Meeting Abstract
Jellyfish using their nematocysts to inject venom, mantis shrimp harpooning passing fish, and hunters shooting with bow and arrows are all examples of a common prey-capture strategy: ballistic puncture. Across seven orders of magnitude, these disparate systems are unified by a predator’s weapon (nematocyst, spine, arrow, etc.) delivering energy to prey in order to cause damage and even death. The commonality of these systems offers an opportunity to explore how organisms at different scales and with different materials, morphologies, and kinematics utilize energy to perform ballistic puncture. In order to establish a framework for exploring puncture mechanics across biological scales, we examined the effects of size and velocity in a controlled ballistic puncture system. Arrows of identical tip shape but varying in mass and flight speed were shot into cubes of ballistic gelatin. Observations from high-speed videography of impacts suggest that when arrow speed exceeds the speed that stress waves propagate through the gelatin, puncture can occur with minimal deformation to the gelatin. By varying the mass and speed of the arrows, we examined how the kinematics and energetics of the projectile affected puncture mechanics. Depth of penetration (a measure of the effectiveness of puncture) is closely correlated with the kinetic energy of arrows during flight, more so than either momentum or velocity. These results demonstrate the important role energy plays in ballistic puncture mechanics. By expanding the scale of analyses in future work, we hope to establish a common ground for comparing ballistic puncture behaviors across biological scales, opening the door to exploring the evolution of biomechanical systems across major clades.
