09 October 2019

Spiders detect electrical fields and use them for ballooning

Everyone knows that spiders fly through the air on strands of their silk.  But it's not just a matter of chance and favorable winds.  The relevance of a surprising factor (earth's electrical field) is explained in a recent issue of Cell:Current Biology:
... the involvement of electrostatic forces in ballooning has never been tested. Several issues have emerged when models using aerodynamic drag alone are employed to explain ballooning dispersal. For example, many spiders balloon using multiple strands of silk that splay out in a fan-like shape. Instead of tangling and meandering in light air currents, each silk strand is kept separate, pointing to the action of a repelling electrostatic force. Questions also arise as to how spiders are able to rapidly emit ballooning silk into the air with the low wind speeds observed in ballooning; the mechanics of silk production requires sufficient external forces to pull silk from spinnerets during spinning...

In the early 20th century, atmospheric electricity was intensively studied, establishing the ubiquity of the atmospheric potential gradient (APG); from fair to stormy weather, an APG is always present, varying in strength and polarity with local meteorological conditions. Over a flat field on a day with clear skies, the APG is approximately 120 Vm−1... Closer to the tree, around sharp leaf, needle, and branch tips, e-fields easily reach tens of kilovolts per meter... the spider’s unlearned response to e-fields is to engage in ballooning, and, on becoming airborne, switching the e-field on and off results in the spider moving upward (on) or downward (off) [video at the link].
Ed Yong discusses this research in his Atlantic column.
Plants, being earthed, have the same negative charge as the ground that they grow upon, but they protrude into the positively charged air. This creates substantial electric fields between the air around them and the tips of their leaves and branches—and the spiders ballooning from those tips.

Many of the spiders actually managed to take off, despite being in closed boxes with no airflow within them.

4 comments:

  1. ed yong wrote that great book 'i contain multitudes' - all about microbiomes and how we interact with all the little critters around us.

    I-)

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    Replies
    1. http://tywkiwdbi.blogspot.com/2019/06/i-contain-multitudes-ed-yong.html

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  2. I look for spiders everywhere and even name some I find in the yard around my house (or inside the house, to my spouse's dismay). Yet I've never seen any ballooning. They're probably too small for me to see, but I also can't find anything that says Aranea cavatica, whose beautiful webs I find every fall, balloons.
    That's the spider that inspired, and plays the title role in, Charlotte's Web.
    I still hold out hope that some spring I'll see them floating by.

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  3. Nature is simply...amazing. As are the lucky people who get to spend their days making discoveries as described in this post.

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