Full metal jacket: the silver ant shimmers in the heat (Image: Norman Nan Shi and Nanfang Yu, Columbia Engineering)
Call it the ultimate sunshade. During the hottest part of the day, tiny hairs on the back of the Saharan silver ant repel the sun鈥檚 rays and also shed excess heat back toward the sky.
It was their metallic look that intrigued from Columbia University in New York. On desert sands they remind him of 鈥渁 droplet of mercury鈥�, he says.
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The ant鈥檚 adaption resembles cutting-edge, heat-resistant surfaces 鈥� and may inspire new approaches to such materials.
We know that Saharan silver ants (Cataglyphis bombycina) are extremely heat tolerant, and that they eke out a living in their formidable habitat. So specialised is their lifestyle that it even has its own name: thermophilic scavenging.
They scavenge the corpses of less-fortunate insects and arthropods. But they must be swift 鈥� the ants die if their body temperatures climbs above 53.6 掳C.
The silver ants leave their nest and forage for about 10 minutes when predatory ant lizards retire to the shade, usually under full midday sun, when sand temperatures reach some 70 掳C.
The ants have 10 minutes to find food before they fry (Image: Vincent Amouroux, Mona Lisa production/ Science Photo Lab)
The ants have a suite of adaptations to help them survive in the desert, including long legs and 鈥渉eat shock鈥� proteins. They also climb on rocks and dead vegetation above the hot sand for breaks in cooler air higher up.
Yu鈥檚 team has now found that the ant鈥檚 silvery appearance comes from a dense array of uniquely shaped triangular hairs, which also reflect lots of visible and near-infrared light 鈥� wavelengths at which the sun is hottest.
But at mid-infrared wavelengths, those same hairs allow excess heat to be re-emitted in a process called 鈥渂lack body radiation鈥� 鈥� effectively cooling the ants by radiating away heat.
Yu鈥檚 team鈥檚 models show that the structure of the micron-thick hairs gives them the heat shielding powers. The hairs are about the same size as the sun鈥檚 warming rays, which scatter or bounce off their triangular walls.
But they鈥檙e much smaller than mid-infrared wavelengths of light, which means they form a dull surface that can glow and emit light instead of reflecting it.
To confirm that the hairs were key, the team shaved some ant specimens and then exposed both shaved and hairy ants to a hot xenon lamp and a cold plate that simulated sun and sky.
The unique triangular hairs radiate heat away (Image: Norman Nan Shi and Nanfang Yu, Columbia Engineering)
They found that the ants with hair had body temperatures 5 to 10 degrees lower than those that had been shaved 鈥� a big difference in the scorching Sahara.
And the ants have another trick up their sleeve: they are hairy on their top and sides, but not underneath, where their hair would be detrimental as it would absorb the infrared radiation from the hot sand that it normally emits towards the cooler sky.
Many animals have evolved structures that interact with light, but the Saharan silver ant is special in the breadth of wavelengths it employs to stay cool.
鈥淭he combination of doing something in the visible and the mid-infrared is very unusual,鈥� says from the Stanford University in California.
Raman develops materials that reflect sunlight and re-emit heat just like the silver ants do 鈥� surfaces that could be put on rooftops to cut cooling bills, for example, or to make solar panels more efficient.
鈥淚t鈥檚 kind of remarkable and pretty cool 鈥� no pun intended 鈥� that there鈥檚 an analogue in nature to the way we鈥檙e thinking about these problems,鈥� Raman says.
Yu鈥檚 team now hopes to recreate the hairs synthetically, to see if the ants鈥� strategy can be applied to build self-cooling surfaces.
Journal reference: Science,
