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Sticky Silky Feet

The feet of zebra tarantulas can produce silk threads that may help them get a firmer grip.

Comic book superhero Spider-Man uses tiny hairs on his fingertips to climb up walls. But he could have had another secret weapon to help him stick.

Scientists have now found that some spiders can also make silk in their feet, which may sometimes help them get a firmer grip on a surface.

A zebra tarantula can produce silk from its feet.

A zebra tarantula can produce silk from its feet.

S. Niederegger and S. Gorb, Max Planck Society

Spiders are good at gripping walls with their legs. Thousands of little hairs on their feet make it possible. To test whether spiders also make these hairs wet to improve grip, scientists watched zebra tarantulas crawl up glass slides.

When they tilted a glass slide until it was almost vertical, the spider slipped a few millimeters before attaching itself again. The scientists were surprised to see little threads stretching from its feet to the slide. When they studied the spider's feet under a special microscope, they found tiny silk-shooting spouts among the hairs.

This was a surprise because scientists had previously thought spiders only use special organs near their stomachs to make silk.

A zebra tarantula from Costa Rica.

A zebra tarantula from Costa Rica.

S. Niederegger and S. Gorb, Max Planck Society

It's possible that, a long time ago, feet were the first body parts of spiders to produce silk. Only later in their evolutionary history did spiders develop spinnerets on their abdomens to produce silk for webs.

If so, the researchers say, this could mean that the silk's original purpose was to help spiders climb and stick, rather than to build homes or trap prey.—C. Gramling

Going Deeper:

Cunningham, Aimee. 2006. Silky feet. Science News 170(Oct. 7):238. Available at http://www.sciencenews.org/articles/20061007/note14.asp .

Jaffe, Eric. 2006. Not slippery when wet. Science News for Kids (June 14). Available at http://www.sciencenewsforkids.org/articles/20060614/Note2.asp .

Sohn, Emily. 2003. How a gecko defies gravity. Science News for Kids (Nov. 19). Available at http://www.sciencenewsforkids.org/articles/20031119/Feature1.asp .

LabZone

Spy on a Spider

http://www.sciencenewsforkids.org/articles/20040519/LZActivity.asp

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