gecko feet

How the setae on gecko feet work.

Credit - Ltikorea CC-BY-SA

Credit – Ltikorea CC-BY-SA

Leaving out the home, contact, downloads and welcome pages, these posts are the best of 2014 by visit.

14. Near Death Experience – Part Three
What happened to parts One and Two? How does the third one outrank the others?

13. Flesch Reading Ease
This surprises me. Why is there so much interest in a method for rating how easy it is to read text?

12. Yawning
Of things our bodies do, including Synesthesia, Smell (1, 2 & 3), Earworms and Handedness, yawning is the most popular.

11. Ball Lightning – Part Three
Again part three is first.

10. Ball Lightning
And it appears readers jumped right over Part Two to read these.

9. BitTorrent Bundles
Good. I’m glad people are interested in my BitTorrent Bundle. No idea how this fits in with the rest, though.

8. Gecko Feet
I’m glad to see this. I have a soft spot for these little guys.

7. Altocumulus Castellanus
This is the only entry from the Cloud of the Day series. Maybe because it sounds so grand?

6. Collective Nouns
I like this series. It’s a lot of fun. Even Part Two.

5. Aquatic Ape – The Theory Evolves
The Bipedal series did well, taking three of the top five spots.

4. Whispering Galleries
This is no surprise. There’s something intrinsically interesting about whispering galleries.

3. Spanking for Love
This is no surprise either. Humans, eh?

2. Bipedal – The Aquatic Ape Theory
The Aquatic Ape is popular, but the Savanna Ape is even more so.

1. Bipedal – The Savanna Theory
This post got more than twice the number of views of the two Aquatic Ape posts combined.

That’s what you were looking at in 2014. Thank you for your interest, and thank you for keeping it interesting for me. Without you, it could be a pretty bleak job maintaining Green Comet’s home on the Internet. You encourage me to carry on, both with this site and with the sequel to the novel, which should be ready in the middle of 2015.

That was the best of 2014. See you in the new year.


Geckos aren’t the only animals that use van der Waals force to stick to the ceiling. Scientists in Germany and Switzerland have been using electron microscopes to look at the feet of jumping spiders. There they’ve found the same hairs-covered-by-hairs combination that gecko feet have. Once again the hairlets are so small that they can fit into the force fields around molecules and stick fast. Calculations show that the total sticking power of their feet could theoretically hold 173 times their weight.

The jumping spiders – hunters, not web builders – have an added twist to their use of van der Waals force fields. They don’t simply make passive use of the force. The structure of the setules, the smaller hairlets on their feet, allows their van der Waals forces to combine into a very strong overall force on each foot. The spiders are producing their own adhesion, not just making use of the existing forces in the ceiling.

Like geckos, jumping spiders can stick to the ceiling even if it’s wet or oily, no matter how smooth it is. That’s because the setules and the molecules of the ceiling meet in spaces so small that concepts of roughness and wetness simply don’t compute.

This research opens up interesting possibilities for adhesives. Dry, all-purpose, all-weather, reusable duct tape comes to mind.

Jumping spiders sound like the nightmares of the small world. Unlike some other species of spiders, which can have their eight eyes arranged all around their heads, hunting spiders tend to have theirs clustered on the front. All the better to focus on their prey, I imagine. Some of them also bungee jump. They go after flying prey, including birds for some larger spiders, by jumping into the open air. If they miss they haul back up the strand of web to where it’s attached at their launch site and wait for the next meal on wings.

All this and sticky feet, too. Their ability to cling to any surface, focus acutely on moving objects and jump great distances add up to an extremely efficient hunter. It makes you wonder if any of them hunts geckos. Hunter and prey running across the same molecular force field.


Since the characters in Green Comet have “gecko feet,” I thought it would be good to republish an original article from my erstwhile newspaper column, “Tech Nickels.” This was originally published when biomimetic scientists were first uncovering the marvels of these little creatures’ feet.

Gecko Feet

Geckos are small, carnivorous lizards, usually found in the tropics. They work the night shift, eating insects. They’re harmless to humans and are generally welcome in and around homes. An adult gecko weighs about 50 grams, or about as much as a small box of tea.

A gecko can run across a dusty road and straight up a wall. Its feet are so sticky that it could hang from smooth glass by one toe. People have been amazed by the phenomenon for millennia and have been trying to figure it out for as long. We know now that the answer is in the gecko’s hairy feet.

Each of its four feet has about five hundred thousand hairs which can be seen with an optical microscope. But the real secret is smaller than that; smaller than the wavelength of light even. An electron microscope shows that the end of each hair has hundreds of smaller hairs, each tipped with a flat pad. These structures are so small that they can take advantage of the force binding the wall’s molecules together.

It doesn’t use suction or hooks or sticky goo. Unlike suction, as used by salamanders, gecko feet can stick without a pressure differential. Without hooks or grapples, as used by cockroaches, gecko feet can stick to surfaces too smooth to be hooked or grabbed. Without glue, as used by snails, gecko feet stick wet or dry. The little pads on the little hairs covering the contact surfaces of a gecko’s fantastic feet are so small that they can squeeze into the little bubbles of van der Waal’s force around the atoms and molecules in whatever surface they’re on.

Wouldn’t that be great for hanging a picture? I don’t mean using a gecko to stick it to a wall. That would be inconsiderate of the gecko. I mean manufacturing a kind of tape that could be used repeatedly. And since the combined adhesion of all of its feet would hold up a gecko the size of a large hockey player, such a tape would have many uses. It would certainly hold on a car fender, for instance.

Naturally this hasn’t gone unnoticed. A recent branch of science called “biomimetics” devotes itself to learning how it’s been done in nature and seeing if it’s possible to mimic in the laboratory. In the case of gecko feet, they’ve done quite well. So far their gecko tape can support a little more than the real thing.

When something new appears like this, it’s tempting to try to guess where it will show up in the day-to-day world. In medicine? On rock climbers? It will probably inspire a new razor. These things usually do.

See the companion post on spider feet.