It has been believed since ages that spiders cannot fly, due to lack of wings. However, they still go air bourne sometimes. These creatures go to an exposed point and raise their abdomens in the sky. After this, they force out strands of silk and float away. This process is called ballooning.
By this method, spiders can float away from their predators or any competitors. They can even go to any new land where there is an abundance of resources. It is an effective way of traveling for spiders a report by The Atlantic explained. The spiders have been observed to have gone as high as two-and-a-half miles up in the air and as far as 1,000 miles out in the sea.
It is generally believed that ballooning can work as the silk strands catch the wind and tend to drag the spider along with the flow. However, it has been observed that spiders balloon only when there is light wind speed. But such low wind speed can barely move the silk strands let alone move the entire spider or provide high acceleration.
Scientists at the University of Bristol have now shown that spiders can sense the electric field of the Earth, and use it for launching themselves into the air. “When one thinks of airborne organisms, spiders do not usually come to mind,” Erica Morley and Daniel Robert, the researchers from the University of Bristol, said in their study.
Approximately 40,000 thunderstorms happen around the world every day which collectively turn our planet’s atmosphere into a huge electrical circuit with the upper atmosphere having a positive charge and the Earth’s surface having a negative charge. On cloudless sunny days, the Earth’s air carries around 100 volts for each metre over the ground. If there are foggy or stormy conditions, in that case, the voltage might rise to tens of thousands of volts per metre.
The spiders which are ballooning, work within the electric field of the Earth. When the silk strands leave their bodies, it takes up a negative charge, which helps the spider repel the negative charge present on the surface and creates sufficient energy to lift the spider in the air. This force can be further increased if the spider climbs on to twigs, leaves, or blades of grass.
Plants that are being earthed, have a negative charge just like the ground however they rise towards the positive charged air. Because of this, substantial electric fields between the tips of the leaves and branches and the surrounding air which helps the ballooning spiders.
This particular concept of flight through electrostatic repulsion was initially proposed way back in the early 1800s, during the time of Charles Darwin’s voyage.
“Charles Darwin mused over how thermals might provide the forces required for ballooning as he watched hundreds of spiders alight on the Beagle on a calm day out at sea,” the researchers explained in the paper.
The idea was later revived in 2013 by a physicist called Peter Gorham who showed that it was reasonable mathematically and the researchers at the University of Bristol checked it by testing real spiders.
First of all, the researchers showed spiders are able to detect electric fields. They put the spiders (arachnids) on a vertical strip of cardboard in the centre of a polycarbonate box. they then generated electric fields in between the ceiling and the floor, similar to what they would find outside. These fields moved the small sensory hair on the feet of the spiders known as trichobothria.
To this, spiders did a set of movements which is termed as tiptoeing, that is, they stood on the ends of their legs and stuck their abdomens in the air. Many spiders even took off even though they were in a closed environment with no airflow. When the researchers turned off the electric fields, the spiders that were ballooning dropped.