323 — Electric Fields Elicit Ballooning in Spiders

Morley & Robert (10.1016/j.cub.2018.05.057)

Read on 09 July 2018
#spider  #silk  #flight  #atmosphere  #APG  #electricity  #behavior  #arachnid  #biology 

Flying spiders (which is one of the worst things I’ve ever heard of) are one of the coolest things I’ve ever heard of. Certain species of spider are able to float in the air, effectively flying (albeit with presumably very little control over trajectory). Older research suggested that spiders let out threads of silk and used these to catch air currents. But this didn’t explain why the same spiders were equally able to lift off in slow air currents. (In fact, most ballooning spiders only take off in low wind-speeds.) More recently, further research proposed an electric mechanism: The spiders were perhaps leveraging the electric field disparity between the negatively-charged surface of the earth and the positively charged atmosphere.

These researchers prove this by showing that not only does an artificial electric field induce the same “waving” behavior in spiders; the electric potential of the atmosphere is also physically strong enough (the atmospheric potential gradient, or APG, is around 120V per meter) to enable “ballooning” flight.

This explains why spiders crawl to “pointy” structures to start ballooning: Just like how the spikes on a plane wing concentrate the ambient APG to prevent damage, sticks and twigs on a tree concentrate APG and produce a perfect take-off location for spiders to leverage the electric gradient. Morley & Robert also show that hairs on the legs of spiders — acting in the exact same way but at smaller scale — are effectively electro-receptors, letting the spider know when the surrounding air is sufficient for takeoff.