With Butterfly Wings, There’s More Than Meets The Eye

IRA FLATOW: This is Science Friday. I’m Ira Flatow. When it comes to winged insects, the butterfly wins the beauty contest, right? Beautiful reds and oranges, deep blues and greens, vibrant yellows. But as it turns out, scientists are learning that the butterfly wing is more than just a pretty membrane.

It’s actually alive. And its living cells are responsible for some important biological functions, like regulating the wing’s temperature so it doesn’t crisp up in the sun. And there’s even a wing heart. Mhm. Joining me to talk more about what she found probing these structural mysteries of the butterfly wing is Dr. Naomi Pierce, Professor of Biology and Curator of Lepidoptera– I love that word– at the Museum of Comparative Zoology at Harvard. Welcome to Science Friday.

NAOMI E. PIERCE: Hi, Ira. Nice to be here.

IRA FLATOW: Nice to have you. Now, for a long time, people thought that the butterfly wing was just a little lifeless membrane. All the important stuff was inside the body.

NAOMI E. PIERCE: Well, yes, more or less. The story usually is, if you take an entomology course or even sometimes if you teach one, you would say, well, the wing is at metamorphosis when the insect pops out of that chrysalis.

It pumps open its wings with the hemolymph or the blood of the insect. And that it pumps open the wings. It takes about two minutes. And then the wings harden and the insect withdraws the blood back after it’s hard. And now the butterfly can fly. And the wings are nice and hard and not too sensitive.

And the sense was that most of the hemolymph at that point is gone from those wing veins and the wings are there to fly, but all the action in terms of blood flow in the insect is really happening in the thorax. So I– and I ascribe– I think many entomologists had that– it’s a simple understanding of the circulatory system of butterflies or moths. But it turned out to be a little more complicated than that.

IRA FLATOW: Such as? We– the wing was actually alive?

NAOMI E. PIERCE: Well, that was the fun– [LAUGHS] it was a fun journey. So I got together with a physicist, Nanfang Yu, at Columbia University. And we started looking at the scales on the surface of the wings of butterflies and found that they were very heterogeneous across the surface of the wings.

So in some places, the scales were modified– sort of sculptured in this nano-sculpturing. Sculptured in a way that made them act like perfect black body absorbers in the near-infrared. That means that they have very high emissivity and they were reflecting back the energy coming from the sun that was in the near-infrared. But then other– in other parts of the wing, the scales looked very different– different colors or different shapes– and they weren’t specially contoured.

So we started exploring that more and found that really it was over the parts of the wing that you would call living parts of the wing– so along the wing veins– or also at these androconial patches. Those are sometimes the male butterflies have special areas where the cells in the wing produce pheromones that they use to attract lovely odors for the females. And over those patches especially, we found these highly specialized scales that were acting– reflecting near-infrared in that way.

So we– I mean, it just became more and more intriguing. Finally, we started to write a paper about how really it looked like this patterning of the scales and also the thickness of the cuticle itself– the thickness of the– the cuticle is the skin or the crispy outside bits of the insect– that that was contoured in a way to keep the butterfly cool– keep parts cool underneath. And those all ran along wing veins and these androconial organs.

So a reviewer– when we wrote the paper, a reviewer said, well, how do you know those wing veins are even alive? Are you sure there’s hemo– there’s blood, hemolymph, flowing through those wing veins? So we went back and we took some butterflies. We carefully removed live ones and kept them cool so they’d be comfortable on ice. And then carefully took off the scales so we can peek inside those wing veins. And sure enough, there was a hemolymph pumping away.

And in many insects, the blood is– it’s a tidal flow. It goes in and out, and in and out. It’s not– it doesn’t circulate around. So that’s what we were seeing in the main wing veins– in and out– and we could measure it. And in fact, that tidal flow continues at a regular pace right through the entire life of the adult butterfly. So day 24 for a painted lady, she’s still pumping away.

[LAUGHTER]

IRA FLATOW: Is there a little– is there a heart? You say pumping, I get an image of an actual little heart in there.

NAOMI E. PIERCE: Well, the heart– yes, the heart is– it runs along the dorsum of the insect. It’s called the dorsal organ. And it’s– there you’re thinking the fuselage.

IRA FLATOW: Yeah.

NAOMI E. PIERCE: Not the– not the wings, and the thorax and the main part of the body. And I’m aware of that. And I assumed that that was where– but there’s interaction with the breathing tube. So also in those wing veins are these breathing tubes called trachea. And they expand and contract, and expand and contract. So the two things go together. They sort of– that functions– we think they are coordinated to help pump the blood in and out.

IRA FLATOW: Wow. That’s fascinating.

NAOMI E. PIERCE: But then when we looked at the androconial organ, that little male organ, we saw something quite different. That it was a directional flow. So there the blood was only– it was coming in and out at a regular pace, about 20 times– but it was only going down to the bottom corner. I mean, it wasn’t going back again.

