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In October 1832, a young naturalist by the name of Charles Darwin delighted to observe hundreds of tiny spiders hanging from short silk threads floating on HMS Beagle as the ship was taking him to Buenos Aires
. at least 60 miles before reaching the ship. But even though he was amazed at their aerial antics, a debate was going on about how the spiders got to be in the air in the first place.
Some scientists have said that spider silk caught the wind and carried it in the air. But others believed that the strands were electrostatically charged and, in doing so, allowed the spiders to roll over the natural electric fields of the Earth.
In a new study, scientists from the University of Bristol have looked into the matter. They report the first tests of whether electrostatic forces are involved in what aficionados call "spoon ballooning". After a series of experiments conducted with spiders in a Faraday cage, they conclude that insects can actually fly on electric fields.
When a spider wants to take flight, she usually climbs to the top of a plant, tip on its tip. abdomen in the air and eject quickly up to a meter of silk. In some species, the insect ejects a number of silk strands that spread like a fan. Anyway, in the blink of an eye, the spider is blown into the air.
To capture spiders to study, Erica Morley, who works on sensory biophysics in Bristol, went to a nearby field and set up traps. sticks with spilled bottles on the ends. Back in the lab, she introduced the insects, one by one, into a transparent polycarbonate box in a room that formed a Faraday cage, which meant that she was isolated from the atmospheric electric field.
Morley put the box in place so that she could recreate inside the types of electric fields that are commonly found in nature. On a clear day, the electrical potential of the atmosphere could be 120 volts per meter, but it can be ten times stronger than when clouds gather.
When the electric field was cut, Morley found that spiders made few attempts to fly. from a vertical cardboard tape that she had placed in the middle of the box. But as she increased the field, spiders took more and more flight. Once at altitude, their altitude could then be controlled. "When they take off, you can turn off the electric field and watch them fall, then turn on and see them get up again," she said.
In other experiments, Morley and Daniel Robert, who study how organisms feel their environment, swayed the laser light of spiders to reveal how tiny hairs were moving on their paws in the presence of electric fields, helping insects to detect them. Together, the findings, reported in Current Biology, suggest that while air currents are certainly important to the balloon, spiders can also exploit electric fields.
After Darwin's trip to HMS Beagle, scientists recorded spiders. They can also reach staggering altitudes, according to some testimonies. In 1939, PA Glick, an assistant entomologist of the United States Department of Agriculture, published a technical bulletin on the distribution of insects, spiders and mites in the air that claimed to find spiders more than three kilometers away. Beyond the flight, insects can skate, and even navigate, on the water.
Although Darwin described the aerial excursions of HMS Beagle spiders as "inexplicable", ballooning undoubtedly contributes to the dispersal of insects. And the sooner they start the better. "Spider-egg sacs can hold hundreds of eggs and spiders are cannibals, so it's probably advisable to disperse shortly after hatching," Morley said. . "It might not be as imprudent as we suppose."
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