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Militaries Study Animals for Cutting-Edge Camouflage

By James Owen in England
for National Geographic News
March 12, 2003
 
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.

"If you know how to manipulate the way light moves and reflects then you can make a surface brighter or darker," he said.

Other butterfly species are able to produce different types of iridescence.

"If nature evolved blue morpho butterflies to be bright and blue, all it has to do to that scale structure is tweak it slightly, alter the dimensions, and it produces a different color such as green," Vukusic said.

The challenge for scientists like Vukusic is to create a surface able to reflect different colors of the light spectrum, a surface able to mimic its surroundings, so providing a cloak of invisibility for troops and their weapons.

Vukusic believes moths could provide a similar template for nighttime camouflage.

Moths have evolved modifications in their wing scales that swallow up light so their wings appear black.

"Instead of multilayers, some types of moth wing have thousands of tiny, nipple-shaped structures arranged in a hexagonal array. If they are really small, half the wavelength of light, then their effect is to reduce reflection from the wing surface," Vukusic said.

The scientist also speculates about the possibility of being able to design a surface that is black at different wavelengths. So instead of being black visibly, it would be black at infrared, making it invisible to certain types of military night-vision equipment. "If we understand how nature does this, in theory it would be possible to change the dimensions of the structure to make it appropriate for infrared anti-reflection," said Vukusic.

Bio-camouflage System

Below the waves, kaleidoscopic cuttlefish match the blue morpho's electric display. They can rapidly alter their vivid coloring to blend into the background. This helps them escape predators and ambush their prey.

English-based scientists are developing a bio-camouflage system based on the color-generating abilities of cuttlefish. Applied as a gel, it could be used to hide tanks and other military equipment.

Alex Parfitt, from Bath University's Centre for Biomimetics and Natural Technologies, in England, said: "The cuttlefish is the fastest color-changing animal on the planet. But when we looked at it a little deeper the system was far simpler than we expected."

Just below the skin are organs called chromatophores. They consist of little elastic sacs filled with pigment. An attached muscle allows these to contract or expand, triggering an instant change of appearance. "You can think of it like controlling pixel size," Parfitt said.

But the cuttlefish holds just three colors in its chromatophores: brown, red, and orange. Although these can be stretched into other shades like beige, pink, and yellow, the animal has another trick up its sleeve when swimming in places that are mainly green or blue.

Contained deeper under the skin are white patches which include cells called leucophores. These reflect back the predominant light wavelength in the cuttlefish's immediate environment.

"So if a cuttlefish swims along under green seaweed, the green wavelength coming from it will hit the cuttlefish and be reflected back," Parfitt said. "It's like a sort of mirror system. Without even thinking about it the animal is able to camouflage itself really well."

Parfitt and his colleagues have now come up with a color-changing gel based on the cuttlefish's light-reflecting system. It could even replace the traditional green-and-brown camouflage splotches used on military equipment since the First World War.

In warfare, as in nature, you have to evolve to stay ahead of the game. So it's no wonder the scientists are turning to the natural world for inspiration.

As Peter Vukusic says, "it's all out there—nature has absolutely beaten us to every structure we think we've designed."
 

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