Saharan silver ants can control electromagnetic waves over extremely broad spectrum range

June 18, 2015
Left: Sahara silver ants forage in the midday sun and look like droplets of mercury rolling on the desert surface. Right: The silvery appearance is created by a dense array of uniquely shaped hairs. Credit: Norman Nan Shi and Nanfang Yu, Columbia Engineering

Nanfang Yu, assistant professor of applied physics at Columbia Engineering, and colleagues from the University of Zürich and the University of Washington, have discovered two key strategies that enable Saharan silver ants to stay cool in one of the hottest terrestrial environments on Earth. Yu's team is the first to demonstrate that the ants use a coat of uniquely shaped hairs to control electromagnetic waves over an extremely broad range from the solar spectrum (visible and near-infrared) to the thermal radiation spectrum (mid-infrared), and that different physical mechanisms are used in different spectral bands to realize the same biological function of reducing body temperature. Their research, "Saharan silver ants keep cool by combining enhanced optical reflection and radiative heat dissipation," is published June 18 in Science magazine.

"This is a telling example of how evolution has triggered the adaptation of physical attributes to accomplish a physiological task and ensure survival, in this case to prevent Sahara silver ants from getting overheated," Yu says. "While there have been many studies of the physical optics of living systems in the ultraviolet and visible range of the spectrum, our understanding of the role of infrared light in their lives is much less advanced. Our study shows that light invisible to the human eye does not necessarily mean that it does not play a crucial role for living organisms."

The project was initially triggered by wondering whether the ants' conspicuous silvery coat was important in keeping them cool in blistering heat. Yu's team found that the answer to this question was much broader once they realized the important role of infrared light. Their discovery that that there is a biological solution to a thermoregulatory problem could lead to the development of novel flat optical components that exhibit optimal cooling properties.

"Such biologically inspired cooling surfaces will have high reflectivity in the solar spectrum and high radiative efficiency in the thermal radiation spectrum," Yu explains. "So this may generate useful applications such as a cooling surface for vehicles, buildings, instruments, and even clothing."

The hairs grow parallel to the skin and are separated from the skin by a small air gap. The hairs have triangular cross-sections with two corrugated top facets and a flat bottom facet facing the ant's body. Credit: Norman Nan Shi and Nanfang Yu, Columbia Engineering

Saharan silver ants (Cataglyphis bombycina) forage in the Saharan Desert in the full midday sun when surface temperatures reach up to 70°C (158°F), and they must keep their body temperature below their critical thermal maximum of 53.6°C (128.48°F) most of the time. In their wide-ranging foraging journeys, the ants search for corpses of insects and other arthropods that have succumbed to the thermally harsh desert conditions, which they are able to endure more successfully. Being most active during the hottest moment of the day also allows these ants to avoid predatory desert lizards. Researchers have long wondered how these tiny insects (about 10 mm, or 3/8" long) can survive under such thermally extreme and stressful conditions.

Using electron microscopy and ion beam milling, Yu's group discovered that the ants are covered on the top and sides of their bodies with a coating of uniquely shaped hairs with triangular cross-sections that keep them cool in two ways. These hairs are highly reflective under the visible and near-infrared light, i.e., in the region of maximal solar radiation (the ants run at a speed of up to 0.7 meters per second and look like droplets of mercury on the desert surface). The hairs are also highly emissive in the mid-infrared portion of the electromagnetic spectrum, where they serve as an antireflection layer that enhances the ants' ability to offload excess heat via thermal radiation, which is emitted from the hot body of the ants to the cold sky. This passive cooling effect works under the full sun whenever the insects are exposed to the clear sky.

"To appreciate the effect of thermal radiation, think of the chilly feeling when you get out of bed in the morning," says Yu. "Half of the energy loss at that moment is due to since your skin temperature is temporarily much higher than that of the surrounding environment."

The researchers found that the enhanced reflectivity in the and enhanced thermal radiative efficiency have comparable contributions to reducing the body temperature of silver ants by 5 to 10 degrees compared to if the ants were without the hair cover. "The fact that these silver ants can manipulate electromagnetic waves over such a broad range of spectrum shows us just how complex the function of these seemingly simple biological organs of an insect can be," observes Norman Nan Shi, lead author of the study and PhD student who works with Yu at Columbia Engineering.

The hair coating helps reduce body temperature substantially (via enhanced reflection of solar radiation and enhanced thermal radiation). Credit: Norman Nan Shi and Nanfang Yu, Columbia Engineering

Yu and Shi collaborated on the project with Rüdiger Wehner, professor at the Brain Research Institute, University of Zürich, Switzerland, and Gary Bernard, electrical engineering professor at the University of Washington, Seattle, who are renowned experts in the study of insect physiology and ecology. The Columbia Engineering team designed and conducted all experimental work, including optical and infrared microscopy and spectroscopy experiments, thermodynamic experiments, and computer simulation and modeling. They are currently working on adapting the engineering lessons learned from the study of Saharan silver ants to create flat optical components, or "metasurfaces," that consist of a planar array of nanophotonic elements and provide designer optical and thermal radiative properties.

Yu and his team plan next to extend their research to other animals and organisms living in extreme environments, trying to learn the strategies these creatures have developed to cope with harsh environmental conditions.

"Animals have evolved diverse strategies to perceive and utilize electromagnetic waves: deep sea fish have eyes that enable them to maneuver and prey in dark waters, butterflies create colors from nanostructures in their wings, honey bees can see and respond to ultraviolet signals, and fireflies use flash communication systems," Yu adds. "Organs evolved for perceiving or controlling often surpass analogous man-made devices in both sophistication and efficiency. Understanding and harnessing natural design concepts deepens our knowledge of complex biological systems and inspires ideas for creating novel technologies."

