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Apparently some species of spiders can fly… and it turns out they don’t even need the wind to do it.

Hosted by: Hank Green

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Sources:
https://www.cell.com/current-biology/fulltext/S0960-9822(18)30693-6
https://www.biorxiv.org/content/early/2018/03/26/206334
http://www.sciencemag.org/news/2018/04/watch-ballooning-spider-take-flight
http://www.lastwordonnothing.com/2018/04/19/guest-post-ballooning-spiders/
https://arxiv.org/pdf/1309.4731v1.pdf

Images:
https://commons.wikimedia.org/wiki/File:Xysticus_audax_tiptoeing.ogv
https://commons.wikimedia.org/wiki/File:Ballooning_spiderlings.jpg
[♩INTRO].

So you’re walking along, minding your own business, when you notice something out of the corner of your eye and look up. That’s when you see thousands upon thousands of spiders on long silk balloons falling from the sky all at once.

You’ve just witnessed one of the most incredible,and terrifying, natural phenomena on the planet: spider rains. For a long time, scientists assumed that, like kites, ballooning spiders can fly because their silken threads generate enough lift to ride currents of air. But according to a study published in Current Biology this week by researchers at the University of Bristol in the UK, they don’t actually need a breeze at all.

Turns out, spiders can fly using the electricity in our atmosphere. Spider ballooning was first documented by an English naturalist in the 17th century, and ever since, scientists have been trying to figure out exactly what they’re doing and why they’re doing it. A lot of the time, the ballooners are baby spiders looking for a place of their own to settle down.

They can reach altitudes of almost 5 kilometers and fly for hundreds of kilometers. Talk about putting some space between you and your parents. But instead of loading up their Volvos and moving to Montana, to take off, the spiders find somewhere high up, then stand tall, raise their rears, and emit thin, meter-long silk threads in the shape of a sail.

When they let go, they’re pulled into the air with surprising speed, even on calm days. And that speed is one of the things that has never quite added up with the idea that these spiders ride the wind. Biologists have seen spiders ballooning when winds are almost imperceptible, or even when it’s raining.

And the wind hypothesis doesn’t explain how the spiders eject their silk so forcefully without the help of their legs, or how the strands maintain a fan-like shape without tangling. So the team from the University of Bristol decided to test something no one else had: whether the spiders can ride electricity. The idea that electrostatic forces provide the necessary lift has been around for centuries, but no one ever really looked at it.

Then, in 2013, a physicist from the University of Hawaii worked out some of the theoretical details. He released his paper as a preprint that was never officially published, but the authors of the new study thought it was worth investigating. The whole thing hinges around the fact that no matter what the weather is, there’s a difference in electric charge between the ground and the sky that creates an electric field.

So if the spiders’ silk picked up some static charge, those threads could be pushed by the electric field. Since like charges repel one another, the charge of the ground, or whatever the spider is standing on, would propel the silk out and up. And enough pushing could fling the spider into the sky.

But since the 2013 paper was purely theoretical, the new study’s authors decided to put it to the test. They took ballooning spiders and placed them on a small cardboard pedestal in a special chamber designed to have no electric field or air movement. Then they induced electric fields of different magnitudes, and watched what the spiders did.

Even in the complete absence of wind, the spiders began to get into that rump-raising position that sets them up for ballooning. And with a strong enough field, they started to spin silk, and even flew. Once airborne, the researchers could make the spiders rise or fall just by turning the electric field on or off.

An earlier study, published last month in PLOS Biology, noted that these spiders seem to test the wind with their legs before they start to spin their silk sails. And this week’s study found that the hairs on the spiders’ legs moved in response to changes in electric fields, too. But those hair movements were different from the way they moved in response to wind, which means the spiders might be feeling around for both of those things.

Riding electricity could explain some of the weirder aspects of their flight like how they take off on seemingly windless days or in the rain. But most of the time, air isn’t completely still, so the spiders probably use a combination of electricity and wind to fly. There are still some parts of this left to figure out, though like how the spiders’ silk becomes charged in the first place, or whether they can control their flight to decide where to land.

Learning more about how spiders fly can help biologists predict when they’re going to do it, and get a better understanding of their ecological needs. And it might also make it easier to predict those rare episodes of spider rain. Because I don’t know about you, but if ten thousand spiders are going to land in my neighborhood,.

I’d would prefer to know that that’s going to happen before it happens. Thanks for watching SciShow News. If you want to share your love of SciShow with the world, we finally have created new merch.

New shirts, stickers, and mugs. Check them out at DFTBA.com/SciShow. And thank you! [♩OUTRO].