Despite the fact that only 0.1% of spider species are dangerous to humans, most tend to dread them. Now, a team of scientists from the University of Bristol (England) has discovered a fascinating quality of tiny arachnids . And it is that the aerodynamic capabilities of spiders have intrigued scientists for hundreds of years. Charles Darwin himself reflected on how hundreds of creatures managed to perch on the Beagle on a calm day at sea and then take off from the ship at high speeds on a windless day. “Darwin’s observation, however, did not provide further supporting evidence,” the authors comment.
Scientists have attributed the flying behavior of these wingless arthropods to “balloon flight,” where spiders can travel thousands of kilometers by releasing trails of silk that propel them up and out into the wind. However, when there is no wind, cloudy days or even rain, how do spiders take off with such low levels of aerodynamic drag?
Researchers have discovered that spiders are expert navigators of the electricity of the air. The electric fields that they detect thanks to the hairs on their legs, give them lift: they lift the abdomen, ‘stand on tiptoe’ and release a silk thread in order to be carried away by atmospheric electricity, even without the slightest breeze.
“When you think of airborne organisms, spiders don’t usually come to mind,” explained researchers Erica Morley and Daniel Robert of the University of Bristol, in the study published in the journal Current Biology. “However, these wingless arthropods have been found 4 kilometers in the sky, scattering for hundreds of kilometers .”
They travel through the atmospheric potential gradient , an electrical circuit between Earth and the ionosphere, the part of Earth’s upper atmosphere ionized by solar radiation. Electrical storms act like a giant battery for this atmospheric potential gradient, charging and maintaining electric fields in the atmosphere.
In 2013, a different group of researchers came up with a theory that electric fields could be at least part of the spiders’ expansion strategy, and Morley and Roberts were interested in seeing if spiders actually responded to electric fields and their effects. fluctuations.
They captured spiders of the genus Erigone (present in America, Eurasia, Africa and Oceania), spiders of a very small size and arranged them for several controlled experiments. In one of them they created a slight breeze; in another they eliminated it, but added an electric potential similar to that which exists in the atmosphere. In this way, turning the artificial electric field on and off they discovered that the spiders swelled when the field was on, and the electrostatic forces of the field alone were sufficient to drive their movement ; It is the same force that lifts your hair if you rub a balloon on your head. When the researchers turned off the electric field, the spiders would go down.
Thus, insects can detect both the atmospheric potential gradient and the electric fields that surround matter. This is due to sensory hairs (tricobothria) that move in response to the electric field, which the researchers believe is what spiders use to detect the atmospheric potential gradient.
Although science has taught us a lot, these types of studies show how much remains to be learned about the tricks that spiders have with their eight tiny legs.
Reference: ‘Electric fields elicit ballooning in spiders’ by E. Morley and D. Robert, Current Biology (2018). DOI: 10.1016 / j.cub.2018.05.057, www.cell.com/current-biology/f… 0960-9822 (18) 30693-6