And when we looked down in that bottom corner, there it was beating away this little wing heart. So a little piece of tissue, a bit like your own heart. You don’t think about your own heart beating. And the butterfly doesn’t either. The little wing heart is beating all the time, pulling these blood cells through the organ, so presumably nourishing and keeping that organ–

IRA FLATOW: That’s fascinating. That’s fascinating. We have a new movie Wing Heart coming up. I want to bring on someone else who has studied the structure of butterfly wings and found that a wing’s color– because we all know– we’re looking at wings, we see the beautiful colors. And he’s found that a wing’s color can be determined by its structure. Dr. Nipam Patel, Director of Marine Biological Labs in Woods Hole. Dr. Patel, welcome to Science Friday.

NIPAM PATEL: Oh, Thank you very much.

IRA FLATOW: You looked at how color is made on the wings and how the structure influences color. Explain that to us.

NIPAM PATEL: Yeah. So normally when we think of color, we think of pigments. We think of molecules whose atomic structure absorbs a particular wavelength of light. Then what’s left is reflected and we see that as color. So for example, something that’s yellow has a molecule in it that absorbs blue light. What’s left is red and green, and we perceive that as yellow.

But there is another way to make color, which is through what’s called structural coloration. And the idea there is that you have very– at least in the case of butterflies– you have very thin material made of chiton, which Naomi described to you as the material that makes the exoskeleton. That you pattern that very precisely in very thin layers, and then light will interact with that in a way that certain wavelengths will interfere with one another to cancel each other out or they’ll reinforce each other.

And so often, in butterflies, what you see is green and blue is not made by pigment. That is made by these nanostructures instead. And these have been described by physicists for a long time. And what we’re very excited about is trying to understand how the cells actually make these structures.

IRA FLATOW: How do they? Do they have a talent for doing this?

NIPAM PATEL: Yeah. So it’s quite fastening. First of all, it’s extremely diverse. There’s lots and lots of different nanostructures that they can make. So I like to think about it as that the butterfly is constrained by the laws of physics in that it only has this material chiton to work with. But within that, it can come up with some very fascinating ways of doing this.

The simplest one is just to make a very precise layer of chiton, which is just right to basically give what’s called constructive interference of a particular wavelength to create a color like blue or green. But then you can have the example of brilliant blue morphos, which have really elaborate nanostructures. So they can be made in lots of different ways and that’s one of the things we’re trying to study.

So there’s no one answer as to how they do it. There’s going to be many answers. But it’s all related to the question of individual cells, scale cells, how they can actually pattern things very, very precisely either by laying down layers in a precise way or creating really unusual geometries by taking the internal skeleton of the cell while it’s still alive and bending it in very particular ways and then making that– laying down chiton and having a permanent structure.

IRA FLATOW: Well, why would they have two separate ways then?

NIPAM PATEL: That is a great question. So it turns out that it’s actually very rare, not just in butterflies, but throughout the animal kingdom to actually have pigments that are good at absorbing long wavelengths. The big exception to this in the world is chlorophyll, which is why the world is so green. But in fact, there’s very few molecules that are actually able to do that because of their chemical structure.

So instead, you often find solutions that are what we describe as structural or physicists have described as structural. And again, it doesn’t only apply to butterflies. The same is also true in birds and in beetles. Even human blue eyes are not made by a blue pigment, but are rather made by a structural component.

IRA FLATOW: I just learned something brand new there. That was a– did you know that Dr. Pierce?

NAOMI E. PIERCE: Not all the details.

[LAUGHTER]

That’s wonderful.

IRA FLATOW: Dr. Pierce does it surprise you about the structure of the wings?

NAOMI E. PIERCE: Well, I knew about the–

IRA FLATOW: About the colors?

NAOMI E. PIERCE: –structural colors. But we were surprised– we were surprised at the properties in the near-infrared. So lots of work has focused on colors in the visible. And of course, I knew about structural colors like the beautiful blue wings of morphos. But you don’t think about the colors you can’t see.

So it was a big discovery back in the ’70s when one of my original advisors, Bob Silvergleid found that pieridae butterflies are a little cabbage– what we would call a sulfur cabbage white– reflect UV on the surface of their wings and can use that as a private channel communications signal. And I mean, I loved this. You take these two butterflies that look exactly the same to us. But if you put it under UV, one of them is shining in the UV and the other one’s not. I just– I loved that when I first heard about it.

And so when we started thinking about longer wavelengths, I was excited. I thought, gee, maybe we’re going to find a private channel communication in these longer wavelengths too. And I wondered– nobody had looked at it before. So I was really very eager to see. And we did find– we found all this reflectins in the longer wavelengths, but most of it seems to be really involved in modulating heat, keeping the wings cool.

