Relationship between peak normal force and corresponding shear force along the (projected) axis of the leg for individual steps.

<p>Filled circles denote steps in which the arolium made visible surface contact, whereas steps with detached arolium are marked with open circles. Lines show standardised major axis regressions on both types of steps. In most steps where the adhesive pad made contact, the legs were pulling, whereas steps without visible arolium contact occurred mostly when legs pushed. The drawings illustrate the direction of the normal forces (<i>F</i>_<i>N</i>) and shear forces (<i>F</i>_<i>S</i>) and the presence or absence of adhesive pad contact (black or white filling of the pad).</p

Single-leg vertical forces in weaver ants climbing on a vertical glass surface, as a function of leg orientation.

<p>Leg orientation is given as an angle ranging from -90° (pointing downward; <i>N</i>_<i>front</i> = 3, <i>N</i>_{<i>middle</i>} = 8, <i>N</i>_<i>hind</i> = 18) to 0° (horizontal) to +90° (pointing upward; <i>N</i>_<i>front</i> = 9, <i>N</i>_{<i>middle</i>} = 10, <i>N</i>_<i>hind</i> = 8). For all legs with negative angles, the foot position was below the CoM, and positive angles corresponded to foot positions above the CoM.</p

Reflected-light microscopy images of the tarsal hairs in contact with the smooth surface.

<p>(A) side contact of the hairs (B) tiny droplets left on the surface after pull-off.</p

Typical friction force trace from tarsal hair fields against a smooth and rough surface.

<p>(A) SEM image showing the tarsal hairs of the 3^rd and 4^th tarsomeres (the part in contact with the surface is outlined with a dashed line). (B) Contact area of the hairs in pulling orientation using coaxial illumination on a stereo-microscope. (C) Hairs at the point of buckling. (D) Hairs re-orientated under pushing shear forces. (E) Force trace of tarsal hairs under different preloads and shearing directions on smooth and rough surfaces. Images in sub-figures (B-D) were taken at the points marked with squares in the raw trace curve. Circles mark characteristic ‘kinks’ in the force curve indicating the buckling of the hairs. Darker shaded regions indicate the time period during which the motorised stage moved the sample in the pushing direction.</p

EndleinFederle_Data_PONE-D-15-22788

Raw data for all figures presented in the manuscript

Adhesive forces of tarsal hairs on a smooth and rough surface (1 μm asperity size) after pushing slides under different normal loads (30, 60 and 100 μN).

<p>Adhesive forces of tarsal hairs on a smooth and rough surface (1 μm asperity size) after pushing slides under different normal loads (30, 60 and 100 μN).</p

Morphology of tarsal hairs in <i>O. smaragdina</i> ants and generated friction forces.

<p>(A) Morphology of hairs on the underside of the tarsus. Ta4 & Ta5: 4^th & 5^th tarsomere, respectively; Cl: Claws; Ar: Arolium; (B) Friction forces of tarsal hairs on a smooth and a rough substrate. Slides were performed in the pulling and pushing direction with a constant normal load of 30, 60 and 100 μN. The dashed line indicates the ants’ body weight (82 μN).</p

Friction forces of tarsal hairs in the pushing direction.

<p>(A) on a smooth and (B) on a rough surface for varying normal preloads (30, 60 and 100 μN). The dashed lines show the results of a linear regression on the median for each normal force level.</p

Tarsomere angle of freely walking weaver ants.

<p>(A) Level walking. Here, the ants stood mainly on their 3^rd and 4^th tarsomeres and held the 5^th tarsomeres away from the substrate (5^th tarsomere angle <0°; see photo). (B) Inverted climbing. Here, the 5^th tarsomere angle of was mostly positive, allowing the adhesive pad (arolium) to make contact (see also photo).</p

Set-up for ground reaction force recordings.

<p>(A) Weaver ants climbing on a vertical surface stepped onto a small, transparent glass plate attached to a sensitive force transducer. (B) Forces in the normal (Z) and vertical (X) directions, and contact area of the arolium for the step of a front leg above the CoM.</p