturing them; increasing the effectiveness of the spider web in capturing its prey.

UC Berkeley post-doctoral fellow Victor Manuel Ortega-Jimenez used electrically charged dead insects, a spider web, and high speed video cameras to test his hypothesis. Dropping the electrically dead flies into the web while filming it, showed that before the insects hit the web, the silk deforms and touches the insects; ensuring capture.

Spider Webs and Electrically Charged Prey

Flapping insects build up an electrical charge that may make them more easily snared by spider webs, according to a new study by University of California, Berkeley, biologists.

The positive charge on an insect such as a bee or fly attracts the web, which is normally negatively or neutrally charged, increasing the chances that an insect flying by will contact and stick to the web, said UC Berkeley post-doctoral fellow Victor Manuel Ortega-Jimenez.

He also suspects that light flexible spider silk, the kind used for make the spirals on top of the stiffer silk that forms the spokes of a web, may have developed because it more easily deforms in the wind and electrostatic charges to aid prey capture.

"Electrostatic charges are everywhere, and we propose that this may have driven the evolution of specialized webs," he said.

Ortega-Jimenez, who normally studies hummingbird flight, became interested in spider webs while playing with his four-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."

Video: Electrostatic Charges Attract Spider Web

In fact, insects easily 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 and which gives us a shock when we touch a doorknob, but is sufficient to allow a bee to electrostatically draw pollen off a flower before landing.

To test his spider web hypothesis, Ortega-Jimenez sought out cross-spider (Araneus diadematus) webs along streams in Berkeley and brought them into the 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 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 at UC Berkeley to determine whether this effect occurs in the wild, and find out whether static charges on webs attract more dirt and pollen and thus are a major reason orb web weavers rebuild them daily.


University of California - Berkeley
Scientific Reports
Kinds of Spiders and the Secret Behind The Strength of Their Webs
New Species of Trapdoor Spider Discovered: The Auburn Tiger Trapdoor Spider
New Spider Family Trogloraptoridae Discovered In Oregon
Brown Widow Spiders Invade Southern California Displaces Black Widow Spiders