Robophysical and simulation modeling of how leg posture affects vibration sensing in orb weaving spiders

Orb-weaving spiders, which make 2-D webs, are functionally blind and use legs to sense web vibrations to identify and locate prey on the web. When doing so, they often adjust their leg posture. Recent simulation of black widows, which make 3-D cob webs (Mhatre et al. 2018 biorxiv), suggested that spiders may adjust leg posture to "tune in" to certain vibration frequencies to enhance target identification (whether it is prey, a mate, or another object). Here we developed a robophysical model spider to test whether this is true in a real system. Each leg consisted of two joints with torsion springs and variable equilibrium angles to adjust leg posture and accelerometers to measure leg vibration. We also developed a multi-body dynamics simulation robot, which can be used for easier systematic parameter variation and more comprehensive measurements of vibration dynamics. As a first step, we applied an impact on one leg in both the physical and simulation robots while fixing the other legs. Changing leg posture indeed significantly altered the sensed vibration, confirming the hypothesis. We are validating simulation against experiment and adding a 2-D web in both experiment and simulation to understand the principles of vibration sensing modulation by leg posture on the web.