Spiders can detect the Earth’s electric field, and use it to lift off and fly through the air, according to new research.
Spiders can travel many hundreds of miles through the air by releasing silk and floating away. Researchers had thought that ballooning behavior required drag forces from wind or thermals.
Now, researchers reporting in the journal Current Biology show that electric fields at strengths found in nature not only trigger ballooning but also provide lift, even in the absence of any air movement.
“Many spiders balloon using multiple strands of silk that splay out in a fan-like shape, which suggests that there must be a repelling electrostatic force involved,”
“Current theories fail to predict patterns in spider ballooning using wind alone as the driver. Why is it that some days there are large numbers that take to the air, while other days no spiders will attempt to balloon at all? We wanted to find out whether there were other external forces as well as aerodynamic drag that could trigger ballooning and what sensory system they might use to detect this stimulus.”
– Lead researcher Dr. Erica Morley, an expert in sensory biophysics.
The team carried out experiments in the lab with Linyphiid spiders (Erigone). The laboratory environment allowed them to remove other stimuli, such as air movement, and provide a uniform electric field for the spiders.
Their experiments showed a significant increase in ballooning when electric fields were switched on. That change in the spiders’ behavior confirmed that spiders can indeed detect APG-like electric fields and that they respond to those electric fields by ballooning. Once the spiders were airborne, switching the electric field on and off led them to move upward or downward, respectively.
The secret to airborne arachnids is down to a set of hairs known as trichobothria that cover their eight legs. Trichobothria can sense the Earth’s electric field and the difference in electric potential between the Earth’s positively charged atmosphere and negatively charged surface.
Erica L. Morley. Electric Fields Elicit Ballooning in Spiders. Current Biology July 5th. DOI: 10.1016 / j.cub.2018.05.057.