UC Berkeley researcher studies controlled descent of spiders, flight evolution

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Researchers studied a species of “sky-diving” spiders in South America that exhibits a unique controlled movement when it descends, a behavior that may have significant implications for the evolution of arachnid — and possibly other aerial animal — flight.

A video shot by Steve Yanoviak, an associate professor in the department of biology at the University of Louisville, shows how the spider controls its trajectory after being dropped from a tree canopy, landing back on the trunk below moments later. The research was compiled in a paper published in the Journal of the Royal Society Interface on Aug. 19.

Such behavior, according to Robert Dudley, a UC Berkeley integrative biology professor and co-author of the paper, was previously unexpected in spiders.

“It’s a great example that so much still remains to be discovered in the tropical rainforest,” Yanoviak said.

The paper studies nocturnal hunting spiders of the genus Selenops that live in the canopies of trees in Peru and Panama. They move with ease on the surface of trees and do not have a drag line, or thread, with which many spiders can pull themselves up after they drop, according to Dudley.

Dudley said the spider immediately uprights itself after it is dropped. He said this behavior — called an aerial righting reflex — is important in arachnid evolution, as it allows the spider to always land on its feet.

The video also shows the spider changing the position of its front two legs to steer itself. Dudley compares the spider’s righting, steering and control of landing to similar skills of human skydivers, who control their postures in the sky with small changes in the angling of their limbs.

Kipling Will — a UC Berkeley associate professor of environmental science, policy and management who mainly studies insect systematics — said this research is a prime example of the flight dynamics of spiders.

“(The spiders’ behavior) fits into the theory of flight evolution of all animals,” Dudley said. “It’s the same idea for birds and bats with different morphologies.”

Yanoviak said that he has been working with Dudley on studying similar gliding behaviors in ants for approximately a decade and that he characterizes their work as an “outstanding productive collaboration.” He added that their research on this particular species of spiders is exploring new angles of the same story.

According to Yanoviak, the duo will continue to look more closely at the biomechanics of the spider and the sensory information the arachnid uses to control its movements.

As for future research, Dudley said he is interested in investigating the controlled descent of lizards and mammals living in trees, as well as how this current study can be applied to the righting and landing techniques of drones and small robots.

Contact Tianyi Dong at [email protected] and follow her on Twitter at @dong_tianyi.