Spiders inspire eight-legged Post-it notes

Arachnid molecular adhesion

Scientists have discovered that spider on a ceiling could hold 170 times its own bodyweight before gravity would pull it from its perch.

And what use is this fascinating piece of information being put to? The betterment of mankind perhaps? Not a chance: it'll be used to make Post-it notes that stick even when wet.

Despite the rather daft application, the back-story is quite interesting. A team from Germany and Switzerland used a scanning electron micrograph to take pictures of a jumping spider's foot.

scanning electron microscope shot of the foot of a jumping spider

There are tufts of hairs on the bottom of the spider’s leg. Bristling out from each of these are more hairs, called setules, and they are what makes the spider stick.

The team published their findings: "Getting a grip on spider attachment", this week in the Institute of Physics journal Smart Materials. They found that it is the Vander Waals force that makes the spider stick. This is an attractive but short-range force that acts between molecules. Each of the setules is attracted to the molecules of the surface the spider is on.

The huge strength of the force is down to the vast number of setules on each foot: in total the jumping spider has around 600,000 to play with. According to Andrew Martin, from the Institute of Technical Zoology and Bionics in Germany, this is sufficient to allow it to support 170 times its own weight. "That’s like Spiderman clinging to the flat surface of a window on a building by his fingertips and toes only, whilst rescuing 170 adults who are hanging on to his back,” he is quoted as saying.

We'll be keeping an eye out for the terrible Hollywood action movie that is bound to follow this research: Watch Spidey as he battles for control of the office supplies cupboard against an evil cybernetic office manager armed with stapler. But we digress.

The interesting thing about the Vander Waals force is that it will work regardless of the surface: i.e., things will stick when wet or greasy etc. The only factor affecting its strength is the distance between the two surfaces.

But wait: how do you get the post-it unstuck? If it is sticking with such a huge force, you'll need to be pretty sure about where you stick it, surely? Fortunately no. The researchers believe as the spider raises its leg the setules are lifted successively rather than all at once. So all you'd need to do to get rid of your friendly neigbourhood yellow memo is peel it off slowly.

Thanks goodness too, that the researchers have more ideas as to what their discovery could be used for. Professor Antonia Kesel, head of the research group in Bremen suggests that “You could also imagine astronauts using spacesuits that help them stick to the walls of a spacecraft – just like a spider on the ceiling”.

Much better than a super heroic Post-it note, we are sure you'll agree. ®

Related links


The IOP publication
The Institute of Physics
A basic guide to Vander Waals forces
Normal Post-it notes

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