Adhesion of dry and wet cribellate capture silk

Abstract

We demonstrate the impressive adhesive qualities of Uloborid spider orbweb capture when dry, which are lost when the nano-filament threads are wetted. A force sensor with a 50 nN-1mN detection sensitively allowed us to measure quantitatively the stress-strain characteristics of native silk threads in both the original dry state and after wetting by controlled application of water mist with droplet sizes ranging between 3 and 5 m and densities ranging between 104 and 105 per mm3. Stress forces of between 1 and 5 N/m2 in the native, dry multifilament thread puffs were reduced to between 0.1 and 0.5 N/m2 in the wetted collapsed state, with strain displacements reducing from between 2 and 5 mm in the dry to 0.10-0.12mm in the wetted states. We conclude that wetting cribellate threads reduce their van der Waals adhesion with implications on the threads adhesive strength under tension. This should be considered when discussing the evolutionary transitions of capture silks from the ancestral dry-state nanofilaments of the cribellate spider taxa to the wet-state glue droplets of the ecribellate taxa.