Meeting Abstract
Trap-jaw ants strike with such extreme accelerations and speeds that they must use springs, rather than muscles, to power their movement. Therefore, elastic energy storage structures and the mechanism for delivering elastic energy are both essential to understanding how mandible strikes are actuated. We measured the kinematics and morphology of Odontomachus brunneus (Ponerinae) trap-jaw ants and quantified the energetics and power of their mandible strikes. We tested whether the adductor apodeme or the head capsule served as the primary elastic energy storage structure and calculated their relative elastic strains. We found that each individual mandible has 24.2 ± 6.0 µJ of elastic energy delivered to it in no more than 77.1 ± 7.4 µs during a strike. The mandibles struck at up to 64 m/s and 106 m/s2 with a power density of 105 W/kg. To drive this motion, the mandible moment arm needs to be translated at least 138 ± 13 µm by the displacement of the elastic structures. The head capsule recoiled at least 105 ± 18.6 µm (with 64 ± 14.5 µm in the anterior head capsule and 41 ± 8.9 µm in lateral sides of the head capsule), yielding at least 76% of the necessary strain. Therefore, the head capsule stores the majority of the needed energy and the apodeme most likely provides the rest. In conjunction with these measurements, we also developed a forward dynamic model that matches the mandible kinematics and estimates spring stiffness and damping. Our finding of elastic energy storage via head capsule deformation rather than through apodeme stretching offers insights into the shifting roles of tendon-like structures as struts versus springs in animal movements, particularly in the context of loading and length scale in spring-actuated systems.
