Scientists have long known that spiders can travel by air. In a technique called ballooning, they simply raise their abdomens, extrude some silk, and float away. They have been found a thousand miles out at sea. Neat!
But the mystery is spiders only seem to balloon during light winds. Exactly how can they travel long distances?
Two researchers from the University of Bristol, Erica Morley and Daniel Robert, may have figured it out. They’ve discovered spiders can sense the Earth’s electric field. The key is the 40,000 thunderstorms that appear every day around the world. This turns the atmosphere into a giant electrical circuit — the upper atmosphere has a positive charge, and the surface is negative. Depending upon the weather, the atmosphere can carry a voltage of from 100 to tens of thousands of volts for every meter above the ground.
Ballooning spiders operate within this electric field. Spun silk usually acquires a negative charge, which of course repels the negative charges on the surfaces on which the spiders sit. This generates enough force to get spiders into the air. The concept is flight by electrostatic repulsion, and was originally proposed in the early 1800s. Physicist Peter Gorham rediscovered the idea in 2013 and showed it was mathematically possible. Thanks to Morley and Robert, we now know it works for spiders.
For a more detailed explanation see “Spiders Can Fly Hundreds of Miles Using Electricity” by Ed Yong (https://www.theatlantic.com/science/archive/2018/07/the-electric-flight-of-spiders/564437/?). The photo came from that article.