Sticky silky feet.

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.

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.

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.