Meet the paragliding spiders of South America

New York: Biologists have discovered a type of nocturnal hunting spider that is able to change its direction while falling - much like a wingsuit flyer - in order to return to the tree from which it fell. The spider, about two inches across, and discovered in the forests of South America, joins a small number of non-flying insects known to have the ability to manoeuvre while falling instead of dropping like a rock.

"If a predator comes along, the aerial gliding frees the animal to jump if it has a time-tested way of gliding to the nearest tree rather than landing in the understory or in a stream," said co-author professor Robert Dudley from the University of California-Berkeley. The spider, from the genus Selenops, is the only arachnid the researchers found that was able to do this.

Other arachnids - scorpions, pseudoscorpions, whip scorpions and even other types of spiders - merely plummeted to earth. The 59 individual Selenops spiders they studied were all well adapted to skydiving. "They are wafer thin and flexible. They manoeuvre by spreading their legs wide in order to use lift and drag to steer themselves toward the tree trunk when they fall," Dudley said.

"If they fall upside down, they're able to right themselves in midair," he added. Dudley is interested in directed aerial descent because controlled gliding, he thinks, may have been the predecessor to flying, as animals learned how to use their arms and legs to gain lift in addition to manoeuvring in free fall. "This type of aerial behaviour preceded the origin of wings," he said. The findings are scheduled to appear in the Interface of the Royal Society journal.