The evolution of physiological characteristics can be strongly influenced by physics. Animals whose physiology allows them to better escape predators will live longer, on average, and be more likely to pass on the genes that led to these favorable traits. In this interrupted case study, students design a method to compare the motion and leg characteristics of different spiders, make hypotheses based on the actual experiment, and analyze the scientists' actual data and scatter plots. Since spider locomotion can be modeled as three different types of pendulums, this case can be used as an application activity following a unit on pendulums or energy conservation. The case was originally written for an introductory calculus-based physics class; however calculus is not required for the analysis, so this case would also be appropriate for an algebra-based college physics class or even a high school physics class that covers pendulum motion and energy concepts.