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Shell protects from heat: desert snail


Desert snail, Sphincterochila prophetarum / Jonathan Gro.. / LicenseCC-by-nc-sa - Attribution Non-commercial Share Alike

The shell of some desert snails helps them survive extreme heat using light reflectance and architecturally-derived, insulating layers of air.

"Thermobiosis is not limited to hydrothermal vent faunas, but also occurs in terrestrial species. For example, the desert snail Sphincterochila boisseri can survive in the desert at temperatures of up to 50 °C…" (Islam & Schulze-Makuch 2007:207)

How desert snails survive high temperatures: The surface of the shell is highly reflective, resulting in 95% reflectance within the near infrared, 90% in the visible spectrum (a). While the maximum air temperature might reach 43 °C (109 °F) , surface temperatures can reach 65 °C (149 °F). However, shading and the rough surface of the soil results in a temperature of 60 °C (140 °F) (d). During the heat of the day, the snail retreats into an upper whorl where the temperature is an even cooler 50 °C (122 °F) (b). Heat flows in the direction of lower temperature, result in heat flow through the shell, with resultant decrease higher in the shell (c). Copyright Biomimicry 3.8 Institute.

"It will be a surprise to many biologists that snails are found in large numbers on the dry, barren surfaces of certain hot deserts. The present study is concerned with one such snail, Sphincterochila boissieri, which occurs in the deserts of the Near East. Live specimens of this snail, withdrawn in the shell and dormant, can be found on the desert surface in mid-summer, fully exposed to sun and heat. The surface temperature of these deserts may reach 70 °C and more than a year may pass between rains

"The maximum air temperature, reached at noon, was 42.6 °C, and the maximum soil surface temperature in the sun, reached at 13.00, was 65.3 °C. Under the snail, in the space between the soil surface and the smooth shell, the maximum temperature was 60.1 °C, or 5.2 °C below the adjacent soil surface in the open sun. The lower temperature under the shell is expected, for the shell provides shade for that particular spot of the soil surface on which it sits. Inside the shell in the largest whorl, located in contact with the ground, the maximum temperature was 56.2 °C. In the second and third whorls the temperature was lower, reaching a maximum of 50.3 °C.

"It is important that the animal, when withdrawn, does not fill the shell and leaves most of the largest whorl filled with air
The snail, withdrawn to the upper parts of the shell, is significantly cooler

"Why does the snail not heat up to the same temperature as the soil surface? The answer lies in its high reflectivity in combination with the slow conduction of heat from the substrate. Within the visible part of the solar spectrum (which contains about one-half of the total incident solar radiant energy) the reflectance of these snails is about 90%. In the near infrared, up to 1350 nm, the reflectance is similar to that of magnesium oxide and is estimated to be 95%. In the total range of the solar spectrum, therefore, we can say that the snails reflect well over 90% of the incident radiant energy.

"…heat flow, however, is impeded by two important circumstances. Firstly, the snail shell is in direct contact with the rough soil surface only in a few spots, and a layer of still air separates much of its bottom surface from the ground, forming an insulatng [sic] air cushion. Next, and perhaps more important, the snail is withdrawn into the upper parts of the shell and the largest whorl is filled with air; this constitutes a further impediment to heat flow into the snail." (Schmidt-Nielsen et al. 1971:385, 388-9)
About the inspiring organism

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Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

Bioinspired products and application ideas

Application Ideas: Building design for hot, arid environments.

Industrial Sector(s) interested in this strategy: Architecture, building

Islam MR; Schulze-Makuch D. 2007. Adaptations to environmental extremes by multicellular organisms. International Journal of Astrobiology. 6(3): 199-215.
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Schmidt-Nielsen K; Taylor CR; Shkolnik A. 1971. Desert snails: problems of heat, water and food. Journal of Experimental Biology. 55: 385-398.
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It seems that the name of the organism in the "summary" section has been spelt incorrectly - my research keeps on seeing the following spelling: Sphincterochila boissiEri
Has any further research been done on this? Any building design proposal in hot climate?
over 4 years ago
Unfortunately, we don't have time to do additional research for you on this. You should try to get the papers cited and check the researchers' websites for more information.
over 4 years ago
hi my name is mustafa salah , i want to ask about the shape of shell if it affects by any way in control the temperature because i want to try this strategy for building facades to maintaine temperature for buildings in hot,arid climate.
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