The phenomenon of baby spiders flying through the air at the end of a length of spun silk has been known for centuries. Now scientists have discovered the surprising mechanism by which the feat is realized.
Charles Darwin described the gossamer spiders as “small aeronauts” that he had observed following him on a sea voyage. They achieved this through a practice called “ballooning”, which involves spinning a small silk sail and jumping from a high platform. Until recently, we thought it was wind that enabled their flights.
However, ballooning was observed in windless conditions, which raises the question of how spiders take flight. Researchers at the University of Bristol in the United Kingdom now believe they have clarified this mystery.
Their study, reported in the journal Current Biology, shows that naturally occurring electromagnetic fields can not only trigger this process, but also provide lift and speed, even in the absence of breezes.
“We don’t yet know whether electric fields are required to allow spider ballooning,” says biologist Erica Morley. “We do, however, know that they are sufficient.”
Insects can detect the electric field around us – bumblebees, for example, use them to find their way to the flowers – but it is now clear that spiders are equipped in the same way to react to the atmospheric charge.
In their study, Morley and her colleague Daniel Robert created stable fields of electromagnetic current in sealed tanks, eliminating other stimuli such as air movement. They then introduced the baby spiders from the family Linyphiidae.
The researchers noticed that ballooning increased considerably when the fields were on. In addition, turning the electric field on and off once the spiders were in the air would cause them to move up or down, respectively.
Research has also revealed that spider’s trichobothria, tiny sensory hairs on the surface of arachnid exoskeletons that have been shown to respond to sound, also appear to be stimulated by electric fields.
There are days when thousands of spiders take to the air in mass ballooning events and others where no one scatters at all. The new findings suggest that this could be explained by fluctuations in the strength of the APG.
Researchers believe that more work is needed. ” The next step will involve looking to see whether other animals also detect and use electric fields in ballooning. We also hope to carry out further investigations into the physical properties of ballooning silk and carry out ballooning studies in the field, ” Morley said.