Web-borne vibrations are the main source of many spiders' sensory information. Most famously, they inform spiders of the location of prey trapped in the web; web vibrations also carry signals from potential mates and alert spiders to the presence of their own predators. Some of these predators in turn exploit web vibrations to send misleading signals that trick spiders into ambushes or to "hide" their approach among other web disturbances. Understanding how web geometry and composition (webs are woven from several types of silk) affect transmission of these cues thus plays an important role in understanding spiders' behavior and ecology. Biologists have investigated these phenomena experimentally, for example, measuring web frequency responses resulting from different geometries. Much less attention has been directed to modeling web vibrations, despite the additional insight such models would provide. In the frequency response study, for instance, the experimenters were limited to working with natural webs or those with threads removed, and could not test the effects of arbitrarily altering thread patterns or types, which would be crucial for understanding web design. This project will fill this gap by exploring the design of spider webs through computational models for the vibration of string networks backed up by a new generation of experiments on biological and artificially-constructed webs. The key broader impact of the proposed work is making sophisticated modern vibration models available to biologists and others whose expertise is not in dynamical systems. How spiders find their prey is a compelling story and will inspire K-12 students with the interplay between physics, math, biology, and engineering; the PIs will develop a simplified 'teaching' version of the interface, to be distributed through Oregon State University's middle-school outreach program and the Berkeley Chapter of "Expanding your Horizons," an organization to promote the inclusion of middle school girls in STEM fields.
In particular the PI will investigate how a web's geometry and composition affects the transmission of vibratory signals that spiders use to locate and identify trapped prey items. The PI will apply modern dynamical systems theory and experimental techniques to a recognized need in biological study, and in doing so expands understanding of the physics of networks of strings. Compared to previous research in this area, the proposed work will be the first to explicitly and quantitatively consider whole-web vibration energy pathways, look for nonlinear effects in the vibration response, and experimentally record the full motion of points in the vibrating web. The proposed work will also be the first study to quantitatively investigate the mechanics of "active probing" behavior, in which the spider plucks or shakes its web to look for changes in its dynamic properties, which would indicate the presence of a prey or predator animal in the web.
