London, Jan 19 (IANS): Thanks to our size, doing a convincing Spiderman stunt may never be possible for humans as researchers have found that there is a size limit to sticky footpads as an evolutionary solution to climbing -- and that turns out to be about the size of a gecko.

We would need about 40 percent of our total body surface, or roughly 80 percent of our front, to be covered in sticky footpads if we wanted to do a convincing Spiderman impression, the researchers estimated.

The study, published in the journal PNAS, showed that in climbing animals from mites and spiders up to tree frogs and geckos, the percentage of body surface covered by adhesive footpads increases as body size increases, setting a limit to the size of animal that can use this strategy because larger animals would require impossibly big feet.

Geckos are the largest animals able to scale smooth vertical walls.

Once an animal is big enough to need a substantial fraction of its body surface to be covered in sticky footpads, the necessary morphological changes would make the evolution of this trait impractical, said one of the researchers David Labonte from University of Cambridge.

"If a human, for example, wanted to walk up a wall the way a gecko does, we would need impractically large sticky feet - our shoes would need to be a European size 145 or a US size 114," senior study author Walter Federle from University of Cambridge noted.

The researchers believe that these insights into the size limits of sticky footpads could have profound implications for developing large-scale bio-inspired adhesives, which are currently only effective on very small areas.

For the study, the researchers compared the weight and footpad size of 225 climbing animal species including insects, frogs, spiders, lizards and even a mammal.

"There is a size limit to sticky footpads as an evolutionary solution to climbing - and that turns out to be about the size of a gecko," Labonte noted.

Larger animals have evolved alternative strategies to help them climb, such as claws and toes to grip with.