In October 1832, during his voyage around the world on HMS Beagle, Charles Darwin was out at sea off Argentina when the ship was invaded by something quite odd – swarms of flying spiders. "All the ropes were coated and fringed with Gossamer web. I caught some of the Aeronaut spiders which must have come at least 60 miles," he wrote.
The spiders had glided far out to sea on their fine threads of silk trailing in the air, and Darwin guessed they sailed away on the wind to find new homes. But he also noticed that the threads of gossamer repelled each other as if they were charged up with static electricity, much like rubbing a comb on wool. And he guessed this static electricity might also explain how quite large spiders got airborne even in calm weather.
And now support for Darwin's idea has come from a physicist. Writing in the website arXiv blog, Peter Gorham at the University of Hawaii calculated that that as spider silk glides through dry air it becomes charged up and is propelled by the electric field of the Earth's atmosphere. The gossamer may also become electrified when the spider first shoots out its thread to launch itself into the air off the ground.
All of which helps explain how spiders can fly at remarkable speeds in little or no wind, how their silky threads repel each other and how even hefty spiders get airborne.
