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August 20, 2015

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Move over, Spiderman: actual spider excels at thread-free air stunt

Aug. 20, 2015
Courtesy of the Royal Society
and World Science staff

Crea­tures liv­ing high in the rain­for­est trees some­times fall off the branches, per­haps as they’re try­ing to es­cape a pred­a­tor.

But dropping down 30 me­ters (yards) or more can be dan­ger­ous. Not least is the risk of drop­ping on­to un­fa­mil­iar ground where a new ar­ray of pred­a­tors lurks.

A "flattie" glides in a spi­ral path to­ward a tree trunk. (Cour­tesy of the Roy­al Soc­iety)


Sci­en­tists al­ready know that some ants can con­trol a fall from such heights, glid­ing to­wards a safe land­ing site. It now turns out that a spe­cial, flat-bodied spi­der can do im­pres­sive ma­neu­vers of a si­mi­lar type, a study re­ports.

“These spi­ders rep­re­sent a re­mark­a­ble ev­o­lu­tion­ary ad­ven­ture in the an­i­mal con­quest of the air,” mem­bers of the re­search team wrote. They add that the spi­ders are “un­likely if not truly un­gain­ly” aer­i­al ac­ro­bats but that their skill could in­spire robotic de­sign.

The re­search­ers set about find­ing out if spi­ders of the ge­nus Se­len­ops, nick­named “flat­ties,” might be able to glide to safe­ty.

The meth­od was sim­ple: the sci­en­tists dropped the spi­ders from tree­tops. The spi­ders righted them­selves mid-air to swoop head first to­wards the safe­ty of a tree trunk, the study found.

The flat bod­ies may con­trib­ute to the ex­cel­lent glid­ing abil­ity, the in­ves­ti­ga­tors said.

Sky-diving spi­der in a ver­tical wind tun­nel shows the glid­ing body shape.  (Cour­tesy of the Roy­al Soc­iety)


In the drop tests 93 per­cent of the spi­ders land­ed suc­cess­fully on a tree trunk. The rest land­ed on the for­est floor. The team tested spi­ders from oth­er spe­cies and found they weren’t such grace­ful glid­ers. Some man­aged to right them­selves in free-fall but did­n’t show any ob­vi­ous con­trol over the di­rec­tion of their de­scent.

The team filmed the drop tests in slow mo­tion and an­a­lyzed the spi­ders’ body shapes as they fell. With most of their legs spread be­hind them, the flat­ties go head first with their two front legs raised. The sci­en­tists noted that the spi­ders steered them­selves us­ing these front legs.

The study was pub­lished Aug. 19 in the Jour­nal of the Roy­al So­ci­e­ty In­ter­face.

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Creatures living high in the rainforest trees sometimes lose their footing and fall, perhaps as they’re trying to escape from a predator. But falling down that 30 meters (yards) or more can be dangerous. Not least is the risk of dropping onto unfamiliar ground where a new array of predators lurks. Scientists already know that some ants can control a fall from such heights, gliding towards a safe landing site. It now turns out that a special, flat-bodied spider can do impressive maneuvers of this type as well, a study reveals. Researchers set about finding out if spiders of the genus Selenops, nicknamed “flatties,” might also be able to glide to safety. The method was simple: the scientists dropped the spiders from treetops. The spiders righted themselves mid-air to swoop head first towards the safety of a tree trunk, the study found. The flat bodies may contribute to the excellent gliding ability, the investigators said. In the drop tests 93% of the spiders landed successfully on a tree trunk. The rest landed on the forest floor. The team tested spiders from other species and found they weren’t such graceful gliders. Some managed to right themselves in free-fall but didn’t show any obvious control over the direction of their descent. The team filmed the drop tests in slow motion and analyzed the spiders’ body shapes as they fell. With most of their legs spread behind them, the flatties head first with their two front legs raised. The scientists observed that the spiders steered themselves to safety using these front legs. The study was published Aug. 19 in the Journal of the Royal Society Interface. “These spiders represent a remarkable evolutionary adventure in the animal conquest of the air,” members of the research team wrote. They add that the spiders are “unlikely if not truly ungainly” aerial acrobats but that their skill could inspire robotic design.