These are gecko feet.
Notice their crazy toes.
The “stripes” are made of modified scales covered in thousands of “hairs,” only twice as long as our hairs are thick.
Each hair branches into thousands of tips.
Each tip branches into hundreds of tinier tips.
These tiny-tips are so tiny (like size-of-the-wavelength-of-visible-light tiny) that they fit against all the microscopic nooks and crannies of even apparently smooth surfaces.
This puts the gecko in nearly complete contact with that surface, magnifying profoundly the atomic-level attraction of all materials, know as as Van der Waals force, and making the gecko able to stick to or climb up almost anything.
The image above was created by one of the scientists behind the original discovery that Van der Waals force is the gecko’s key to success, Dr. Kellar Autumn (see more at kellarautumn.com). Autumn highlighted the diversity among gecko feet by magnifying and color-adjusting close-up photos he took of the toes of several kinds of gecko.
National Geographic grantee Travis Hagey has worked with Autumn, and clued us in to the many groups represented, and some of their special powers. Clockwise from top right:
The Blue One: This is a Tokay gecko, scientific name Gekko gecko. It’s the “white rat of gecko adhesion. We do everything with that species.”
The Brown One: This one is from the group called Pachydactylus, from Africa. They are beloved in the pet trade for interesting behaviors and colors.
The Orange One: Behold the tell-tale foot of geckos in the Ptychozoon group. These are flying geckos from Southeast Asia. Hagey pointed to the webbing between the toes and added that they have “little flaps between their armpits and their hips [to aid in gliding], but not as developed as those of a flying squirrel.”
The Green One: This is a species in the Rhacodactylus genus from the islands of New Caledonia, east of Australia, a group that also includes the largest living species of gecko. (Read blog posts from an unrelated expedition to New Caledonia.)
The Pink One: Last but not least, we have a fan-toed Ptyodactylus, from the Middle East and Eastern Europe. Wondering why the toes have that split top? So is Travis. “Nobody’s looked at that yet,” he said. “My personal opinion might be that if you split up the left and right sides, they may be able to work independently, so it might work better on rougher surfaces, although that’s an untested hypothesis.”
From his office at the University of Idaho, Travis also explained the science behind the stickiness: “What happens is you’ve got your electrons flying around the nucleus of whatever material you have, and at any split second, all your electrons might happen to be on one side of your molecule. For that split second your molecule has a positive side and a negative side, and so if your molecule is sitting near another molecule, at any split second, the other molecule’s electrons might be on one side or the other side, so it can have a really quick fleeting charge also. It’s that really quick, fleeting, positive-to-negative attraction that’s Van der Waals. It’s magnetism but at a really really small, really really weak scale. It’s present in anything, not just metals.”
Hagey studies geckos and their incredibly sticky feet, and is investigating connections he found between leg-length, the kind of perch and terrain they traverse, and toe-stickiness. Geckos and anoles share common ancestors roughly 200 million years ago, but have since then branched off to become very different (learn more about anoles from explorer Neil Losin). In both groups, toes that take advantage of Van der Waals force have evolved, but the specifics of what shape the pads and hairs take, how sticky the feet are, how long the legs are, and more are all largely unexplored. Travis hopes to change that this fall as he begins his post-doctoral work examining how the shapes of hairs affect how they work.
It Gets Even Weirder
Lest you think you’ve gotten an exhaustive look at the many wonders of the world of geckos, Travis was quick to point out that there’s much, much more still to be studied.
“There’s a handful of genera that also have the same kind of adhesive pad on the tip of their tail. And a lot of geckos don’t have toe pads,” he said.
“And then, what’s really wild is there’s a group of Australian geckos that don’t have legs.”