Some predatory arthropods use adhesive capture threads to arrest prey in traps. These capture threads are composites with two primary components: underlying silk fibers surrounded by an adhesive material – an aqueous glue or sticky nanofibrils. The silk fibers in these systems were once thought to primarily suspend the adhesive component with little or no active role in adhesion. However, studies of glue-coated viscid threads used by orb webs spider found that the compliant underlying fibers can perform up to 50% of the work of adhesion as forces are effectively transferred from the glue. To determine if other arthropod capture threads operate as similarly integrated systems, the effects of mechanical plasticization and hidden-length were tested on the glue-coated fishing lines of Arachnocampa tasmaniensis glowworms and spider cribellate silk – threads using ‘dry adhering’ nanofibrils rather than glue. In capture threads of glowworms and the cribellate spider Hickmania troglodytes, silk fibers are mechanically plasticized by the atmospheric water of the wet environments these animals inhabit. This allows transfer of adhesive forces to the more compliant silk fiber and improves work of adhesion. In at least 23 spider families that use cribellate threads, H. troglodytes being an exception, hidden length is present in the form of coiled fibers that confer extreme extensibility of 500-1400%. Experimental cutting of coiled fibers or behavioral manipulation during production that reduces coiled fiber length dramatically reduces thread extensibility and work to fracture, which leads to decreased work of adhesion. Increased compliance of silk fibers through structural or material properties leading to improved adhesive performance may represent an emerging principle in how these threads operate as prey-capture devices.