Living upside-down helps spiders' energy

MADRID, March 27 (UPI) -- A Spanish- and Croatian-led study suggests spiders that live, feed and walk upside-down have a high energy efficiency.

The majority of land animals evolved to use the ground as the main support for their motion, the scientists said, but many spider species spend most of their lives hanging suspended by their legs, and "walk" by swinging under the influence of gravity.

The researchers studied more than 100 spider species, comparing how they handle both types of movement.

"We discovered spiders that live upside-down have evolved disproportionately longer legs relative to 'normal' spiders, which enables them to move faster while bridging than while 'normally walking' on the ground," said Jordi Moya-Larano of the Spanish Higher Council for Scientific Research, who led the study.

"Particularly 'clumsy' walkers are larger spiders, because their long legs -- otherwise so convenient for bridging -- do not allow an easy lifting of their relatively large body mass," said Moya-Larano.

"With this research we finally proved the energetic efficiency of such motion stems from the same physical principle used to run the grandfather's clock -- motion of a pendulum under the influence of gravity," said researcher Dejan Vinkovic, an astrophysicist from Croatia.

The findings are reported in the online journal PLoS One.