A Swiss/German research team have published an article in Smart Materials and Structures analyzing the feet of jumping spiders. These feet covered in nanoscale fibers depending from thicker hairs, and the overall bundle is small enough that the van de Waals force -- "an interesting form of adhesion is that, unlike many glues, the surrounding environment does not affect it" -- creates a very high degree of waterproof, grease-proof, dirt-proof stickiness.

"We found out that when all 600,000 tips are in contact with an underlying surface the spider can produce an adhesive force of 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!"

...The total van der Waals force on the spider's feet is very strong, but it is the sum of many very small forces on each molecule. The researchers believe the spider lifts its leg so that the setules are lifted successively, not all at once, and it does not need to be very strong to do this. All you would have to do to lift a future kind of Post-it® note is peel it off slowly.

Link