Riparian spiders make pyriform silk attachment discs that stick better when wet

Abstract:Adhesion in wet conditions presents significant challenges due to the disruptive effects of water on interfacial bonding, spreading and curing. Many organisms have evolved adhesives that adhere strongly in damp or submerged environments. However, the pyriform silk AQ5 attachment discs of the western black widow spider lose ∼8 times their adhesive strength when wet. Here, we tested the hypothesis that riparian species of spiders have evolved attachment discs that are resistant to the adverse effects of water on adhesion. We compared AQ6 adhesion of attachment discs from three terrestrial spiders from relatively dry habitats with those of three riparian spider species when discs were loaded under both dry and wet conditions. Failure modes shifted from dragline breakage in dry conditions to adhesive failure in wet conditions across all species, highlighting the impact of water on interfacial bonding. However, riparian species’ attachment discs maintained adhesive force when wet while terrestrial species experienced ∼50% reduction in peak force and work of adhesion in wet conditions. These findings suggest that riparian spider silks have evolved specializations that maintain adhesive performance of pyriform attachment discs in wet environments, offering insights into bioinspired design for water-resistant adhesives.Description of the data:This is the final dataset used for the statistical analysis. It excludes samples that were damaged or incomplete. It summarizes the reported Peak Force and Work for each sample tested from the tensile tests.Glass microscope slides were cleaned using 90% ethanol, rinsed thoroughly with deionized (DI) water, and then dried. This standardized the potential influence of varying ion concentrations and pH of water on molecular structure of pyriform silk proteins. Attachment discs were applied to the clean slides in a dry environment (~40-60% relative humidity). Each slide was first fitted with a cardboard “C”-shaped cutout, creating a 10 mm gap between the glass surface and the upper edge of the cutout, which was folded perpendicular to the slide. This design enabled the dragline to be secured to the top of the “C” after the attachment discs were placed on the glass. All spiders, except W. clara, were restrained using a nylon loop “lasso” made from fishing line passed through a syringe, which allowed the loop to tighten around the spider’s pedicel. This setup permitted the spiders to walk semi-naturally while still controlling the placement location of the attachment discs. The spider was first positioned on the glass slide with its spinnerets directly under the upper edge of the cutout and gently guided until an attachment disc was spun. The spider was then gently lifted towards the upper edge of the cutout, minimizing pull on the dragline. The dragline was then attached to the upper edge of the cutout using double sided tape, and the trailing end was cut to separate the spider from the sample. A small square of cardboard was placed on the tape to secure the dragline. Wendilgarda clara were significantly smaller than other species so the “lasso” could not be used. Instead, W. clara spiders were placed on the glass slide and allowed to walk freely across the surface until an attachment disc was placed. The slide was then flipped over, causing the spider to hang from the dragline and making it possible to install the “C” cutout and secure the dragline in the frame. These discs were observed closely before testing to ensure they were not visibly damaged from the weight of the spider hanging from the dragline before the frame was placed and the dragline was secured.The sample was then placed in a Nano Bionix tensile tester (MTS System Corp., Oak Ridge, TN, USA), with the lower grip holding the slide and the upper grip holding the cardboard cutout where the dragline was secured. The cardboard “C” was cut near its midpoint, separating the dragline end from the attachment disc end, and the sample was adjusted in the X-Y plane to ensure that the dragline pulled the attachment disc perpendicular to the slide surface, controlling for the effect of different pulling angles. The dragline was pulled at a rate of 0.01 mm/sec until complete failure was observed (Blackledge et al., 2005; Swanson et al., 2006). The *W. clara *samples were pulled at 0.015 mm/sec due to a difference in the Nano Bionix program settings. The force, time, and displacement were recorded, and work was calculated. Dry loading condition tests were performed at room humidity (~40-60% RH). For the wet loading condition tests, the spider placed an attachment disc on a dry slide, which was then mounted in the Nano Bionix tensile tester, and sprayed with DI water from an atomizer until the disc was visibly covered by water droplets.Variables:Species: The abbreviated species name (DT is Dolomedes triton, TE is Tetragnatha elongata, WC is Wendilgarda clara, LC is Larinioides cornutus, LH is Latrodectus hesperus, AP is Agelenopsis pennsylvanica).Condition: The testing condition, either Dry or Wet.Test: The attachment disc repeat number for the individual spider (1, 2), followed by the mean.Failure Type: The observed failure type of the sample (C is cohesive, D is dragline, A is adhesive). In samples where the failure type was unclear and exhibited intermediate characteristics between two failure types (e.g. A/C is adhesive and cohesive) (n=23, ~10% of discs), two separate columns were analyzed – one coding all failures as adhesive and the other coding them all as cohesive.ForceAtPeak (uN): The peak force achieved by the sample in uN.Work to Release (J): The total work of the sample before failure in J. Extension (mm): The total extension of the sample before failure in mm.Habitat: The habitat group that the sample species belongs to (either riparian or terrestrial).Spider ID: The spider identity (e.g. TE1 is Tetragnatha elongata #1).Failure Type A>C>D: The failure type with unclear failure type samples coded in favor of adhesive failure (e.g. a sample coded as A/C in "Failure type" column would be coded as A here).Failure Type D>C>A: The failure type with unclear failure type samples coded in favor of dragline failure (e.g. a sample coded as D/C in "Failure type" column would be coded as D here).