Speaker 1: Welcome to Brainstuff, a production of iHeartRadio, Hey brain Stuff
Speaker 1: Lauren vogelbaumb here. Butterflies possess some of the most striking
Speaker 1: color displays found in nature, especially considering their small size.
Speaker 1: As they fly from flower to flower gathering nectar, their
Speaker 1: brightly colored wings shimmer and shift before your eyes. Pilots
Speaker 1: flying above the rainforests of South America can see the
Speaker 1: bright blues of the morpho butterfly up to half a
Speaker 1: mile away. A butterflies patterns and colors can act as camouflage,
Speaker 1: help identify or attract mates, or confuse or worn off predators.
Speaker 1: Part of what makes butterflies colors so intense is that
Speaker 1: you're not just looking at ordinary pigmented color. They also
Speaker 1: have what's called structural color, which appears when the physical
Speaker 1: structure of a surface has tiny layers and shapes that
Speaker 1: reflect light to your eyes in specific ways. Okay, many
Speaker 1: things in nature get their color from chemical pigments that
Speaker 1: absorb certain wavelengths of light and reflect others. For example,
Speaker 1: the pigment chlorophyll gives many plants their green color. The
Speaker 1: chlorophyll soaks up the blue and red wavelengths of the
Speaker 1: spectrum but not the green, so that's what you see
Speaker 1: when it bounces off a plant to your eye. Most
Speaker 1: butterflies get their different shades of brown, gray, and black
Speaker 1: from melanin, which is the same pigment that might make
Speaker 1: your skin deepen or tan or freckle in the summer
Speaker 1: and can help give humanize their color. Some butterflies with reds, oranges, yellows, creams,
Speaker 1: and even blues and blue greens get that color from
Speaker 1: various pigments, but structural color doesn't come from pigments. We
Speaker 1: talked about this a bit in our episode about human
Speaker 1: eye colors. Human eyes never contain any blue pigment. Rather,
Speaker 1: eyes that are pure blue have very low concentrations of
Speaker 1: melanin in the iris, so when light hits that pale
Speaker 1: but still textured and fibrous iris, the light scatters, and
Speaker 1: blue light happens to scatter really well, so that's what
Speaker 1: we perceive. Butterfly wings are made up of wafers of kitan,
Speaker 1: given support and shape by a structure of veins. Kitan
Speaker 1: is the same strong stuff that our hair and nails
Speaker 1: are made of, and makes up butterflies and other insects
Speaker 1: exoskeletons too. It's transparent by itself, but can carry pigments
Speaker 1: and or structural color. If you look closely at a
Speaker 1: butterfly's wings with your naked eye, you might notice it
Speaker 1: looks a little soft or fuzzy, feathery, or sort of satiny.
Speaker 1: That's because their wings are covered in thousands or millions
Speaker 1: of tiny scales, overlapping like tiles on a roof. The
Speaker 1: name of their taxonomical order means scaled wings. These scales
Speaker 1: are each less than one hundred micrometers in size, smaller
Speaker 1: than the width of a human hair or a droplet
Speaker 1: of mist on a foggy morning, and these scales often
Speaker 1: do contain pigment like melanin, but it's sometimes the microscopic
Speaker 1: shape of the surface of the scales that gives a
Speaker 1: wing its color, just like with human eyes. The most
Speaker 1: vibrantly blue butterflies contain no blue pigments. The microstructure of
Speaker 1: butterfly scales can come in different shapes that produce different
Speaker 1: colors and effects on different species. So let's take the
Speaker 1: blue morpho butterfly for example. Its wings are a shimmering
Speaker 1: blue that can look almost aqua to near indigo, depending
Speaker 1: on how the light hits them and the angle that
Speaker 1: you're observing them from. A couple of things are happening here.
Speaker 1: The overall blue color comes from the structure of the
Speaker 1: blue morphose scales. Each blue scale has a surface covered
Speaker 1: in many rows of tiny tree shapes. If you look
Speaker 1: at it under a scanning electron microscope like you do,
Speaker 1: each row looks sort of like the cross section of
Speaker 1: a lego pine tree, like if you took a little
Speaker 1: cookie cutter in the shape of a spindly Christmas tree
Speaker 1: and pushed plato through it to create a long rope
Speaker 1: in a tree shape. And each scale has an orderly
Speaker 1: orchard of these tree shaped rows on it. These shapes
Speaker 1: are transparent, but when normal full spectrum light shines onto
Speaker 1: the scale, it hits the top of these tree rows
Speaker 1: and bounces off of each branch on the tree. And
Speaker 1: there's about six to ten branches, and these microstructures are
Speaker 1: just the right shape and size to reflect blue and
Speaker 1: only blue light. The rest gets scattered or absorbed by
Speaker 1: the brown melanin on the undercoating of the scales. Notably,
Speaker 1: this only word an open air. If you get the
Speaker 1: scales wet, that changes how light reflects off of them,
Speaker 1: and they'll appear clear with the brownish undercoating. But okay,
Speaker 1: what about the iridescence of the butterfly's wing. Iridescence is
Speaker 1: the quality of colors shifting as your point of view changes.
