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Silver Ants' Triangular Hair Protects Them From Extreme Heat

1006 Silver Ants' Triangular Hair Protects Them From Extreme Heat
The ants are found right across northern Africa, scavenging in the Sahara. Willot et al. 2016

Despite looking like little space men exploring a distant planet, Saharan silver ants are very much Earthbound. But not many critters can do what these insects do, as they spend their days searching for prey in temperatures that would kill most other animals. New research, published in PLOS One, has revealed one of the aspects that allow the ants to manage this, and it’s all down to the structure of the tiny hairs on their silvery pelt.

Living in the deserts of northern Africa, the ants (Cataglyphis bombycina) have developed cunning behavior to not only avoid their main predators, but to also ensure a plentiful supply of prey to feed on. For most of the day, they seek refuge within their nests buried in the sand, waiting for the temperature to climb as the Sun reaches its highest point. 


When the air temperature hits around 50°C (122°F) and the sand temperature reaches as high as 70°C (158°F), the ants launch their foraging parties in a frenzy of activity. At this temperature, most other animals die, including an abundant supply of other insects caught out in the midday sun, which the ants can then simply walk up to and take. But even the silver ants have their limitations, and are only able to cope with roughly 10 minutes of intense heat before their bodies reach a maximum of 53.6°C (128.5°F) and they have to return to their nests or else fall victim to the Sun. So specialized is this form of behavior, that it even has its own term: thermal scavenging.  

The silver ants' hair, as seen under a scanning electron microscope, with its triangular shape and the ridges on the surface that help reflect light. Willot et al. 2016

The ants have developed a whole suite of both physical and behavioral adaptations to survive in such an extreme environment. Their legs are proportionally longer than other ant species with similar body shapes in order to keep them above the burning sand, and when out foraging in the intense heat, they take regular stops – often on rocks or wood – and spin around to get a better sense of direction. But it's the feature that gives them their name, the silver hair on their backs, that is the most intriguing.

Earlier studies have shown that the hair's structure, which is triangular when looked at in cross-section, helps to reflect visible and infrared light in a way not too dissimilar to a mirror. This not only has the effect of keeping the insects cool, but also gives them their silvery sheen. Now, new research has found that the triangular hairs actually cause total internal reflection of light, making them almost 10 times more reflective than control ants, which the researchers anesthetized and then shaved.


“The ability to reflect solar radiation by means of total internal reflection is a novel adaptive mechanism in desert animals, which gives an efficient thermal protection against the intense solar radiation,” explains Serge Aron, co-author of the latest study, in a statement. “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.”

They found that the triangular hairs were able to keep the ants up to 2°C (3.2°F) cooler than when they were shaved, giving them a crucial edge within their toasty timeslot in the desert to not only evade their predators, but collect the dead too. 


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