Spiders Flying by Electrical Charge

  • #1
BillTre
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Main Question or Discussion Point

Some spiders are known to fly on the breezes by extruding silk strands (like web material) from their abdomen. This is commonly thought to be caught in the wind and carry them away. This would explain the occasional spider you might see drifting by when you are outside.
Many (including that shrewd observer of nature, Charles Darwin, in the 1830's) were not convinced this provided a full explanation.

It is now reported that by making use of the planets earth's electric field (ground (-) vs. surrounding (+)), of 100 V/m (I'm surprised at the size of this, but I guess air has low conductivity (unless ionized)).

They can sense this by changes in how little hairs on their legs respond to electric field.
Insects have lot of hairs that are innervated at their base, and detect movement of air over the surface of the body. This is information that can be used for many different purposes, flight control, wind detection, air movement from local objects, resonating to particular sounds. (Some detector hairs can be specialized for particular purposes.) Other kinds of hairs may have chemical detectors (smell/taste).

The negatively (-) charged silk strands the spider extrudes will naturally go in the positive direction (up). Getting the process started, and providing at least some upward force.

NY Times video (its very good) and article on the aerodynamics of spider flying, but voltage not considered.

Short article on electrical aspects in "The Atlantic".
 

Answers and Replies

  • #2
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Recently the media had a buzz about the testing of spiders ballooning on electrostatic or magnetic and wind currents. Scientists were able to cause the spiders to lift and descend by changing the electric field in the air.

So I'm wondering, if that's true then does the "wing" (in this case fine silk threads) follow a 2 dimensional ratio for lift, like wings (twice as long and twice as wide = x4) or can a 3 dimensional wing (like multiple layers) catch and drift on the field, like how the molecules in the top of my head are affected by gravity the same as my arms, legs, bones, etc?

For this hypothetical electrostatic wing, in other words, can the "wing" bulk be reduced like old biplanes?
 
  • #3
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Do you have a link? Otherwise, we have no idea what you are talking about.
 
  • #4
phinds
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Interesting article but I wonder if anyone can expound on the statement:
Every day, around 40,000 thunderstorms crackle around the world, collectively turning Earth’s atmosphere into a giant electrical circuit. The upper reaches of the atmosphere have a positive charge, and the planet’s surface has a negative one. Even on sunny days with cloudless skies, the air carries a voltage of around 100 volts for every meter above the ground. In foggy or stormy conditions, that gradient might increase to tens of thousands of volts per meter.
I'm curious about the bolded part (my bolding). It just seems so unlikely.
 
  • #5
BillTre
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I'm curious about the bolded part (my bolding). It just seems so unlikely.
Yeah.
The numbers seemed high to me.
Could be a magnitude accident accident in writing by a science reporter.
Could be low conductivity of air. However I don't understand the source of the charge difference, but maybe sun's radiation hitting the atmosphere?

On the other hand I was reading a book about mitochondria function and the huge electrical potential they have across their membrane when scaled up to a meter.
This a voltage of >100mv (or 0.1 V, a conservative estimate) distributed across a bilayer lipid membrane of about 7-8 nm ((7 to 8) x 10-9m) has a huge field strength of:
my estimate = ((>between 7 and 8) x 108)V/m.
Surprised me, but that's numbers for you.
 

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