DOI: 10.5061/dryad.zkh1893k5
title: Tensile metrics of black widow attachment disc adhesion in wet and dry conditions

description: 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 which biological structures
 are produced and those in which the structures perform as
 potentially independent factors for performance. Our results also
 suggest that adhesion in wet conditions can challenge
 some spiders, potentially leading to specialization of attachment
 discs for riparian or aquatic species.
description: Attachment discs are observed prior to testing under a compound
 microscope <em>(Leica DMLB 2 Clinical Microscope, Leica
 microsystems) </em>at 10x magnification, and images are taken using
 an <em>Olympus Q-Color5 imaging system (Olympus Confocal)</em>
 for area and morphology analysis. The sample is then placed in a
 <em>Nano Bionix tensile tester (MTS System Corp., Oak Ridge, TN,
 USA)</em> 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
 sample is then placed back in the compound microscope where images are
 taken of the attachment disc again to determine the failure type
 (cohesive, adhesive, or dragline). Tests are conducted
 under two different conditions (dry and wet) for a total of four
 treatments (placement condition - loading condition): Dry-Dry, Wet-Dry,
 Dry-Wet, and Wet-Wet. Dry loading condition tests are conducted at room
 humidity (40-60%). For wet-placed dry-loading conditions (Wet-Dry), excess
 surface water is removed carefully using Kimtech wipes after the disc is
 placed. The samples are then allowed to fully dry in a desiccator for 5
 minutes before testing. For the wet loading condition tests (Dry-Wet and
 Wet-Wet), samples are continuously sprayed with DI water from the atomizer
 until mounted and tested 5 minutes later. Water droplets visibly coated
 the attachment discs during wet loading. For the Dry-Wet condition, the
 spider places an attachment disc on a dry slide which is then immediately
 (within ~5-10 seconds) wetted using the DI water atomizer for 5 min before
 testing. For the Wet-Wet condition, the slide is wet while the attachment
 disc is placed, and the disc remains saturated with water from then on,
 including during loading. All samples are allowed to dry after tensile
 testing, before microscope imaging and failure type analysis.
description: # 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 samples were damaged in the preparation process, resulting in only four individual spiders having three successful attachment disc samples in all conditions, three individuals having three successful attachment discs in three conditions and two successful discs in one condition, and one individual having lost two discs for one condition but had three discs for the other conditions. This resulted in the total sample size of n=24 for Dry-Dry conditions, n=23 for Wet-Dry, n=23 for Dry-Wet, and n=21 for Wet-Wet, with a total n=91 across all conditions. The attachment disc sample is placed in a Nano Bionix tensile tester (MTS System Corp., Oak Ridge, TN, USA). The dragline was then pulled at 0.1mm/sec until complete failure is observed. The force, time, and displacement are recorded, and work is calculated. Tests are conducted under two different conditions (dry and wet) for a total of four treatments (placement condition - loading condition): Dry-Dry, Wet-Dry, Dry-Wet, and Wet-Wet. Dry loading condition tests are conducted at room humidity (40-60%). For wet-placed dry-loading conditions (Wet-Dry), excess surface water is removed carefully using Kimtech wipes after the disc is placed. The samples are then allowed to fully dry in a desiccator for 5 minutes before testing. For the wet loading condition tests (Dry-Wet and Wet-Wet), samples are continuously sprayed with DI water from the atomizer until mounted and tested 5 minutes later. Water droplets visibly coated the attachment discs during wet loading. For the Dry-Wet condition, the spider places an attachment disc on a dry slide which is then immediately (within ~5-10 seconds) wetted using the DI water atomizer for 5 min before testing. For the Wet-Wet condition, the slide is wet while the attachment disc is placed, and the disc remains saturated with water from then on, including during loading. ### Files and variables #### File: Black\_Widow\_Data\_Manuscript.xlsx **Description:**  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 as well as the failure type. ##### Variables * BS#: the spider identification number. * Species: all species included in this dataset are Latrodectus hesperus (LH). * AD#: the attachment disc repeat number. Each spider had 3 attachment discs collected in for each condition tested. * D/W: the condition being tested, labeled in the form "Placement condition-Loading condition". "d" is Dry-Dry, "dw" is Dry-Wet, "wd" is Wet-Dry, "ww" is Wet-Wet. * Failure: the observed failure type of the sample. "d" is dragline failure, "c" is cohesive failure, "a" is adhesive failure. * ForceAtPeak: the peak force achieved by the sample in uN. * Work to Release: the total work of the sample before failure in J. * Average Force: The mean peak force of the three repeated attachment disc samples in uN. * Average Work: The mean work of the three repeated attachment disc samples in J. * Area: the measured area of the attachment disc in um^2. * Force no dragline: the separated peak force values for samples that did not experience dragline failure in uN. * Work no dragline: the separated work values for samples that did not experience dragline failure in J. * AVG force no dragline: the mean peak force of the three repeated attachment discs excluding samples that experienced dragline failure in uN. * AVG work no dragline: the mean work until failure of the three repeated attachment discs excluding samples that experienced dragline failure in J. Missing values are left as blank cells. #### File: All\_Tensile\_Tests\_Raw\_Force\_Curves.xlsx **Description:**  This is the raw tensile test force curves from each attachment disc tested. Each sheet includes the entirety of the data collected for an individual attachment disc sample. ##### Variables * Sheet Names: each sheet is labeled as "BS#_XX#". BS# is the spider identification number. XX# is the condition and number of attachment disc repeat, so spider number 50's Dry-Wet repeat 3 sample is labeled "BS50_DW3". * True strain, True stress, Engineering stress, Engineering strain: these values are from a previous method that the current method was built on but have not been tested for accuracy in the context of the current experimental setup. They are not used in any analysis and can be ignored. * Extension: the column title is misleading as this is the height position coordinate of the Nano Bionix upper grip in mm. The extension is calculated by subtracting the starting position value from the position value at the attachment disc failure point.  * Load on Specimen: the raw force load in mN on the sample. * Time: the time in seconds.