Embodied Latch Mechanism of the Mandible to Power at an Ultrahigh Speed in the Trap-jaw Ants Odontomachus kuroiwae

Quick movements faster than muscle contraction are mediated by a mechanical network of springs and latches. The latch system centers the network operation, but the refined anatomical embodiment remains obscure. The trap-jaw ant Odontomachus kuroiwae closes the mandible extremely fast to capture prey and to perform mandible-powered defensive jumps to avoid potential threat. The jump is mediated by mechanical spring and latch systems embodied in the mandible. The ant hits the tip of the mandible on the surface of an obstacle (prey, predator, or ground) to bounce its body. The angular velocity of the closing mandible was 2.3×104 rad/s. Latching the joint is one of the most important mechanisms to accumulate the energy and power the mandibles. We identified the fine structure of the latch on the mandible forming a ‘ball-joint’ using an X-ray micro-computational tomography system (X-ray micro-CT) and X-ray live imaging with a synchrotron. We here highlight a fine projection on the surface of the ball lip and the surface of the inner section of the socket. The height of the projections on the surface of the ball was 3.8±1.8 μm and on the socket was 6.8±2.7 μm. The X-ray live imaging and movement of the 3D model show that the ball with the detent ridge slipped into the socket and over the socket ridge before snapping back at the groove edge. The snapping back movement is quantified in the ultra-fast systems. Our results give an insight into the complex, tightly coupled spring-latch system.