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Adhesion measurements on the attachment devices of the jumping spider Evarcha arcuata

A. B. Kesel^*, A. Martin and T. Seidl

Department of Zoology, Technical Biology and Bionics, Saarland University, D-66041 Saarbrücken, Germany

View larger version (101K): [in a new window]   Fig. 1. (A) Lateral view of the tarsal adhesive apparatus of E. arcuata, showing both claws (Cl) and the scopula (Sc). (B) Ventral view of the scopula; the differentiation into single setae is clearly visible. The plotted oval is used to estimate the scopula area (here: 3.2x104 µm2; mean: 3.7x104 µm2).

View larger version (15K): [in a new window]   Fig. 4. Original registration of a force–distance curve recorded on a single setule. Points labelled in the diagram are as follows: (A) Probe not in contact with sample. (B) Contact between probe and sample is established. (C) The sample is indented by the probe with a defined force, F. (D) Turning point (F=maximum), retraction begins. (E) During retraction, the force between the probe and the sample decreases. (F) Due to adhesive forces, the probe remains in contact with the sample during retraction. (G) Contact abruptly breaks off (`pull-off' event); the registered force value during this sudden cantilever instability represents the adhesive force Fa [here: 23.3 nN; mean (± S.D.) for all measurements: 38.12±14.6 nN; N=45].

View larger version (106K): [in a new window]   Fig. 2. (A) Each seta is covered by numerous setules, which are tapered on the seta's dorsal side. (B) On the seta's ventral side, the setule density is noticeably higher. Here, setules are broadened towards their ends, forming a sail-like shape.

View larger version (98K): [in a new window]   Fig. 3. (A) The terminal setule broadening represents the contact point between the spider and the substrate. (B) A setule density of 1.5 setules µm-2 (mean setule density: 2.1±1.0 setules µm-2; N=48) as well as a mean setule area of 1x105 nm2 (±0.34x105 nm2; N=7) can be calculated from the above figure.