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

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 attachment discs of the western black widow spider lose ∼8x of their adhesive strength when wet. Here, we test the hypothesis that riparian species of spiders have evolved attachment discs that are resistant to water's adverse effects on adhesion. We compare adhesion of attachment discs from three terrestrial, relatively dry habitats to three riparian spider species when discs are 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 water's impact on interfacial bonding. However, riparian species attachment discs maintained adhesive force when wet while terrestrial species experienced ∼50% reductions 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 disks in wet environments, offering insights into bioinspired design for water-resistant adhesives.