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EarthSky // Earth, Science Wire Release Date: Jan 17, 2014

How electricity helps spider webs snatch prey

Spider webs actively spring towards prey, thanks to electrically conductive glue spread across their surface, Oxford University scientists have discovered.

Spider webs via Kate Genet

The glue that coats a spider web strand has electrostatic properties that causes the web to reach out to grab all charged particles, from pollen to flying insects and even pollutants, according to a new Oxford study.

The researchers also showed that the glue spirals can distort Earth’s electric field within a few millimeters of the web, which may enable insects to spot the webs with their antennae ‘e-sensors’.

The study, published in Naturwissenschaften, shows how a quirk of physics causes webs to move towards all airborne objects, regardless of whether they are positively or negatively charged. This explains how webs are able to collect small airborne particles so efficiently and why they spring towards insects.

The research also showed that webs like that of the garden cross spider also cause local distortions in the Earth’s electric field since they behave like conducting discs. Many insects are able to detect small electrical disturbances, including bees that can sense the electric fields of different flowers and other bees. Professor Fritz Vollrath of Oxford University’s Department of Zoology led the study. He said:

Pretty much all flying insects should be capable of sensing electrical disturbances. Their antennae act as “e-sensors” when the tips are connected to the body by insulating materials, meaning the charge at the tip will be different from the rest of the insect. As insects approach charged objects, the tips of their antennae will move by a small amount, which they may be able to feel. Bees already use e-sensors to sense flowers and other bees, so it now remains to be seen whether they might also use them to avoid webs and thus becoming dinner.

Electrical disturbances caused by spider webs are extremely short-ranged, so it is not yet clear whether insects would be able to sense them before the web snaps out to grab them. Either way, it is clear that electrostatic charges play an important role in the insect world. Vollrath said:

People often underestimate the static electricity that builds up in airborne objects, but it is important at all scales. The Hindenburg disaster might have been caused by a discharge of static electricity, and helicopters have been known to explode if they discharge suddenly when landing.

Everything that moves through the air develops static charge, so it’s fascinating to see how spider webs make use of this to actively catch prey. It’s a great bonus for us that this also causes them to attract pollutants, making them a cheap and natural way of tracking pesticides and air quality around the world.’

Bottom line: An Oxford study, published in Naturwissenschaften, shows that the glue that coats a spider web strand has electrostatic properties that causes the web to reach out to grab all charged particles, from pollen to flying insects. The researchers also showed that the glue spirals can distort Earth’s electric field within a few millimeters of the web.

Read more from University of Oxford