for National Geographic News
No defense budget could ever match nature's resources. Evolution, a hundred-million-year arms race between predator and prey, has perfected an extraordinary array of camouflage.
There are caterpillars disguised as bird dung, frogs shaped like dead leaves, and bizarre, seaweed-mimicking seahorses. All have evolved ingenious solutions to the life-or-death business of avoiding detection.
But scientists have turned to two rather more colorful animals in their search for new systems of military concealment. Butterflies and cuttlefish perform stunning optical illusions. And by understanding the processes involved, researchers hope to create materials that could make advancing armies almost invisible.
Butterflies and moths make up the biological order Lepidoptera. The Latin word comes from the tiny scales that coat each wing (lepis: scale, pteron: wing). What interests scientists is how these wings shimmer in sunlight.
The blue morpho family of butterflies, from the rainforests of Central and South America, catch the light in their wings to conjure dazzling displays. Males, which can be seen up to a thousand yards (1 kilometer) away by humans, use them to declare their territory to other males and attract females.
The butterfly's blueness does not come from pigment—the natural color of their wings is actually a dull brown—but thousands of semi-transparent scales.
Peter Vukusic, a physicist at Exeter University in England, has been studying how these wing scales influence light waves.
"If you shine white light at one of these butterflies you get multiple reflections from structures within the wing," he said. "Those structures are designed to produce an intense blue reflection. A male with a very bright color can have a lot of territory and a lot of females."
The scales consist of multiple layers of keratin (a fibrous protein similar to that which forms nails and hair in humans) which filter blue from the visible spectrum and radiate it out from the wings. While some reflected light waves cancel each other out, known as negative interference, others have a reinforcing effect—constructive interference—which produce intense iridescence. Blue morpho scales can reflect over 75 percent of blue light.
High Visibility
Ridges within the keratin multilayers also scatter light through diffraction, so broadening the angles from which the butterfly can be seen.
Making oneself as visible as possible isn't a great tactic from a military perspective. But Vukusic says that understanding the light-altering mechanism of blue morpho butterflies is the first step to creating a revolutionary type of camouflage.
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