Figure 2.

(a) Typically observed force–distance curves (during the retraction phase) for a seta with an array of four spatulae at its tip. Three different types of curve were observed: type 1, a pull-off force of approximately 10 nN suggesting contact of only one spatula; type 2, pull-off force of roughly 20 nN, corresponding to joint detachment of two spatulae; type 3, two pull-off force maxima, suggesting sequential detachment of two spatulae. The inset renders this curve in more detail. All curves (except inset) are the result of two measurements, which superimpose exactly in these plots. (b) Frequency histogram of all 260 measurements showing two strong peaks at 10.8±1.0 nN and 20.4±1.9 nN. A weak peak is seen at ∼30 nN. The peaks are attributed to the detachment of one, two (and three) spatulae (e) from the glass substrate.