Among the most curious and fascinating aspects of the behavior of spiders there is the ability to move to a raised place, lift the abdomen and secrete large quantities of cloth, and then let oneself be lifted into the air and transport hundreds of kilometers away.
The technique known as ballooning (from balloon, hot air balloon) allows arachnids to escape predators and land in distant areas that are richer in food, "flying" even up to 4 km in height. Perhaps it will surprise you, but exactly what the propellant of these flights is not yet completely clear.
There is something in the air … The two main hypotheses are that small creatures fly by the wind, or that they are raised by electrostatic forces. The first supposition is undoubtedly true, but spiders try ballooning even on days without a gust of wind. The second hypothesis had not yet been verified, at least until today: according to a study just published in Current Biology, the natural terrestrial electric field is sufficient, by itself, to explain the ability of spiders to "take flight".Occasionally it happens: the invasion of spiders. | REUTERS / Daniel Munoz
As an article published in the Atlantic tells, every day around 40, 000 thunderstorms transform the Earth into a gigantic electrical circuit, in which the high atmosphere is positively charged, and the surface of the planet that acts as a negative pole. Even on sunny days, the electric potential difference for every meter of air above the surface is about 100 volts; on bad weather days, this gradient can increase tens of thousands of times. Spiders, it seems, cleverly exploit this difference in charges and the forces that derive from it for their air travels.
Erica Morley and Daniel Robert of the University of Bristol (United Kingdom) subjected some Linyphiidae family spiders to a laboratory experiment: in environments isolated from drafts they tried to generate, and then deactivate, a uniform electric field.Video: How do spiders fly off?
Fly! When the electric field was activated, spiders increased ballooning production. When they were flying, turning the electric field on or off made them rise or fall in altitude. Not only are the small aviators able to perceive these forces: they use them to move!
How do they notice it? For researchers, using some sensory hairs on the surface of their exoskeleton, which rise and fall in response to electrostatic forces (like our hair, for example if we approach a balloon after rubbing it with a woolen cloth). The two "thrusts", the electric one and the air one, would not be alternatives, but rather complementary.