Spiders in the sky

Even without wings, spiders have found a clever way to take to the skies

On his voyage across the oceans, Charles Darwin noted that spiders would appear on the deck of The Beagle, only to vanish a while later. The arachnids were able to create tiny fans from multiple silk strands that seemed to allow them float on the breeze. The technique was named spider ballooning, and it was found to be very efficient – spiders have been found four kilometres (2.5 miles) up in the air and can travel hundreds of miles with little effort.

 

In case the thought of spiders flying on the wind wasn’t unsettling enough, people began to observe that they could be seen travelling through the air even on still days. Scientists at the University of Bristol set out to work out what was going on, and now they think they’ve found the answer: electricity.

 

Even without any movement in the air, spiders can take off with their fans thanks to the atmospheric potential gradient (APG) – a form of electric field present around the world. The electrostatic forces repel the strands of silk enough to let the arachnids launch themselves from a high point and become airborne before using their fans like parachutes to float along.

 

It was understood that insects like bees could detect electric fields, but spiders weren’t known to have the ability until now. Specialised hairs appear to be able to sense the presence of electric fields, helping spiders to decide where and when to take off. They’re so sensitive they can even tell the difference between electrostatic forces and air currents.

 

These discoveries have changed what we know about spiders, and the use of electric fields to fly could one day be used by engineers and designers.

 

Image: Laurent Jégou/flickr