Living in a tropical tree canopy can be dangerous business for small creatures. If something knocks you off a branch, you could fall to the crowded, complex forest floor where lizards, birds and ants will probably gobble you right up.
It appears that one kind of tropical spider has developed an unusual behavior to avoid such a nasty fate: gliding through the air and landing safely on trees.
Researchers believe they are the first to document this gliding behavior in spiders, and published their findings this week in the Journal of the Royal Society Interface.
Stephen P. Yanoviak, an associate biology professor at the University of Louisville, and colleagues examined spiders in the genus Selenops called "flatties," an extremely flat kind of spider that typically measures two inches in diameter. These spiders aren't known to be aggressive, and blend in very well with tree trunks.
The spider research began as a side project 10 years ago as Yanoviak and colleagues examined gliding behavior of ants in Panama and Peru. "Ever since that time, we've just been dropping whatever we can find out of trees to just see what is the range of organisms that can do this," Yanoviak said. "We realized at that time that living in trees is not easy if you don't have wings."
So, they dropped 59 spiders and analyzed their "flight" path. What they saw was the spiders didn't float aimlessly. Almost every single one had directed, targeted trajectories and landed on nearby tree trunks, researchers write.
Not only do the spiders seem to float to targets, they can also adjust themselves mid-flight.
"It doesn't really matter what angle the initial trajectory we give them is when we drop them, they will always turn themselves right side-up in fractions of a second and will start gliding," Yanoviak said.
The spiders seem to take on a "disc-like" shape when falling as they hold their legs to the sides of their bodies. "It gives them a crab-like appearance," Yanoviak said. The spiders might be using their front legs to guide their path and change directions, but that suspicion is only a correlation at this point.
Spiders don't depend on flight or wings because silk allows them to move through the air. But "this particular spider is jumping and gliding like Superman," Yanoviak said.
Flatties may use the gliding technique to get away from predators, such as ants, or to save themselves if something knocks them off a tree limb, researchers noted. But they don't seem to use gliding to just get around, since the endeavor can expose them to other risks, such as birds snatching them mid-air.
"This reveals the fact that there's a heck of a lot to be discovered in the rain forests of the world," Yanoviak said.