Spiders Fly with Electricity
Scientists have known about spider “ballooning” for a long time, but only recently have they determined that spiders use electricity to fly.
When we think of flying creatures, we probably don’t think of spiders. But it’s true: some species of spider can fly long distances on air currents, using strands of silk as parachutes. This has been observed for a long time. A press release from the University of Bristol points out that Charles Darwin puzzled over this, wondering how hundreds of spiders showed up on ships at sea and took off again even on windless days.
A recent paper in Current Biology reports that ballooning spiders use electricity to get aloft. Somehow, they are able to sense the level of static electricity in the air. They respond by standing on tip-toe and releasing silk strands out their abdomens, catching even slight air currents to rise up into the air. With electrical forces, they can fly miles high into the air! A video in the press release says, “Of all the great flyers the world has ever known, it may come as a surprise that one of the best aviators in the animal kingdom doesn’t even possess wings.” Maybe a new verse should be added to “The Spider and the Fly.” The researchers begin their paper,
When one thinks of airborne organisms, spiders do not usually come to mind. However, these wingless arthropods have been found 4 km up in the sky, dispersing hundreds of kilometers. To disperse, spiders “balloon,” whereby they climb to the top of a prominence, let out silk, and float away. The prevailing view is that drag forces from light wind allow spiders to become airborne, yet ballooning mechanisms are not fully explained by current aerodynamic models. The global atmospheric electric circuit and the resulting atmospheric potential gradient (APG) provide an additional force that has been proposed to explain ballooning. Here, we test the hypothesis…. We find that the presence of a vertical e-field elicits ballooning behavior and takeoff in spiders. We also investigate the mechanical response of putative sensory receivers in response to both e-field and air-flow stimuli, showing that spider mechanosensory hairs are mechanically activated by weak e-fields. Altogether, the evidence gathered reveals an electric driving force that is sufficient for ballooning.
Despite knowing about spider ballooning for many years, nobody ever tested the electrostatic force on the behavior till now. By putting spiders in a Faraday Cage, the researchers were able to control the amount of static, writes Alison George at New Scientist. The Bristol research team led by Erica Morley watched the spiders take up their ballooning posture when the static rose, tiptoeing for take-off. The press release includes a video showing how they ran their experiments. They also measured the effect on altitude:
The second part of the experiment examined the effect of the electric field on airborne spiders, and found that the height of the spiders could be controlled by raising or lowering the electrical field. “If you switch the voltage off, you see the spiders slowly start to drop. You can play with their altitude,” says Morley.
Spider silk, being a good insulator, collects a net negative charge on its outer surface that interacts with the atmosphere, where a potential gradient can provide lift. In addition, the spider’s mechanosensors can respond to the twitching of silk strands when atmospheric static changes, so that they know the best time to assume flight posture and let out the silk.
Now that this physical effect has been demonstrated in spiders, a theoretical physicist envisions engineers using it for technology. No batteries would be required:
Other researchers are impressed that this long-standing conundrum has been solved. “It is very satisfying to see this proved in such a convincing way,” says physicist Peter Gorham of the University of Hawaii, whose theoretical calculations of the plausibility of electrostatic spider flight inspired Morley’s study.
It is theoretically possible that tiny, light-weight drones could one day take to the air in the same way as ballooning spiders, he speculates. “Spiders weighing 100mg can balloon. That’s more than enough to fly a tiny microprocessor and camera.”
Morley’s team wants to continue researching to see if other small animals make use of atmospheric electrostatic forces. Bumblebees, for instance, can detect electrostatic fields around flowers to guide them to food sources. “We also hope to carry out further investigations into the physical properties of ballooning silk and carry out ballooning studies in the field,” Morley says.
Of all the great flyers the world has ever known, it may come as a surprise that one of the best aviators in the animal kingdom doesn’t even possess wings.
The subject of electrostatic ecology seems wide open for ecological study and even weather forecasting. The researchers note that “Quite surprisingly, APG is rarely invoked, let alone quantified, in conventional weather descriptors and parameters collected by weather stations.” And yet electric fields around vegetation provide opportunities to study the interaction of small creatures with their environment.
You can make your hair stand on end by touching a Van de Graaf generator. Don’t expect to float off into the air, though; you have too much mass. You do, however, have sensors in your hair follicles that can detect the movement. Maybe you could do experiments on how static electricity provides you with useful information about your surroundings. What can your hair tell you in pitch darkness? Test your hypothesis on body hair and whiskers, too. For both sexes, most parts of the skin (the largest organ of the human body) contain hairs, even tiny transparent ones that are invisible without a microscope. We are covered with sensors!
Spider ballooning is but another remarkable example of how living creatures can use information from the environment to navigate and migrate. Fish and birds follow fluid currents. Spiders and bees take advantage of electricity; electric fish even produce it. Perhaps the most astonishing example is using the earth’s magnetic field to navigate, as shown in Illustra Media’s films Living Waters and Metamorphosis. This spatial information, too weak for humans to sense, provides a global map that sea turtles can utilize to swim thousands of miles. Thirty years later, that stored information can help them return to the exact same beach they hatched from. Salmon use this sense, too, in the open sea. Perhaps magnetic field information is a component of navigation in butterflies as well.
Static electricity can lift spiders miles into the sky, but doesn’t help them get back. They don’t need to; they can set up shop wherever they land. It’s a remarkable method of long-distance travel that spiders employ to colonize the planet. Don’t freak out over this; they eat flies, after all.