Desert Ants’ Shiny Silver Hair Keeps Them Cool

P. Landmann, Willott, et al. in PLOS ONE
P. Landmann, Willott, et al. in PLOS ONE / P. Landmann, Willott, et al. in PLOS ONE

Silver hair is very cool right now, perhaps nowhere more so than in the desert habitats of silver ants. Researchers say the ants actually deflect heat with the super shiny silver hairs that cover their bodies. The report was published this week in the journal PLOS ONE. 

Your average ant is pretty shiny to begin with, but the rear ends of silver ants (Cataglyphis bombycina) gleam like polished chrome. But they’re more famous for another reason: their ability to withstand ludicrous levels of heat. The ants make their homes in the Sahara and Sinai deserts, where daytime temperatures can reach 122°F. Other desert animals will retreat to cool caves or burrows to wait out the worst of the midday heat, but not the silver ants. As everyone else is bunkering down, workers emerge from the nest and set out to scavenge the bodies of animals that couldn’t stand the heat. 

It’s a pretty terrific strategy, the researchers note in their paper: “By restricting foraging activity to the hottest period of the day, the ants minimize the chances of encountering their most frequent predator—a lizard that ceases all activities when the temperature becomes unbearable.” For a little while every day, the desert becomes an all-you-can-eat carrion buffet.

Scientists suspected that the ants’ impressive lacquer and their heat resistance were related. A study published last year showed that tiny, triangular hairs all over the ants’ bodies were responsible for the shine, and that those hairs prevented sunlight and heat from ever reaching the insects’ insides. Exactly how the hairs were doing it remained unclear. 

So a new team of researchers took a closer look. They traveled to an ant colony in the sand dunes of Morocco and scooped up workers, then brought them back to the lab. The scientists left half of the ants shiny and hairy, but the other half were given a shave with teeny tiny razors. We are not making this up.

All of the ants were euthanized and their parts examined under three different kinds of microscopes (scanning electron, transmission electron, and optical). Some of the ants’ bodies were implanted with little rectal thermometers and subjected to high heat from a sunlight simulator.

SEM and TEM images of ant hair. Image credit: Willot et al.

The researchers found that the triangular shape of the ants’ hair actually created a prism effect, bouncing the light inside each hair in a process called total internal reflection (TIR). The surface of the hair was jagged, which increased the reflection even further. At certain angles, a single hair was able to reflect almost 100 percent of the light aimed at it, making it essentially a long, thin silver mirror. The bodies of hairy ants reflected as much as 10 times more light than those of the ants who had been shaved. Consequently, hairy ants’ bodies were incredibly resistant to heat. In sunlight, they stayed up to 35°F cooler than their bald counterparts. 

Amount of reflectance by hairy and shaved ants. Image Credit: Willot et al.

The silver ants are not the first organisms to use TIR, but they are the first in the desert.

“The ability to reflect solar radiation by mean of total internal reflection is a novel adaptive mechanism in desert animals,” co-author Serge Aron said in a press statement, “which gives an efficient thermal protection against the intense solar radiation. To the best of our knowledge, this is also the first time that total internal reflection is shown to determine the color of an organism."