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| Africa : NASA picture |
In the scorching sands of Saharan desert why doesn't the Cataglyphis bombycina get roasted like a peanut? These tiny creatures go by the common name Saharan silver ants. As the name suggests these ants are native to the hot Saharan desert and have a silvery glaze. Saharan desert, stretching across northern Africa, skirted by the Atlantic ocean on the west, the Red sea on the East and the Mediterranean sea on the north is not at all a friendly terrain to pitch a hut. Here ambient temperature can soar to 54 degree Celsius and sand temperature could be as high as 80 deg.C. Most of the desert creatures are crepuscular, that is they come out either during dawn or dusk. But alas poor silver ants can't afford to forage during twilight hours because of predators. So to avoid being caught and made into a meal these ants forage when the predators are having their siesta; that is at noon, when the Sun is at the peak. Professor Rüdiger Wehner and his team at the University of Zurich have been fascinated by these ants for quite some time. They have been looking into the the neurophysiology and behavioral pattern of these ants with special emphasis on vision as a strong cognitive capability. In the 17th July issue of Science magazine Professor Wehner and his team provide answers to the critical question : How do these tiny insects keep their cool ? They could very well have asked why are these ants so shiny.
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| Community dinner: courtesy wikipedia |
There are several interesting things about C. bombycina. Their unusually long legs lift the body 4-5 mm above the ground. Such high ground clearance means, the ellipsoidal body, not more than a cm in size is considerably cooler than the scorching sand below. Long legs also mean speed. These ants can run fast and far off in search of food. This has been captured in a excellent video. If it goes far off, how does it get back to its burrough? It seems smell and sights of the starting point stored in their brain guide it safely back to home ground.
But how does it ward off the heat? Prof. Wehner and his team provide the answers in their paper. The silvery sheen is not just a beauty enhancer. It is indeed a very effective thermoregulation feature. The shine is due to a thick mop of fine silvery hair covering the dorsal and lateral sides of the body. The morphology of the hair has been studied by electron microscopy . triangular cross section and taper off to the tip. These hairs perform multiple tasks, strictly in accordance with the Laws of Physics. The triangular surfaces facilitate total internal reflection and thus enhance reflectivity in the visible and near infra-red regions of the solar spectrum and in the mid infrared region the hair layer demonstrates very high emissivity. In other words exactly opposite of what solar panels do. For excellent performance a typical solar heating panel must have zero reflectivity ( very high absorprtivity) at low wavelengths to capture maximum heat and very low emissivity at high wavelengths to minimize radiation heat loss.
Desert creatures have evolved several adaptive strategies to encounter the twin threats of high heat and lack of water. For example certain types of desert rodents generate water as a metabolic by-product. At the cellular level, heat shock proteins see to it that heat and dryness don't impair the structure and hence the function of biological molecules.
But how does it ward off the heat? Prof. Wehner and his team provide the answers in their paper. The silvery sheen is not just a beauty enhancer. It is indeed a very effective thermoregulation feature. The shine is due to a thick mop of fine silvery hair covering the dorsal and lateral sides of the body. The morphology of the hair has been studied by electron microscopy . triangular cross section and taper off to the tip. These hairs perform multiple tasks, strictly in accordance with the Laws of Physics. The triangular surfaces facilitate total internal reflection and thus enhance reflectivity in the visible and near infra-red regions of the solar spectrum and in the mid infrared region the hair layer demonstrates very high emissivity. In other words exactly opposite of what solar panels do. For excellent performance a typical solar heating panel must have zero reflectivity ( very high absorprtivity) at low wavelengths to capture maximum heat and very low emissivity at high wavelengths to minimize radiation heat loss.
Desert creatures have evolved several adaptive strategies to encounter the twin threats of high heat and lack of water. For example certain types of desert rodents generate water as a metabolic by-product. At the cellular level, heat shock proteins see to it that heat and dryness don't impair the structure and hence the function of biological molecules.
References:
1. Keeping cool: Enhanced optical reflection and radiative heat dissipation in Saharan silver ants. Nan Shi et al Science 17 July 2015 vo. 349 pp 298-301
2. Smells like home: Desert ants cataglyphis fortis use olefactory landmarks to pinpoint the nests
3. The amazing Cataglyphis ant
4. Passive radiative cooling below ambient air temperature under direct sunlight: Raman et al Nature 515.pp540-44(2014)
5.Heat Shock protein synthesis and thermotolerance in cataglyphis, an ant from Saharan desert -Gehring and Wehner : PNAS 92, 2994- 2998 (19995)
3. The amazing Cataglyphis ant
4. Passive radiative cooling below ambient air temperature under direct sunlight: Raman et al Nature 515.pp540-44(2014)
5.Heat Shock protein synthesis and thermotolerance in cataglyphis, an ant from Saharan desert -Gehring and Wehner : PNAS 92, 2994- 2998 (19995)