Speaker 1: You can see it in mother of pearl, on fish scales,
Speaker 1: and on peacock feathers. It happens when light passes through
Speaker 1: a transparent, multi layered surface and is reflected towards your
Speaker 1: eye more than once. The multiple reflections can compound one
Speaker 1: another to intensify colors, or can disrupt one another to
Speaker 1: dim or cancel out colors as the light travels to
Speaker 1: your eye. It's helpful here to remember that light is
Speaker 1: a wave and can be described as a wave length,
Speaker 1: a wavelength being the distance between identical points on a wave.
Speaker 1: A waves can also be described by their phase, the
Speaker 1: position of their crests or high points, and trough or
Speaker 1: low points. When two waves have the same phase, their
Speaker 1: crests and troughs would align if you stack them on
Speaker 1: top of one another. A simple example of iridescence is
Speaker 1: the colors that appear on soap bubbles. The soap self
Speaker 1: is transparent and the bubble's surfaces are reflective, so a
Speaker 1: light first passes through the bit of the bubble that's
Speaker 1: closest to you, which reflects some of that light to
Speaker 1: your eye. But light also passes through to the far
Speaker 1: bit of the bubble, which also reflects some light back
Speaker 1: to you. Depending on the time it takes the second
Speaker 1: reflection to join the first, plus a few other factors,
Speaker 1: the two waves may or may not line up or
Speaker 1: have the same phase. If the phase of the two
Speaker 1: waves is different by some multiple of one full wavelength,
Speaker 1: the waves are said to have constructive interference. If the
Speaker 1: two waves differ by half a wave length or an
Speaker 1: odd multiple of debt, they have destructive interference. The math
Speaker 1: there is a little beyond our scope today, but basically,
Speaker 1: the degrees of constructive and destructive interference change as your
Speaker 1: point of view changes, thus bringing different colors to your eye.
Speaker 1: Here's how it works. Constructive interference causes two waves to
Speaker 1: complement each other and thus amplify a given color. That's
Speaker 1: why eardescence can create such intense, almost glowing colors. Destructive
Speaker 1: interference causes the two waves to cancel each other out,
Speaker 1: dimming a given color. So bouncing off of a single
Speaker 1: and technically transparent surface you'll see different colors or shades
Speaker 1: as those factors of distance and interference change. The same
Speaker 1: principle of eardescence behind soap bubbles applies to a blue
Speaker 1: morpho butterfly's wings. Because of the structure of the aforementioned scales,
Speaker 1: the branches on the turn and the heights of the
Speaker 1: different rows create multiple reflections that can constructively or destructively
Speaker 1: interfere with each other. This changes the exact intensities and
Speaker 1: shades of blue that hit your eye from different portions
Speaker 1: of the wing, or as the butterfly moves, or as
Speaker 1: you move around it, and again. The blue morpho is
Speaker 1: just one species of butterfly. Other species in the genus
Speaker 1: and other genera of butterflies have microstructures on their wing
Speaker 1: scales that produce entirely different colors and effects. For example,
Speaker 1: the peacock's swallowtail has tiny cups on its scales that
Speaker 1: reflect yellow from the bottom but blue from the sides.
Speaker 1: The two colors combine to appear green when you look
Speaker 1: at the wing head on, but if you look at
Speaker 1: it from the flat edge, you can only see the blue.
Speaker 1: Some structural color displays on butterflies even extend into the
Speaker 1: ultraviolet part of the spectrum, which is visible to those
Speaker 1: butterflies but not to humans and not even to all
Speaker 1: other butterflies, thus helping them identify potential mates and beyond displays,
Speaker 1: the structure of the scales can help butterflies manage things
Speaker 1: like water runoff and body temperature. These microstructures are so
Speaker 1: intricate that we don't know how to replicate them yet,
Speaker 1: but researchers hope that studying how butterflies build their wing
Speaker 1: scales will help us figure out how to build better
Speaker 1: and more beautiful materials in the future. Today's episode is
Speaker 1: based on the article where do Butterflies get their striking colors?
Speaker 1: On how stuffworks dot Com written by Jennifer Horton. Brainstuff
Speaker 1: is production of iHeartRadio in partnership with how stuffworks dot
Speaker 1: Com and is produced by Tyler Klang. Four more podcasts
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