Explore further: Underground ants can't take the heat: Climage change models may not look closely enough at microhabitats

More information: Keeping cool: Enhanced optical reflection and heat dissipation in silver ants, … 1126/science.aab3564

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not rated yet Jun 18, 2015
They run at 0.7 meters per second? Can that be right? I cant imagine an ant covering almost a meter every second. Thats 2.5km/hr
5 / 5 (2) Jun 18, 2015
This kind of surface structure could possibly be placed on made made items such as cars or buildings to keep them cool.
1.3 / 5 (3) Jun 18, 2015
Here's how I've evolved in the drinking of hot tea:

1.8 / 5 (5) Jun 19, 2015
So how did the millions of intermediate Saharan Silver fore-ant progenitors, say starting from its single-celled progenitor until the penultimate Saharan Silver ant progenitor, handle the heat during that "evolutionary" progression to the current heat-proof Saharan Silver ant? All of these millions of intermediate forms must have been heat-proof also, somehow.
Jun 19, 2015
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5 / 5 (5) Jun 19, 2015

[ Zero science involved.

Every time I think you couldn't say more outrageously false you manage to do just that.

Why is a creationist idiot commenting on a science site?
1 / 5 (1) Jun 19, 2015
This kind of surface structure could possibly be placed on made made items such as cars or buildings to keep them cool.

And if Jeb wins the election that type of buildings should be called Bush housing.
5 / 5 (7) Jun 19, 2015
All of these millions of intermediate forms must have been heat-proof also

Why would you think that? And why would you think that all the progenitors all the way back lived in that same spot?

It goes like this. An ur-ant colony lives somewhere (we could go back to the first cell, but lets start with some ur-ant. The argument that will follow can readily be used iteratively for the ur-ant back to the first cell)

So one queen of these ur-ants has a mutation that allows a tiny bit of heat resistance (say, a discoloration that is more reflective than that of the other ur-ants). This allows that queen to have her nest in sliiiightly hotter areas than others - which means they have no competition for food sources there. Thousands/millions of years later another mutation is added by one of its distant offspring queens that gives even better heat resistance...allowing THAT queen to move into even hotter areas. Rinse. Repeat.
Until you end up with the Saharan silver ant.
1 / 5 (3) Jun 19, 2015
Brilliant example of how science progresses by going beyond the arbitrary bounds of human "sense certainty." Contrary to the faulty logic of reductionists like Hume.
not rated yet Jun 19, 2015
Brilliant example of how science progresses by going beyond the arbitrary bounds of human "sense certainty." Contrary to the faulty logic of reductionists like Hume.

Nothing about this goes beyond the bounds of human sense certainty, it was all verified with tools that allowed them to apprehend things with their senses. Hume was an anti rationalist who said that causality could never be justified by rationality.
5 / 5 (5) Jun 20, 2015
Totally wrong logic!...your beliefs are built upon the huge fantasy. Zero science involved.
Says the Young Earth Creationist.
The expression of one's meaning by using language that normally signifies the opposite, typically for humorous or emphatic effect.
un·in·ten·tion·al i·ro·ny
/əninˈten(t)SH(ə)n(ə)l/ /ˈīrənē/
Religious fundamentalists accusing science of fallacious logic.
5 / 5 (4) Jun 20, 2015
They run at 0.7 meters per second? Can that be right? I [can't] imagine an ant covering almost a meter every second. Thats 2.5km/hr
Apparently so, as remarkable as it sounds. Here are two quotes from a NYT article on the same species:
In its movements across the burning desert floor, the silver ant tries to touch the ground as little as possible. Like a beachgoer who has forgotten her flip-flops, the ant alternately sprints and hips and hops, sometimes running with two of its six legs held up in the air as it navigates the too-hot sand.
"These ants simply do not walk," Dr. Wehner said. "They sprint." The ants can run a distance that corresponds to 100 of their body lengths per second, an ability that no other animal is known to match. During these spectacular sprints, the ants even hold their breath to conserve every drop of precious body moisture. [end of quote]
5 / 5 (3) Jun 20, 2015
[ctd] That said, the body length of some of these ants are only 1mm, so the 100 body length metric would give us a speed of 0.1 m/s, but the larger the body length grows, the faster it goes.
Even more amazingly, they can dash a zigzag pattern across the desert floor for up to a quarter hour, looking for dead insects, while taking sun sightings every few seconds, and from this are able to calculate the exact direction for a beeline run straight back to the next without backtracking. Even at 0.1 m/s that's a 90 meter trek, up to over 600 meters of random course changes at 0.7 m/s, while retaining the ability to return straight to the next w/o a chemical trail. I wouldn't have thought that possible, given the diminutive size of their tiny brains, but the observations say otherwise.
I remember Douglas Hofstadter talking quite a bit about ant messaging in GEB. I think he may have considerably underestimated their cognitive capacity, but that was written, what, 40 years ago?
5 / 5 (3) Jun 21, 2015
@adam_russell_9615: Actually, that speed is correct! They can only be out for a few minutes before hiding again and minimize touching the ground (as stated by @PhotonX above). Search "Sahara silver ant" on YouTube; the video looks sped-up even though it isn't. Cool! (pun intended)
not rated yet Jun 23, 2015
This ant has six legs but only use 4 legs in order to keep cool. These legs are very long, to keep the ants away from the heat of the ground. The thermal conductivity of air is very low compared to solid. I think the trapped air among the microsized hair that cover the surface of the ant, has to strong effect on the cooling process.
not rated yet Jun 23, 2015
The ant can keep cool by rejecting heat using three mechanism. Conduction , there comes the air with very low thermal conductivity, convection there comes the speed of the ant as it forged in the desert with the air and the highly reflective hair that covers the ant, and radiation.

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