Insects are so weirdly amazing it hurts!
Sometimes the Internet makes my head smart and I don’t mean more knowledgeable so much as, “ow! That smarts!”
It always starts innocently enough, like earlier in the week, after I took a photo of a winged insect walking on the outside of the plate glass window in front of my counter seat in a West Broadway Avenue restaurant.
What could I say about this insect, or, more accurately, what could the Internet tell me about it?
Not much, it turned out. After a lot of searching I still couldn’t identify it as anything, definitively; not as a kind of wasp or flying ant. But it was when I decided to focus on how such an insect can walk on glass that things got, er, hairy.
Some, insects, such as house flies, and other other arthropods, have two soft, cushion-like pads called pulvilli located at the base of the claws on the ends of their “feet”. These pads are covered in ultra-fine hairs and function as adhesive pads to allow walking on walls and ceilings and glass.
However, between its claws, my insect appears to have the single arolia adhesive pad, of bees and ants. The mechanics of this pad varies between different insects.
In the case of flies and beetles the arolia is covered with very fine hairs which effect adhesion variously, like the pulvilli, by hooking or even by molecular effects (see geckos below). On ants, bee and roaches, the arolia is a flat flexible cuticle. In many cases, insects secrete a viscous fluid onto the arolia that allows it to function like a wet suction cup.
A few years ago, a researcher famously snapped an amazing photograph of an Asian weaver ant that really showed the adhesive power of the arolia. The weaver ant was holding a 500 mg weight (equaling about 100 times the weight of the ant) while the ant was suspended upside down on a sheet of glass!
The weird science of a gecko walking
The weaver ant is amazing enough but reading a little further, I find that the tropical gecko lizard’s ability to run up smooth surfaces such as glass appears to involve nothing quite so mundane as suction. The gecko is actually using the subtle nuclear, or electrostatic, attraction called van der Waals force (just like some of the insects apparently).
Every square milimetre of the bottom of a gecko’s feet is covered by thousands of microscopic hairs, or setae, which further branch off into 100-1000 spatulae that are each narrower than the wavelength of visible light — below 300 nanometres (ouch)!
Thus, the gecko’s feet stick to the smoothest surfaces because, at their absolute tips, these hairs are capable of molecular entanglement with the molecules in whatever surface the gecko is walking on!
Oww! Oww! Head hurts. Make it stop. Make it stop! Click the image to enlarge it.