Butterfly scales

[Ciro Pabón]

I've never seen aerodynamic surfaces like this:

Scales on butterfly wing


Close up of one scale


What's the purpose? They seem like rows of Gurney flaps, but with those tiny ridges in front. The "teeth" on top of each ridge have even tinier ridges on each one.

How do they work? Any theories?

What would do to a Gurney flap those little ridges? Is this an "idea" that can be used in a racing wing?

Please, don't explain what a vortex generator is, we already know.

My best guess is that the "holes" in front of the "Gurney" somehow interact with the laminar flow to keep it attached to the wing. That's not a vortex generator, if true.

This seems more complicated. Notice the shape of the little ridges: they are twisted with all ridges pointing in the same direction.

[Jeffsvilleusa]

Wouldn't the behavior of the aerodynamics respond fundamentally differently because of the vast difference in scale?

Maybe the example isn't entirely appropriate, but likewise water bugs can stand on the surface of water due to water tension, but if they were scaled up it would be impossible.

Along those lines, It seemed to me when teams scale to 50% models in the wind tunnel that there would be a margin for error that exists simply due to scale. Don't know if that is the case, just my layman's perspective.

Not dismissing the notion of investigating the function of these scales, but wondering if our set of aerodynamic concepts apply.

[hollus]

It looks to me like a minimum weight way of achieving enough structural strength and flexibility, while having the ability to get biological color patterns. The color patterns are as important to a butterfly as its ability to fly! Notice the sub-micrometer repetition pattern(s), ideal to diffract visible light in a wavelength sensitive manner.

I would not think on the usual aerodynamic terms about how butterflies fly, though. There is no thrust and lift like in a plane of an racing car. Butterflies fly by a mechanism more akin to using a parachute like if it was an accordion! Speed and efficiency are not their main concern, I would think; rather growing fast, not being eaten and mating, none of which requires particularly good flying skills for the butterfly lifestyle.

Sometimes nature does not optimize for a function, but arrives there by sheer accident and then gets stuck with a rather inefficient mechanism.

[Richard]

I'd say butterflies are very specialised and hence likely to be highly optimised, just not for flight compared to an eagle, dragonfly, wasp or albatross.

Having said that, some species migrate thousands of miles on those funny flappy wings. Their tiny body mass means they can't store much energy, so they must be very very efficient in their use of that energy.

Butterflies are characterized by their scale-covered wings. The coloration of butterfly wings is created by minute scales. These scales are pigmented with melanins that give them blacks and browns, but blues, greens, reds and iridescence are usually created not by pigments but the microstructure of the scales. This structural coloration is the result of coherent scattering of light by the photonic crystal nature of the scales. The scales cling somewhat loosely to the wing and come off easily without harming the butterfly.

Now that is fascinating - butterflies wings are black and brown like a moth!

[Mr Alcatraz]

I have a serving tray that came from Guyana that is underlayed with wings very similar to these. I never noticed until you brought it up that the edges are in fact brown