Tensile metrics of black widow attachment disc adhesion in wet and dry conditions

Spiders use piriform silk attachment discs to adhere threads during web construction and to secure safety lines. Water could degrade attachment disc adhesion either by interfering with placement of the discs or later reducing adhesion during loading. We tested the effect of water on the adhesion of attachment discs for the spider Latrodectus hesperus, which spins webs in mostly dry environments. We compared adhesion for discs spun on wet versus dry glass that were subsequently loaded in either wet or dry conditions. Attachment discs placed on wet glass showed similar adhesion to discs placed on dry glass. However, water significantly decreased both peak force of adhesion and work of adhesion when loading occurred under wet conditions, regardless of initial placement conditions. Furthermore, failure mode shifted from rupture of draglines in dry loading conditions to adhesive failure of discs in wet loading conditions. Our results show the importance of considering both the conditions in ..., Attachment discs are observed prior to testing under a compound microscope (Leica DMLB 2 Clinical Microscope, Leica microsystems) at 10x magnification, and images are taken using an Olympus Q-Color5 imaging system (Olympus Confocal) for area and morphology analysis. The sample is then placed in a Nano Bionix tensile tester (MTS System Corp., Oak Ridge, TN, USA) with the upper grip holding the slide and the lower grip holding the cardboard cutout where the dragline is secured. The cardboard “C” is cut near its midpoint, separating the dragline end from the attachment disc end, and the sample adjusted in the X-Y plane to ensure that the dragline will pull the attachment disc perpendicular to the slide surface, to control for the effect of differing pulling angles (Sahni et al., 2012). The dragline was then pulled at 0.1mm/sec until complete failure is observed (Blackledge et al., 2005)(Swanson et al., 2006). The force, time, and displacement are recorded, and work is calculated. The sampl..., , # Tensile metrics of black widow attachment disc adhesion in wet and dry conditions

[https://doi.org/10.5061/dryad.zkh1893k5](https://doi.org/10.5061/dryad.zkh1893k5)

## Description of the data and file structure

Attachment discs were deposited onto clean glass microscope slides under dry (ambient humidity ~ 40-60 RH) and wet conditions. For the wet conditions, slides were wetted using an atomizer filled with DI water and fitted with aquarium tubing to spray atomized water onto the slide. Spiders were restrained using a nylon thread “lasso” constructed from a loop of nylon fishing line protruding through a syringe such that the loop could be pulled tight around the spider’s pedicel (the joint between the abdomen and the cephalothorax). This allowed spiders to walk semi-naturally while mostly controlling placement of attachment discs. Three attachment discs were tested in each of the four conditions for each of the 8 individual western black widows (i.e. 120 discs total). Some of the...