Mother Nature’s mindboggling nano-engineering that helps reptiles and insects stick to surfaces

It is mind-boggling to think how over time, this remarkable bit of nano-technology might have evolved, but that’s not the end of it. A gecko had to unstick its remarkable feet to move over the surface — often at speed — while chasing or escaping from prey or predators. It was found that the setae don’t stand up perpendicularly out of the toes (like a mohawk hairstyle perhaps), but lie at an acute angle to the surface, to enable more sticking power, and being able to support the gecko’s weight. (To this end, the gecko helps itself by pressing its body close to the surface). The grip is broken when the angle of the setae is slightly changed enabling the gecko to scuttle ahead at a speed of 20 body-lengths per second (rather like Velcro which uses a system of hooks and loops)! The flexibility and ‘stretchiness’ of the setae enable it to absorb the shock and thump of landing after a leap — it’s like they just spread out and hug the surface they land on, for dear life!

Setae incidentally are made of that remarkable natural raw material: keratin, which is what our hair and fingernails are made of, as are the horns of rhinos.

Spiders too have setae at the ends of their toes and have modified their cuticles into a specialised array of highly sensitive bristles. Equipped with eight legs, web spinners usually have three claws — the middle one being the smallest. But their setae serve a different purpose: since spiders don’t have feelers or antennae their setae have taken up the role and pick up scents, sounds, vibrations and the faintest of air currents.

But spiders too are able to scuttle up walls and look at you, upside down from the ceiling — and hunting spiders, too, have thousands of ultra-fine hairs at the end of their setae that are split into as many as 1000 branches, stuffed between the paired claws at the tips of their feet. These are called scopulae and also use van der Wals forces to enable the arachnid to adhere to a vertical surface.

For locomotion, however, spiders use hydraulics and not the usual extensor and flexor muscles as used by other arthropods. Spiders can generate pressures up to eight times their resting level to extend their legs and the tiny jewel-eyed jumping spiders can leap 50 body lengths, by suddenly increasing the ‘blood’ pressure in their rear legs. Larger spiders, however, use their flexor muscles to generate the propulsion for their leaps. (This is the muscle that contracts when you bring your elbow up, Popeye style, I guess!)

Grasshoppers use a unique catapult mechanism to send them leaping off when you tickle their bums! They have two sets of muscles attached to those thunder thighs — the flexor running along the inside of their thighs, and the more powerful extensor above, both connected to the thigh bone by tendons. At the point where the thigh meets the shin (our knee equivalent), is a tough mass of elastic cuticle attached to the extensor muscle. The grasshopper flexes the lower part of its leg where the flexor muscle lives and is now contracting, bringing up the shin and pressing down the foot flat and hard. Now the powerful extensor muscle contracts, slowly but powerfully, like when you pull back on a catapult’s rubber. The elastic cuticle bulges as it absorbs and stores this energy, and then the flexor muscle suddenly relaxes releasing the pent-up energy and boing! The grasshopper is airborne, leaping 20 times its own length, generating 20g — or 20 times the force of gravity!

So, there we have it: nano-technology, hydraulics and catapult engineering, all evolved and perfected by Mother Nature, aeons before we were even aware of the concepts, let alone the physics and chemistry involved. Not that Mother Nature went to IIT or MIT: she just developed what worked and eradicated what didn’t. Simple as that!