Adhesion of dry and wet electrostatic capture silk of uloborid spider
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We demonstrate the impressive adhesive qualities of uloborid spider orb-web capture when dry, which are lost when the nano-filament threads are wetted. A force sensor with a 50 nN–1 mN 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 μm and densities ranging between 104 and 105 per mm3. Stress forces of between 1 and 5 μN/μm2 in the native, dry multifilament thread puffs were reduced to between 0.1 and 0.5 μN/μm2 in the wetted collapsed state, with strain displacements reducing from between 2 and 5 mm in the dry to 0.10–0.12 mm in the wetted states. We conclude that wetting cribellate threads reduce their van der Waals adhesion with implications on the thread’s adhesive strength under tension. This should be considered when discussing the evolutionary transitions of capture silks from the ancestral dry-state nano-filaments of the cribellate spider taxa to the wet-state glue-droplets of the ecribellate taxa.
KeywordsSpider Web Glue Electrostatic Evolution Prey capture
We all thank the Royal Society of London (International Exchange grant IE130506), the Paris group also thanks the Agence Nationale Reseaux (grant 09-JCJC-0022-01), La Ville de Paris (grant Programme Emergence) and the CNRS (grant PEPS PTI) while FV also thanks the US Air Force (AFOSR grant FA9550-12-1-0294) and the European Research Council (ERC grant SP2-GA-2008-233409). Last but not least, we thank the journal’s reviewers for improving comments. Data accessibility: All data and methods are reported within this paper and with the electronic supplementary material.
Mist is sent onto cribellate capture thread, revealing the uloborid puffs in the first instants, before collapsing them into non-sticky spindle-knots. This reduced significantly the adhesion properties of the capture thread, effectively destroying its primary biological function. (MOV 5475 kb)
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