Meeting Abstract
Trap-jaw ants close their mandibles with extraordinary accelerations and generate impact forces that exceed their body weight by two orders of magnitude. They use their mandibles to strike prey and intruders, and to catapult themselves through the air to escape potential threats. The strikes have an initial energy budget set by musculature and an elastic exoskeleton, yet the energetic efficiency of these strikes as they interact with targets is presently unknown. The extreme accelerations of tiny structures present challenges to characterizing the energetics of impacts, because of their transient strike durations and high peak forces. We examine the impact dynamics of trap-jaw mandibles and their targets using a novel pendulum setup. We measured energy transfer between the trap-jaw ant Odontomachus brunneus (Ponerinae) and its target during a mandible strike. A plastic bead (11.5 mg) and an ant (4-6 mg) were each attached to a thin strand to form two separate pendulums. The paths of both the ant and the bead after the impact were recorded with high speed imaging (12500 fps). Kinetic energy of both the bead and ant was then calculated. We found considerable variance in the total post-strike kinetic energy (kinetic energy of the bead plus that of the ant). The kinetic energy of the ant after the mandible strike ranged over two orders of magnitude (average 0.78 μJ) as did the bead’s kinetic energy (average 0.38 μJ). We then divided the total post-strike kinetic energy by the kinetic energy of the closing mandibles to calculate the efficiency of energy transfer which averaged 7%. This study offers new insights into the methods for study tiny impacts and the potentially low efficiency of energy transfer during tiny, high acceleration impacts.
