Discovery could aid in development of new devices for environmental science
It was a Halloween mystery that baffled Charles Darwin to the end of his days. On Oct. 31, 1832, thousands of tiny red spiders suddenly started dropping from a clear sky onto Darwin’s ship, the HMS Beagle, prompting shock, amazement and a lot of itching.
Winds were calm, the young biologist noted, spiders don’t have wings, and they were not dumped by migrating birds.
So how did they travel 60 miles over water from the Argentine coast?
The evolutionist said the invasion was “inexplicable.” And it was, until now.
Thanks to UCLA researchers repurposing Hollywood special effects, scientists can now more fully understand how tiny spiders escaping predators can soar two miles up into the air and then “balloon” hundreds of miles from home.
And the emerging answers may influence the shape and materials used in future “smart structures” — from Martian rovers to biometric robots.
Nature’s neat spider trick, says M. Khalid Jawed, assistant professor of mechanical and aerospace engineering at the UCLA Samueli School of Engineering, is using the arachnid’s webcasting abilities to achieve an unprecedented style of liftoff.
Working in close partnership with professor Charbel Habchi of Notre Dame University-Louaize in Lebanon, Jawed has used computational modelling to illustrate how spiders can shoot webs into the air, where the silk is “powered up” by the earth’s electrical field. Their research was published in APS Physics in March.
This force not only gives spiders both lift and direction but also prevents the webs, sometimes shot out in bolts that are dozens of meters long, from entangling each other.
This challenges the traditional view that spiders are randomly “blown” around the world, although aerial currents certainly play a part.
Zoologists have shown that spiders can “read” the planet’s weak but vast electrical field that is generated by 40,000 daily thunderstorms, among other factors.
Spiders sense when they can shoot strands of negatively charged silk into the air to react with positively charged twigs and leaves around them, creating a propulsive reaction that launches them upward and outward.
Jawed and Habchi’s computer program shows how such amazing journeys begin, using a simulation of an Erigone dwarf spider that can eject up to eight web bolts simultaneously to take off. The bigger the spider, the more threads it generates to take off.
“We adapted a computer simulation algorithm called Discrete Elastic Rods (DER) that was originally developed by the computer graphics community for realistic animation of hair and other filamentary structures for Hollywood movies,” M. Khalid Jawed said.
“We adapted a computer simulation algorithm called Discrete Elastic Rods (DER) that was originally developed by the computer graphics community for realistic animation of hair and other filamentary structures for Hollywood movies,” Jawed said. “We used it to model the deformation of each spider web under the influence of the electric field of the earth and the drag from the air.”
Movie hits such as “The Hobbit” and the recent “Planet of the Apes” series have used DER to simulate hair, which functions physically in ways similar to spider webs.
The computer algorithm divides each thread into many spaghetti-like segments that can bend, stretch and twist. The simulations represent the spider as a 2-millimeter-wide solid sphere with two, four or eight threads attached at the top of its body, oriented vertically at the start but spreading out as they interact with the Earth’s magnetic field.
Each thread is coated with electric charges. The researchers accounted for gravity; the atmosphere’s electric field, which decreases with height; the threads’ electric charge; and air resistance on the threads.
“What we have set out to do is to speed up the rendering to real time or better so we can use the program not only to investigate mysteries such as spider flight but also predict how similar rod-like structures work and what we can learn to apply to smart building proposals,” Habchi said.
Until now, there has been little research into harnessing the propulsive power of the world’s electro-magnetic field, but the possibilities are vast, according to the research team.
Habchi says that the work could help in the development of new devices for environmental science, such as ballooning sensors deployed as probes into the upper atmosphere. Clouds of tiny sensors could be uploaded without fossil fuel into the atmosphere to measure sunlight, wind and pollution.
“They could be stabilized at set heights above or below aircraft lanes by the length or number of the threads,” M. Khalid Jawed said
“They could be stabilized at set heights above or below aircraft lanes by the length or number of the threads,” Jawed said, adding that the filaments could be spun from artificial silk or similar materials. “We could see this happen in 10 years, depending on the demand for such data from environmental scientists.”
As a mechanician, Jawed’s work directing research at the Structures-Computer Interaction Laboratory seeks both pure science and real-world answers to questions varying from how to mimic a bacterium to building a “soft” flexibly structured robot to measuring the wrist power needed to tie a knot in a shoelace. Understanding the data-driven evidence behind such phenomena could change lives, he says.
The spider experiment built on previous one-dimensional models showing ballooning due to electrostatic forces.
“Our method is computationally efficient and allows us to perform 3D simulations where we show the shape of threads during ballooning,” says Jawed. “We highlight the importance of the coulomb (electrical charge) repelling forces that prevent web entanglement. It’s an amazing process to watch — we have so much to learn from nature!”
UCLA Magazine managing editor John Harlow contributed to the story.