Ballooning Spiders on the Mississippi

By Kate Crowley

Last week while we were traveling on the Mississippi River, I began to notice strands of filament floating above the water.  They almost looked like fishing line, but they were out in the middle of the river and drifting at least 20 feet above the surface.  Later on we noticed that the bow of the boat (it is a Paddlewheel) was festooned with streamers of the same type of filament, all caught on the rigging and ropes and streaming to the right with the wind.  I had realized by this time that we were seeing the apparatus and migratory technique used by some spiders, called ballooning
 Charles Darwin noticed the same phenomena when he was traveling aboard the Beagle on his epic voyage of discovery.  In his notes he wrote “In the evening all the ropes were coated & fringed with Gossamer web. I caught some of the aeronaut spiders, which must have come at least 60 miles: How inexplicable is the cause which induces these small insects, as it now appears in both hemispheres, to undertake their aerial excursions.”    Darwin noticed that the stands of ‘silk’ seemed to repel one another and so he assumed (correctly) that there was some electrostatic force at work.  He watched a smaller spider raise its abdomen, release some silk and then fly off with “unaccountable” speed.  Another, larger spider released several strands more than a yard long, than released its hold on its perch and flew away in a manner similar manner to the one my son Jon uses to launch himself with his paraglider.
By releasing strands of silk from their bodies into the open air, the arachnids (not true insects) are able to float as high as 2.5 miles above the earth, sailing out over oceans to reach new lands and going without food for as long as 25 days.  Up until just recently the assumption has been that most of the flight is determined by the thermal currents in the wind, but new research indicates that it is more the work of electrostatic energy.  The Earth’s atmosphere provides some of that charge, but some comes from the friction between the silk and dry air.  The negative charges found in the strands of silk causes them to fan out, giving more lift. It is the same energy you get when you walk across a rug in your socks and get a zap when you touch something and release that energy.
“Flying” spiders can be found in both city and country.  In fact, in Chicago a hotel will inform  their guests to keep their windows closed at certain times of the year because these ballooning spiders will drift up as high as the top of the John Hancock building (95 stories) seeking cracks and crevices where there is ample food.
I have to admit that I never thought of spiders migrating through the sky like the birds are doing right now, but there you have it, another bit of wonder and enchantment to be found in our  natural world. 



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