And that was– is new. It’s partly new because the tools are now available to be able to look at the temperature of a thin membrane like a wing. In the past, it would have been very hard because it’s such a light and thin material. But now there’s– we can really appreciate a lot about these–

IRA FLATOW: That’s interesting.

NAOMI E. PIERCE: –scales.

IRA FLATOW: Dr. Patel, I’ve got to wonder why the Director of the Marine Biological Laboratory is interested–

[LAUGHTER]

–in butterfly wings.

NIPAM PATEL: Well, first of all, so the Marine Biological Laboratory, it is certainly true that we’re great in marine biology and things like that. But we also do a lot of very basic science. And the story is that I actually started collecting butterflies when I was eight years old. And my parents definitely indulged me in that hobby. And so I’ve always been fascinated by making them part of the science that I do.

So yeah, about half my lab works on a marine organism, but the other half works on butterflies because it’s great basic biology. I think the excitement is that there are all sorts of– in any biological system, as you look closer and closer, there’s lots of fascinating details. And butterfly wings are a fantastic example of that. The more we look at them, the more things we discover.

IRA FLATOW: Well, are there creatures in the oceans that have the same kind of color system?

NIPAM PATEL: Yeah, there are. So in water it’s a little bit different, because in terrestrial environments you’re going from air into another material. And water is closer in what– it’s termed refractive index– than the material that biological structures are made of. So the physics has to work a little bit differently. The equations are a little different. But you can do the same thing. So you can create structural color under water.

The other thing we study, which is also quite remarkable when you really dig into it, is transparency. So a lot of butterflies are also transparent. And it turns out that’s actually not–

IRA FLATOW: Wait, wait, wait, wait, back that up for a second.

[LAUGHTER]

How do we see them if they’re transparent?

NIPAM PATEL: So that’s great. So they’re called glasswing butterflies is one group of them. And in fact, they are very hard to see. When you go to photograph them, the camera focuses through the wing to whatever is on the background. But one of the problems is they’re like– they can be like glass. Which is fine, it looks transparent in the shade. But if you put it in the sun, it reflects light.

But on the other hand, butterflies have also evolved nanostructures to keep the light from being reflected like that. So they really, really look transparent. And that’s another thing that scientists have understood that for a while. But we’re actually now just trying to understand how the butterfly makes these kinds of things.

IRA FLATOW: Dr. Pierce, if it’s transparent, how does it have that plumbing system in the heart there–

[LAUGHTER]

–to do all that stuff?

NAOMI E. PIERCE: Well, that’s a good question. And that’s something to study next. I’m hoping that we can find that out from Dr. Patel.

IRA FLATOW: Well, it’s so fascinating to hear that something that we have seen our whole lives and we think we know about still holds all these secrets, Dr. Patel.

NIPAM PATEL: Yeah, I know, it is amazing. And one of the things we’ve really been trying to do is to watch the living wing get made. So as Naomi said, you think about the butterfly comes out of the chrysalis. It pumps up its– sorry– it pumps up the wing. But of course, it was alive when it was in the chrysalis, and it was making all these cells and these structures.

And normally that’s been inaccessible to us. But one of the things we’ve been working on are ways to visualize what’s going on inside of that living chrysalis. And actually to visualize it in incredibly fine detail, because these structures that it’s making are smaller than a 1/2 wavelength of light, so something that’s not easy to see with a microscope. But recent breakthroughs have made it possible to watch what it’s actually doing.

IRA FLATOW: Fascinating. You ever think you’d get tired of it? No? I doubt it.

NAOMI E. PIERCE: Never. There’s a very practical side to this– the consequence of learning about these scales incidentally. So my collaborator, Nanfang Yu, is an applied physicist. And he was interested in trying to– trying to– bioinspired uses of this. And he developed a paint.

It’s a very– it’s a simple and inexpensive paint that has a polymer base with little holes in it that are just very similar to the holes that you find in the scales of the insects. And if you paint them on buildings in hot areas like– they tested in Bangladesh, New York, and Phoenix– it can lower the energy costs of air conditioning–

IRA FLATOW: Wow.

NAOMI E. PIERCE: –by 30%.

IRA FLATOW: I’m going to have to stop you there, because we’ve run out of time. But you’ve peaked our interest.

[LAUGHS]

NAOMI E. PIERCE: Yeah, a practical effect coming from a lovely–

IRA FLATOW: Absolutely. Dr. Naomi Pierce at Harvard and Dr. Nipam Patel at Woods Hole, thank you both for taking time to be with us today.

NIPAM PATEL: Thank you very much.

NAOMI E. PIERCE: It was a pleasure.

Copyright © 2020 Science Friday Initiative. All rights reserved. Science Friday transcripts are produced on a tight deadline by 3Play Media. Fidelity to the original aired/published audio or video file might vary, and text might be updated or amended in the future. For the authoritative record of Science Friday’s programming, please visit the original aired/published recording. For terms of use and more information, visit our policies pages at http://www.sciencefriday.com/about/policies/