Journal
NATURWISSENSCHAFTEN
Volume 96, Issue 8, Pages 933-941Publisher
SPRINGER
DOI: 10.1007/s00114-009-0551-8
Keywords
Clunio imago; Submersion in water; Microtrichia; Air layer on cuticle; Air bubble formation; Surf tolerance
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Funding
- Nees-Institut fur Biodiversit t der Pflanzen, University of Bonn
- Zoological Institute, University of Cologne
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The intertidal midge Clunio, which reproduces on exposed rocky seashores, becomes enclosed in an irregularly shaped air bubble during short submersion by incoming waves. This water-repellent property of Clunio's cuticle is caused by a complete cover of hydrophobic microtrichia offering an effective surf tolerance. These microtrichia not only trap a thin air layer above the cuticle but also maintain a larger air bubble between the insect's ventral side and legs. The effectiveness of the water repellence was quantitatively characterised on the basis of a known model (Crisp and Thorpe, Discuss Faraday Soc 3:210-220, 1948). The parameters of the model are the contact angle theta (> 90A degrees) at the contact line of air/water/microtrichia and the distance between individual microtrichia and their radius. When the microtrichia are 1.1 mu m apart and have a radius of 0.1 mu m and an estimated contact angle theta of 140A degrees, the air layer is stable against hydrostatic pressures of up to 3 m water column. As shown by a modified version of the model, considerably larger air bubbles can be trapped by the microtrichia cover of the legs up to distances of 0.5 mm from the body. The widely spaced (about 8 mu m apart) and longer setae of Clunio are not involved in the formation of air layers and air bubble.
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