Do you recall the end of the book Charlotte's Web, when Wilbur was delighted to see hundreds of Charlotte's babies had hatched, but then almost all of them flew away? Flying spiders of all kinds scare people by throwing out silk that carries them on the wind. Aerodynamics engineer Moonsung Cho observed crab spiders to see how they fly.
He gathered 14 of them and placed them on a small, dome-shaped structure in a Berlin park to see how they reacted to natural winds. He also studied them in the lab using controlled wind tunnels. He found that before flying away, the spiders would lay down an anchor silk strand for safety. They would then reach one of their front legs into the air to evaluate how fast the wind was blowing, and from which direction. That’s the spider equivalent of licking your finger and sticking it in the air.
If the wind conditions were just right—which, for these crab spiders, meant less than 7.3 miles per hour (3.3 meters per second) with a nice upward draft—they stood up very straight, stuck their butts in the air, and produced 50 to 60 nanoscale silks that lifted them into the skies. On average, those silks were nearly 10 feet long. Once they let go of their anchor strands, they were gone.
Cho studied the silk and determined that these strands are so fine that they are thinner than the air they float on. Read more about the research, and see a crab spider take off, at Gizmodo.
(Image credit: Moonsung Cho)