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First published online November 24, 2003
Journal of Experimental Biology 207, 67-74 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00716

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Biomechanics of ant adhesive pads: frictional forces are rate- and temperature-dependent

Walter Federle^1,*, Werner Baumgartner² and Bert Hölldobler¹

¹ Zoologie II, Biozentrum, Am Hubland, D-97074 Würzburg, Germany
² Institute of Anatomy and Cell Biology, University of Würzburg, Koellikerstrasse 6, D-97070 Würzburg, Germany

View larger version (35K): [in a new window]   Fig. 1. (A) Measurement of contact area of the extended arolium in O. smaragdina. The arrow shows the sliding direction. Scale bar, 100 µm. (B) Scaling of pad contact area (mean of two hind legs, µm2) with body mass (mg). A model II regression was performed.

View larger version (35K): [in a new window]   Fig. 2. (A) Video image of an O. smaragdina ant on the Plexiglas turntable rotating at 2470 revs min-1. Dotted arrow shows the sliding trajectory. Note the two hindlegs in contact. (B) Gradual slide of O. smaragdina ant on a smooth turntable at 20°C. (C) Relationship between friction force and velocity for the data shown in B; model II regression. (D) Plot of regression residuals.

View larger version (13K): [in a new window]   Fig. 3. Temperature dependence of static and dynamic friction in O. smaragdina. (A) Static shear stress. (B) Velocity-dependent increase of shear stress. Values are means ± S.D. of 13 ants at 15°C and 16 ants at 30°C (mean of 2 'slides' each).

View larger version (9K): [in a new window]   Fig. 4. Temperature dependence of perpendicular detachment forces in O. smaragdina. N=15 ants were tested at each temperature (maximum of three runs per ant). Central horizontal lines denote medians, boxes denote the inner two quartiles, and whiskers mark maxima and minima.

View larger version (6K): [in a new window]   Fig. 5. Simple 'wet adhesion' model of insect adhesive contact. (A) Liquid film of constant height between the pad and the surface forming a meniscus. (B) When the pad slides (arrow), the meniscus is deformed, resulting in different contact angles 1 and 2 at the leading and trailing edges of the pad.