Why tarantulas poop silk out of their feet

Tarantulas earned their fear-inducing reputation not because they're particularly deadly - they aren't, at least not to humans - but because they're so huge. In fact, they're so large that they shouldn't be able to climb walls without falling off.

That's where the feet-pooping comes into play. Researchers have now confirmed the controversial 2006 finding that these spiders eject silk from their feet as an added measure to keep themselves stuck to vertical surfaces. Like all spiders, tarantulas have hairs on their feet which are used to keep them attached to walls, but this isn't enough when these spiders are so huge.

German researchers had first announced this discovery five years ago, but a rival study argued that the silk came not from the tarantula's feet but instead from its silk-producing organs, and any silk found on the feet was just incidental. Dr. Claire Rind of the University of Newcastle set out to determine the truth. She designed an experiment where the spiders would climb up a glass surface, which would then be gently shaken to see how the tarantulas responded.

Dr. Rind explains:

"We couldn't see any traces of silk with the naked eye, but when we removed the slides and examined them under the microscope, we saw up to 30 silken threads at the point where the tarantula's foot slipped. So our experiments to dislodge the spider made it release silk through its feet."

Unlike other spiders, it appears that all tarantulas have two different silk-producing - or, because I'm hopeless immature, silk-pooping - mechanisms. One is found in the spinnerets, the organ that all other spiders have. But they have a second mechanism found in their feet, and that's what allow these unusually large spiders to maintain their grip as they climb up walls.

Journal of Experimental Biology via BBC News.