Gecko footpads’ stickiness is put to the test when grabbing leaves to break a fall
As many action movies have shown us, heroes falling to their doom can regularly catch themselves with one hand, simply by getting their fingers onto some kind of nearby handhold. This is of course ridiculous, because none of these movies follow the exciting adventures of geckos (sadly.) Researchers have long known that these small lizards could use their specialized footpads to climb vertical surfaces, but analysis always found their adhesion to be stronger than was really necessary. Evolution normally weeds out wasted energy or materials, so this raised some questions, at least until gecko behavior was factored in.
Sticking a leafy landing
Geckos in a lab are most likely going to scuttle up a surface provided by researchers. They might be nervous in captivity, but few people really give them the obstacle course that they’ve evolved to deal with in a more forested environment like a rain forest’s canopy. Given the chance though, geckos are actually rather acrobatic, easily jumping a foot into the air from a standstill, on top of being sticky, and they combine these strengths like our aforementioned action hero to leap from danger, even if it means falling half-way down a tree before catching themselves with only their fingers.
Researchers investigating gecko adhesion first built up a number of simulated models concerning gecko weight, movement and frictional capacity. Under calmer climbing conditions, geckos always have plenty of wiggle room. However, a good fall apparently does start to max-out the lizard’s footpads can handle. A evasive jump from a tree’s canopy can quickly become too much for a single foot to safely handle, while two feet can successfully stop a fall.
Slowing to a stop
Looking to actual gecko behavior, researchers found that geckos look to leaves along their descent as a good way to brake their falls. Reaching out to the leaf, the footpads stick to the surface of the leave, but don’t necessarily bring the gecko to a full stop on first contact. There’s a little bit of sliding involved, which when combined with the natural range of movement of a leaf or stem on a tree, slows down the descent just a bit. By spreading that movement over time, the geckos effectively lower the impact force on their limbs— in a way, the bounce of a leaf is a bit like the crumple zones in your car that avoid transferring all the energy of a sudden stop to your body at once. That’s not to say that this kind of stop is especially comfortable for the geckos, but as our action heroes have taught us, sometimes these daring feats are the only way to safety.
Source: Leaping Lizards, Scienmag