Orb weavers intercept insects using non-hardening bioadhesive droplets, supported by two flagelliform fibers. Droplets contain an adhesive glycoprotein core and aqueous layer that confers hygroscopicity. The first study investigates the durability of these droplets to cycling, or repeatedly adhering, extending, and pulling off. Droplets of four species proved resilient, cycling 40 times. Cycling, coupled with droplet humidity responsiveness, qualifies them as smart materials. However, thread adhesion is complex, relying on an integrated performance of multiple droplets and the flagelliform fibers. As insects struggle, the flagelliform fibers bow and the droplets extend, forming a suspension bridge configuration whose biomechanics sum the adhesion of droplets and dissipate the energy of struggling insects. Given this performance, the second study predicts that the material properties of both thread components have evolved in a complementary way. Comparative phylogenetics of 14 study species revealed that their elastic moduli are correlated, with glycoproteins being six times more elastic than flagelliform fibers. Spider mass affects the amount of each material, but not their properties. Since glycoprotein performance changes with humidity, we hypothesized that orb weavers generate greater adhesion at their foraging humidity. After delimiting low and high humidity species groups (eight and six species, respectively), bridge force was determined as total contributing droplet adhesion at three humidities. Only three spiders generated greater adhesion outside of their foraging humidity. The distribution of force along a suspension bridge differed from a previously reported pattern. We also characterize the sheet configuration, which generates force similar to suspension bridges. / Master of Science / In nature, adhesives are used for a variety of functions. Many animals use adhesives use adhesives when climbing. Examples include toe pads of geckos, tarsal pads of ants, and tube feet of and sea urchins. Here, adhesion is repeatedly generated and released as the animal moves. However, some animals depend on permanent adhesives to anchor to surfaces. Marine mussels and barnacles, whose adult forms are sessile, use adhesives to resist the powerful action of waves and currents. Adhesion also plays a critical role in prey capture, where it prevents prey from escaping. The sticky droplets of a sundew plants and the adhesive capture threads of spider orb webs trap flies. Biologists and engineers study these bioadiehsives in search of inspiration and principles that will guide the development of new materials, including adhesives that function underwater, harden rapidly, or remaining pliable after adhering. This study investigated the material properties of capture threads spun by orb weaving spiders, which rely on non-hardening sticky droplets, supported by two protein fibers to capture insects. Inside each droplet is an adhesive core allows droplets to adhere to an insect and to extend as it struggles to escape. Surrounding this core is an aqueous layer that attracts atmospheric water, causing droplets to track changes in ambient humidity. A study of the cycling (or reusability) of four species' droplets repeatedly adhered a droplet to a surface and extending it to pull-off. These droplets were very resilient, cycling 40 times. Cycling, coupled with droplet humidity responsiveness, qualifies them as smart materials. However, prey capture is more complex, relying on the integration of multiple droplets and their supporting flagelliform fibers. As insects struggle, these fibers bow and the droplets extend, forming a suspension bridge configuration whose biomechanics sum the adhesion of droplets to resist an insect escape. The threads of 14 species were examined to test the hypothesis that material properties of both thread components have evolved in a complementary way to optimize adhesive performance. This revealed that the elasticities of the two capture thread components were correlated, with support fiber elasticity being greater. Capture threads generated the greatest adhesion at humidities during times that a spider feeds, although the distribution of this force across a suspension bridge showed different patterns among the species. The functional integration of a capture thread's components and its ability to respond to environmental humidity gives it exciting biomimicry potential.

Webs are fundamental to the ecology of Nephila clavipes, the golden orb-weaver spider, because they serve as sites for prey capture, reproduction, competition, predation, and parasitism. In addition to the presence of the female N. clavipes, males and kleptoparasites reside on the web in varying numbers. Webs are also found in clusters with conspecific females. Web site selection and length of web tenure is a behavioral decision vital to the spider’s fitness and the ecology of her species. I conducted a field census to quantify these factors and analyze their influence on web tenure, compare web ecology between a forest and non-forest habitat, as well as explain the significance of N. clavipes’ web as central to many interactions. Web tenure, as well, was influenced differently by the factors between both environments. In the forest habitat, increase in prey capture rate decreased web tenure and inclusion in cluster increased web tenure. In the non-forest habitat, only increase in spider size was related to increased web tenure. There were significant differences between the two habitats in the sizes of the female spider and quantity of males and kleptoparasites. Results also showed that spider size influenced quantity of males and web diameter influenced quantity of kleptoparasites. Explanation of these results can be attributed to the complex relationships among the variables and the consequences of living in habitats impacted by human occupation.

Webs are fundamental to the ecology of Nephila clavipes, the golden orb-weaver spider, because they serve as sites for prey capture, reproduction, competition, predation, and parasitism. In addition to the presence of the female N. clavipes, males and kleptoparasites reside on the web in varying numbers. Webs are also found in clusters with conspecific females. Web site selection and length of web tenure is a behavioral decision vital to the spider’s fitness and the ecology of her species. I conducted a field census to quantify these factors and analyze their influence on web tenure, compare web ecology between a forest and non-forest habitat, as well as explain the significance of N. clavipes’ web as central to many interactions. Web tenure, as well, was influenced differently by the factors between both environments. In the forest habitat, increase in prey capture rate decreased web tenure and inclusion in cluster increased web tenure. In the non-forest habitat, only increase in spider size was related to increased web tenure. There were significant differences between the two habitats in the sizes of the female spider and quantity of males and kleptoparasites. Results also showed that spider size influenced quantity of males and web diameter influenced quantity of kleptoparasites. Explanation of these results can be attributed to the complex relationships among the variables and the consequences of living in habitats impacted by human occupation.