Evolution of adhesive mechanisms in cribellar spider prey capture thread: evidence for van der Waals and hygroscopic forces

Abstract

Sticky prey capture threads are produced by many members of the spider infraorder Araneomorphae. Cribellar threads are plesiomorphic for this clade, and viscous threads are apomorphic. The outer surface of cribellar thread is formed of thousands of fine, looped fibrils. Basal araneomorphs produce non‐noded cribellar fibrils, whereas more derived members produce noded fibrils. Cribellar fibrils snag and hold rough surfaces, but other forces are required to explain their adherence to smooth surfaces. Threads of Hypochilus pococki (Hypochilidae) formed of non‐noded fibrils held to a smooth plastic surface with the same force under low and high humidities. In contrast, threads of Hyptiotes cavatus and Uloborus glomosus (Uloboridae) formed of noded fibrils held with greater force to the same surface at intermediate and high humidities. This supports the hypothesis that van der Waals forces allow non‐noded cribellar fibrils to adhere to smooth surfaces, whereas noded fibrils, owing to the hydrophilic properties of their nodes, add hygroscopic forces at intermediate and high humidities. Thus, there appear to have been two major events in the evolution of adhesive mechanisms in spider prey capture thread: the addition of hydrophilic nodes to the fibrils of cribellar threads and the replacement of cribellar fibrils by viscous material and glycoprotein glue. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 77, 1–8.

van der Waals and hygroscopic forces of adhesion generated by spider capture threads

“…Thus, we believe that there is maximum contact between cribellar fibrils and this surface. At a relative humidity (RH) of around 50%, noded cribellar thread sticks to this surface with a force comparable to that with which it holds fleshfly wings (Hawthorn and Opell, 2002). Thus, measured forces are in the range of those registered by a representative insect surface.…”

“…In a recent study (Hawthorn and Opell, 2002), we demonstrated that, when tested with a smooth surface, cribellar threads formed of non-noded fibrils registered the same stickiness under low and high humidity. By contrast, threads formed of noded fibrils registered greater stickiness under high humidity.…”

Unraveling the mechanical properties of composite silk threads spun by cribellate orb-weaving spiders

“…Instead of aqueous glue, the axial fibers of cribellate capture silk are surrounded by puffs of tiny cribellar fibrils that can be as thin as 10·nm in diameter (Peters, 1984;Peters, 1992). Although cribellar fibrils are dry, they achieve stickiness through a combination of van der Waals and hygroscopic forces (Hawthorn and Opell, 2002;Hawthorn and Opell, 2003) that allows cribellar fibrils to adhere to even very smooth surfaces (Opell, 1994a).…”

Physical characterization of functionalized spider silk: electronic and sensing properties

“…The key to the structure of the spider protein repeating sequences (fibroins) is the combination of crystal-forming blocks (β-sheet crystals) and amorphous (sometimes helical) network chains that are part of the amino acid sequence motifs [1][2][3]. For instance, the percentages of alanine, glycine and proline affect the degree of crystallinity, helicity (amorphous structure) [4,5], elasticity [6,7], hygroscopicity and adhesiveness [8].…”