Spiral silk threads moved 1-2 mm from their resting positions in the direction of the insects

Biologists from the University of California, Berkeley, have discovered that charged prey significantly improves the capture success of spider webs by inducing marked deformations. The results were published this week in Scientific Reports journal.

Rubbing a balloon against your hair can cause some electrons to get stuck to the balloon leaving your hair positively charged. The same is the case with flying insects. “Just imagine the high friction produced between the wings and air particles of some flying flies,” said Victor M. Ortega in an email to this Correspondent. This charge has been known to help honeybees detach pollen from flowers. Dr. Ortega is a co-author of the paper.

On the other hand, most plants carry a negative charge in fair weather conditions. “As spider orb-webs are usually attached to plants, they should have the same negative charge,” he explained.

Since unlike charges attract each other, Dr. Ortega decided to test if these electrically charged insects make them easy prey for spiders. He and Robert Dudley, another co-author of the paper, collected orb webs of the cross-spider, and insects of diverse sizes — honeybees, green bottle flies, fruit flies and aphids.

These freshly killed insects were then positively charged with an electrostatic generator to levels comparable to that in nature. A high speed camera was then used to film them being dropped into the spider webs. The scientists did the same with neutral insects as comparison, and also with charged water drops to simulate electrically charged raindrops.

Ortega’s initial hunch proved right as most of the videos did indeed show that the charged insects were attracting spider webs. The spiral silk threads moved a maximum of 1-2 mm from their resting positions towards the direction of the insects quickening capture. The amount of deformation depends on the size of the charged body. The silk threads showed no such deformation in the case of uncharged insects.

Though fingers and metal tools have previously been shown to produce attraction to spiderwebs, “this is the first study to clearly show that charged insects of diverse size can produce evident deformations on spider webs,” according to Dr. Ortega. Such deformations likely increase the risk of capture for free-flying prey, they write.

Dr. Ortega next plans to determine if this same effect can be reproduced in the wild.

“Using charged insects with a natural charge, and not artificially induced as in the experiment, can make stronger the evidence,” he noted.

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