Spiders Use Electric Fields to Fly

 

Spiders can fly hundreds of miles using electricity. They have been found two and a half miles up in the air, and 1,000 miles out to sea. Spiders have no wings, but they can take to the air nonetheless. They’ll climb to an exposed point, raise their abdomens to the sky, extrude strands of silk, and float away. This behavior is called ballooning. It might carry spiders away from predators and competitors, or toward new lands with abundant resources.

Many people believe that ballooning works because the silk catches the wind and pulls the spider with it. But this doesn’t fully explain how it works, especially since spiders only balloon when the wind is light. Spiders don’t shoot silk from their bodies, and it's hard to believe that such gentle winds could pull out the threads, especially for larger spiders.

Darwin himself thought the speed of the spiders' flight was hard to understand. But researchers Erica Morley and Daniel Robert from the University of Bristol have an answer. They found that spiders can sense Earth's electric field and use it to lift themselves into the air.

Around the world, there are about 40,000 thunderstorms each day, making Earth's atmosphere a huge electrical circuit. The upper atmosphere is positively charged, while the ground has a negative charge. Even on clear days, the air has about 100 volts of electricity for every meter above the ground. In stormy conditions, this can rise to tens of thousands of volts per meter.

Spiders use this electric field to balloon. When their silk leaves their body, it usually picks up a negative charge, which pushes it away from the similarly negative charges on surfaces the spiders sit on. This creates enough force to lift the spider into the air. By climbing plants, which are connected to the ground and have the same negative charge, the spider can increase this force because plants stick out into the positively charged air.

This idea of flight through electric forces was suggested in the 1800s during Darwin’s time. It was brought up again in 2013 by physicist Peter Gorham, and now, Morley and Robert have tested it with real spiders. First, they showed that spiders can sense electric fields. They placed spiders on strips of cardboard inside a plastic box and created electric fields similar to what spiders would experience outside. These fields caused tiny hairs on the spiders' feet to move, like when you rub a balloon and hold it near your hair.

In response, the spiders did a behavior called tiptoeing, where they stood on the tips of their legs and raised their abdomens into the air. Many of the spiders actually lifted off, even though they were inside closed boxes with no airflow. When the electric fields were turned off, the spiders fell.

This discovery is important because it shows that spiders can physically detect electric fields. It opens up many interesting questions, like how different electric field strengths affect their takeoff, flight, and landing. Researchers wonder if spiders use information about the weather to decide when to break down or build webs.

Air currents may still have some role in ballooning. The same hairs that detect electric fields may also help spiders sense wind direction and speed. A study also showed that spiders get ready for flight by raising their front legs into the wind, possibly to measure its strength. However, Morley and Robert's study shows that electric fields alone are enough to get the spiders off the ground. According to Gorham, this is excellent science. He had guessed that electric fields played a big role but couldn’t be sure how biology made it work. Now, Morley and Robert have confirmed it in a way that goes beyond his expectations.

by Vicky Verma at X @Unexplained2020 on January 2, 2025