Neutral Spider Web Seeking Positively Charged Insects

[ Watch the Video: Falling Insects Electrostatically Deform Web ]

Michael Harper for – Your Universe Online

A new study from the University of California claims spider webs don’t attract the prey; rather, the prey attracts the web. As insects such as aphids or bees fly through the air, carried by their tiny and quickly beating wings, they build up a positive electrostatic charge. This charge may be enough to attract the thin and flexible strands of spider’s silk which contains a neutral or negative charge.

According to Victor Manuel Ortega-Jimenez, a post-doctorate fellow at the University of California Berkeley (UC Berkeley), sticky spider’s silk gets some help from static electricity in the effort to ensnare passing insects. Furthermore, he now wonders if the lighter form of silk eventually developed due to its light weight and ability to deform and come away from the web to grab hold of passing insects. Ortega-Jimenez’s work is now published in the journal Scientific Reports.

“Electrostatic charges are everywhere, and we propose that this may have driven the evolution of specialized webs,” said Ortega-Jimenez in a statement.

He normally studies the way hummingbirds fly but says he became interested in a potential positive charge on insect’s wings when he was playing with his young 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.”

A flying insect’s wings will naturally build up a positive charge as they push through the air. As the wings beat against air molecules, friction is built up, resulting in a positive charge. In some ways this phenomenon is similar to walking across a carpet on a dry day just before touching a doorknob. When we experience a build-up of positive charge, we can see a spark leap from the metal door knob. When bees experiences the same type of charge (on a markedly smaller scale), they’re able to attract pollen to their legs when they land on flowers.

As it can sometimes be tricky to coerce a bee to fly into a spider’s web (and even harder to document it), Ortega-Jimenez worked with dead insects such as aphids, bees and fruit flies. He then applied a positive charge to the dead bugs with an electrostatic generator and dropped them on neutral spider webs in a lab environment.

“Using a high speed camera, you can clearly see the spider web is deforming and touching the insect before it reaches the web,” said Ortega-Jimenez. In the high speed photos and videos, tiny strands of thinner silk are reaching out like the positive peaks of a sound wave.

“You would expect that if the web is charged negatively, the attraction would increase.” He pointed out this attraction between web and bug is not observed when the insects are not positively charged.

This effect would not be seen if it weren’t for the different types of silk a spider produces. The thicker and more resilient silk used to create the spokes give the web its strength and structure which a thinner and more flexible silk fill it out. This new study suggests this finer silk may do more than just add some surface area to the overall web; it also reaches out and grabs an attractive insect passing by.